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                 static public void Error_CannotConvertType (Location loc, Type source, Type target)
  23                 {
  24                         Report.Error (30, loc, "Cannot convert type '" +
  25                                       TypeManager.CSharpName (source) + "' to '" +
  26                                       TypeManager.CSharpName (target) + "'");
  27                 }
  28
  29                 static EmptyExpression MyEmptyExpr;
  30                 static public Expression ImplicitReferenceConversion (Expression expr, Type target_type)
  31                 {
  32                         Type expr_type = expr.Type;
  33
  34                         if (expr_type == null && expr.eclass == ExprClass.MethodGroup){
  35                                 // if we are a method group, emit a warning
  36
  37                                 expr.Emit (null);
  38                         }
  39
  40                         //
  41                         // notice that it is possible to write "ValueType v = 1", the ValueType here
  42                         // is an abstract class, and not really a value type, so we apply the same rules.
  43                         //
  44                         if (target_type == TypeManager.object_type) {
  45                                 //
  46                                 // A pointer type cannot be converted to object
  47                                 //
  48                                 if (expr_type.IsPointer)
  49                                         return null;
  50
  51                                 if (expr_type.IsValueType)
  52                                         return new BoxedCast (expr);
  53                                 if (expr_type.IsClass || expr_type.IsInterface || expr_type == TypeManager.enum_type)
  54                                         return new EmptyCast (expr, target_type);
  55                         } else if (target_type == TypeManager.value_type) {
  56                                 if (expr_type.IsValueType)
  57                                         return new BoxedCast (expr);
  58                                 if (expr is NullLiteral)
  59                                         return new BoxedCast (expr);
  60                         } else if (expr_type.IsSubclassOf (target_type)) {
  61                                 //
  62                                 // Special case: enumeration to System.Enum.
  63                                 // System.Enum is not a value type, it is a class, so we need
  64                                 // a boxing conversion
  65                                 //
  66                                 if (expr_type.IsEnum)
  67                                         return new BoxedCast (expr);
  68
  69                                 return new EmptyCast (expr, target_type);
  70                         } else {
  71
  72                                 // This code is kind of mirrored inside ImplicitStandardConversionExists
  73                                 // with the small distinction that we only probe there
  74                                 //
  75                                 // Always ensure that the code here and there is in sync
  76
  77                                 // from the null type to any reference-type.
  78                                 if (expr is NullLiteral){
  79                                         if (target_type.IsPointer)
  80                                                 return NullPointer.Null;
  81
  82                                         if (!target_type.IsValueType)
  83                                                 return new NullCast (expr, target_type);
  84                                 }
  85
  86                                 // from any class-type S to any interface-type T.
  87                                 if (target_type.IsInterface) {
  88                                         if (TypeManager.ImplementsInterface (expr_type, target_type)){
  89                                                 if (expr_type.IsClass)
  90                                                         return new EmptyCast (expr, target_type);
  91                                                 else if (expr_type.IsValueType)
  92                                                         return new BoxedCast (expr, target_type);
  93                                         }
  94                                 }
  95
  96                                 // from any interface type S to interface-type T.
  97                                 if (expr_type.IsInterface && target_type.IsInterface) {
  98                                         if (TypeManager.ImplementsInterface (expr_type, target_type))
  99                                                 return new EmptyCast (expr, target_type);
 100                                         else
 101                                                 return null;
 102                                 }
 103
 104                                 // from an array-type S to an array-type of type T
 105                                 if (expr_type.IsArray && target_type.IsArray) {
 106                                         if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 107
 108                                                 Type expr_element_type = expr_type.GetElementType ();
 109
 110                                                 if (MyEmptyExpr == null)
 111                                                         MyEmptyExpr = new EmptyExpression ();
 112
 113                                                 MyEmptyExpr.SetType (expr_element_type);
 114                                                 Type target_element_type = target_type.GetElementType ();
 115
 116                                                 if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 117                                                         if (ImplicitStandardConversionExists (MyEmptyExpr,
 118                                                                                       target_element_type))
 119                                                                 return new EmptyCast (expr, target_type);
 120                                         }
 121                                 }
 122
 123
 124                                 // from an array-type to System.Array
 125                                 if (expr_type.IsArray && target_type == TypeManager.array_type)
 126                                         return new EmptyCast (expr, target_type);
 127
 128                                 // from any delegate type to System.Delegate
 129                                 if ((expr_type == TypeManager.delegate_type ||
 130                                      expr_type.IsSubclassOf (TypeManager.delegate_type)) &&
 131                                     target_type == TypeManager.delegate_type)
 132                                         return new EmptyCast (expr, target_type);
 133
 134                                 // from any array-type or delegate type into System.ICloneable.
 135                                 if (expr_type.IsArray ||
 136                                     expr_type == TypeManager.delegate_type ||
 137                                     expr_type.IsSubclassOf (TypeManager.delegate_type))
 138                                         if (target_type == TypeManager.icloneable_type)
 139                                                 return new EmptyCast (expr, target_type);
 140
 141                                 return null;
 142
 143                         }
 144
 145                         return null;
 146                 }
 147
 148                 //
 149                 // Tests whether an implicit reference conversion exists between expr_type
 150                 // and target_type
 151                 //
 152                 public static bool ImplicitReferenceConversionExists (Expression expr, Type target_type)
 153                 {
 154                         Type expr_type = expr.Type;
 155
 156                         //
 157                         // This is the boxed case.
 158                         //
 159                         if (target_type == TypeManager.object_type) {
 160                                 if (expr_type.IsClass || expr_type.IsValueType ||
 161                                     expr_type.IsInterface || expr_type == TypeManager.enum_type)
 162                                         return true;
 163                         } else if (expr_type.IsSubclassOf (target_type)) {
 164                                 return true;
 165                         } else {
 166                                 // Please remember that all code below actually comes
 167                                 // from ImplicitReferenceConversion so make sure code remains in sync
 168
 169                                 // from any class-type S to any interface-type T.
 170                                 if (target_type.IsInterface) {
 171                                         if (TypeManager.ImplementsInterface (expr_type, target_type))
 172                                                 return true;
 173                                 }
 174
 175                                 // from any interface type S to interface-type T.
 176                                 if (expr_type.IsInterface && target_type.IsInterface)
 177                                         if (TypeManager.ImplementsInterface (expr_type, target_type))
 178                                                 return true;
 179
 180                                 // from an array-type S to an array-type of type T
 181                                 if (expr_type.IsArray && target_type.IsArray) {
 182                                         if (expr_type.GetArrayRank () == target_type.GetArrayRank ()) {
 183
 184                                                 Type expr_element_type = expr_type.GetElementType ();
 185
 186                                                 if (MyEmptyExpr == null)
 187                                                         MyEmptyExpr = new EmptyExpression ();
 188
 189                                                 MyEmptyExpr.SetType (expr_element_type);
 190                                                 Type target_element_type = target_type.GetElementType ();
 191
 192                                                 if (!expr_element_type.IsValueType && !target_element_type.IsValueType)
 193                                                         if (ImplicitStandardConversionExists (MyEmptyExpr,
 194                                                                                       target_element_type))
 195                                                                 return true;
 196                                         }
 197                                 }
 198
 199                                 // from an array-type to System.Array
 200                                 if (expr_type.IsArray && (target_type == TypeManager.array_type))
 201                                         return true;
 202
 203                                 // from any delegate type to System.Delegate
 204                                 if ((expr_type == TypeManager.delegate_type ||
 205                                      expr_type.IsSubclassOf (TypeManager.delegate_type)) &&
 206                                     target_type == TypeManager.delegate_type)
 207                                         if (target_type.IsAssignableFrom (expr_type))
 208                                                 return true;
 209
 210                                 // from any array-type or delegate type into System.ICloneable.
 211                                 if (expr_type.IsArray ||
 212                                     expr_type == TypeManager.delegate_type ||
 213                                     expr_type.IsSubclassOf (TypeManager.delegate_type))
 214                                         if (target_type == TypeManager.icloneable_type)
 215                                                 return true;
 216
 217                                 // from the null type to any reference-type.
