mcs/mcs/convert.cs

   1 //
   2 // conversion.cs: various routines for implementing conversions.
   3 //
   4 // Authors:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Ravi Pratap (ravi@ximian.com)
   7 //
   8 // (C) 2001, 2002, 2003 Ximian, Inc.
   9 //
  10
  11 namespace Mono.CSharp {
  12         using System;
  13         using System.Collections;
  14         using System.Diagnostics;
  15         using System.Reflection;
  16         using System.Reflection.Emit;
  17
  18         //
  19         // A container class for all the conversion operations
  20         //
  21         public class Convert {
  22 #if GMCS_SOURCE
  23                 static bool TypeParameter_to_Null (Type target_type)
  24                 {
  25                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
  26                         if (gc == null)
  27                                 return false;
  28
  29                         if (gc.HasReferenceTypeConstraint)
  30                                 return true;
  31                         if (gc.HasClassConstraint && !TypeManager.IsValueType (gc.ClassConstraint))
  32                                 return true;
  33
  34                         return false;
  35                 }
  36
  37                 static Type TypeParam_EffectiveBaseType (GenericConstraints gc)
  38                 {
  39                         ArrayList list = new ArrayList ();
  40                         list.Add (gc.EffectiveBaseClass);
  41                         foreach (Type t in gc.InterfaceConstraints) {
  42                                 if (!TypeManager.IsGenericParameter (t))
  43                                         continue;
  44
  45                                 GenericConstraints new_gc = TypeManager.GetTypeParameterConstraints (t);
  46                                 if (new_gc != null)
  47                                         list.Add (TypeParam_EffectiveBaseType (new_gc));
  48                         }
  49                         return FindMostEncompassedType (list);
  50                 }
  51 #endif
  52
  53                 //
  54                 // From a one-dimensional array-type S[] to System.Collections.IList<S> and base
  55                 // interfaces of this interface.
  56                 //
  57                 // From a one-dimensional array-type S[] to System.Collections.IList<T> and base
  58                 // interfaces of this interface, provided there is an implicit reference conversion
  59                 // from S to T.
  60                 //
  61                 static bool Array_To_IList (Type array, Type list)
  62                 {
  63 #if GMCS_SOURCE
  64                         if (!array.IsArray || (array.GetArrayRank () != 1) || !list.IsGenericType)
  65                                 return false;
  66
  67                         Type gt = list.GetGenericTypeDefinition ();
  68                         if ((gt != TypeManager.generic_ilist_type) &&
  69                             (gt != TypeManager.generic_icollection_type) &&
  70                             (gt != TypeManager.generic_ienumerable_type))
  71                                 return false;
  72
  73                         Type element_type = TypeManager.GetElementType (array);
  74                         Type arg_type = TypeManager.GetTypeArguments (list) [0];
  75
  76                         if (element_type == arg_type)
  77                                 return true;
  78
  79                         if (MyEmptyExpr == null)
  80                                 MyEmptyExpr = new EmptyExpression ();
  81                         MyEmptyExpr.SetType (TypeManager.GetElementType (array));
  82
  83                         return ImplicitReferenceConversionExists (MyEmptyExpr, arg_type);
  84 #else
  85                         return false;
  86 #endif
  87                 }
  88
  89                 static Expression ImplicitTypeParameterConversion (Expression expr,
  90                                                                    Type target_type)
  91                 {
  92 #if GMCS_SOURCE
  93                         Type expr_type = expr.Type;
  94
  95                         GenericConstraints gc = TypeManager.GetTypeParameterConstraints (expr_type);
  96
  97                         if (gc == null) {
  98                                 if (target_type == TypeManager.object_type)
  99                                         return new BoxedCast (expr, target_type);
 100
 101                                 return null;
 102                         }
 103
 104                         // We're converting from a type parameter which is known to be a reference type.
 105                         Type base_type = TypeParam_EffectiveBaseType (gc);
 106
 107                         if (TypeManager.IsSubclassOf (base_type, target_type))
 108                                 return new ClassCast (expr, target_type);
 109
 110                         if (target_type.IsInterface) {
 111                                 if (TypeManager.ImplementsInterface (base_type, target_type))
 112                                         return new ClassCast (expr, target_type);
 113
 114                                 foreach (Type t in gc.InterfaceConstraints) {
 115                                         if (TypeManager.IsSubclassOf (t, target_type))
 116                                                 return new ClassCast (expr, target_type);
 117                                         if (TypeManager.ImplementsInterface (t, target_type))
 118                                                 return new ClassCast (expr, target_type);
 119                                 }
 120                         }
 121
 122                         foreach (Type t in gc.InterfaceConstraints) {
 123                                 if (!TypeManager.IsGenericParameter (t))
 124                                         continue;
 125                                 if (TypeManager.IsSubclassOf (t, target_type))
 126                                         return new ClassCast (expr, target_type);
 127                                 if (TypeManager.ImplementsInterface (t, target_type))
 128                                         return new ClassCast (expr, target_type);
 129                         }
 130 #endif
 131                         return null;
 132                 }
 133
 134                 static bool ExplicitTypeParameterConversionExists (Type source_type, Type target_type)
 135                 {
 136 #if GMCS_SOURCE
 137                         if (target_type.IsInterface)
 138                                 return true;
 139
 140                         if (TypeManager.IsGenericParameter (target_type)) {
 141                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
 142                                 if (gc == null)
 143                                         return false;
 144
 145                                 foreach (Type iface in gc.InterfaceConstraints) {
 146                                         if (!TypeManager.IsGenericParameter (iface))
 147                                                 continue;
 148
 149                                         if (TypeManager.IsSubclassOf (source_type, iface))
 150                                                 return true;
 151                                 }
 152                         }
 153 #endif
 154                         return false;
 155                 }
 156
 157                 static Expression ExplicitTypeParameterConversion (Expression source, Type target_type)
 158                 {
 159 #if GMCS_SOURCE
 160                         Type source_type = source.Type;
 161
 162                         if (target_type.IsInterface)
 163                                 return new ClassCast (source, target_type);
 164
 165                         if (TypeManager.IsGenericParameter (target_type)) {
 166                                 GenericConstraints gc = TypeManager.GetTypeParameterConstraints (target_type);
 167                                 if (gc == null)
 168                                         return null;
 169
 170                                 foreach (Type iface in gc.InterfaceConstraints) {
 171                                         if (!TypeManager.IsGenericParameter (iface))
 172                                                 continue;
 173
 174                                         if (TypeManager.IsSubclassOf (source_type, iface))
 175                                                 return new ClassCast (source, target_type);
 176                                 }
 177                         }
 178 #endif
 179                         return null;
 180                 }
 181
 182                 static EmptyExpression MyEmptyExpr;
 183                 static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
 184                 {
 185                         Type expr_type = expr.Type;
 186
 187                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
 188                                 // if we are a method group, emit a warning
 189
 190                                 expr.Emit (null);
 191                         }
 192
 193                         if (expr_type == TypeManager.void_type)
 194                                 return null;
 195
 196                         if (TypeManager.IsGenericParameter (expr_type))
 197                                 return ImplicitTypeParameterConversion (expr, target_type);
 198
 199                         //
 200                         // notice that it is possible to write "ValueType v = 1", the ValueType here
 201                         // is an abstract class, and not really a value type, so we apply the same rules.
 202                         //
 203                         if (target_type == TypeManager.object_type) {
 204                                 //
 205                                 // A pointer type cannot be converted to object
 206                                 //
 207                                 if (expr_type.IsPointer)
 208                                         return null;
 209
 210                                 if (TypeManager.IsValueType (expr_type))
 211                                         return new BoxedCast (expr, target_type);
 212                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type){
 213                                         if (expr_type == TypeManager.anonymous_method_type)
 214                                                 return null;
 215                                         return new EmptyCast (expr, target_type);
 216                                 }
 217
 218                                 return null;
 219                         } else if (target_type == TypeManager.value_type) {
 220                                 if (TypeManager.IsValueType (expr_type))
 221                                         return new BoxedCast (expr, target_type);
 222                                 if (expr_type == TypeManager.null_type)
 223                                         return new EmptyConstantCast ((Constant)expr, target_type);
 224
 225                                 return null;
 226                         } else if (TypeManager.IsSubclassOf (expr_type, target_type)) {
 227                                 //
 228                                 // Special case: enumeration to System.Enum.
 229                                 // System.Enum is not a value type, it is a class, so we need
 230                                 // a boxing conversion
 231                                 //
 232                                 if (expr_type.IsEnum || TypeManager.IsGenericParameter (expr_type))
 233                                         return new BoxedCast (expr, target_type);
 234
 235                                 return new EmptyCast (expr, target_type);
 236                         }
 237
 238                         // This code is kind of mirrored inside ImplicitStandardConversionExists
 239                         // with the small distinction that we only probe there
 240                         //
 241                         // Always ensure that the code here and there is in sync
 242
 243                         // from the null type to any reference-type.
 244                         if (expr_type == TypeManager.null_type) {
 245                                 NullConstant nc = (NullConstant)expr;
 246                                 return nc.ToType(target_type);
 247                         }
 248
 249                         // from any class-type S to any interface-type T.
 250                         if (target_type.IsInterface) {
 251                                 if (target_type != TypeManager.iconvertible_type &&
 252                                     expr_type.IsValueType && (expr is Constant) &&
 253                                     !(expr is IntLiteral || expr is BoolLiteral ||
 254                                       expr is FloatLiteral || expr is DoubleLiteral ||
 255                                       expr is LongLiteral || expr is CharLiteral ||
 256                                       expr is StringLiteral || expr is DecimalLiteral ||
 257                                       expr is UIntLiteral || expr is ULongLiteral)) {
 258                                         return null;
 259                                 }
 260
 261                                 if (TypeManager.ImplementsInterface (expr_type, target_type)){
 262                                         if (TypeManager.IsGenericParameter (expr_type) || TypeManager.IsValueType (expr_type))
 263                                                 return new BoxedCast (expr, target_type);
 264                                         else
 265                                                 return new EmptyCast (expr, target_type);
 266                                 }
 267                         }
 268
 269                         // from any interface type S to interface-type T.
