mono/mini/local-propagation.c

   1 /*
   2  * local-propagation.c: Local constant, copy and tree propagation.
   3  *
   4  * To make some sense of the tree mover, read mono/docs/tree-mover.txt
   5  *
   6  * Author:
   7  *   Paolo Molaro (lupus@ximian.com)
   8  *   Dietmar Maurer (dietmar@ximian.com)
   9  *   Massimiliano Mantione (massi@ximian.com)
  10  *
  11  * (C) 2006 Novell, Inc.  http://www.novell.com
  12  */
  13
  14
  15 #include <string.h>
  16 #include <stdio.h>
  17 #ifdef HAVE_ALLOCA_H
  18 #include <alloca.h>
  19 #endif
  20
  21 #include <mono/metadata/debug-helpers.h>
  22 #include <mono/metadata/mempool.h>
  23 #include <mono/metadata/opcodes.h>
  24 #include "mini.h"
  25 #include "ir-emit.h"
  26
  27 #ifndef MONO_ARCH_IS_OP_MEMBASE
  28 #define MONO_ARCH_IS_OP_MEMBASE(opcode) FALSE
  29 #endif
  30
  31 static inline MonoBitSet*
  32 mono_bitset_mp_new_noinit (MonoMemPool *mp,  guint32 max_size)
  33 {
  34         int size = mono_bitset_alloc_size (max_size, 0);
  35         gpointer mem;
  36
  37         mem = mono_mempool_alloc (mp, size);
  38         return mono_bitset_mem_new (mem, max_size, MONO_BITSET_DONT_FREE);
  39 }
  40
  41 /*
  42  * mono_local_cprop:
  43  *
  44  *  A combined local copy and constant propagation pass.
  45  */
  46 void
  47 mono_local_cprop (MonoCompile *cfg)
  48 {
  49         MonoBasicBlock *bb;
  50         MonoInst **defs;
  51         gint32 *def_index;
  52         int max;
  53
  54 restart:
  55
  56         max = cfg->next_vreg;
  57         defs = mono_mempool_alloc (cfg->mempool, sizeof (MonoInst*) * (cfg->next_vreg + 1));
  58         def_index = mono_mempool_alloc (cfg->mempool, sizeof (guint32) * (cfg->next_vreg + 1));
  59
  60         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
  61                 MonoInst *ins;
  62                 int ins_index;
  63                 int last_call_index;
  64
  65                 /* Manually init the defs entries used by the bblock */
  66                 MONO_BB_FOR_EACH_INS (bb, ins) {
  67                         if ((ins->dreg != -1) && (ins->dreg < max)) {
  68                                 defs [ins->dreg] = NULL;
  69 #if SIZEOF_REGISTER == 4
  70                                 defs [ins->dreg + 1] = NULL;
  71 #endif
  72                         }
  73                         if ((ins->sreg1 != -1) && (ins->sreg1 < max)) {
  74                                 defs [ins->sreg1] = NULL;
  75 #if SIZEOF_REGISTER == 4
  76                                 defs [ins->sreg1 + 1] = NULL;
  77 #endif
  78                         }
  79                         if ((ins->sreg2 != -1) && (ins->sreg2 < max)) {
  80                                 defs [ins->sreg2] = NULL;
  81 #if SIZEOF_REGISTER == 4
  82                                 defs [ins->sreg2 + 1] = NULL;
  83 #endif
  84                         }
  85                 }
  86
  87                 ins_index = 0;
  88                 last_call_index = -1;
  89                 MONO_BB_FOR_EACH_INS (bb, ins) {
  90                         const char *spec = INS_INFO (ins->opcode);
  91                         int regtype, srcindex, sreg;
  92
  93                         if (ins->opcode == OP_NOP) {
  94                                 MONO_DELETE_INS (bb, ins);
  95                                 continue;
  96                         }
  97
  98                         g_assert (ins->opcode > MONO_CEE_LAST);
  99
 100                         /* FIXME: Optimize this */
 101                         if (ins->opcode == OP_LDADDR) {
 102                                 MonoInst *var = ins->inst_p0;
 103
 104                                 defs [var->dreg] = NULL;
 105                                 /*
 106                                 if (!MONO_TYPE_ISSTRUCT (var->inst_vtype))
 107                                         break;
 108                                 */
 109                         }
 110
 111                         if (MONO_IS_STORE_MEMBASE (ins)) {
 112                                 sreg = ins->dreg;
 113                                 regtype = 'i';
 114
 115                                 if ((regtype == 'i') && (sreg != -1) && defs [sreg]) {
 116                                         MonoInst *def = defs [sreg];
 117
 118                                         if ((def->opcode == OP_MOVE) && (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg])) && !vreg_is_volatile (cfg, def->sreg1)) {
 119                                                 int vreg = def->sreg1;
 120                                                 //printf ("CCOPY: R%d -> R%d\n", sreg, vreg);