 218                                 if (expr is NullLiteral && !target_type.IsValueType &&
 219                                     !TypeManager.IsEnumType (target_type))
 220                                         return true;
 221
 222                         }
 223                         return false;
 224                 }
 225
 226                 /// <summary>
 227                 ///   Implicit Numeric Conversions.
 228                 ///
 229                 ///   expr is the expression to convert, returns a new expression of type
 230                 ///   target_type or null if an implicit conversion is not possible.
 231                 /// </summary>
 232                 static public Expression ImplicitNumericConversion (EmitContext ec, Expression expr,
 233                                                                     Type target_type, Location loc)
 234                 {
 235                         Type expr_type = expr.Type;
 236
 237                         //
 238                         // Attempt to do the implicit constant expression conversions
 239
 240                         if (expr is Constant){
 241
 242                                 if (expr is IntConstant){
 243                                         Expression e;
 244
 245                                         e = TryImplicitIntConversion (target_type, (IntConstant) expr);
 246
 247                                         if (e != null)
 248                                                 return e;
 249                                 } else if (expr is LongConstant && target_type == TypeManager.uint64_type){
 250                                         //
 251                                         // Try the implicit constant expression conversion
 252                                         // from long to ulong, instead of a nice routine,
 253                                         // we just inline it
 254                                         //
 255                                         long v = ((LongConstant) expr).Value;
 256                                         if (v > 0)
 257                                                 return new ULongConstant ((ulong) v);
 258                                 }
 259                         }
 260
 261                         Type real_target_type = target_type;
 262
 263                         if (expr_type == TypeManager.sbyte_type){
 264                                 //
 265                                 // From sbyte to short, int, long, float, double.
 266                                 //
 267                                 if (real_target_type == TypeManager.int32_type)
 268                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 269                                 if (real_target_type == TypeManager.int64_type)
 270                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 271                                 if (real_target_type == TypeManager.double_type)
 272                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 273                                 if (real_target_type == TypeManager.float_type)
 274                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 275                                 if (real_target_type == TypeManager.short_type)
 276                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
 277                         } else if (expr_type == TypeManager.byte_type){
 278                                 //
 279                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 280                                 //
 281                                 if ((real_target_type == TypeManager.short_type) ||
 282                                     (real_target_type == TypeManager.ushort_type) ||
 283                                     (real_target_type == TypeManager.int32_type) ||
 284                                     (real_target_type == TypeManager.uint32_type))
 285                                         return new EmptyCast (expr, target_type);
 286
 287                                 if (real_target_type == TypeManager.uint64_type)
 288                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 289                                 if (real_target_type == TypeManager.int64_type)
 290                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 291                                 if (real_target_type == TypeManager.float_type)
 292                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 293                                 if (real_target_type == TypeManager.double_type)
 294                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 295                         } else if (expr_type == TypeManager.short_type){
 296                                 //
 297                                 // From short to int, long, float, double
 298                                 //
 299                                 if (real_target_type == TypeManager.int32_type)
 300                                         return new EmptyCast (expr, target_type);
 301                                 if (real_target_type == TypeManager.int64_type)
 302                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 303                                 if (real_target_type == TypeManager.double_type)
 304                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 305                                 if (real_target_type == TypeManager.float_type)
 306                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 307                         } else if (expr_type == TypeManager.ushort_type){
 308                                 //
 309                                 // From ushort to int, uint, long, ulong, float, double
 310                                 //
 311                                 if (real_target_type == TypeManager.uint32_type)
 312                                         return new EmptyCast (expr, target_type);
 313
 314                                 if (real_target_type == TypeManager.uint64_type)
 315                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 316                                 if (real_target_type == TypeManager.int32_type)
 317                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
 318                                 if (real_target_type == TypeManager.int64_type)
 319                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 320                                 if (real_target_type == TypeManager.double_type)
 321                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 322                                 if (real_target_type == TypeManager.float_type)
 323                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 324                         } else if (expr_type == TypeManager.int32_type){
 325                                 //
 326                                 // From int to long, float, double
 327                                 //
 328                                 if (real_target_type == TypeManager.int64_type)
 329                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 330                                 if (real_target_type == TypeManager.double_type)
 331                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 332                                 if (real_target_type == TypeManager.float_type)
 333                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 334                         } else if (expr_type == TypeManager.uint32_type){
 335                                 //
 336                                 // From uint to long, ulong, float, double
 337                                 //
 338                                 if (real_target_type == TypeManager.int64_type)
 339                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 340                                 if (real_target_type == TypeManager.uint64_type)
 341                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 342                                 if (real_target_type == TypeManager.double_type)
 343                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 344                                                                OpCodes.Conv_R8);
 345                                 if (real_target_type == TypeManager.float_type)
 346                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 347                                                                OpCodes.Conv_R4);
 348                         } else if (expr_type == TypeManager.int64_type){
 349                                 //
 350                                 // From long/ulong to float, double
 351                                 //
 352                                 if (real_target_type == TypeManager.double_type)
 353                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 354                                 if (real_target_type == TypeManager.float_type)
 355                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 356                         } else if (expr_type == TypeManager.uint64_type){
 357                                 //
 358                                 // From ulong to float, double
 359                                 //
 360                                 if (real_target_type == TypeManager.double_type)
 361                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 362                                                                OpCodes.Conv_R8);
 363                                 if (real_target_type == TypeManager.float_type)
 364                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R_Un,
 365                                                                OpCodes.Conv_R4);
 366                         } else if (expr_type == TypeManager.char_type){
 367                                 //
 368                                 // From char to ushort, int, uint, long, ulong, float, double
 369                                 //
 370                                 if ((real_target_type == TypeManager.ushort_type) ||
 371                                     (real_target_type == TypeManager.int32_type) ||
 372                                     (real_target_type == TypeManager.uint32_type))
 373                                         return new EmptyCast (expr, target_type);
 374                                 if (real_target_type == TypeManager.uint64_type)
 375                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
 376                                 if (real_target_type == TypeManager.int64_type)
 377                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
 378                                 if (real_target_type == TypeManager.float_type)
 379                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R4);
 380                                 if (real_target_type == TypeManager.double_type)
 381                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 382                         } else if (expr_type == TypeManager.float_type){
 383                                 //
 384                                 // float to double
 385                                 //
 386                                 if (real_target_type == TypeManager.double_type)
 387                                         return new OpcodeCast (expr, target_type, OpCodes.Conv_R8);
 388                         }
 389
 390                         return null;
 391                 }
 392
 393
 394                 /// <summary>
 395                 ///  Same as ImplicitStandardConversionExists except that it also looks at
 396                 ///  implicit user defined conversions - needed for overload resolution
 397                 /// </summary>
 398                 public static bool ImplicitConversionExists (EmitContext ec, Expression expr, Type target_type)
 399                 {
 400                         if (ImplicitStandardConversionExists (expr, target_type) == true)
 401                                 return true;
 402
 403                         Expression dummy = ImplicitUserConversion (ec, expr, target_type, Location.Null);
 404
 405                         if (dummy != null)
 406                                 return true;
 407
 408                         return false;
 409                 }
 410
 411                 public static bool ImplicitUserConversionExists (EmitContext ec, Type source, Type target)
 412                 {
 413                         Expression dummy = ImplicitUserConversion (
 414                                 ec, new EmptyExpression (source), target, Location.Null);
 415                         return dummy != null;
 416                 }
 417
 418                 /// <summary>
 419                 ///  Determines if a standard implicit conversion exists from
 420                 ///  expr_type to target_type
 421                 /// </summary>
 422                 public static bool ImplicitStandardConversionExists (Expression expr, Type target_type)
 423                 {
 424                         Type expr_type = expr.Type;
 425
 426                         if (expr_type == TypeManager.void_type)
 427                                 return false;
 428
 429                         if (expr_type == target_type)
 430                                 return true;
 431
 432                         // First numeric conversions
 433
 434                         if (expr_type == TypeManager.sbyte_type){
 435                                 //
 436                                 // From sbyte to short, int, long, float, double.
