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 static int
  13 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 = 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 = 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_MUL) {    \
  55                         int power2;     \
  56                         if (inst->inst_i1->inst_c0 == 1) {      \
  57                                 *inst = *(inst->inst_i0);       \
  58                                 return; \
  59                         } else if (inst->inst_i1->inst_c0 == -1) {      \
  60                                 inst->opcode = CEE_NEG; \
  61                                 return; \
  62                         }       \
  63                         power2 = is_power_of_two (inst->inst_i1->inst_c0);      \
  64                         if (power2 < 0) return; \
  65                         inst->opcode = CEE_SHL; \
  66                         inst->inst_i1->inst_c0 = power2;        \
  67                 } \
  68                 return;
  69
  70 #define FOLD_BINOPZ(name,op,cast)       \
  71         case name:      \
  72                 if (inst->inst_i1->opcode == OP_ICONST && inst->opcode == CEE_REM_UN && inst->inst_i1->inst_c0 == 2) {  \
  73                         inst->opcode = CEE_AND; \
  74                         inst->inst_i1->inst_c0 = 1;     \
  75                         return; \
  76                 }       \
  77                 if (inst->inst_i1->opcode == OP_ICONST) {       \
  78                         /* let the runtime throw the exception. */      \
  79                         if (!inst->inst_i1->inst_c0) return;    \
  80                         if (inst->inst_i0->opcode == OP_ICONST) {       \
  81                                 inst->inst_c0 = (cast)inst->inst_i0->inst_c0 op (cast)inst->inst_i1->inst_c0;   \
  82                                 inst->opcode = OP_ICONST;       \
  83                         } else {        \
  84                                 int power2 = is_power_of_two (inst->inst_i1->inst_c0);  \
  85                                 if (power2 < 0) return; \
  86                                 if (inst->opcode == CEE_REM_UN) {       \
  87                                         inst->opcode = CEE_AND; \
  88                                         inst->inst_i1->inst_c0 = (1 << power2) - 1;     \
  89                                 } else if (inst->opcode == CEE_DIV_UN) {        \
  90                                         inst->opcode = CEE_SHR_UN;      \
  91                                         inst->inst_i1->inst_c0 = power2;        \
  92                                 }       \
  93                         }       \
  94                 } \
  95                 return;
  96
  97 #define FOLD_BINOPA(name,op,cast)       \
  98         case name:      \
  99                 if (inst->inst_i0->opcode != OP_ICONST) \
 100                         return; \
 101                 if (inst->inst_i1->opcode == OP_ICONST) {       \
 102                         inst->opcode = OP_ICONST;       \
 103                         inst->inst_c0 = (cast)inst->inst_i0->inst_c0 op (cast)inst->inst_i1->inst_c0;   \
 104                 } \
 105                 return;
 106
 107 #define FOLD_CXX(name,op,cast)  \
 108         case name:      \
 109                 if (inst->inst_i0->opcode != OP_COMPARE)        \
 110                         return; \
 111                 if (inst->inst_i0->inst_i0->opcode != OP_ICONST)        \
 112                         return; \
 113                 if (inst->inst_i0->inst_i1->opcode == OP_ICONST) {      \
 114                         inst->opcode = OP_ICONST;       \
 115                         inst->inst_c0 = (cast)inst->inst_i0->inst_i0->inst_c0 op (cast)inst->inst_i0->inst_i1->inst_c0; \
 116                 } \
 117                 return;
 118
 119 #define FOLD_UNOP(name,op)      \
 120         case name:      \
 121                 if (inst->inst_i0->opcode != OP_ICONST) \
 122                         return; \
 123                 inst->opcode = OP_ICONST;       \
 124                 inst->inst_c0 = op inst->inst_i0->inst_c0; \
 125                 return;
 126
 127 #define FOLD_BRBINOP(name,op,cast)      \
 128         case name:      \
 129                 if (inst->inst_i0->opcode != OP_COMPARE)        \
 130                         return; \
 131                 if (inst->inst_i0->inst_i0->opcode != OP_ICONST)        \
 132                         return; \
 133                 if (inst->inst_i0->inst_i1->opcode == OP_ICONST) {      \
 134                         if ((cast)inst->inst_i0->inst_i0->inst_c0 op (cast)inst->inst_i0->inst_i1->inst_c0)     \
 135                                 inst->opcode = CEE_BR;  \
 136                         else    \
 137                                 inst->opcode = CEE_NOP; \
 138                 } \
 139                 return;
 140
 141 /*
 142  * Helper function to do constant expression evaluation.