 270                         if (expr_type.IsInterface && target_type.IsInterface) {
 271                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 272                                         return new EmptyCast (expr, target_type);
 273                                 else
 274                                         return null;
 275                         }
 276
 277                         // from an array-type S to an array-type of type T
 278                         if (expr_type.IsArray && target_type.IsArray) {
 279                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 280
 281                                         Type expr_element_type = TypeManager.GetElementType (expr_type);
 282
 283                                         if (MyEmptyExpr == null)
 284                                                 MyEmptyExpr = new EmptyExpression ();
 285
 286                                         MyEmptyExpr.SetType (expr_element_type);
 287                                         Type target_element_type = TypeManager.GetElementType (target_type);
 288
 289                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 290                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 291                                                                                       target_element_type))
 292                                                         return new EmptyCast (expr, target_type);
 293                                 }
 294                         }
 295
 296                         // from an array-type to System.Array
 297                         if (expr_type.IsArray && target_type == TypeManager.array_type)
 298                                 return new EmptyCast (expr, target_type);
 299
 300                         // from an array-type of type T to IList<T>
 301                         if (expr_type.IsArray && Array_To_IList (expr_type, target_type))
 302                                 return new EmptyCast (expr, target_type);
 303
 304                         // from any delegate type to System.Delegate
 305                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 306                             target_type == TypeManager.delegate_type)
 307                                 return new EmptyCast (expr, target_type);
 308
 309                         // from any array-type or delegate type into System.ICloneable.
 310                         if (expr_type.IsArray ||
 311                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 312                                 if (target_type == TypeManager.icloneable_type)
 313                                         return new EmptyCast (expr, target_type);
 314
 315                         // from a generic type definition to a generic instance.
 316                         if (TypeManager.IsEqual (expr_type, target_type))
 317                                 return new EmptyCast (expr, target_type);
 318
 319                         return null;
 320                 }
 321
 322                 //
 323                 // Tests whether an implicit reference conversion exists between expr_type
 324                 // and target_type
 325                 //
 326                 public static bool ImplicitReferenceConversionExists (Expression expr, Type target_type)
 327                 {
 328                         if (target_type.IsValueType)
 329                                 return false;
 330
 331                         Type expr_type = expr.Type;
 332
 333                         if (TypeManager.IsGenericParameter (expr_type))
 334                                 return ImplicitTypeParameterConversion (expr, target_type) != null;
 335
 336                         //
 337                         // This is the boxed case.
 338                         //
 339                         if (target_type == TypeManager.object_type) {
 340                                 if (expr_type.IsClass || TypeManager.IsValueType (expr_type) ||
 341                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 342                                         if (target_type != TypeManager.anonymous_method_type)
 343                                         return true;
 344
 345                                 return false;
 346                         } else if (TypeManager.IsSubclassOf (expr_type, target_type))
 347                                 return true;
 348
 349                         // Please remember that all code below actually comes
 350                         // from ImplicitReferenceConversion so make sure code remains in sync
 351
 352                         // from any class-type S to any interface-type T.
 353                         if (target_type.IsInterface) {
 354                                 if (target_type != TypeManager.iconvertible_type &&
 355                                     expr_type.IsValueType && (expr is Constant) &&
 356                                     !(expr is IntLiteral || expr is BoolLiteral ||
 357                                       expr is FloatLiteral || expr is DoubleLiteral ||
 358                                       expr is LongLiteral || expr is CharLiteral ||
 359                                       expr is StringLiteral || expr is DecimalLiteral ||
 360                                       expr is UIntLiteral || expr is ULongLiteral)) {
 361                                         return false;
 362                                 }
 363
 364                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 365                                         return true;
 366                         }
 367
 368                         // from any interface type S to interface-type T.
 369                         if (expr_type.IsInterface && target_type.IsInterface)
 370                                 if (TypeManager.ImplementsInterface (expr_type, target_type))
 371                                         return true;
 372
 373                         // from an array-type S to an array-type of type T
 374                         if (expr_type.IsArray && target_type.IsArray) {
 375                                 if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 376
 377                                         Type expr_element_type = expr_type.GetElementType ();
 378
 379                                         if (MyEmptyExpr == null)
 380                                                 MyEmptyExpr = new EmptyExpression ();
 381
 382                                         MyEmptyExpr.SetType (expr_element_type);
 383                                         Type target_element_type = TypeManager.GetElementType (target_type);
 384
 385                                         if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 386                                                 if (ImplicitStandardConversionExists (MyEmptyExpr,
 387                                                                                       target_element_type))
 388                                                         return true;
 389                                 }
 390                         }
 391
 392                         // from an array-type to System.Array
 393                         if (expr_type.IsArray && (target_type == TypeManager.array_type))
 394                                 return true;
 395
 396                         // from an array-type of type T to IList<T>
 397                         if (expr_type.IsArray && Array_To_IList (expr_type, target_type))
 398                                 return true;
 399
 400                         // from any delegate type to System.Delegate
 401                         if ((expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type)) &&
 402                             target_type == TypeManager.delegate_type)
 403                                 if (target_type.IsAssignableFrom (expr_type))
 404                                         return true;
 405
 406                         // from any array-type or delegate type into System.ICloneable.
 407                         if (expr_type.IsArray ||
 408                             expr_type == TypeManager.delegate_type || TypeManager.IsDelegateType (expr_type))
 409                                 if (target_type == TypeManager.icloneable_type)
 410                                         return true;
 411
 412                         // from the null type to any reference-type.
 413                         if (expr_type == TypeManager.null_type){
 414                                 if (target_type.IsPointer)
 415                                         return true;
 416
 417                                 if (!target_type.IsValueType)
 418                                         return true;
 419                         }
 420
 421                         // from a generic type definition to a generic instance.
 422                         if (TypeManager.IsEqual (expr_type, target_type))
 423                                 return true;
 424
 425                         return false;
 426                 }
 427
 428                 /// <summary>
 429                 ///   Implicit Numeric Conversions.
 430                 ///
 431                 ///   expr is the expression to convert, returns a new expression of type
 432                 ///   target_type or null if an implicit conversion is not possible.
 433                 /// </summary>
 434                 static public Expression ImplicitNumericConversion (Expression expr,
 435                                                                     Type target_type)
 436                 {
 437                         Type expr_type = expr.Type;
 438
 439                         //
 440                         // Attempt to do the implicit constant expression conversions
 441
 442                         if (expr is Constant){
 443                                 if (expr is IntConstant){
 444                                         Expression e;
 445
 446                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 447
 448                                         if (e != null)
 449                                                 return e;
 450                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 451                                         //
 452                                         // Try the implicit constant expression conversion
 453                                         // from long to ulong, instead of a nice routine,
 454                                         // we just inline it
 455                                         //
 456                                         long v = ((LongConstant) expr).Value;
 457                                         if (v >= 0)
 458                                                 return new ULongConstant ((ulong) v, expr.Location);
 459                                 }
 460                         }
 461
 462                         Type real_target_type = target_type;
 463
 464                         if (expr_type == TypeManager.sbyte_type){
 465                                 //
 466                                 // From sbyte to short, int, long, float, double, decimal
 467                                 //
 468                                 if (real_target_type == TypeManager.int32_type)
 469                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 470                                 if (real_target_type == TypeManager.int64_type)
 471                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 472                                 if (real_target_type == TypeManager.double_type)
 473                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 474                                 if (real_target_type == TypeManager.float_type)
 475                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 476                                 if (real_target_type == TypeManager.short_type)
 477                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 478                                 if (real_target_type == TypeManager.decimal_type)
 479                                         return new CastToDecimal (expr);
 480                         } else if (expr_type == TypeManager.byte_type){
 481                                 //
 482                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 483                                 //
 484                                 if ((real_target_type == TypeManager.short_type) ||
 485                                     (real_target_type == TypeManager.ushort_type) ||
 486                                     (real_target_type == TypeManager.int32_type) ||
 487                                     (real_target_type == TypeManager.uint32_type))
 488                                         return new EmptyCast (expr, target_type);
 489
 490                                 if (real_target_type == TypeManager.uint64_type)
 491                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 492                                 if (real_target_type == TypeManager.int64_type)
 493                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 494                                 if (real_target_type == TypeManager.float_type)
 495                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 496                                 if (real_target_type == TypeManager.double_type)
 497                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 498                                 if (real_target_type == TypeManager.decimal_type)
 499                                         return new CastToDecimal (expr);
 500
 501                         } else if (expr_type == TypeManager.short_type){
 502                                 //
 503                                 // From short to int, long, float, double, decimal
 504                                 //
 505                                 if (real_target_type == TypeManager.int32_type)
 506                                         return new EmptyCast (expr, target_type);
 507                                 if (real_target_type == TypeManager.int64_type)
 508                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 509                                 if (real_target_type == TypeManager.double_type)
 510                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 511                                 if (real_target_type == TypeManager.float_type)
 512                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 513                                 if (real_target_type == TypeManager.decimal_type)
 514                                         return new CastToDecimal (expr);
 515
 516                         } else if (expr_type == TypeManager.ushort_type){
 517                                 //
 518                                 // From ushort to int, uint, long, ulong, float, double, decimal
 519                                 //
 520                                 if (real_target_type == TypeManager.uint32_type)
 521                                         return new EmptyCast (expr, target_type);
 522
 523                                 if (real_target_type == TypeManager.uint64_type)
 524                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 525                                 if (real_target_type == TypeManager.int32_type)