 437                                 //
 438                                 if ((target_type == TypeManager.int32_type) ||
 439                                     (target_type == TypeManager.int64_type) ||
 440                                     (target_type == TypeManager.double_type) ||
 441                                     (target_type == TypeManager.float_type)  ||
 442                                     (target_type == TypeManager.short_type) ||
 443                                     (target_type == TypeManager.decimal_type))
 444                                         return true;
 445
 446                         } else if (expr_type == TypeManager.byte_type){
 447                                 //
 448                                 // From byte to short, ushort, int, uint, long, ulong, float, double
 449                                 //
 450                                 if ((target_type == TypeManager.short_type) ||
 451                                     (target_type == TypeManager.ushort_type) ||
 452                                     (target_type == TypeManager.int32_type) ||
 453                                     (target_type == TypeManager.uint32_type) ||
 454                                     (target_type == TypeManager.uint64_type) ||
 455                                     (target_type == TypeManager.int64_type) ||
 456                                     (target_type == TypeManager.float_type) ||
 457                                     (target_type == TypeManager.double_type) ||
 458                                     (target_type == TypeManager.decimal_type))
 459                                         return true;
 460
 461                         } else if (expr_type == TypeManager.short_type){
 462                                 //
 463                                 // From short to int, long, float, double
 464                                 //
 465                                 if ((target_type == TypeManager.int32_type) ||
 466                                     (target_type == TypeManager.int64_type) ||
 467                                     (target_type == TypeManager.double_type) ||
 468                                     (target_type == TypeManager.float_type) ||
 469                                     (target_type == TypeManager.decimal_type))
 470                                         return true;
 471
 472                         } else if (expr_type == TypeManager.ushort_type){
 473                                 //
 474                                 // From ushort to int, uint, long, ulong, float, double
 475                                 //
 476                                 if ((target_type == TypeManager.uint32_type) ||
 477                                     (target_type == TypeManager.uint64_type) ||
 478                                     (target_type == TypeManager.int32_type) ||
 479                                     (target_type == TypeManager.int64_type) ||
 480                                     (target_type == TypeManager.double_type) ||
 481                                     (target_type == TypeManager.float_type) ||
 482                                     (target_type == TypeManager.decimal_type))
 483                                         return true;
 484
 485                         } else if (expr_type == TypeManager.int32_type){
 486                                 //
 487                                 // From int to long, float, double
 488                                 //
 489                                 if ((target_type == TypeManager.int64_type) ||
 490                                     (target_type == TypeManager.double_type) ||
 491                                     (target_type == TypeManager.float_type) ||
 492                                     (target_type == TypeManager.decimal_type))
 493                                         return true;
 494
 495                         } else if (expr_type == TypeManager.uint32_type){
 496                                 //
 497                                 // From uint to long, ulong, float, double
 498                                 //
 499                                 if ((target_type == TypeManager.int64_type) ||
 500                                     (target_type == TypeManager.uint64_type) ||
 501                                     (target_type == TypeManager.double_type) ||
 502                                     (target_type == TypeManager.float_type) ||
 503                                     (target_type == TypeManager.decimal_type))
 504                                         return true;
 505
 506                         } else if ((expr_type == TypeManager.uint64_type) ||
 507                                    (expr_type == TypeManager.int64_type)) {
 508                                 //
 509                                 // From long/ulong to float, double
 510                                 //
 511                                 if ((target_type == TypeManager.double_type) ||
 512                                     (target_type == TypeManager.float_type) ||
 513                                     (target_type == TypeManager.decimal_type))
 514                                         return true;
 515
 516                         } else if (expr_type == TypeManager.char_type){
 517                                 //
 518                                 // From char to ushort, int, uint, long, ulong, float, double
 519                                 //
 520                                 if ((target_type == TypeManager.ushort_type) ||
 521                                     (target_type == TypeManager.int32_type) ||
 522                                     (target_type == TypeManager.uint32_type) ||
 523                                     (target_type == TypeManager.uint64_type) ||
 524                                     (target_type == TypeManager.int64_type) ||
 525                                     (target_type == TypeManager.float_type) ||
 526                                     (target_type == TypeManager.double_type) ||
 527                                     (target_type == TypeManager.decimal_type))
 528                                         return true;
 529
 530                         } else if (expr_type == TypeManager.float_type){
 531                                 //
 532                                 // float to double
 533                                 //
 534                                 if (target_type == TypeManager.double_type)
 535                                         return true;
 536                         }
 537
 538                         if (ImplicitReferenceConversionExists (expr, target_type))
 539                                 return true;
 540
 541                         if (expr is IntConstant){
 542                                 int value = ((IntConstant) expr).Value;
 543
 544                                 if (target_type == TypeManager.sbyte_type){
 545                                         if (value >= SByte.MinValue && value <= SByte.MaxValue)
 546                                                 return true;
 547                                 } else if (target_type == TypeManager.byte_type){
 548                                         if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
 549                                                 return true;
 550                                 } else if (target_type == TypeManager.short_type){
 551                                         if (value >= Int16.MinValue && value <= Int16.MaxValue)
 552                                                 return true;
 553                                 } else if (target_type == TypeManager.ushort_type){
 554                                         if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
 555                                                 return true;
 556                                 } else if (target_type == TypeManager.uint32_type){
 557                                         if (value >= 0)
 558                                                 return true;
 559                                 } else if (target_type == TypeManager.uint64_type){
 560                                          //
 561                                          // we can optimize this case: a positive int32
 562                                          // always fits on a uint64.  But we need an opcode
 563                                          // to do it.
 564                                          //
 565                                         if (value >= 0)
 566                                                 return true;
 567                                 }
 568
 569                                 if (value == 0 && expr is IntLiteral && TypeManager.IsEnumType (target_type))
 570                                         return true;
 571                         }
 572
 573                         if (expr is LongConstant && target_type == TypeManager.uint64_type){
 574                                 //
 575                                 // Try the implicit constant expression conversion
 576                                 // from long to ulong, instead of a nice routine,
 577                                 // we just inline it
 578                                 //
 579                                 long v = ((LongConstant) expr).Value;
 580                                 if (v > 0)
 581                                         return true;
 582                         }
 583
 584                         if ((target_type == TypeManager.enum_type ||
 585                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
 586                              expr is IntLiteral){
 587                                 IntLiteral i = (IntLiteral) expr;
 588
 589                                 if (i.Value == 0)
 590                                         return true;
 591                         }
 592
 593                         if (target_type == TypeManager.void_ptr_type && expr_type.IsPointer)
 594                                 return true;
 595
 596                         return false;
 597                 }
 598
 599                 //
 600                 // Used internally by FindMostEncompassedType, this is used
 601                 // to avoid creating lots of objects in the tight loop inside
 602                 // FindMostEncompassedType
 603                 //
 604                 static EmptyExpression priv_fmet_param;
 605
 606                 /// <summary>
 607                 ///  Finds "most encompassed type" according to the spec (13.4.2)
 608                 ///  amongst the methods in the MethodGroupExpr
 609                 /// </summary>
 610                 static Type FindMostEncompassedType (ArrayList types)
 611                 {
 612                         Type best = null;
 613
 614                         if (priv_fmet_param == null)
 615                                 priv_fmet_param = new EmptyExpression ();
 616
 617                         foreach (Type t in types){
 618                                 priv_fmet_param.SetType (t);
 619
 620                                 if (best == null) {
 621                                         best = t;
 622                                         continue;
 623                                 }
 624
 625                                 if (ImplicitStandardConversionExists (priv_fmet_param, best))
 626                                         best = t;
 627                         }
 628
 629                         return best;
 630                 }
 631
 632                 //
 633                 // Used internally by FindMostEncompassingType, this is used
 634                 // to avoid creating lots of objects in the tight loop inside
 635                 // FindMostEncompassingType
 636                 //
 637                 static EmptyExpression priv_fmee_ret;
 638
 639                 /// <summary>
 640                 ///  Finds "most encompassing type" according to the spec (13.4.2)
 641                 ///  amongst the types in the given set
 642                 /// </summary>
 643                 static Type FindMostEncompassingType (ArrayList types)
 644                 {
 645                         Type best = null;
 646
 647                         if (priv_fmee_ret == null)
 648                                 priv_fmee_ret = new EmptyExpression ();
 649
 650                         foreach (Type t in types){
 651                                 priv_fmee_ret.SetType (best);
 652
 653                                 if (best == null) {
 654                                         best = t;
 655                                         continue;
 656                                 }
 657
 658                                 if (ImplicitStandardConversionExists (priv_fmee_ret, t))
 659                                         best = t;
 660                         }
 661
 662                         return best;
 663                 }
 664
 665                 //
 666                 // Used to avoid creating too many objects
 667                 //
 668                 static EmptyExpression priv_fms_expr;
 669
 670                 /// <summary>
 671                 ///   Finds the most specific source Sx according to the rules of the spec (13.4.4)
 672                 ///   by making use of FindMostEncomp* methods. Applies the correct rules separately
 673                 ///   for explicit and implicit conversion operators.
