mono/mini/cfold.c

   1 /*
   2  * cfold.c: Constant folding support
   3  *
   4  * Author:
   5  *   Paolo Molaro (lupus@ximian.com)
   6  *   Dietmar Maurer (dietmar@ximian.com)
   7  *
   8  * (C) 2003 Ximian, Inc.  http://www.ximian.com
   9  */
  10 #include "mini.h"
  11
  12 int
  13 mono_is_power_of_two (guint32 val)
  14 {
  15         int i, j, k;
  16
  17         for (i = 0, j = 1, k = 0xfffffffe; i < 32; ++i, j = j << 1, k = k << 1) {
  18                 if (val & j)
  19                         break;
  20         }
  21         if (i == 32 || val & k)
  22                 return -1;
  23         return i;
  24 }
  25
  26 #define FOLD_BINOP(name,op)     \
  27         case name:      \
  28                 if (inst->inst_i0->opcode != OP_ICONST) \
  29                         return; \
  30                 if (inst->inst_i1->opcode == OP_ICONST) {       \
  31                         inst->opcode = OP_ICONST;       \
  32                         inst->inst_c0 = (gint32)(inst->inst_i0->inst_c0 op inst->inst_i1->inst_c0);     \
  33                 } \
  34                 return;
  35
  36 /*
  37  * We try to put constants on the left side of a commutative operation
  38  * because it reduces register pressure and it matches the usual cpu
  39  * instructions with immediates.
  40  */
  41 #define FOLD_BINOPCOMM(name,op) \
  42         case name:      \
  43                 if (inst->inst_i0->opcode == OP_ICONST) {\
  44                         if (inst->inst_i1->opcode == OP_ICONST) {       \
  45                                 inst->opcode = OP_ICONST;       \
  46                                 inst->inst_c0 = (gint32)(inst->inst_i0->inst_c0 op inst->inst_i1->inst_c0);     \
  47                                 return; \
  48                         } else { \
  49                                 MonoInst *tmp = inst->inst_i0;  \
  50                                 inst->inst_i0 = inst->inst_i1;  \
  51                                 inst->inst_i1 = tmp;    \
  52                        } \
  53                 } \
  54                 if (inst->inst_i1->opcode == OP_ICONST && inst->opcode == CEE_ADD) {    \
  55                         if (inst->inst_i1->inst_c0 == 0) { \
  56                                 *inst = *(inst->inst_i0); \
  57                                 return; \
  58                         } \
  59                 } \
  60                 if (inst->inst_i1->opcode == OP_ICONST && inst->opcode == CEE_MUL) {    \
  61                         int power2;     \
  62                         if (inst->inst_i1->inst_c0 == 1) {      \
  63                                 *inst = *(inst->inst_i0);       \
  64                                 return; \
  65                         } else if (inst->inst_i1->inst_c0 == -1) {      \
  66                                 inst->opcode = CEE_NEG; \
  67                                 return; \
  68                         }       \
  69                         power2 = mono_is_power_of_two (inst->inst_i1->inst_c0); \
  70                         if (power2 < 0) return; \
  71                         inst->opcode = CEE_SHL; \
  72                         inst->inst_i1->inst_c0 = power2;        \
  73                 } \
  74                 return;
  75
  76 /*
  77  * We can't let this cause a division by zero exception since the division
  78  * might not be executed during runtime.
  79  */
  80 #define FOLD_BINOPZ(name,op,cast)       \
  81         case name:      \
  82                 if (inst->inst_i1->opcode == OP_ICONST && inst->opcode == CEE_REM_UN && inst->inst_i1->inst_c0 == 2) {  \
  83                         inst->opcode = CEE_AND; \
  84                         inst->inst_i1->inst_c0 = 1;     \
  85                         return; \
  86                 }       \
  87                 if (inst->inst_i1->opcode == OP_ICONST) {       \
  88                         if (!inst->inst_i1->inst_c0) return;    \
  89                         if (inst->inst_i0->opcode == OP_ICONST) {       \
  90                 if ((inst->inst_i0->inst_c0 == G_MININT32) && (inst->inst_i1->inst_c0 == -1)) \
  91                     return; \
  92                                 inst->inst_c0 = (cast)inst->inst_i0->inst_c0 op (cast)inst->inst_i1->inst_c0;   \
  93                                 inst->opcode = OP_ICONST;       \
  94                         } else {        \
  95                                 int power2 = mono_is_power_of_two (inst->inst_i1->inst_c0);     \
  96                                 if (power2 < 0) return; \
  97                                 if (inst->opcode == CEE_REM_UN) {       \
  98                                         inst->opcode = CEE_AND; \
  99                                         inst->inst_i1->inst_c0 = (1 << power2) - 1;     \
 100                                 } else if (inst->opcode == CEE_DIV_UN) {        \
 101                                         inst->opcode = CEE_SHR_UN;      \
 102                                         inst->inst_i1->inst_c0 = power2;        \
 103                                 }       \
 104                         }       \
 105                 } \
 106                 return;
 107
 108 #define FOLD_BINOPA(name,op,cast)       \