 121                                                 ins->dreg = vreg;
 122                                         }
 123                                 }
 124                         }
 125
 126                         for (srcindex = 0; srcindex < 2; ++srcindex) {
 127                                 MonoInst *def;
 128
 129                                 regtype = srcindex == 0 ? spec [MONO_INST_SRC1] : spec [MONO_INST_SRC2];
 130                                 sreg = srcindex == 0 ? ins->sreg1 : ins->sreg2;
 131
 132                                 if ((regtype == ' ') || (sreg == -1) || (!defs [sreg]))
 133                                         continue;
 134
 135                                 def = defs [sreg];
 136
 137                                 /* Copy propagation */
 138                                 /*
 139                                  * The first check makes sure the source of the copy did not change since
 140                                  * the copy was made.
 141                                  * The second check avoids volatile variables.
 142                                  * The third check avoids copy propagating local vregs through a call,
 143                                  * since the lvreg will be spilled
 144                                  * The fourth check avoids copy propagating a vreg in cases where
 145                                  * it would be eliminated anyway by reverse copy propagation later,
 146                                  * because propagating it would create another use for it, thus making
 147                                  * it impossible to use reverse copy propagation.
 148                                  */
 149                                 /* Enabling this for floats trips up the fp stack */
 150                                 /*
 151                                  * Enabling this for floats on amd64 seems to cause a failure in
 152                                  * basic-math.cs, most likely because it gets rid of some r8->r4
 153                                  * conversions.
 154                                  */
 155                                 if (MONO_IS_MOVE (def) &&
 156                                         (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg])) &&
 157                                         !vreg_is_volatile (cfg, def->sreg1) &&
 158                                         /* This avoids propagating local vregs across calls */
 159                                         ((get_vreg_to_inst (cfg, def->sreg1) || !defs [def->sreg1] || (def_index [def->sreg1] >= last_call_index) || (def->opcode == OP_VMOVE))) &&
 160                                         !(defs [def->sreg1] && defs [def->sreg1]->next == def) &&
 161                                         (!MONO_ARCH_USE_FPSTACK || (def->opcode != OP_FMOVE)) &&
 162                                         (def->opcode != OP_FMOVE)) {
 163                                         int vreg = def->sreg1;
 164
 165                                         //printf ("CCOPY: R%d -> R%d\n", sreg, vreg);
 166                                         if (srcindex == 0)
 167                                                 ins->sreg1 = vreg;
 168                                         else
 169                                                 ins->sreg2 = vreg;
 170
 171                                         /* Allow further iterations */
 172                                         srcindex = -1;
 173                                         continue;
 174                                 }
 175
 176                                 /* Constant propagation */
 177                                 /* FIXME: Make is_inst_imm a macro */
 178                                 /* FIXME: Make is_inst_imm take an opcode argument */
 179                                 /* is_inst_imm is only needed for binops */
 180                                 if ((((def->opcode == OP_ICONST) || ((sizeof (gpointer) == 8) && (def->opcode == OP_I8CONST))) &&
 181                                          (((srcindex == 0) && (ins->sreg2 == -1)) || mono_arch_is_inst_imm (def->inst_c0))) ||
 182                                         (!MONO_ARCH_USE_FPSTACK && (def->opcode == OP_R8CONST))) {
 183                                         guint32 opcode2;
 184
 185                                         /* srcindex == 1 -> binop, ins->sreg2 == -1 -> unop */
 186                                         if ((srcindex == 1) && (ins->sreg1 != -1) && defs [ins->sreg1] && (defs [ins->sreg1]->opcode == OP_ICONST) && defs [ins->sreg2]) {