 674                 /// </summary>
 675                 static public Type FindMostSpecificSource (MethodGroupExpr me, Expression source,
 676                                                            bool apply_explicit_conv_rules,
 677                                                            Location loc)
 678                 {
 679                         ArrayList src_types_set = new ArrayList ();
 680
 681                         if (priv_fms_expr == null)
 682                                 priv_fms_expr = new EmptyExpression ();
 683
 684                         //
 685                         // If any operator converts from S then Sx = S
 686                         //
 687                         Type source_type = source.Type;
 688                         foreach (MethodBase mb in me.Methods){
 689                                 ParameterData pd = Invocation.GetParameterData (mb);
 690                                 Type param_type = pd.ParameterType (0);
 691
 692                                 if (param_type == source_type)
 693                                         return param_type;
 694
 695                                 if (apply_explicit_conv_rules) {
 696                                         //
 697                                         // From the spec :
 698                                         // Find the set of applicable user-defined conversion operators, U.  This set
 699                                         // consists of the
 700                                         // user-defined implicit or explicit conversion operators declared by
 701                                         // the classes or structs in D that convert from a type encompassing
 702                                         // or encompassed by S to a type encompassing or encompassed by T
 703                                         //
 704                                         priv_fms_expr.SetType (param_type);
 705                                         if (ImplicitStandardConversionExists (priv_fms_expr, source_type))
 706                                                 src_types_set.Add (param_type);
 707                                         else {
 708                                                 if (ImplicitStandardConversionExists (source, param_type))
 709                                                         src_types_set.Add (param_type);
 710                                         }
 711                                 } else {
 712                                         //
 713                                         // Only if S is encompassed by param_type
 714                                         //
 715                                         if (ImplicitStandardConversionExists (source, param_type))
 716                                                 src_types_set.Add (param_type);
 717                                 }
 718                         }
 719
 720                         //
 721                         // Explicit Conv rules
 722                         //
 723                         if (apply_explicit_conv_rules) {
 724                                 ArrayList candidate_set = new ArrayList ();
 725
 726                                 foreach (Type param_type in src_types_set){
 727                                         if (ImplicitStandardConversionExists (source, param_type))
 728                                                 candidate_set.Add (param_type);
 729                                 }
 730
 731                                 if (candidate_set.Count != 0)
 732                                         return FindMostEncompassedType (candidate_set);
 733                         }
 734
 735                         //
 736                         // Final case
 737                         //
 738                         if (apply_explicit_conv_rules)
 739                                 return FindMostEncompassingType (src_types_set);
 740                         else
 741                                 return FindMostEncompassedType (src_types_set);
 742                 }
 743
 744                 //
 745                 // Useful in avoiding proliferation of objects
 746                 //
 747                 static EmptyExpression priv_fmt_expr;
 748
 749                 /// <summary>
 750                 ///  Finds the most specific target Tx according to section 13.4.4
 751                 /// </summary>
 752                 static public Type FindMostSpecificTarget (MethodGroupExpr me, Type target,
 753                                                            bool apply_explicit_conv_rules,
 754                                                            Location loc)
 755                 {
 756                         ArrayList tgt_types_set = new ArrayList ();
 757
 758                         if (priv_fmt_expr == null)
 759                                 priv_fmt_expr = new EmptyExpression ();
 760
 761                         //
 762                         // If any operator converts to T then Tx = T
 763                         //
 764                         foreach (MethodInfo mi in me.Methods){
 765                                 Type ret_type = mi.ReturnType;
 766
 767                                 if (ret_type == target)
 768                                         return ret_type;
 769
 770                                 if (apply_explicit_conv_rules) {
 771                                         //
 772                                         // From the spec :
 773                                         // Find the set of applicable user-defined conversion operators, U.
 774                                         //
 775                                         // This set consists of the
 776                                         // user-defined implicit or explicit conversion operators declared by
 777                                         // the classes or structs in D that convert from a type encompassing
 778                                         // or encompassed by S to a type encompassing or encompassed by T
 779                                         //
 780                                         priv_fms_expr.SetType (ret_type);
 781                                         if (ImplicitStandardConversionExists (priv_fms_expr, target))
 782                                                 tgt_types_set.Add (ret_type);
 783                                         else {
 784                                                 priv_fms_expr.SetType (target);
 785                                                 if (ImplicitStandardConversionExists (priv_fms_expr, ret_type))
 786                                                         tgt_types_set.Add (ret_type);
 787                                         }
 788                                 } else {
 789                                         //
 790                                         // Only if T is encompassed by param_type
 791                                         //
 792                                         priv_fms_expr.SetType (ret_type);
 793                                         if (ImplicitStandardConversionExists (priv_fms_expr, target))
 794                                                 tgt_types_set.Add (ret_type);
 795                                 }
 796                         }
 797
 798                         //
 799                         // Explicit conv rules
 800                         //
 801                         if (apply_explicit_conv_rules) {
 802                                 ArrayList candidate_set = new ArrayList ();
 803
 804                                 foreach (Type ret_type in tgt_types_set){
 805                                         priv_fmt_expr.SetType (ret_type);
 806
 807                                         if (ImplicitStandardConversionExists (priv_fmt_expr, target))
 808                                                 candidate_set.Add (ret_type);
 809                                 }
 810
 811                                 if (candidate_set.Count != 0)
 812                                         return FindMostEncompassingType (candidate_set);
 813                         }
 814
 815                         //
 816                         // Okay, final case !