 526                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 527                                 if (real_target_type == TypeManager.int64_type)
 528                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 529                                 if (real_target_type == TypeManager.double_type)
 530                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 531                                 if (real_target_type == TypeManager.float_type)
 532                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 533                                 if (real_target_type == TypeManager.decimal_type)
 534                                         return new CastToDecimal (expr);
 535                         } else if (expr_type == TypeManager.int32_type){
 536                                 //
 537                                 // From int to long, float, double, decimal
 538                                 //
 539                                 if (real_target_type == TypeManager.int64_type)
 540                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 541                                 if (real_target_type == TypeManager.double_type)
 542                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 543                                 if (real_target_type == TypeManager.float_type)
 544                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 545                                 if (real_target_type == TypeManager.decimal_type)
 546                                         return new CastToDecimal (expr);
 547                         } else if (expr_type == TypeManager.uint32_type){
 548                                 //
 549                                 // From uint to long, ulong, float, double, decimal
 550                                 //
 551                                 if (real_target_type == TypeManager.int64_type)
 552                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 553                                 if (real_target_type == TypeManager.uint64_type)
 554                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 555                                 if (real_target_type == TypeManager.double_type)
 556                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 557                                                                OpCodes.Conv_R8);
 558                                 if (real_target_type == TypeManager.float_type)
 559                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 560                                                                OpCodes.Conv_R4);
 561                                 if (real_target_type == TypeManager.decimal_type)
 562                                         return new CastToDecimal (expr);
 563                         } else if (expr_type == TypeManager.int64_type){
 564                                 //
 565                                 // From long/ulong to float, double
 566                                 //
 567                                 if (real_target_type == TypeManager.double_type)
 568                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 569                                 if (real_target_type == TypeManager.float_type)
 570                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 571                                 if (real_target_type == TypeManager.decimal_type)
 572                                         return new CastToDecimal (expr);
 573                         } else if (expr_type == TypeManager.uint64_type){
 574                                 //
 575                                 // From ulong to float, double
 576                                 //
 577                                 if (real_target_type == TypeManager.double_type)
 578                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 579                                                                OpCodes.Conv_R8);
 580                                 if (real_target_type == TypeManager.float_type)
 581                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 582                                                                OpCodes.Conv_R4);
 583                                 if (real_target_type == TypeManager.decimal_type)
 584                                         return new CastToDecimal (expr);
 585                         } else if (expr_type == TypeManager.char_type){
 586                                 //
 587                                 // From char to ushort, int, uint, long, ulong, float, double, decimal
 588                                 //
 589                                 if ((real_target_type == TypeManager.ushort_type) ||
 590                                     (real_target_type == TypeManager.int32_type) ||
 591                                     (real_target_type == TypeManager.uint32_type))
 592                                         return new EmptyCast (expr, target_type);
 593                                 if (real_target_type == TypeManager.uint64_type)
 594                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 595                                 if (real_target_type == TypeManager.int64_type)
 596                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 597                                 if (real_target_type == TypeManager.float_type)
 598                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 599                                 if (real_target_type == TypeManager.double_type)
 600                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 601                                 if (real_target_type == TypeManager.decimal_type)
 602                                         return new CastToDecimal (expr);
 603                         } else if (expr_type == TypeManager.float_type){
 604                                 //
 605                                 // float to double
 606                                 //
 607                                 if (real_target_type == TypeManager.double_type)
 608                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 609                         }
 610
 611                         return null;
 612                 }
 613
 614                 /// <summary>
 615                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 616                 ///  implicit user defined conversions - needed for overload resolution
 617                 /// </summary>
 618                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 619                 {
 620 #if GMCS_SOURCE
 621                         if (expr is NullLiteral) {
 622                                 if (TypeManager.IsGenericParameter (target_type))
 623                                         return TypeParameter_to_Null (target_type);
 624
 625                                 if (TypeManager.IsNullableType (target_type))
 626                                         return true;
 627                         }
 628 #endif
 629                         if (ImplicitStandardConversionExists (expr, target_type))
 630                                 return true;
 631
 632                         return ImplicitUserConversion (ec, expr, target_type, Location.Null) != null;
 633                 }
 634
 635                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 636                 {
 637                         return ImplicitUserConversion (ec, new EmptyExpression (source), target, Location.Null) != null;
 638                 }
 639
 640                 /// <summary>
 641                 ///  Determines if a standard implicit conversion exists from
 642                 ///  expr_type to target_type
 643                 ///
 644                 ///  ec should point to a real EmitContext if expr.Type is TypeManager.anonymous_method_type.
 645                 /// </summary>
 646                 public static bool ImplicitStandardConversionExists (Expression expr, Type target_type)
 647                 {
 648                         Type expr_type = expr.Type;
 649 #if GMCS_SOURCE
 650                         if (TypeManager.IsNullableType (target_type)) {
 651                                 // if implicit standard conversion S -> T exists, S -> T? and S? -> T? also exists
 652                                 target_type = TypeManager.GetTypeArguments (target_type) [0];
 653
 654                                 // S? -> T?
 655                                 if (TypeManager.IsNullableType (expr_type)) {
 656                                         EmptyExpression new_expr = EmptyExpression.Grab ();
 657                                         new_expr.SetType (TypeManager.GetTypeArguments (expr_type) [0]);
 658                                         bool retval = ImplicitStandardConversionExists (new_expr, target_type);
 659                                         EmptyExpression.Release (new_expr);
 660                                         return retval;
 661                                 }
 662                         }
 663 #endif
 664                         if (expr_type == TypeManager.void_type)
 665                                 return false;
 666
 667                         //Console.WriteLine ("Expr is {0}", expr);
 668                         //Console.WriteLine ("{0} -> {1} ?", expr_type, target_type);
 669                         if (expr_type.Equals (target_type))
 670                                 return true;
 671
 672
 673                         // First numeric conversions
 674
 675                         if (expr_type == TypeManager.sbyte_type){
 676                                 //
 677                                 // From sbyte to short, int, long, float, double, uintptr, decimal
 678                                 //
 679                                 if ((target_type == TypeManager.int32_type) ||
 680                                     (target_type == TypeManager.int64_type) ||
 681                                     (target_type == TypeManager.double_type) ||
 682                                     (target_type == TypeManager.float_type)  ||
 683                                     (target_type == TypeManager.short_type) ||
 684                                     (target_type == TypeManager.uintptr_type) ||
 685                                     (target_type == TypeManager.decimal_type))
 686                                         return true;
 687
 688                         } else if (expr_type == TypeManager.byte_type){
 689                                 //
 690                                 // From byte to short, ushort, int, uint, long, ulong, float, double, decimal
 691                                 //
 692                                 if ((target_type == TypeManager.short_type) ||
 693                                     (target_type == TypeManager.ushort_type) ||
 694                                     (target_type == TypeManager.int32_type) ||
 695                                     (target_type == TypeManager.uint32_type) ||
 696                                     (target_type == TypeManager.uint64_type) ||
 697                                     (target_type == TypeManager.int64_type) ||
 698                                     (target_type == TypeManager.float_type) ||
 699                                     (target_type == TypeManager.double_type) ||
 700                                     (target_type == TypeManager.decimal_type))
 701                                         return true;
 702
 703                         } else if (expr_type == TypeManager.short_type){
 704                                 //
 705                                 // From short to int, long, double, float, decimal and uintptr
 706                                 //
 707                                 if ((target_type == TypeManager.int32_type) ||
 708                                     (target_type == TypeManager.int64_type) ||
 709                                     (target_type == TypeManager.double_type) ||
 710                                     (target_type == TypeManager.float_type) ||
 711                                     (target_type == TypeManager.uintptr_type) ||
 712                                     (target_type == TypeManager.decimal_type))
 713                                         return true;
 714
 715                         } else if (expr_type == TypeManager.ushort_type){
 716                                 //
 717                                 // From ushort to int, uint, long, ulong, double, float, decimal
 718                                 //
 719                                 if ((target_type == TypeManager.uint32_type) ||
 720                                     (target_type == TypeManager.uint64_type) ||
 721                                     (target_type == TypeManager.int32_type) ||
 722                                     (target_type == TypeManager.int64_type) ||
 723                                     (target_type == TypeManager.double_type) ||
 724                                     (target_type == TypeManager.float_type) ||
 725                                     (target_type == TypeManager.decimal_type))
 726                                         return true;
 727
 728                         } else if (expr_type == TypeManager.int32_type){
 729                                 //
 730                                 // From int to long, double, float, decimal, uintptr
 731                                 //
 732                                 if ((target_type == TypeManager.int64_type) ||
 733                                     (target_type == TypeManager.double_type) ||
 734                                     (target_type == TypeManager.float_type) ||
 735                                     (target_type == TypeManager.uintptr_type) ||
 736                                     (target_type == TypeManager.decimal_type))
 737                                         return true;
 738
 739                         } else if (expr_type == TypeManager.uint32_type){
 740                                 //
 741                                 // From uint to long, ulong, double, float, decimal
 742                                 //
 743                                 if ((target_type == TypeManager.int64_type) ||
 744                                     (target_type == TypeManager.uint64_type) ||
 745                                     (target_type == TypeManager.double_type) ||
 746                                     (target_type == TypeManager.float_type) ||
 747                                     (target_type == TypeManager.decimal_type))
 748                                         return true;
 749
 750                         } else if ((expr_type == TypeManager.uint64_type) ||
 751                                    (expr_type == TypeManager.int64_type)) {
 752                                 //
 753                                 // From long/ulong to double, float, decimal
 754                                 //
 755                                 if ((target_type == TypeManager.double_type) ||
 756                                     (target_type == TypeManager.float_type) ||
 757                                     (target_type == TypeManager.decimal_type))
 758                                         return true;
 759
 760                                 //
 761                                 // From uint64 to IntPtr, from the extra conversions.