 143  * We do constant folding of integers only, FP stuff is much more tricky,
 144  * int64 probably not worth it.
 145  */
 146 void
 147 mono_constant_fold_inst (MonoInst *inst, gpointer data)
 148 {
 149         switch (inst->opcode) {
 150
 151         /* FIXME: the CEE_B* don't contain operands, need to use the OP_COMPARE instruction */
 152         /*FOLD_BRBINOP (CEE_BEQ,==,gint32)
 153         FOLD_BRBINOP (CEE_BGE,>=,gint32)
 154         FOLD_BRBINOP (CEE_BGT,>,gint32)
 155         FOLD_BRBINOP (CEE_BLE,<=,gint32)
 156         FOLD_BRBINOP (CEE_BLT,<,gint32)
 157         FOLD_BRBINOP (CEE_BNE_UN,!=,guint32)
 158         FOLD_BRBINOP (CEE_BGE_UN,>=,guint32)
 159         FOLD_BRBINOP (CEE_BGT_UN,>,guint32)
 160         FOLD_BRBINOP (CEE_BLE_UN,<=,guint32)
 161         FOLD_BRBINOP (CEE_BLT_UN,<,guint32)*/
 162
 163         FOLD_BINOPCOMM (CEE_MUL,*)
 164
 165         FOLD_BINOPCOMM (CEE_ADD,+)
 166         FOLD_BINOP (CEE_SUB,-)
 167         FOLD_BINOPZ (CEE_DIV,/,gint32)
 168         FOLD_BINOPZ (CEE_DIV_UN,/,guint32)
 169         FOLD_BINOPZ (CEE_REM,%,gint32)
 170         FOLD_BINOPZ (CEE_REM_UN,%,guint32)
 171         FOLD_BINOPCOMM (CEE_AND,&)
 172         FOLD_BINOPCOMM (CEE_OR,|)
 173         FOLD_BINOPCOMM (CEE_XOR,^)
 174         FOLD_BINOP (CEE_SHL,<<)
 175         FOLD_BINOP (CEE_SHR,>>)
 176         case CEE_SHR_UN:
 177                 if (inst->inst_i0->opcode != OP_ICONST)
 178                         return;
 179                 if (inst->inst_i1->opcode == OP_ICONST) {
 180                         inst->opcode = OP_ICONST;
 181                         inst->inst_c0 = (guint32)inst->inst_i0->inst_c0 >> (guint32)inst->inst_i1->inst_c0;
 182                 }
 183                 return;
 184         FOLD_UNOP (CEE_NEG,-)
 185         FOLD_UNOP (CEE_NOT,~)
 186         FOLD_CXX (OP_CEQ,==,gint32)
 187         FOLD_CXX (OP_CGT,>,gint32)
 188         FOLD_CXX (OP_CGT_UN,>,guint32)
 189         FOLD_CXX (OP_CLT,<,gint32)
 190         FOLD_CXX (OP_CLT_UN,<,guint32)
 191         /* we should be able to handle isinst and castclass as well */
 192         case CEE_ISINST:
 193         case CEE_CASTCLASS:
 194         /*
 195          * TODO:
 196          *      conv.* opcodes.
 197          *      *ovf* opcodes? I'ts slow and hard to do in C.
 198          *      switch can be replaced by a simple jump
 199          */
 200         default:
 201                 return;
 202         }
 203 }
 204
 205 void
 206 mono_constant_fold (MonoCompile *cfg)
 207 {
 208         MonoBasicBlock *bb;
 209
 210         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
 211                 MonoInst *ins;
 212                 for (ins = bb->code; ins; ins = ins->next)
 213                         mono_inst_foreach (ins, mono_constant_fold_inst, NULL);
 214         }
 215 }
 216