 817                         //
 818                         if (apply_explicit_conv_rules)
 819                                 return FindMostEncompassedType (tgt_types_set);
 820                         else
 821                                 return FindMostEncompassingType (tgt_types_set);
 822                 }
 823
 824                 /// <summary>
 825                 ///  User-defined Implicit conversions
 826                 /// </summary>
 827                 static public Expression ImplicitUserConversion (EmitContext ec, Expression source,
 828                                                                  Type target, Location loc)
 829                 {
 830                         return UserDefinedConversion (ec, source, target, loc, false);
 831                 }
 832
 833                 /// <summary>
 834                 ///  User-defined Explicit conversions
 835                 /// </summary>
 836                 static public Expression ExplicitUserConversion (EmitContext ec, Expression source,
 837                                                                  Type target, Location loc)
 838                 {
 839                         return UserDefinedConversion (ec, source, target, loc, true);
 840                 }
 841
 842                 /// <summary>
 843                 ///   Computes the MethodGroup for the user-defined conversion
 844                 ///   operators from source_type to target_type.  `look_for_explicit'
 845                 ///   controls whether we should also include the list of explicit
 846                 ///   operators
 847                 /// </summary>
 848                 static MethodGroupExpr GetConversionOperators (EmitContext ec,
 849                                                                Type source_type, Type target_type,
 850                                                                Location loc, bool look_for_explicit)
 851                 {
 852                         Expression mg1 = null, mg2 = null;
 853                         Expression mg5 = null, mg6 = null, mg7 = null, mg8 = null;
 854                         string op_name;
 855
 856                         op_name = "op_Implicit";
 857
 858                         MethodGroupExpr union3;
 859
 860                         mg1 = Expression.MethodLookup (ec, source_type, op_name, loc);
 861                         if (source_type.BaseType != null)
 862                                 mg2 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
 863
 864                         if (mg1 == null)
 865                                 union3 = (MethodGroupExpr) mg2;
 866                         else if (mg2 == null)
 867                                 union3 = (MethodGroupExpr) mg1;
 868                         else
 869                                 union3 = Invocation.MakeUnionSet (mg1, mg2, loc);
 870
 871                         mg1 = Expression.MethodLookup (ec, target_type, op_name, loc);
 872                         if (mg1 != null){
 873                                 if (union3 != null)
 874                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
 875                                 else
 876                                         union3 = (MethodGroupExpr) mg1;
 877                         }
 878
 879                         if (target_type.BaseType != null)
 880                                 mg1 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
 881
 882                         if (mg1 != null){
 883                                 if (union3 != null)
 884                                         union3 = Invocation.MakeUnionSet (union3, mg1, loc);
 885                                 else
 886                                         union3 = (MethodGroupExpr) mg1;
 887                         }
 888
 889                         MethodGroupExpr union4 = null;
 890
 891                         if (look_for_explicit) {
 892                                 op_name = "op_Explicit";
 893
 894                                 mg5 = Expression.MemberLookup (ec, source_type, op_name, loc);
 895                                 if (source_type.BaseType != null)
 896                                         mg6 = Expression.MethodLookup (ec, source_type.BaseType, op_name, loc);
 897
 898                                 mg7 = Expression.MemberLookup (ec, target_type, op_name, loc);
 899                                 if (target_type.BaseType != null)
 900                                         mg8 = Expression.MethodLookup (ec, target_type.BaseType, op_name, loc);
 901
 902                                 MethodGroupExpr union5 = Invocation.MakeUnionSet (mg5, mg6, loc);
 903                                 MethodGroupExpr union6 = Invocation.MakeUnionSet (mg7, mg8, loc);
 904
 905                                 union4 = Invocation.MakeUnionSet (union5, union6, loc);
 906                         }
 907
 908                         return Invocation.MakeUnionSet (union3, union4, loc);
 909                 }
 910
 911                 /// <summary>
 912                 ///   User-defined conversions
 913                 /// </summary>
 914                 static public Expression UserDefinedConversion (EmitContext ec, Expression source,
 915                                                                 Type target, Location loc,
 916                                                                 bool look_for_explicit)
 917                 {
 918                         MethodGroupExpr union;
 919                         Type source_type = source.Type;
 920                         MethodBase method = null;
 921
 922                         union = GetConversionOperators (ec, source_type, target, loc, look_for_explicit);
 923                         if (union == null)
 924                                 return null;
 925
 926                         Type most_specific_source, most_specific_target;
 927 #if BLAH
 928                         foreach (MethodBase m in union.Methods){
 929                                 Console.WriteLine ("Name: " + m.Name);
 930                                 Console.WriteLine ("    : " + ((MethodInfo)m).ReturnType);
 931                         }
 932 #endif
 933
 934                         most_specific_source = FindMostSpecificSource (union, source, look_for_explicit, loc);
 935                         if (most_specific_source == null)
 936                                 return null;
 937
 938                         most_specific_target = FindMostSpecificTarget (union, target, look_for_explicit, loc);
 939                         if (most_specific_target == null)
 940                                 return null;
 941
 942                         int count = 0;
 943
 944
 945                         foreach (MethodBase mb in union.Methods){
 946                                 ParameterData pd = Invocation.GetParameterData (mb);
 947                                 MethodInfo mi = (MethodInfo) mb;
 948
 949                                 if (pd.ParameterType (0) == most_specific_source &&
 950                                     mi.ReturnType == most_specific_target) {
 951                                         method = mb;
 952                                         count++;
 953                                 }
 954                         }
 955
 956                         if (method == null || count > 1)
 957                                 return null;
 958
 959
 960                         //
 961                         // This will do the conversion to the best match that we
 962                         // found.  Now we need to perform an implict standard conversion
 963                         // if the best match was not the type that we were requested
 964                         // by target.
 965                         //
 966                         if (look_for_explicit)
 967                                 source = ExplicitConversionStandard (ec, source, most_specific_source, loc);
 968                         else
 969                                 source = ImplicitConversionStandard (ec, source, most_specific_source, loc);
 970
 971                         if (source == null)
 972                                 return null;
 973
 974                         Expression e;
 975                         e =  new UserCast ((MethodInfo) method, source, loc);
 976                         if (e.Type != target){
 977                                 if (!look_for_explicit)
 978                                         e = ImplicitConversionStandard (ec, e, target, loc);
 979                                 else
 980                                         e = ExplicitConversionStandard (ec, e, target, loc);
 981                         }
 982
 983                         return e;
 984                 }
 985
 986                 /// <summary>
 987                 ///   Converts implicitly the resolved expression `expr' into the
 988                 ///   `target_type'.  It returns a new expression that can be used
 989                 ///   in a context that expects a `target_type'.
 990                 /// </summary>
 991                 static public Expression ImplicitConversion (EmitContext ec, Expression expr,
 992                                                           Type target_type, Location loc)
 993                 {
 994                         Type expr_type = expr.Type;
 995                         Expression e;
 996
 997                         if (target_type == null)
 998                                 throw new Exception ("Target type is null");
 999
1000                         e = ImplicitConversionStandard (ec, expr, target_type, loc);
1001                         if (e != null)
1002                                 return e;
1003
1004                         e = ImplicitUserConversion (ec, expr, target_type, loc);
1005                         if (e != null)
1006                                 return e;
1007
1008                         return null;
1009                 }
1010
1011
1012                 /// <summary>
1013                 ///   Attempts to apply the `Standard Implicit
1014                 ///   Conversion' rules to the expression `expr' into
1015                 ///   the `target_type'.  It returns a new expression
1016                 ///   that can be used in a context that expects a
1017                 ///   `target_type'.
1018                 ///
1019                 ///   This is different from `ImplicitConversion' in that the
1020                 ///   user defined implicit conversions are excluded.
1021                 /// </summary>
1022                 static public Expression ImplicitConversionStandard (EmitContext ec, Expression expr,
1023                                                                      Type target_type, Location loc)
1024                 {
1025                         Type expr_type = expr.Type;
1026                         Expression e;
1027
1028                         if (expr_type == target_type && !(expr is NullLiteral))
1029                                 return expr;
1030
1031                         e = ImplicitNumericConversion (ec, expr, target_type, loc);
1032                         if (e != null)
1033                                 return e;
1034
1035                         e = ImplicitReferenceConversion (expr, target_type);
1036                         if (e != null)
1037                                 return e;
1038
1039                         if ((target_type == TypeManager.enum_type ||
1040                              target_type.IsSubclassOf (TypeManager.enum_type)) &&
1041                             expr is IntLiteral){
1042                                 IntLiteral i = (IntLiteral) expr;
1043
1044                                 if (i.Value == 0)
1045                                         return new EnumConstant ((Constant) expr, target_type);
1046                         }
1047
1048                         if (ec.InUnsafe) {
1049                                 if (expr_type.IsPointer){
1050                                         if (target_type == TypeManager.void_ptr_type)
1051                                                 return new EmptyCast (expr, target_type);
1052
1053                                         //
1054                                         // yep, comparing pointer types cant be done with
1055                                         // t1 == t2, we have to compare their element types.
1056                                         //
1057                                         if (target_type.IsPointer){
1058                                                 if (target_type.GetElementType() == expr_type.GetElementType())
1059                                                         return expr;
1060                                         }
1061                                 }
1062
1063                                 if (target_type.IsPointer) {
1064                                         if (expr is NullLiteral)
1065                                                 return new EmptyCast (expr, target_type);
1066
1067                                         if (expr_type == TypeManager.void_ptr_type)
1068                                                 return new EmptyCast (expr, target_type);
1069                                 }
1070                         }
1071
1072                         return null;
1073                 }
1074
1075                 /// <summary>
1076                 ///   Attemps to perform an implict constant conversion of the IntConstant
1077                 ///   into a different data type using casts (See Implicit Constant
1078                 ///   Expression Conversions)
1079                 /// </summary>
1080                 static public Expression TryImplicitIntConversion (Type target_type, IntConstant ic)
1081                 {
1082                         int value = ic.Value;
1083
1084                         if (target_type == TypeManager.sbyte_type){
1085                                 if (value >= SByte.MinValue && value <= SByte.MaxValue)
1086                                         return new SByteConstant ((sbyte) value);
1087                         } else if (target_type == TypeManager.byte_type){
1088                                 if (Byte.MinValue >= 0 && value <= Byte.MaxValue)
1089                                         return new ByteConstant ((byte) value);
1090                         } else if (target_type == TypeManager.short_type){
1091                                 if (value >= Int16.MinValue && value <= Int16.MaxValue)
1092                                         return new ShortConstant ((short) value);
1093                         } else if (target_type == TypeManager.ushort_type){
1094                                 if (value >= UInt16.MinValue && value <= UInt16.MaxValue)
1095                                         return new UShortConstant ((ushort) value);
1096                         } else if (target_type == TypeManager.uint32_type){
1097                                 if (value >= 0)
1098                                         return new UIntConstant ((uint) value);
1099                         } else if (target_type == TypeManager.uint64_type){
1100                                 //
1101                                 // we can optimize this case: a positive int32
1102                                 // always fits on a uint64.  But we need an opcode
1103                                 // to do it.