 762                                 //
 763                                 if (target_type == TypeManager.intptr_type && expr_type == TypeManager.uint64_type)
 764                                         return true;
 765
 766                         } else if (expr_type == TypeManager.char_type){
 767                                 //
 768                                 // From char to ushort, int, uint, ulong, long, float, double, decimal
 769                                 //
 770                                 if ((target_type == TypeManager.ushort_type) ||
 771                                     (target_type == TypeManager.int32_type) ||
 772                                     (target_type == TypeManager.uint32_type) ||
 773                                     (target_type == TypeManager.uint64_type) ||
 774                                     (target_type == TypeManager.int64_type) ||
 775                                     (target_type == TypeManager.float_type) ||
 776                                     (target_type == TypeManager.double_type) ||
 777                                     (target_type == TypeManager.decimal_type))
 778                                         return true;
 779
 780                         } else if (expr_type == TypeManager.float_type){
 781                                 //
 782                                 // float to double
 783                                 //
 784                                 if (target_type == TypeManager.double_type)
 785                                         return true;
 786                         } else if (expr_type == TypeManager.uintptr_type){
 787                                 if ((target_type == TypeManager.sbyte_type) ||
 788                                     (target_type == TypeManager.short_type) ||
 789                                     (target_type == TypeManager.int32_type))
 790                                         return true;
 791                         } else if (expr_type == TypeManager.intptr_type){
 792                                 if (target_type == TypeManager.uint64_type)
 793                                         return true;
 794                         }
 795
 796                         if (expr.eclass == ExprClass.MethodGroup){
 797                                 if (TypeManager.IsDelegateType (target_type) && RootContext.Version != LanguageVersion.ISO_1){
 798                                         MethodGroupExpr mg = expr as MethodGroupExpr;
 799                                         if (mg != null){
 800                                                 return DelegateCreation.ImplicitStandardConversionExists (mg, target_type) != null;
 801                                         }
 802                                 }
 803                         }
 804
 805                         if (ImplicitReferenceConversionExists (expr, target_type))
 806                                 return true;
 807
 808                         //
 809                         // Implicit Constant Expression Conversions
 810                         //
 811                         if (expr is IntConstant){
 812                                 int value = ((IntConstant) expr).Value;
 813
 814                                 if (target_type == TypeManager.sbyte_type){
 815                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 816                                                 return true;
 817                                 } else if (target_type == TypeManager.byte_type){
 818                                         if (value >= 0 && value <= Byte.MaxValue)
 819                                                 return true;
 820                                 } else if (target_type == TypeManager.short_type){
 821                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 822                                                 return true;
 823                                 } else if (target_type == TypeManager.ushort_type){
 824                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 825                                                 return true;
 826                                 } else if (target_type == TypeManager.uint32_type){
 827                                         if (value >= 0)
 828                                                 return true;
 829                                 } else if (target_type == TypeManager.uint64_type){
 830                                          //
 831                                          // we can optimize this case: a positive int32
 832                                          // always fits on a uint64.  But we need an opcode
 833                                          // to do it.
 834                                          //
 835                                         if (value >= 0)
 836                                                 return true;
 837                                 }
 838
 839                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 840                                         return true;
 841                         }
 842
 843                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 844                                 //
 845                                 // Try the implicit constant expression conversion
 846                                 // from long to ulong, instead of a nice routine,
 847                                 // we just inline it
 848                                 //
 849                                 long v = ((LongConstant) expr).Value;
 850                                 if (v >= 0)
 851                                         return true;
 852                         }
 853
 854                         if ((target_type == TypeManager.enum_type ||
 855                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 856                              expr is IntLiteral){
 857                                 IntLiteral i = (IntLiteral) expr;
 858
 859                                 if (i.Value == 0)
 860                                         return true;
 861                         }
 862
 863                         //
 864                         // If `expr_type' implements `target_type' (which is an iface)
 865                         // see TryImplicitIntConversion
 866                         //
 867                         if (target_type.IsInterface && target_type.IsAssignableFrom (expr_type))
 868                                 return true;
 869
 870                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 871                                 return true;
 872
 873                         if (expr_type == TypeManager.anonymous_method_type){
 874                                 if (!TypeManager.IsDelegateType (target_type))
 875                                         return false;
 876
 877                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
 878                                 return ame.ImplicitStandardConversionExists (target_type);
 879                         }
 880
 881                         return false;
 882                 }
 883
 884                 /// <summary>
 885                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 886                 ///  amongst the methods in the MethodGroupExpr
 887                 /// </summary>
 888                 static Type FindMostEncompassedType (ArrayList types)
 889                 {
 890                         Type best = null;
 891
 892                         if (types.Count == 0)
 893                                 return null;
 894
 895                         if (types.Count == 1)
 896                                 return (Type) types [0];
 897
 898                         EmptyExpression expr = EmptyExpression.Grab ();
 899
 900                         foreach (Type t in types) {
 901                                 if (best == null) {
 902                                         best = t;
 903                                         continue;
 904                                 }
 905
 906                                 expr.SetType (t);
 907                                 if (ImplicitStandardConversionExists (expr, best))
 908                                         best = t;
 909                         }
 910
 911                         expr.SetType (best);
 912                         foreach (Type t in types) {
 913                                 if (best == t)
 914                                         continue;
 915                                 if (!ImplicitStandardConversionExists (expr, t)) {
 916                                         best = null;
 917                                         break;
 918                                 }
 919                         }
 920
 921                         EmptyExpression.Release (expr);
 922
 923                         return best;
 924                 }
 925
 926                 /// <summary>
 927                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 928                 ///  amongst the types in the given set
 929                 /// </summary>
 930                 static Type FindMostEncompassingType (ArrayList types)
 931                 {
 932                         Type best = null;
 933
 934                         if (types.Count == 0)
 935                                 return null;
 936
 937                         if (types.Count == 1)
 938                                 return (Type) types [0];
 939
 940                         EmptyExpression expr = EmptyExpression.Grab ();
 941
 942                         foreach (Type t in types) {
 943                                 if (best == null) {
 944                                         best = t;
 945                                         continue;
 946                                 }
 947
 948                                 expr.SetType (best);
 949                                 if (ImplicitStandardConversionExists (expr, t))
 950                                         best = t;
 951                         }
 952
 953                         foreach (Type t in types) {
 954                                 if (best == t)
 955                                         continue;
 956                                 expr.SetType (t);
 957                                 if (!ImplicitStandardConversionExists (expr, best)) {
 958                                         best = null;
 959                                         break;
 960                                 }
 961                         }
 962
 963                         EmptyExpression.Release (expr);
 964
 965                         return best;
 966                 }
 967
 968                 /// <summary>
 969                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 970                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 971                 ///   for explicit and implicit conversion operators.
 972                 /// </summary>
 973                 static public Type FindMostSpecificSource (IList list,
 974                                                            Expression source, bool apply_explicit_conv_rules)
 975                 {
 976                         ArrayList src_types_set = new ArrayList ();
 977
 978                         //
 979                         // If any operator converts from S then Sx = S
 980                         //
 981                         Type source_type = source.Type;
 982                         foreach (MethodBase mb in list){
 983                                 ParameterData pd = TypeManager.GetParameterData (mb);
 984                                 Type param_type = pd.ParameterType (0);
 985
 986                                 if (param_type == source_type)
 987                                         return param_type;
 988
 989                                 src_types_set.Add (param_type);
 990                         }
 991
 992                         //
 993                         // Explicit Conv rules
 994                         //
 995                         if (apply_explicit_conv_rules) {
 996                                 ArrayList candidate_set = new ArrayList ();
 997
 998                                 foreach (Type param_type in src_types_set){
 999                                         if (ImplicitStandardConversionExists (source, param_type))
1000                                                 candidate_set.Add (param_type);
1001                                 }
1002
1003                                 if (candidate_set.Count != 0)
1004                                         return FindMostEncompassedType (candidate_set);
1005                         }
1006
1007                         //
1008                         // Final case
1009                         //
1010                         if (apply_explicit_conv_rules)
1011                                 return FindMostEncompassingType (src_types_set);
1012                         else
1013                                 return FindMostEncompassedType (src_types_set);
1014                 }
1015
1016                 /// <summary>
1017                 ///  Finds the most specific target Tx according to section 13.4.4
1018                 /// </summary>
1019                 static public Type FindMostSpecificTarget (IList list,
1020                                                            Type target, bool apply_explicit_conv_rules)
1021                 {
1022                         ArrayList tgt_types_set = new ArrayList ();
1023
1024                         //
1025                         // If any operator converts to T then Tx = T
1026                         //
1027                         foreach (MethodInfo mi in list){
1028                                 Type ret_type = mi.ReturnType;
1029                                 if (ret_type == target)
1030                                         return ret_type;
1031
1032                                 tgt_types_set.Add (ret_type);
1033                         }
1034
1035                         //
1036                         // Explicit conv rules
1037                         //
1038                         if (apply_explicit_conv_rules) {
1039                                 ArrayList candidate_set = new ArrayList ();
1040
1041                                 EmptyExpression expr = EmptyExpression.Grab ();
1042
1043                                 foreach (Type ret_type in tgt_types_set){
1044                                         expr.SetType (ret_type);
1045
1046                                         if (ImplicitStandardConversionExists (expr, target))
1047                                                 candidate_set.Add (ret_type);
1048                                 }
1049
1050                                 EmptyExpression.Release (expr);
1051
1052                                 if (candidate_set.Count != 0)
1053                                         return FindMostEncompassingType (candidate_set);
1054                         }
1055
1056                         //
1057                         // Okay, final case !