 109         case name:      \
 110                 if (inst->inst_i0->opcode != OP_ICONST) \
 111                         return; \
 112                 if (inst->inst_i1->opcode == OP_ICONST) {       \
 113                         inst->opcode = OP_ICONST;       \
 114                         inst->inst_c0 = (cast)inst->inst_i0->inst_c0 op (cast)inst->inst_i1->inst_c0;   \
 115                 } \
 116                 return;
 117
 118 #define FOLD_CXX(name,op,cast)  \
 119         case name:      \
 120                 if (inst->inst_i0->opcode != OP_COMPARE)        \
 121                         return; \
 122                 if (inst->inst_i0->inst_i0->opcode != OP_ICONST)        \
 123                         return; \
 124                 if (inst->inst_i0->inst_i1->opcode == OP_ICONST) {      \
 125                         inst->opcode = OP_ICONST;       \
 126                         inst->inst_c0 = (cast)inst->inst_i0->inst_i0->inst_c0 op (cast)inst->inst_i0->inst_i1->inst_c0; \
 127                 } \
 128                 return;
 129
 130 #define FOLD_UNOP(name,op)      \
 131         case name:      \
 132                 if (inst->inst_i0->opcode == OP_ICONST) {       \
 133                         inst->opcode = OP_ICONST;       \
 134                         inst->inst_c0 = op inst->inst_i0->inst_c0; \
 135                 } else if (inst->inst_i0->opcode == OP_I8CONST) { \
 136                         inst->opcode = OP_I8CONST;      \
 137                         inst->inst_l = op inst->inst_i0->inst_l; \
 138                 } return;
 139
 140 #define FOLD_BRBINOP(name,op,cast)      \
 141         case name:      \
 142                 if (inst->inst_i0->opcode != OP_COMPARE)        \
 143                         return; \
 144                 if (inst->inst_i0->inst_i0->opcode != OP_ICONST)        \
 145                         return; \
 146                 if (inst->inst_i0->inst_i1->opcode == OP_ICONST) {      \
 147                         if ((cast)inst->inst_i0->inst_i0->inst_c0 op (cast)inst->inst_i0->inst_i1->inst_c0)     \
 148                                 inst->opcode = OP_BR;   \
 149                         else    \
 150                                 inst->opcode = OP_NOP;  \
 151                 } \
 152                 return;
 153
 154 /*
 155  * Helper function to do constant expression evaluation.
 156  * We do constant folding of integers only, FP stuff is much more tricky,
 157  * int64 probably not worth it.
 158  */
 159 void
 160 mono_constant_fold_inst (MonoInst *inst, gpointer data)
 161 {
 162         switch (inst->opcode) {
 163
 164         /* FIXME: the CEE_B* don't contain operands, need to use the OP_COMPARE instruction */
 165         /*FOLD_BRBINOP (CEE_BEQ,==,gint32)
 166         FOLD_BRBINOP (CEE_BGE,>=,gint32)
 167         FOLD_BRBINOP (CEE_BGT,>,gint32)
 168         FOLD_BRBINOP (CEE_BLE,<=,gint32)
 169         FOLD_BRBINOP (CEE_BLT,<,gint32)
 170         FOLD_BRBINOP (CEE_BNE_UN,!=,guint32)
 171         FOLD_BRBINOP (CEE_BGE_UN,>=,guint32)
 172         FOLD_BRBINOP (CEE_BGT_UN,>,guint32)
 173         FOLD_BRBINOP (CEE_BLE_UN,<=,guint32)
 174         FOLD_BRBINOP (CEE_BLT_UN,<,guint32)*/
 175
 176         FOLD_BINOPCOMM (CEE_MUL,*)
 177
 178         FOLD_BINOPCOMM (CEE_ADD,+)
 179         FOLD_BINOP (CEE_SUB,-)
 180         FOLD_BINOPZ (CEE_DIV,/,gint32)
 181         FOLD_BINOPZ (CEE_DIV_UN,/,guint32)
 182         FOLD_BINOPZ (CEE_REM,%,gint32)
 183         FOLD_BINOPZ (CEE_REM_UN,%,guint32)
 184         FOLD_BINOPCOMM (CEE_AND,&)
 185         FOLD_BINOPCOMM (CEE_OR,|)
 186         FOLD_BINOPCOMM (CEE_XOR,^)
 187         FOLD_BINOP (CEE_SHL,<<)
 188         FOLD_BINOP (CEE_SHR,>>)
 189         case CEE_SHR_UN:
 190                 if (inst->inst_i0->opcode != OP_ICONST)
 191                         return;
 192                 if (inst->inst_i1->opcode == OP_ICONST) {
 193                         inst->opcode = OP_ICONST;
 194                         inst->inst_c0 = (guint32)inst->inst_i0->inst_c0 >> (guint32)inst->inst_i1->inst_c0;
 195                 }
 196                 return;
 197         FOLD_UNOP (CEE_NEG,-)
 198         FOLD_UNOP (CEE_NOT,~)
 199         FOLD_CXX (OP_CEQ,==,gint32)
 200         FOLD_CXX (OP_CGT,>,gint32)
 201         FOLD_CXX (OP_CGT_UN,>,guint32)
 202         FOLD_CXX (OP_CLT,<,gint32)
 203         FOLD_CXX (OP_CLT_UN,<,guint32)
 204         case CEE_CONV_I8:
 205                 if (inst->inst_i0->opcode == OP_ICONST) {
 206                         inst->opcode = OP_I8CONST;
 207                         inst->inst_l = inst->inst_i0->inst_c0;
 208                 }
 209                 return;
 210         case CEE_CONV_I:
 211         case CEE_CONV_U:
 212                 if (inst->inst_i0->opcode == OP_ICONST) {
 213                         inst->opcode = OP_ICONST;
 214                         inst->inst_c0 = inst->inst_i0->inst_c0;
 215                 } else if (inst->inst_i0->opcode == CEE_LDIND_I) {
 216                         *inst = *inst->inst_i0;
 217                 }
 218                 return;
 219         /* we should be able to handle isinst and castclass as well */
 220         case CEE_ISINST:
 221         case CEE_CASTCLASS:
 222         /*
 223          * TODO:
 224          *      conv.* opcodes.