1104                                 //
1105                                 if (value >= 0)
1106                                         return new ULongConstant ((ulong) value);
1107                         } else if (target_type == TypeManager.double_type)
1108                                 return new DoubleConstant ((double) value);
1109                         else if (target_type == TypeManager.float_type)
1110                                 return new FloatConstant ((float) value);
1111
1112                         if (value == 0 && ic is IntLiteral && TypeManager.IsEnumType (target_type)){
1113                                 Type underlying = TypeManager.EnumToUnderlying (target_type);
1114                                 Constant e = (Constant) ic;
1115
1116                                 //
1117                                 // Possibly, we need to create a different 0 literal before passing
1118                                 // to EnumConstant
1119                                 //n
1120                                 if (underlying == TypeManager.int64_type)
1121                                         e = new LongLiteral (0);
1122                                 else if (underlying == TypeManager.uint64_type)
1123                                         e = new ULongLiteral (0);
1124
1125                                 return new EnumConstant (e, target_type);
1126                         }
1127                         return null;
1128                 }
1129
1130                 static public void Error_CannotImplicitConversion (Location loc, Type source, Type target)
1131                 {
1132                         string msg = "Cannot convert implicitly from `"+
1133                                 TypeManager.CSharpName (source) + "' to `" +
1134                                 TypeManager.CSharpName (target) + "'";
1135
1136                         Report.Error (29, loc, msg);
1137                 }
1138
1139                 /// <summary>
1140                 ///   Attemptes to implicityly convert `target' into `type', using
1141                 ///   ImplicitConversion.  If there is no implicit conversion, then
1142                 ///   an error is signaled
1143                 /// </summary>
1144                 static public Expression ImplicitConversionRequired (EmitContext ec, Expression source,
1145                                                                      Type target_type, Location loc)
1146                 {
1147                         Expression e;
1148
1149                         e = ImplicitConversion (ec, source, target_type, loc);
1150                         if (e != null)
1151                                 return e;
1152
1153                         if (source is DoubleLiteral && target_type == TypeManager.float_type){
1154                                 Report.Error (664, loc,
1155                                               "Double literal cannot be implicitly converted to " +
1156                                               "float type, use F suffix to create a float literal");
1157                         }
1158
1159                         Error_CannotImplicitConversion (loc, source.Type, target_type);
1160
1161                         return null;
1162                 }
1163
1164                 /// <summary>
1165                 ///   Performs the explicit numeric conversions
1166                 /// </summary>
1167                 static Expression ExplicitNumericConversion (EmitContext ec, Expression expr, Type target_type, Location loc)
1168                 {
1169                         Type expr_type = expr.Type;
1170
1171                         //
1172                         // If we have an enumeration, extract the underlying type,
1173                         // use this during the comparison, but wrap around the original
1174                         // target_type
1175                         //
1176                         Type real_target_type = target_type;
1177
1178                         if (TypeManager.IsEnumType (real_target_type))
1179                                 real_target_type = TypeManager.EnumToUnderlying (real_target_type);
1180
1181                         if (ImplicitStandardConversionExists (expr, real_target_type)){
1182                                 Expression ce = ImplicitConversionStandard (ec, expr, real_target_type, loc);
1183
1184                                 if (real_target_type != target_type)
1185                                         return new EmptyCast (ce, target_type);
1186                                 return ce;
1187                         }
1188
1189                         if (expr_type == TypeManager.sbyte_type){
1190                                 //
1191                                 // From sbyte to byte, ushort, uint, ulong, char
1192                                 //
1193                                 if (real_target_type == TypeManager.byte_type)
1194                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U1);
1195                                 if (real_target_type == TypeManager.ushort_type)
1196                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U2);
1197                                 if (real_target_type == TypeManager.uint32_type)
1198                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U4);
1199                                 if (real_target_type == TypeManager.uint64_type)
1200                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_U8);
1201                                 if (real_target_type == TypeManager.char_type)
1202                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I1_CH);
1203                         } else if (expr_type == TypeManager.byte_type){
1204                                 //
1205                                 // From byte to sbyte and char
1206                                 //
1207                                 if (real_target_type == TypeManager.sbyte_type)
1208                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_I1);
1209                                 if (real_target_type == TypeManager.char_type)
1210                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U1_CH);
1211                         } else if (expr_type == TypeManager.short_type){
1212                                 //
1213                                 // From short to sbyte, byte, ushort, uint, ulong, char
1214                                 //
1215                                 if (real_target_type == TypeManager.sbyte_type)
1216                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_I1);
1217                                 if (real_target_type == TypeManager.byte_type)
1218                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U1);
1219                                 if (real_target_type == TypeManager.ushort_type)
1220                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U2);
1221                                 if (real_target_type == TypeManager.uint32_type)
1222                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U4);
1223                                 if (real_target_type == TypeManager.uint64_type)
1224                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_U8);
1225                                 if (real_target_type == TypeManager.char_type)
1226                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I2_CH);
1227                         } else if (expr_type == TypeManager.ushort_type){
1228                                 //
1229                                 // From ushort to sbyte, byte, short, char
1230                                 //
1231                                 if (real_target_type == TypeManager.sbyte_type)
1232                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I1);
1233                                 if (real_target_type == TypeManager.byte_type)
1234                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_U1);
1235                                 if (real_target_type == TypeManager.short_type)
1236                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_I2);
1237                                 if (real_target_type == TypeManager.char_type)
1238                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U2_CH);
1239                         } else if (expr_type == TypeManager.int32_type){
1240                                 //
1241                                 // From int to sbyte, byte, short, ushort, uint, ulong, char
1242                                 //
1243                                 if (real_target_type == TypeManager.sbyte_type)
1244                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I1);
1245                                 if (real_target_type == TypeManager.byte_type)
1246                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U1);
1247                                 if (real_target_type == TypeManager.short_type)
1248                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_I2);
1249                                 if (real_target_type == TypeManager.ushort_type)
1250                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U2);
1251                                 if (real_target_type == TypeManager.uint32_type)
1252                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U4);
1253                                 if (real_target_type == TypeManager.uint64_type)
1254                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_U8);
1255                                 if (real_target_type == TypeManager.char_type)
1256                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I4_CH);
1257                         } else if (expr_type == TypeManager.uint32_type){
1258                                 //
1259                                 // From uint to sbyte, byte, short, ushort, int, char
1260                                 //
1261                                 if (real_target_type == TypeManager.sbyte_type)
1262                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I1);
1263                                 if (real_target_type == TypeManager.byte_type)
1264                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U1);
1265                                 if (real_target_type == TypeManager.short_type)
1266                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I2);
1267                                 if (real_target_type == TypeManager.ushort_type)
1268                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_U2);
1269                                 if (real_target_type == TypeManager.int32_type)
1270                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_I4);
1271                                 if (real_target_type == TypeManager.char_type)
1272                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U4_CH);
1273                         } else if (expr_type == TypeManager.int64_type){
1274                                 //
1275                                 // From long to sbyte, byte, short, ushort, int, uint, ulong, char
1276                                 //
1277                                 if (real_target_type == TypeManager.sbyte_type)
1278                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I1);
1279                                 if (real_target_type == TypeManager.byte_type)
1280                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U1);
1281                                 if (real_target_type == TypeManager.short_type)
1282                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I2);
1283                                 if (real_target_type == TypeManager.ushort_type)
1284                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U2);
1285                                 if (real_target_type == TypeManager.int32_type)
1286                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_I4);
1287                                 if (real_target_type == TypeManager.uint32_type)
1288                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U4);
1289                                 if (real_target_type == TypeManager.uint64_type)
1290                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_U8);
1291                                 if (real_target_type == TypeManager.char_type)
1292                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.I8_CH);
1293                         } else if (expr_type == TypeManager.uint64_type){
1294                                 //
1295                                 // From ulong to sbyte, byte, short, ushort, int, uint, long, char
1296                                 //