1058                         //
1059                         if (apply_explicit_conv_rules)
1060                                 return FindMostEncompassedType (tgt_types_set);
1061                         else
1062                                 return FindMostEncompassingType (tgt_types_set);
1063                 }
1064
1065                 /// <summary>
1066                 ///  User-defined Implicit conversions
1067                 /// </summary>
1068                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
1069                                                                  Type target, Location loc)
1070                 {
1071                         return UserDefinedConversion (ec, source, target, loc, false);
1072                 }
1073
1074                 /// <summary>
1075                 ///  User-defined Explicit conversions
1076                 /// </summary>
1077                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
1078                                                                  Type target, Location loc)
1079                 {
1080                         return UserDefinedConversion (ec, source, target, loc, true);
1081                 }
1082
1083                 static void AddConversionOperators (ArrayList list,
1084                                                     Expression source, Type target_type,
1085                                                     bool look_for_explicit,
1086                                                     MethodGroupExpr mg)
1087                 {
1088                         if (mg == null)
1089                                 return;
1090
1091                         Type source_type = source.Type;
1092                         EmptyExpression expr = EmptyExpression.Grab ();
1093                         foreach (MethodInfo m in mg.Methods) {
1094                                 ParameterData pd = TypeManager.GetParameterData (m);
1095                                 Type return_type = m.ReturnType;
1096                                 Type arg_type = pd.ParameterType (0);
1097
1098                                 if (source_type != arg_type) {
1099                                         if (!ImplicitStandardConversionExists (source, arg_type)) {
1100                                                 if (!look_for_explicit)
1101                                                         continue;
1102                                                 expr.SetType (arg_type);
1103                                                 if (!ImplicitStandardConversionExists (expr, source_type))
1104                                                         continue;
1105                                         }
1106                                 }
1107
1108                                 if (target_type != return_type) {
1109                                         expr.SetType (return_type);
1110                                         if (!ImplicitStandardConversionExists (expr, target_type)) {
1111                                                 if (!look_for_explicit)
1112                                                         continue;
1113                                                 expr.SetType (target_type);
1114                                                 if (!ImplicitStandardConversionExists (expr, return_type))
1115                                                         continue;
1116                                         }
1117                                 }
1118
1119                                 list.Add (m);
1120                         }
1121
1122                         EmptyExpression.Release (expr);
1123                 }
1124
1125                 /// <summary>
1126                 ///   Compute the user-defined conversion operator from source_type to target_type.
1127                 ///   `look_for_explicit' controls whether we should also include the list of explicit operators
1128                 /// </summary>
1129                 static MethodInfo GetConversionOperator (EmitContext ec, Expression source, Type target_type, bool look_for_explicit)
1130                 {
1131                         ArrayList ops = new ArrayList (4);
1132
1133                         Type source_type = source.Type;
1134
1135                         if (source_type != TypeManager.decimal_type) {
1136                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1137                                         Expression.MethodLookup (ec, source_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1138                                 if (look_for_explicit) {
1139                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1140                                                 Expression.MethodLookup (
1141                                                         ec, source_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1142                                 }
1143                         }
1144
1145                         if (target_type != TypeManager.decimal_type) {
1146                                 AddConversionOperators (ops, source, target_type, look_for_explicit,
1147                                         Expression.MethodLookup (ec, target_type, "op_Implicit", Location.Null) as MethodGroupExpr);
1148                                 if (look_for_explicit) {
1149                                         AddConversionOperators (ops, source, target_type, look_for_explicit,
1150                                                 Expression.MethodLookup (
1151                                                         ec, target_type, "op_Explicit", Location.Null) as MethodGroupExpr);
1152                                 }
1153                         }
1154
1155                         if (ops.Count == 0)
1156                                 return null;
1157
1158                         Type most_specific_source = FindMostSpecificSource (ops, source, look_for_explicit);
1159                         if (most_specific_source == null)
1160                                 return null;
1161
1162                         Type most_specific_target = FindMostSpecificTarget (ops, target_type, look_for_explicit);
1163                         if (most_specific_target == null)
1164                                 return null;
1165
1166                         MethodInfo method = null;
1167
1168                         foreach (MethodInfo m in ops) {
1169                                 if (m.ReturnType != most_specific_target)
1170                                         continue;
1171                                 if (TypeManager.GetParameterData (m).ParameterType (0) != most_specific_source)
1172                                         continue;
1173                                 // Ambiguous: more than one conversion operator satisfies the signature.
1174                                 if (method != null)
1175                                         return null;
1176                                 method = m;
1177                         }
1178
1179                         return method;
1180                 }
1181
1182                 static DoubleHash explicit_conv = new DoubleHash (100);
1183                 static DoubleHash implicit_conv = new DoubleHash (100);
1184
1185                 /// <summary>
1186                 ///   User-defined conversions
1187                 /// </summary>
1188                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
1189                                                                 Type target, Location loc,
1190                                                                 bool look_for_explicit)
1191                 {
1192                         Type source_type = source.Type;
1193                         MethodInfo method = null;
1194
1195                         object o;
1196                         DoubleHash hash = look_for_explicit ? explicit_conv : implicit_conv;
1197
1198                         if (!(source is Constant) && hash.Lookup (source_type, target, out o)) {
1199                                 method = (MethodInfo) o;
1200                         } else {
1201                                 method = GetConversionOperator (ec, source, target, look_for_explicit);
1202                                 if (!(source is Constant))
1203                                         hash.Insert (source_type, target, method);
1204                         }
1205
1206                         if (method == null)
1207                                 return null;
1208
1209                         Type most_specific_source = TypeManager.GetParameterData (method).ParameterType (0);
1210
1211                         //
1212                         // This will do the conversion to the best match that we
1213                         // found.  Now we need to perform an implict standard conversion
1214                         // if the best match was not the type that we were requested
1215                         // by target.
1216                         //
1217                         if (look_for_explicit)
1218                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
1219                         else
1220                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
1221
1222                         if (source == null)
1223                                 return null;
1224
1225                         Expression e;
1226                         e =  new UserCast (method, source, loc);
1227                         if (e.Type != target){
1228                                 if (!look_for_explicit)
1229                                         e = ImplicitConversionStandard (ec, e, target, loc);
1230                                 else
1231                                         e = ExplicitConversionStandard (ec, e, target, loc);
1232                         }
1233
1234                         return e;
1235                 }
1236
1237                 /// <summary>
1238                 ///   Converts implicitly the resolved expression `expr' into the
1239                 ///   `target_type'.  It returns a new expression that can be used
1240                 ///   in a context that expects a `target_type'.
1241                 /// </summary>
1242                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
1243                                                              Type target_type, Location loc)
1244                 {
1245                         Expression e;
1246
1247                         if (target_type == null)
1248                                 throw new Exception ("Target type is null");
1249
1250                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1251                         if (e != null)
1252                                 return e;
1253
1254                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1255                         if (e != null)
1256                                 return e;
1257
1258                         return null;
1259                 }
1260
1261
1262                 /// <summary>
1263                 ///   Attempts to apply the `Standard Implicit
1264                 ///   Conversion' rules to the expression `expr' into
1265                 ///   the `target_type'.  It returns a new expression
1266                 ///   that can be used in a context that expects a
1267                 ///   `target_type'.
1268                 ///
1269                 ///   This is different from `ImplicitConversion' in that the
1270                 ///   user defined implicit conversions are excluded.
1271                 /// </summary>
1272                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1273                                                                      Type target_type, Location loc)
1274                 {
1275                         Type expr_type = expr.Type;
1276                         Expression e;
1277 #if GMCS_SOURCE
1278                         // TODO: refactor to be a part of constant infrastructure
1279                         if (expr is NullLiteral) {
1280                             if (TypeManager.IsNullableType (target_type))
1281                                 return new Nullable.NullableLiteral (target_type, loc);
1282                         }
1283
1284                         if (TypeManager.IsNullableType (target_type)) {
1285                                 Type target = TypeManager.GetTypeArguments (target_type) [0];
1286
1287                                 if (TypeManager.IsNullableType (expr.Type)) {
1288                                         e = new Nullable.LiftedConversion (
1289                                                 expr, target_type, false, false, loc).Resolve (ec);
1290                                         if (e != null)
1291                                                 return e;
1292                                 } else {
1293                                         e = ImplicitConversion (ec, expr, target, loc);
1294                                         if (e != null)
1295                                                 return Nullable.Wrap.Create (e, ec);
1296                                 }
1297                         }
1298 #endif
1299                         if (expr.eclass == ExprClass.MethodGroup){
1300                                 if (!TypeManager.IsDelegateType (target_type)){
1301                                         return null;
1302                                 }
1303
1304                                 //
1305                                 // Only allow anonymous method conversions on post ISO_1
1306                                 //
1307                                 if (RootContext.Version != LanguageVersion.ISO_1){
1308                                         MethodGroupExpr mg = expr as MethodGroupExpr;
1309                                         if (mg != null)
1310                                                 return ImplicitDelegateCreation.Create (
1311                                                         ec, mg, target_type, loc);
1312                                 }
1313                         }
1314
1315                         if (expr_type.Equals (target_type) && !TypeManager.IsNullType (expr_type))
1316                                 return expr;
1317
1318                         e = ImplicitNumericConversion (expr, target_type);
1319                         if (e != null)
1320                                 return e;
1321
1322                         e = ImplicitReferenceConversion (expr, target_type);
1323                         if (e != null)
1324                                 return e;
1325
1326                         if (TypeManager.IsEnumType (target_type) && expr is IntLiteral){
1327                                 IntLiteral i = (IntLiteral) expr;
1328
1329                                 if (i.Value == 0)
1330                                         return new EnumConstant ((Constant) expr, target_type);
1331                         }
1332
1333                         if (ec.InUnsafe) {
1334                                 if (expr_type.IsPointer){
1335                                         if (target_type == TypeManager.void_ptr_type)
1336                                                 return new EmptyCast (expr, target_type);
1337
1338                                         //
1339                                         // yep, comparing pointer types cant be done with
1340                                         // t1 == t2, we have to compare their element types.