 225          *      *ovf* opcodes? I'ts slow and hard to do in C.
 226          *      switch can be replaced by a simple jump
 227          */
 228 #if SIZEOF_VOID_P == 4
 229         case CEE_CONV_I4:
 230                 if ((inst->inst_left->type == STACK_I4) || (inst->inst_left->type == STACK_PTR)) {
 231                         *inst = *inst->inst_left;
 232                 }
 233                 break;
 234 #endif
 235         default:
 236                 return;
 237         }
 238 }
 239
 240 void
 241 mono_constant_fold (MonoCompile *cfg)
 242 {
 243         MonoBasicBlock *bb;
 244
 245         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
 246                 MonoInst *ins;
 247                 MONO_BB_FOR_EACH_INS (bb, ins)
 248                         mono_inst_foreach (ins, mono_constant_fold_inst, NULL);
 249         }
 250 }
 251
 252 /*
 253  * If the arguments to the cond branch are constants, eval and
 254  * return BRANCH_NOT_TAKEN for not taken, BRANCH_TAKEN for taken,
 255  * BRANCH_UNDEF otherwise.
 256  * If this code is changed to handle also non-const values, make sure
 257  * side effects are handled in optimize_branches() in mini.c, by
 258  * inserting pop instructions.
 259  */
 260 int
 261 mono_eval_cond_branch (MonoInst *ins)
 262 {
 263         MonoInst *left, *right;
 264         /* FIXME: handle also 64 bit ints */
 265         left = ins->inst_left->inst_left;
 266         if (left->opcode != OP_ICONST && left->opcode != OP_PCONST)
 267                 return BRANCH_UNDEF;
 268         right = ins->inst_left->inst_right;
 269         if (right->opcode != OP_ICONST && right->opcode != OP_PCONST)
 270                 return BRANCH_UNDEF;
 271         switch (ins->opcode) {
 272         case CEE_BEQ:
 273                 if (left->inst_c0 == right->inst_c0)
 274                         return BRANCH_TAKEN;
 275                 return BRANCH_NOT_TAKEN;
 276         case CEE_BGE:
 277                 if (left->inst_c0 >= right->inst_c0)
 278                         return BRANCH_TAKEN;
 279                 return BRANCH_NOT_TAKEN;
 280         case CEE_BGT:
 281                 if (left->inst_c0 > right->inst_c0)
 282                         return BRANCH_TAKEN;
 283                 return BRANCH_NOT_TAKEN;
 284         case CEE_BLE:
 285                 if (left->inst_c0 <= right->inst_c0)
 286                         return BRANCH_TAKEN;
 287                 return BRANCH_NOT_TAKEN;
 288         case CEE_BLT:
 289                 if (left->inst_c0 < right->inst_c0)
 290                         return BRANCH_TAKEN;
 291                 return BRANCH_NOT_TAKEN;
 292         case CEE_BNE_UN:
 293                 if ((gsize)left->inst_c0 != (gsize)right->inst_c0)
 294                         return BRANCH_TAKEN;
 295                 return BRANCH_NOT_TAKEN;
 296         case CEE_BGE_UN:
 297                 if ((gsize)left->inst_c0 >= (gsize)right->inst_c0)
 298                         return BRANCH_TAKEN;
 299                 return BRANCH_NOT_TAKEN;
 300         case CEE_BGT_UN:
 301                 if ((gsize)left->inst_c0 > (gsize)right->inst_c0)
 302                         return BRANCH_TAKEN;
 303                 return BRANCH_NOT_TAKEN;
 304         case CEE_BLE_UN:
 305                 if ((gsize)left->inst_c0 <= (gsize)right->inst_c0)
 306                         return BRANCH_TAKEN;
 307                 return BRANCH_NOT_TAKEN;
 308         case CEE_BLT_UN:
 309                 if ((gsize)left->inst_c0 < (gsize)right->inst_c0)
 310                         return BRANCH_TAKEN;
 311                 return BRANCH_NOT_TAKEN;
 312         }
 313         return BRANCH_UNDEF;
 314 }
 315