1297                                 if (real_target_type == TypeManager.sbyte_type)
1298                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I1);
1299                                 if (real_target_type == TypeManager.byte_type)
1300                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U1);
1301                                 if (real_target_type == TypeManager.short_type)
1302                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I2);
1303                                 if (real_target_type == TypeManager.ushort_type)
1304                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U2);
1305                                 if (real_target_type == TypeManager.int32_type)
1306                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I4);
1307                                 if (real_target_type == TypeManager.uint32_type)
1308                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_U4);
1309                                 if (real_target_type == TypeManager.int64_type)
1310                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_I8);
1311                                 if (real_target_type == TypeManager.char_type)
1312                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.U8_CH);
1313                         } else if (expr_type == TypeManager.char_type){
1314                                 //
1315                                 // From char to sbyte, byte, short
1316                                 //
1317                                 if (real_target_type == TypeManager.sbyte_type)
1318                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I1);
1319                                 if (real_target_type == TypeManager.byte_type)
1320                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_U1);
1321                                 if (real_target_type == TypeManager.short_type)
1322                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.CH_I2);
1323                         } else if (expr_type == TypeManager.float_type){
1324                                 //
1325                                 // From float to sbyte, byte, short,
1326                                 // ushort, int, uint, long, ulong, char
1327                                 // or decimal
1328                                 //
1329                                 if (real_target_type == TypeManager.sbyte_type)
1330                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I1);
1331                                 if (real_target_type == TypeManager.byte_type)
1332                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U1);
1333                                 if (real_target_type == TypeManager.short_type)
1334                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I2);
1335                                 if (real_target_type == TypeManager.ushort_type)
1336                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U2);
1337                                 if (real_target_type == TypeManager.int32_type)
1338                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I4);
1339                                 if (real_target_type == TypeManager.uint32_type)
1340                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U4);
1341                                 if (real_target_type == TypeManager.int64_type)
1342                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_I8);
1343                                 if (real_target_type == TypeManager.uint64_type)
1344                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_U8);
1345                                 if (real_target_type == TypeManager.char_type)
1346                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R4_CH);
1347                         } else if (expr_type == TypeManager.double_type){
1348                                 //
1349                                 // From double to byte, byte, short,
1350                                 // ushort, int, uint, long, ulong,
1351                                 // char, float or decimal
1352                                 //
1353                                 if (real_target_type == TypeManager.sbyte_type)
1354                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I1);
1355                                 if (real_target_type == TypeManager.byte_type)
1356                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U1);
1357                                 if (real_target_type == TypeManager.short_type)
1358                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I2);
1359                                 if (real_target_type == TypeManager.ushort_type)
1360                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U2);
1361                                 if (real_target_type == TypeManager.int32_type)
1362                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I4);
1363                                 if (real_target_type == TypeManager.uint32_type)
1364                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U4);
1365                                 if (real_target_type == TypeManager.int64_type)
1366                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_I8);
1367                                 if (real_target_type == TypeManager.uint64_type)
1368                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_U8);
1369                                 if (real_target_type == TypeManager.char_type)
1370                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_CH);
1371                                 if (real_target_type == TypeManager.float_type)
1372                                         return new ConvCast (ec, expr, target_type, ConvCast.Mode.R8_R4);
1373                         }
1374
1375                         // decimal is taken care of by the op_Explicit methods.
1376
1377                         return null;
1378                 }
1379
1380                 /// <summary>
1381                 ///  Returns whether an explicit reference conversion can be performed
1382                 ///  from source_type to target_type
1383                 /// </summary>
1384                 public static bool ExplicitReferenceConversionExists (Type source_type, Type target_type)
1385                 {
1386                         bool target_is_value_type = target_type.IsValueType;
1387
1388                         if (source_type == target_type)
1389                                 return true;
1390
1391                         //
1392                         // From object to any reference type
1393                         //
1394                         if (source_type == TypeManager.object_type && !target_is_value_type)
1395                                 return true;
1396
1397                         //
1398                         // From any class S to any class-type T, provided S is a base class of T
1399                         //
1400                         if (target_type.IsSubclassOf (source_type))
1401                                 return true;
1402
1403                         //
1404                         // From any interface type S to any interface T provided S is not derived from T
1405                         //
1406                         if (source_type.IsInterface && target_type.IsInterface){
1407                                 if (!target_type.IsSubclassOf (source_type))
1408                                         return true;
1409                         }
1410
1411                         //
1412                         // From any class type S to any interface T, provided S is not sealed
1413                         // and provided S does not implement T.
1414                         //
1415                         if (target_type.IsInterface && !source_type.IsSealed &&
1416                             !TypeManager.ImplementsInterface (source_type, target_type))
1417                                 return true;
1418
1419                         //
1420                         // From any interface-type S to to any class type T, provided T is not
1421                         // sealed, or provided T implements S.
1422                         //
1423                         if (source_type.IsInterface &&
1424                             (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type)))
1425                                 return true;
1426
1427
1428                         // From an array type S with an element type Se to an array type T with an
1429                         // element type Te provided all the following are true:
1430                         //     * S and T differe only in element type, in other words, S and T
1431                         //       have the same number of dimensions.
1432                         //     * Both Se and Te are reference types
1433                         //     * An explicit referenc conversions exist from Se to Te
1434                         //
1435                         if (source_type.IsArray && target_type.IsArray) {
1436                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1437
1438                                         Type source_element_type = source_type.GetElementType ();
1439                                         Type target_element_type = target_type.GetElementType ();
1440
1441                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1442                                                 if (ExplicitReferenceConversionExists (source_element_type,
1443                                                                                        target_element_type))
1444                                                         return true;
1445                                 }
1446                         }
1447
1448
1449                         // From System.Array to any array-type
1450                         if (source_type == TypeManager.array_type &&
1451                             target_type.IsArray){
1452                                 return true;
1453                         }
1454
1455                         //
1456                         // From System delegate to any delegate-type
1457                         //
1458                         if (source_type == TypeManager.delegate_type &&
1459                             target_type.IsSubclassOf (TypeManager.delegate_type))
1460                                 return true;
1461
1462                         //
1463                         // From ICloneable to Array or Delegate types
1464                         //
1465                         if (source_type == TypeManager.icloneable_type &&
1466                             (target_type == TypeManager.array_type ||
1467                              target_type == TypeManager.delegate_type))
1468                                 return true;
1469
1470                         return false;
1471                 }
1472
1473                 /// <summary>
1474                 ///   Implements Explicit Reference conversions
1475                 /// </summary>
1476                 static Expression ExplicitReferenceConversion (Expression source, Type target_type)
1477                 {
1478                         Type source_type = source.Type;
1479                         bool target_is_value_type = target_type.IsValueType;
1480
1481                         //
1482                         // From object to any reference type
1483                         //
1484                         if (source_type == TypeManager.object_type && !target_is_value_type)
1485                                 return new ClassCast (source, target_type);
1486
1487
1488                         //
1489                         // From any class S to any class-type T, provided S is a base class of T
1490                         //
1491                         if (target_type.IsSubclassOf (source_type))
1492                                 return new ClassCast (source, target_type);
1493
1494                         //
1495                         // From any interface type S to any interface T provided S is not derived from T
1496                         //
1497                         if (source_type.IsInterface && target_type.IsInterface){
1498                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1499                                         return null;
1500                                 else
1501                                         return new ClassCast (source, target_type);
1502                         }
1503
1504                         //
1505                         // From any class type S to any interface T, provides S is not sealed
1506                         // and provided S does not implement T.