1341                                         //
1342                                         if (target_type.IsPointer){
1343                                                 if (TypeManager.GetElementType(target_type) == TypeManager.GetElementType(expr_type))
1344                                                         return expr;
1345
1346                                                 //return null;
1347                                         }
1348                                 }
1349
1350                                 if (expr_type == TypeManager.null_type && target_type.IsPointer)
1351                                         return new EmptyCast (NullPointer.Null, target_type);
1352                         }
1353
1354                         if (expr_type == TypeManager.anonymous_method_type){
1355                                 AnonymousMethodExpression ame = (AnonymousMethodExpression) expr;
1356
1357                                 int errors = Report.Errors;
1358
1359                                 Expression conv = ame.Compatible (ec, target_type);
1360                                 if (conv != null)
1361                                         return conv;
1362
1363                                 //
1364                                 // We return something instead of null, to avoid
1365                                 // the duplicate error, since am.Compatible would have
1366                                 // reported that already
1367                                 //
1368                                 if (errors != Report.Errors)
1369                                         return new EmptyCast (expr, target_type);
1370                         }
1371
1372                         return null;
1373                 }
1374
1375                 /// <summary>
1376                 ///   Attempts to perform an implicit constant conversion of the IntConstant
1377                 ///   into a different data type using casts (See Implicit Constant
1378                 ///   Expression Conversions)
1379                 /// </summary>
1380                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1381                 {
1382                         int value = ic.Value;
1383
1384                         if (target_type == TypeManager.sbyte_type){
1385                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1386                                         return new SByteConstant ((sbyte) value, ic.Location);
1387                         } else if (target_type == TypeManager.byte_type){
1388                                 if (value >= Byte.MinValue && value <= Byte.MaxValue)
1389                                         return new ByteConstant ((byte) value, ic.Location);
1390                         } else if (target_type == TypeManager.short_type){
1391                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1392                                         return new ShortConstant ((short) value, ic.Location);
1393                         } else if (target_type == TypeManager.ushort_type){
1394                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1395                                         return new UShortConstant ((ushort) value, ic.Location);
1396                         } else if (target_type == TypeManager.uint32_type){
1397                                 if (value >= 0)
1398                                         return new UIntConstant ((uint) value, ic.Location);
1399                         } else if (target_type == TypeManager.uint64_type){
1400                                 //
1401                                 // we can optimize this case: a positive int32
1402                                 // always fits on a uint64.  But we need an opcode
1403                                 // to do it.
1404                                 //
1405                                 if (value >= 0)
1406                                         return new ULongConstant ((ulong) value, ic.Location);
1407                         } else if (target_type == TypeManager.double_type)
1408                                 return new DoubleConstant ((double) value, ic.Location);
1409                         else if (target_type == TypeManager.float_type)
1410                                 return new FloatConstant ((float) value, ic.Location);
1411
1412                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1413                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1414                                 Constant e = (Constant) ic;
1415
1416                                 //
1417                                 // Possibly, we need to create a different 0 literal before passing
1418                                 // to EnumConstant
1419                                 //
1420                                 if (underlying == TypeManager.int64_type)
1421                                         e = new LongLiteral (0, ic.Location);
1422                                 else if (underlying == TypeManager.uint64_type)
1423                                         e = new ULongLiteral (0, ic.Location);
1424
1425                                 return new EnumConstant (e, target_type);
1426                         }
1427
1428                         //
1429                         // If `target_type' is an interface and the type of `ic' implements the interface
1430                         // e.g. target_type is IComparable, IConvertible, IFormattable
1431                         //
1432                         if (target_type.IsInterface && target_type.IsAssignableFrom (ic.Type))
1433                                 return new BoxedCast (ic, target_type);
1434
1435                         return null;
1436                 }
1437
1438                 /// <summary>
1439                 ///   Attempts to implicitly convert `source' into `target_type', using
1440                 ///   ImplicitConversion.  If there is no implicit conversion, then
1441                 ///   an error is signaled
1442                 /// </summary>
1443                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1444                                                                      Type target_type, Location loc)
1445                 {
1446                         Expression e = ImplicitConversion (ec, source, target_type, loc);
1447                         if (e != null)
1448                                 return e;
1449
1450                         source.Error_ValueCannotBeConverted (loc, target_type, false);
1451                         return null;
1452                 }
1453
1454                 /// <summary>
1455                 ///   Performs the explicit numeric conversions
1456                 ///
1457                 /// There are a few conversions that are not part of the C# standard,
1458                 /// they were interim hacks in the C# compiler that were supposed to
1459                 /// become explicit operators in the UIntPtr class and IntPtr class,
1460                 /// but for historical reasons it did not happen, so the C# compiler
1461                 /// ended up with these special hacks.
1462                 ///
1463                 /// See bug 59800 for details.
1464                 ///
1465                 /// The conversion are:
1466                 ///   UIntPtr->SByte
1467                 ///   UIntPtr->Int16
1468                 ///   UIntPtr->Int32
1469                 ///   IntPtr->UInt64
1470                 ///   UInt64->IntPtr
1471                 ///   SByte->UIntPtr
1472                 ///   Int16->UIntPtr
1473                 ///
1474                 /// </summary>
1475                 public static Expression ExplicitNumericConversion (Expression expr, Type target_type)
1476                 {
1477                         Type expr_type = expr.Type;
1478                         Type real_target_type = target_type;
1479
1480                         if (expr_type == TypeManager.sbyte_type){
1481                                 //
1482                                 // From sbyte to byte, ushort, uint, ulong, char, uintptr
1483                                 //
1484                                 if (real_target_type == TypeManager.byte_type)
1485                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U1);
1486                                 if (real_target_type == TypeManager.ushort_type)
1487                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U2);
1488                                 if (real_target_type == TypeManager.uint32_type)
1489                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U4);
1490                                 if (real_target_type == TypeManager.uint64_type)
1491                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_U8);
1492                                 if (real_target_type == TypeManager.char_type)
1493                                         return new ConvCast (expr, target_type, ConvCast.Mode.I1_CH);
1494
1495                                 // One of the built-in conversions that belonged in the class library
1496                                 if (real_target_type == TypeManager.uintptr_type){
1497                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I1_U8);
1498
1499                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1500                                 }
1501                         } else if (expr_type == TypeManager.byte_type){
1502                                 //
1503                                 // From byte to sbyte and char
1504                                 //
1505                                 if (real_target_type == TypeManager.sbyte_type)
1506                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_I1);
1507                                 if (real_target_type == TypeManager.char_type)
1508                                         return new ConvCast (expr, target_type, ConvCast.Mode.U1_CH);
1509                         } else if (expr_type == TypeManager.short_type){
1510                                 //
1511                                 // From short to sbyte, byte, ushort, uint, ulong, char, uintptr
1512                                 //
1513                                 if (real_target_type == TypeManager.sbyte_type)
1514                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_I1);
1515                                 if (real_target_type == TypeManager.byte_type)
1516                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U1);
1517                                 if (real_target_type == TypeManager.ushort_type)
1518                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U2);
1519                                 if (real_target_type == TypeManager.uint32_type)
1520                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U4);
1521                                 if (real_target_type == TypeManager.uint64_type)
1522                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_U8);
1523                                 if (real_target_type == TypeManager.char_type)
1524                                         return new ConvCast (expr, target_type, ConvCast.Mode.I2_CH);
1525
1526                                 // One of the built-in conversions that belonged in the class library
1527                                 if (real_target_type == TypeManager.uintptr_type){
1528                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1529
1530                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1531                                 }
1532                         } else if (expr_type == TypeManager.ushort_type){
1533                                 //
1534                                 // From ushort to sbyte, byte, short, char
1535                                 //
1536                                 if (real_target_type == TypeManager.sbyte_type)
1537                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I1);
1538                                 if (real_target_type == TypeManager.byte_type)
1539                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_U1);
1540                                 if (real_target_type == TypeManager.short_type)
1541                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_I2);
1542                                 if (real_target_type == TypeManager.char_type)
1543                                         return new ConvCast (expr, target_type, ConvCast.Mode.U2_CH);
1544                         } else if (expr_type == TypeManager.int32_type){
1545                                 //
1546                                 // From int to sbyte, byte, short, ushort, uint, ulong, char, uintptr
1547                                 //
1548                                 if (real_target_type == TypeManager.sbyte_type)
1549                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I1);
1550                                 if (real_target_type == TypeManager.byte_type)
1551                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U1);
1552                                 if (real_target_type == TypeManager.short_type)
1553                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_I2);
1554                                 if (real_target_type == TypeManager.ushort_type)
1555                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U2);
1556                                 if (real_target_type == TypeManager.uint32_type)
1557                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U4);
1558                                 if (real_target_type == TypeManager.uint64_type)
1559                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_U8);
1560                                 if (real_target_type == TypeManager.char_type)
1561                                         return new ConvCast (expr, target_type, ConvCast.Mode.I4_CH);
1562
1563                                 // One of the built-in conversions that belonged in the class library
1564                                 if (real_target_type == TypeManager.uintptr_type){
1565                                         Expression u8e = new ConvCast (expr, TypeManager.uint64_type, ConvCast.Mode.I2_U8);
1566
1567                                         return new OperatorCast (u8e, TypeManager.uintptr_type, true);
1568                                 }
1569                         } else if (expr_type == TypeManager.uint32_type){
1570                                 //
1571                                 // From uint to sbyte, byte, short, ushort, int, char
1572                                 //
1573                                 if (real_target_type == TypeManager.sbyte_type)
1574                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I1);
1575                                 if (real_target_type == TypeManager.byte_type)
1576                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U1);
1577                                 if (real_target_type == TypeManager.short_type)
1578                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I2);
1579                                 if (real_target_type == TypeManager.ushort_type)
1580                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_U2);
1581                                 if (real_target_type == TypeManager.int32_type)
1582                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_I4);
1583                                 if (real_target_type == TypeManager.char_type)
1584                                         return new ConvCast (expr, target_type, ConvCast.Mode.U4_CH);
1585                         } else if (expr_type == TypeManager.int64_type){
1586                                 //
1587                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1588                                 //
1589                                 if (real_target_type == TypeManager.sbyte_type)
1590                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I1);
1591                                 if (real_target_type == TypeManager.byte_type)
1592                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U1);
1593                                 if (real_target_type == TypeManager.short_type)
1594                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I2);
1595                                 if (real_target_type == TypeManager.ushort_type)
1596                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U2);
1597                                 if (real_target_type == TypeManager.int32_type)
1598                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_I4);
1599                                 if (real_target_type == TypeManager.uint32_type)
1600                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U4);
1601                                 if (real_target_type == TypeManager.uint64_type)
1602                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_U8);
1603                                 if (real_target_type == TypeManager.char_type)
1604                                         return new ConvCast (expr, target_type, ConvCast.Mode.I8_CH);
1605                         } else if (expr_type == TypeManager.uint64_type){
1606                                 //
1607                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1608                                 //
1609                                 if (real_target_type == TypeManager.sbyte_type)
1610                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I1);
1611                                 if (real_target_type == TypeManager.byte_type)
1612                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U1);
1613                                 if (real_target_type == TypeManager.short_type)
1614                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I2);
1615                                 if (real_target_type == TypeManager.ushort_type)
1616                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U2);
1617                                 if (real_target_type == TypeManager.int32_type)
1618                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I4);
1619                                 if (real_target_type == TypeManager.uint32_type)
1620                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_U4);
1621                                 if (real_target_type == TypeManager.int64_type)
1622                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_I8);
1623                                 if (real_target_type == TypeManager.char_type)
1624                                         return new ConvCast (expr, target_type, ConvCast.Mode.U8_CH);
1625
1626                                 // One of the built-in conversions that belonged in the class library
1627                                 if (real_target_type == TypeManager.intptr_type){
1628                                         return new OperatorCast (new EmptyCast (expr, TypeManager.int64_type),
1629                                                                  TypeManager.intptr_type, true);
1630                                 }
1631                         } else if (expr_type == TypeManager.char_type){
1632                                 //
1633                                 // From char to sbyte, byte, short
1634                                 //
1635                                 if (real_target_type == TypeManager.sbyte_type)
1636                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I1);
1637                                 if (real_target_type == TypeManager.byte_type)
1638                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_U1);
1639                                 if (real_target_type == TypeManager.short_type)
1640                                         return new ConvCast (expr, target_type, ConvCast.Mode.CH_I2);
1641                         } else if (expr_type == TypeManager.float_type){
1642                                 //
1643                                 // From float to sbyte, byte, short,
1644                                 // ushort, int, uint, long, ulong, char
1645                                 // or decimal
1646                                 //
1647                                 if (real_target_type == TypeManager.sbyte_type)
1648                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I1);
1649                                 if (real_target_type == TypeManager.byte_type)
1650                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U1);
1651                                 if (real_target_type == TypeManager.short_type)
1652                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I2);
1653                                 if (real_target_type == TypeManager.ushort_type)
1654                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U2);
1655                                 if (real_target_type == TypeManager.int32_type)
1656                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I4);
1657                                 if (real_target_type == TypeManager.uint32_type)
1658                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U4);
1659                                 if (real_target_type == TypeManager.int64_type)
1660                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_I8);
1661                                 if (real_target_type == TypeManager.uint64_type)
1662                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_U8);
1663                                 if (real_target_type == TypeManager.char_type)
1664                                         return new ConvCast (expr, target_type, ConvCast.Mode.R4_CH);
1665                                 if (real_target_type == TypeManager.decimal_type)
1666                                         return new CastToDecimal (expr, true);
1667                         } else if (expr_type == TypeManager.double_type){
1668                                 //
1669                                 // From double to sbyte, byte, short,
1670                                 // ushort, int, uint, long, ulong,
1671                                 // char, float or decimal
1672                                 //
1673                                 if (real_target_type == TypeManager.sbyte_type)
1674                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I1);
1675                                 if (real_target_type == TypeManager.byte_type)
1676                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U1);
1677                                 if (real_target_type == TypeManager.short_type)
1678                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I2);
1679                                 if (real_target_type == TypeManager.ushort_type)
1680                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U2);
1681                                 if (real_target_type == TypeManager.int32_type)
1682                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I4);
1683                                 if (real_target_type == TypeManager.uint32_type)
1684                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U4);
1685                                 if (real_target_type == TypeManager.int64_type)
1686                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_I8);
1687                                 if (real_target_type == TypeManager.uint64_type)
1688                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_U8);
1689                                 if (real_target_type == TypeManager.char_type)
1690                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_CH);
1691                                 if (real_target_type == TypeManager.float_type)
1692                                         return new ConvCast (expr, target_type, ConvCast.Mode.R8_R4);
1693                                 if (real_target_type == TypeManager.decimal_type)
1694                                         return new CastToDecimal (expr, true);
1695                         } else if (expr_type == TypeManager.uintptr_type){
1696                                 //
1697                                 // Various built-in conversions that belonged in the class library
1698                                 //
1699                                 // from uintptr to sbyte, short, int32
1700                                 //
1701                                 if (real_target_type == TypeManager.sbyte_type){
1702                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1703                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I1);
1704                                 }
1705                                 if (real_target_type == TypeManager.short_type){
1706                                         Expression uint32e = new OperatorCast (expr, TypeManager.uint32_type, true);
1707                                         return new ConvCast (uint32e, TypeManager.sbyte_type, ConvCast.Mode.U4_I2);
1708                                 }
1709                                 if (real_target_type == TypeManager.int32_type)
1710                                         return new EmptyCast (new OperatorCast (expr, TypeManager.uint64_type, true),
1711                                                               TypeManager.int32_type);
1712                         } else if (expr_type == TypeManager.intptr_type){
1713                                 if (real_target_type == TypeManager.uint64_type){
1714                                         return new EmptyCast (new OperatorCast (expr, TypeManager.int64_type, true),
1715                                                               TypeManager.uint64_type);
1716                                 }
1717                         } else if (expr_type == TypeManager.decimal_type) {
1718                                 return new CastFromDecimal (expr, target_type).Resolve ();
1719                         }
1720                         return null;
1721                 }
1722
1723                 /// <summary>
1724                 ///  Returns whether an explicit reference conversion can be performed
1725                 ///  from source_type to target_type
1726                 /// </summary>
1727                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1728                 {
1729                         bool target_is_type_param = TypeManager.IsGenericParameter (target_type);
1730                         bool target_is_value_type = target_type.IsValueType;
1731
1732                         if (source_type == target_type)
1733                                 return true;
1734
1735                         //
1736                         // From generic parameter to any type
1737                         //
1738                         if (TypeManager.IsGenericParameter (source_type))
1739                                 return ExplicitTypeParameterConversionExists (source_type, target_type);
1740
1741                         //
1742                         // From object to a generic parameter
1743                         //
1744                         if (source_type == TypeManager.object_type && target_is_type_param)
1745                                 return true;
1746
1747                         //
1748                         // From object to any reference type
1749                         //
1750                         if (source_type == TypeManager.object_type && !target_is_value_type)
1751                                 return true;
1752
1753                         //
1754                         // From any class S to any class-type T, provided S is a base class of T
1755                         //
1756                         if (TypeManager.IsSubclassOf (target_type, source_type))
1757                                 return true;
1758
1759                         //
1760                         // From any interface type S to any interface T provided S is not derived from T
1761                         //
1762                         if (source_type.IsInterface && target_type.IsInterface){
1763                                 if (!TypeManager.IsSubclassOf (target_type, source_type))
1764                                         return true;
1765                         }
1766
1767                         //
1768                         // From any class type S to any interface T, provided S is not sealed
1769                         // and provided S does not implement T.
1770                         //
1771                         if (target_type.IsInterface && !source_type.IsSealed &&
1772                             !TypeManager.ImplementsInterface (source_type, target_type))
1773                                 return true;
1774
1775                         //
1776                         // From any interface-type S to to any class type T, provided T is not
1777                         // sealed, or provided T implements S.
1778                         //
1779                         if (source_type.IsInterface &&
1780                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1781                                 return true;
1782
1783
1784                         // From an array type S with an element type Se to an array type T with an
1785                         // element type Te provided all the following are true:
1786                         //     * S and T differe only in element type, in other words, S and T
1787                         //       have the same number of dimensions.
1788                         //     * Both Se and Te are reference types
1789                         //     * An explicit referenc conversions exist from Se to Te
1790                         //
1791                         if (source_type.IsArray && target_type.IsArray) {
1792                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1793
1794                                         Type source_element_type = TypeManager.GetElementType (source_type);
1795                                         Type target_element_type = TypeManager.GetElementType (target_type);
1796
1797                                         if (TypeManager.IsGenericParameter (source_element_type) ||
1798                                             (!source_element_type.IsValueType && !target_element_type.IsValueType))
1799                                                 if (ExplicitReferenceConversionExists (source_element_type,
1800                                                                                        target_element_type))
1801                                                         return true;
1802                                 }
1803                         }
1804
1805
1806                         // From System.Array to any array-type
1807                         if (source_type == TypeManager.array_type &&
1808                             target_type.IsArray){
1809                                 return true;
1810                         }
1811
1812                         //
1813                         // From System delegate to any delegate-type
1814                         //
1815                         if (source_type == TypeManager.delegate_type &&
1816                             TypeManager.IsDelegateType (target_type))
1817                                 return true;
1818
1819                         //
1820                         // From ICloneable to Array or Delegate types
1821                         //
1822                         if (source_type == TypeManager.icloneable_type &&
1823                             (target_type == TypeManager.array_type ||
1824                              target_type == TypeManager.delegate_type))
1825                                 return true;
1826
1827                         return false;
1828                 }
1829
1830                 /// <summary>
1831                 ///   Implements Explicit Reference conversions
1832                 /// </summary>
1833                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1834                 {
1835                         Type source_type = source.Type;
1836                         bool target_is_type_param = TypeManager.IsGenericParameter (target_type);
1837                         bool target_is_value_type = target_type.IsValueType;
1838
1839                         //
1840                         // From object to a generic parameter
1841                         //
1842                         if (source_type == TypeManager.object_type && target_is_type_param)
1843                                 return new UnboxCast (source, target_type);
1844
1845                         //
1846                         // Explicit type parameter conversion.