1507                         //
1508                         if (target_type.IsInterface && !source_type.IsSealed) {
1509                                 if (TypeManager.ImplementsInterface (source_type, target_type))
1510                                         return null;
1511                                 else
1512                                         return new ClassCast (source, target_type);
1513
1514                         }
1515
1516                         //
1517                         // From any interface-type S to to any class type T, provided T is not
1518                         // sealed, or provided T implements S.
1519                         //
1520                         if (source_type.IsInterface) {
1521                                 if (!target_type.IsSealed || TypeManager.ImplementsInterface (target_type, source_type))
1522                                         return new ClassCast (source, target_type);
1523                                 else
1524                                         return null;
1525                         }
1526
1527                         // From an array type S with an element type Se to an array type T with an
1528                         // element type Te provided all the following are true:
1529                         //     * S and T differe only in element type, in other words, S and T
1530                         //       have the same number of dimensions.
1531                         //     * Both Se and Te are reference types
1532                         //     * An explicit referenc conversions exist from Se to Te
1533                         //
1534                         if (source_type.IsArray && target_type.IsArray) {
1535                                 if (source_type.GetArrayRank () == target_type.GetArrayRank ()) {
1536
1537                                         Type source_element_type = source_type.GetElementType ();
1538                                         Type target_element_type = target_type.GetElementType ();
1539
1540                                         if (!source_element_type.IsValueType && !target_element_type.IsValueType)
1541                                                 if (ExplicitReferenceConversionExists (source_element_type,
1542                                                                                        target_element_type))
1543                                                         return new ClassCast (source, target_type);
1544                                 }
1545                         }
1546
1547
1548                         // From System.Array to any array-type
1549                         if (source_type == TypeManager.array_type &&
1550                             target_type.IsArray) {
1551                                 return new ClassCast (source, target_type);
1552                         }
1553
1554                         //
1555                         // From System delegate to any delegate-type
1556                         //
1557                         if (source_type == TypeManager.delegate_type &&
1558                             target_type.IsSubclassOf (TypeManager.delegate_type))
1559                                 return new ClassCast (source, target_type);
1560
1561                         //
1562                         // From ICloneable to Array or Delegate types
1563                         //
1564                         if (source_type == TypeManager.icloneable_type &&
1565                             (target_type == TypeManager.array_type ||
1566                              target_type == TypeManager.delegate_type))
1567                                 return new ClassCast (source, target_type);
1568
1569                         return null;
1570                 }
1571
1572                 /// <summary>
1573                 ///   Performs an explicit conversion of the expression `expr' whose
1574                 ///   type is expr.Type to `target_type'.
1575                 /// </summary>
1576                 static public Expression ExplicitConversion (EmitContext ec, Expression expr,
1577                                                           Type target_type, Location loc)
1578                 {
1579                         Type expr_type = expr.Type;
1580                         Type original_expr_type = expr_type;
1581
1582                         if (expr_type.IsSubclassOf (TypeManager.enum_type)){
1583                                 if (target_type == TypeManager.enum_type ||
1584                                     target_type == TypeManager.object_type) {
1585                                         if (expr is EnumConstant)
1586                                                 expr = ((EnumConstant) expr).Child;
1587                                         // We really need all these casts here .... :-(
1588                                         expr = new BoxedCast (new EmptyCast (expr, expr_type));
1589                                         return new EmptyCast (expr, target_type);
1590                                 } else if ((expr_type == TypeManager.enum_type) && target_type.IsValueType &&
1591                                            target_type.IsSubclassOf (TypeManager.enum_type))
1592                                         return new UnboxCast (expr, target_type);
1593
1594                                 //
1595                                 // Notice that we have kept the expr_type unmodified, which is only
1596                                 // used later on to
1597                                 if (expr is EnumConstant)
1598                                         expr = ((EnumConstant) expr).Child;
1599                                 else
1600                                         expr = new EmptyCast (expr, TypeManager.EnumToUnderlying (expr_type));
1601                                 expr_type = expr.Type;
1602                         }
1603
1604                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, loc);
1605
1606                         if (ne != null)
1607                                 return ne;
1608
1609                         ne = ExplicitNumericConversion (ec, expr, target_type, loc);
1610                         if (ne != null)
1611                                 return ne;
1612
1613                         //
1614                         // Unboxing conversion.
1615                         //
1616                         if (expr_type == TypeManager.object_type && target_type.IsValueType){
1617                                 if (expr is NullLiteral){
1618                                         Report.Error (37, "Cannot convert null to value type `" +
1619                                                       TypeManager.CSharpName (expr_type) + "'");
1620                                         return null;
1621                                 }
1622                                 return new UnboxCast (expr, target_type);
1623                         }
1624
1625
1626                         ne = ExplicitReferenceConversion (expr, target_type);
1627                         if (ne != null)
1628                                 return ne;
1629
1630                         if (ec.InUnsafe){
1631                                 if (target_type.IsPointer){
1632                                         if (expr_type.IsPointer)
1633                                                 return new EmptyCast (expr, target_type);
1634
1635                                         if (expr_type == TypeManager.sbyte_type ||
1636                                             expr_type == TypeManager.byte_type ||
1637                                             expr_type == TypeManager.short_type ||
1638                                             expr_type == TypeManager.ushort_type ||
1639                                             expr_type == TypeManager.int32_type ||
1640                                             expr_type == TypeManager.uint32_type ||
1641                                             expr_type == TypeManager.uint64_type ||
1642                                             expr_type == TypeManager.int64_type)
1643                                                 return new OpcodeCast (expr, target_type, OpCodes.Conv_U);
1644                                 }
1645                                 if (expr_type.IsPointer){
1646                                         Expression e = null;
1647
1648                                         if (target_type == TypeManager.sbyte_type)
1649                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I1);
1650                                         else if (target_type == TypeManager.byte_type)
1651                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U1);
1652                                         else if (target_type == TypeManager.short_type)
1653                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I2);
1654                                         else if (target_type == TypeManager.ushort_type)
1655                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U2);
1656                                         else if (target_type == TypeManager.int32_type)
1657                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I4);
1658                                         else if (target_type == TypeManager.uint32_type)
1659                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U4);
1660                                         else if (target_type == TypeManager.uint64_type)
1661                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_U8);
1662                                         else if (target_type == TypeManager.int64_type){
1663                                                 e = new OpcodeCast (expr, target_type, OpCodes.Conv_I8);
1664                                         }
1665
1666                                         if (e != null){
1667                                                 Expression ci, ce;
1668
1669                                                 ci = ImplicitConversionStandard (ec, e, target_type, loc);
1670
1671                                                 if (ci != null)
1672                                                         return ci;
1673
1674                                                 ce = ExplicitNumericConversion (ec, e, target_type, loc);
1675                                                 if (ce != null)
1676                                                         return ce;
1677                                                 //
1678                                                 // We should always be able to go from an uint32
1679                                                 // implicitly or explicitly to the other integral
1680                                                 // types
1681                                                 //
1682                                                 throw new Exception ("Internal compiler error");
1683                                         }
1684                                 }
1685                         }
1686
1687                         ne = ExplicitUserConversion (ec, expr, target_type, loc);
1688                         if (ne != null)
1689                                 return ne;
1690
1691                         Error_CannotConvertType (loc, original_expr_type, target_type);
1692                         return null;
1693                 }
1694
1695                 /// <summary>
1696                 ///   Same as ExplicitConversion, only it doesn't include user defined conversions
1697                 /// </summary>
1698                 static public Expression ExplicitConversionStandard (EmitContext ec, Expression expr,
1699                                                                   Type target_type, Location l)
1700                 {
1701                         Expression ne = ImplicitConversionStandard (ec, expr, target_type, l);
1702
1703                         if (ne != null)
1704                                 return ne;
1705
1706                         ne = ExplicitNumericConversion (ec, expr, target_type, l);
1707                         if (ne != null)
1708                                 return ne;
1709
1710                         ne = ExplicitReferenceConversion (expr, target_type);
1711                         if (ne != null)
1712                                 return ne;
1713
1714                         Error_CannotConvertType (l, expr.Type, target_type);
1715                         return null;
1716                 }
1717         }
1718 }