1847                         //
1848
1849                         if (TypeManager.IsGenericParameter (source_type))
1850                                 return ExplicitTypeParameterConversion (source, target_type);
1851
1852                         //
1853                         // From object to any reference type
1854                         //
1855                         if (source_type == TypeManager.object_type && !target_is_value_type)
1856                                 return new ClassCast (source, target_type);
1857
1858                         //
1859                         // Unboxing conversion.
1860                         //
1861                         if (((source_type == TypeManager.enum_type &&
1862                                 !(source is EmptyCast)) ||
1863                                 source_type == TypeManager.value_type) && target_is_value_type)
1864                                 return new UnboxCast (source, target_type);
1865
1866                         //
1867                         // From any class S to any class-type T, provided S is a base class of T
1868                         //
1869                         if (TypeManager.IsSubclassOf (target_type, source_type))
1870                                 return new ClassCast (source, target_type);
1871
1872                         //
1873                         // From any interface type S to any interface T provided S is not derived from T
1874                         //
1875                         if (source_type.IsInterface && target_type.IsInterface){
1876                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1877                                         return null;
1878                                 else
1879                                         return new ClassCast (source, target_type);
1880                         }
1881
1882                         //
1883                         // From any class type S to any interface T, provides S is not sealed
1884                         // and provided S does not implement T.
1885                         //
1886                         if (target_type.IsInterface && !source_type.IsSealed) {
1887                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1888                                         return null;
1889                                 else
1890                                         return new ClassCast (source, target_type);
1891
1892                         }
1893
1894                         //
1895                         // From any interface-type S to to any class type T, provided T is not
1896                         // sealed, or provided T implements S.
1897                         //
1898                         if (source_type.IsInterface) {
1899                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)) {
1900                                         if (target_type.IsClass)
1901                                                 return new ClassCast (source, target_type);
1902                                         else
1903                                                 return new UnboxCast (source, target_type);
1904                                 }
1905
1906                                 return null;
1907                         }
1908
1909                         // From an array type S with an element type Se to an array type T with an
1910                         // element type Te provided all the following are true:
1911                         //     * S and T differe only in element type, in other words, S and T
1912                         //       have the same number of dimensions.
1913                         //     * Both Se and Te are reference types
1914                         //     * An explicit referenc conversions exist from Se to Te
1915                         //
1916                         if (source_type.IsArray && target_type.IsArray) {
1917                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1918
1919                                         Type source_element_type = TypeManager.GetElementType (source_type);
1920                                         Type target_element_type = TypeManager.GetElementType (target_type);
1921
1922                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1923                                                 if (ExplicitReferenceConversionExists (source_element_type,
1924                                                                                        target_element_type))
1925                                                         return new ClassCast (source, target_type);
1926                                 }
1927                         }
1928
1929
1930                         // From System.Array to any array-type
1931                         if (source_type == TypeManager.array_type &&
1932                             target_type.IsArray) {
1933                                 return new ClassCast (source, target_type);
1934                         }
1935
1936                         //
1937                         // From System delegate to any delegate-type
1938                         //
1939                         if (source_type == TypeManager.delegate_type &&
1940                             TypeManager.IsDelegateType (target_type))
1941                                 return new ClassCast (source, target_type);
1942
1943                         //
1944                         // From ICloneable to Array or Delegate types
1945                         //
1946                         if (source_type == TypeManager.icloneable_type &&
1947                             (target_type == TypeManager.array_type ||
1948                              target_type == TypeManager.delegate_type))
1949                                 return new ClassCast (source, target_type);
1950
1951                         return null;
1952                 }
1953
1954                 /// <summary>
1955                 ///   Performs an explicit conversion of the expression `expr' whose
1956                 ///   type is expr.Type to `target_type'.
1957                 /// </summary>
1958                 static public Expression ExplicitConversionCore (EmitContext ec, Expression expr,
1959                                                                  Type target_type, Location loc)
1960                 {
1961                         Type expr_type = expr.Type;
1962
1963                         // Explicit conversion includes implicit conversion and it used for enum underlying types too
1964                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1965                         if (ne != null)
1966                                 return ne;
1967
1968                         //
1969                         // Unboxing conversions; only object types can be convertible to enum
1970                         //
1971                         if (expr_type == TypeManager.object_type && target_type.IsValueType)
1972                                 return new UnboxCast (expr, target_type);
1973
1974                         if (TypeManager.IsEnumType (expr_type)) {
1975                                 if (expr is EnumConstant)
1976                                         return ExplicitConversionCore (ec, ((EnumConstant) expr).Child, target_type, loc);
1977
1978                                 return ExplicitConversionCore (ec, new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type)), target_type, loc);
1979                         }
1980
1981                         if (TypeManager.IsEnumType (target_type)){
1982                                 if (expr_type == TypeManager.enum_type)
1983                                         return new UnboxCast (expr, target_type);
1984
1985                                 Expression ce = ExplicitConversionCore (ec, expr, TypeManager.EnumToUnderlying (target_type), loc);
1986                                 if (ce != null)
1987                                         return new EmptyCast (ce, target_type);
1988                         }
1989
1990                         ne = ExplicitNumericConversion (expr, target_type);
1991                         if (ne != null)
1992                                 return ne;
1993
1994                         //
1995                         // Skip the ExplicitReferenceConversion because we can not convert
1996                         // from Null to a ValueType, and ExplicitReference wont check against
1997                         // null literal explicitly
1998                         //
1999                         if (expr_type != TypeManager.null_type){
2000                                 ne = ExplicitReferenceConversion (expr, target_type);
2001                                 if (ne != null)
2002                                         return ne;
2003                         }
2004
2005                         if (ec.InUnsafe){
2006                                 ne = ExplicitUnsafe (expr, target_type);
2007                                 if (ne != null)
2008                                         return ne;
2009                         }
2010
2011                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
2012                         if (ne != null)
2013                                 return ne;
2014
2015                         return null;
2016                 }
2017
2018                 public static Expression ExplicitUnsafe (Expression expr, Type target_type)
2019                 {
2020                         Type expr_type = expr.Type;
2021
2022                         if (target_type.IsPointer){
2023                                 if (expr_type.IsPointer)
2024                                         return new EmptyCast (expr, target_type);
2025
2026                                 if (expr_type == TypeManager.sbyte_type ||
2027                                         expr_type == TypeManager.short_type ||
2028                                         expr_type == TypeManager.int32_type ||
2029                                         expr_type == TypeManager.int64_type)
2030                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I);
2031
2032                                 if (expr_type == TypeManager.ushort_type ||
2033                                         expr_type == TypeManager.uint32_type ||
2034                                         expr_type == TypeManager.uint64_type ||
2035                                         expr_type == TypeManager.byte_type)
2036                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
2037                         }
2038
2039                         if (expr_type.IsPointer){
2040                                 if (target_type == TypeManager.sbyte_type)
2041                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
2042                                 else if (target_type == TypeManager.byte_type)
2043                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
2044                                 else if (target_type == TypeManager.short_type)
2045                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
2046                                 else if (target_type == TypeManager.ushort_type)
2047                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
2048                                 else if (target_type == TypeManager.int32_type)
2049                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
2050                                 else if (target_type == TypeManager.uint32_type)
2051                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
2052                                 else if (target_type == TypeManager.uint64_type)
2053                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
2054                                 else if (target_type == TypeManager.int64_type){
2055                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
2056                                 }
2057                         }
2058                         return null;
2059                 }
2060
2061                 /// <summary>
2062                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
2063                 /// </summary>
2064                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
2065                                                                      Type target_type, Location l)
2066                 {
2067                         int errors = Report.Errors;
2068                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
2069                         if (Report.Errors > errors)
2070                                 return null;
2071
2072                         if (ne != null)
2073                                 return ne;
2074
2075                         ne = ExplicitNumericConversion (expr, target_type);
2076                         if (ne != null)
2077                                 return ne;
2078
2079                         ne = ExplicitReferenceConversion (expr, target_type);
2080                         if (ne != null)
2081                                 return ne;
2082
2083                         if (ec.InUnsafe && expr.Type == TypeManager.void_ptr_type && target_type.IsPointer)
2084                                 return new EmptyCast (expr, target_type);
2085
2086                         expr.Error_ValueCannotBeConverted (l, target_type, true);
2087                         return null;
2088                 }
2089
2090                 /// <summary>
2091                 ///   Performs an explicit conversion of the expression `expr' whose
2092                 ///   type is expr.Type to `target_type'.
2093                 /// </summary>
2094                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
2095                         Type target_type, Location loc)
2096                 {
2097                         Expression e;
2098 #if GMCS_SOURCE
2099                         Type expr_type = expr.Type;
2100                         if (TypeManager.IsNullableType (target_type)) {
2101                                 if (TypeManager.IsNullableType (expr_type)) {
2102                                         e = new Nullable.LiftedConversion (
2103                                                 expr, target_type, false, true, loc).Resolve (ec);
2104                                         if (e != null)
2105                                                 return e;
2106                                 } else if (expr_type == TypeManager.object_type) {
2107                                         return new UnboxCast (expr, target_type);
2108                                 } else {
2109                                         Type target = TypeManager.GetTypeArguments (target_type) [0];
2110
2111                                         e = ExplicitConversionCore (ec, expr, target, loc);
2112                                         if (e != null)
2113                                                 return Nullable.Wrap.Create (e, ec);
2114                                 }
2115                         } else if (TypeManager.IsNullableType (expr_type)) {
2116                                 Expression source = Nullable.Unwrap.Create (expr, ec);
2117                                 if (source != null) {
2118                                         e = ExplicitConversionCore (ec, source, target_type, loc);
2119                                         if (e != null)
2120                                                 return e;
2121                                 }
2122                         }
2123 #endif
2124                         e = ExplicitConversionCore (ec, expr, target_type, loc);
2125                         if (e != null)
2126                                 return e;
2127
2128                         expr.Error_ValueCannotBeConverted (loc, target_type, true);
2129                         return null;
2130                 }
2131         }
2132 }