 187                                                 /* Both arguments are constants, perform cfold */
 188                                                 mono_constant_fold_ins (cfg, ins, defs [ins->sreg1], defs [ins->sreg2], TRUE);
 189                                         } else if ((srcindex == 0) && (ins->sreg2 != -1) && defs [ins->sreg2]) {
 190                                                 /* Arg 1 is constant, swap arguments if possible */
 191                                                 int opcode = ins->opcode;
 192                                                 mono_constant_fold_ins (cfg, ins, defs [ins->sreg1], defs [ins->sreg2], TRUE);
 193                                                 if (ins->opcode != opcode) {
 194                                                         /* Allow further iterations */
 195                                                         srcindex = -1;
 196                                                         continue;
 197                                                 }
 198                                         } else if ((srcindex == 0) && (ins->sreg2 == -1)) {
 199                                                 /* Constant unop, perform cfold */
 200                                                 mono_constant_fold_ins (cfg, ins, defs [ins->sreg1], NULL, TRUE);
 201                                         }
 202
 203                                         opcode2 = mono_op_to_op_imm (ins->opcode);
 204                                         if ((opcode2 != -1) && mono_arch_is_inst_imm (def->inst_c0) && ((srcindex == 1) || (ins->sreg2 == -1))) {
 205                                                 ins->opcode = opcode2;
 206                                                 if ((def->opcode == OP_I8CONST) && (sizeof (gpointer) == 4)) {
 207                                                         ins->inst_ls_word = def->inst_ls_word;
 208                                                         ins->inst_ms_word = def->inst_ms_word;
 209                                                 } else {
 210                                                         ins->inst_imm = def->inst_c0;
 211                                                 }
 212                                                 if (srcindex == 0)
 213                                                         ins->sreg1 = -1;
 214                                                 else
 215                                                         ins->sreg2 = -1;
 216
 217                                                 if ((opcode2 == OP_VOIDCALL) || (opcode2 == OP_CALL) || (opcode2 == OP_LCALL) || (opcode2 == OP_FCALL))
 218                                                         ((MonoCallInst*)ins)->fptr = (gpointer)ins->inst_imm;
 219
 220                                                 /* Allow further iterations */
 221                                                 srcindex = -1;
 222                                                 continue;
 223                                         }
 224                                         else {
 225                                                 /* Special cases */
 226 #if defined(__i386__) || defined(__x86_64__)
 227                                                 if ((ins->opcode == OP_X86_LEA) && (srcindex == 1)) {
 228 #if SIZEOF_REGISTER == 8
 229                                                         /* FIXME: Use OP_PADD_IMM when the new JIT is done */
 230                                                         ins->opcode = OP_LADD_IMM;
 231 #else
 232                                                         ins->opcode = OP_ADD_IMM;
 233 #endif
 234                                                         ins->inst_imm += def->inst_c0 << ins->backend.shift_amount;
 235                                                         ins->sreg2 = -1;
 236                                                 }
 237 #endif
 238                                                 opcode2 = mono_load_membase_to_load_mem (ins->opcode);
 239                                                 if ((srcindex == 0) && (opcode2 != -1) && mono_arch_is_inst_imm (def->inst_c0)) {
 240                                                         ins->opcode = opcode2;
 241                                                         ins->inst_imm = def->inst_c0 + ins->inst_offset;
 242                                                         ins->sreg1 = -1;
 243                                                 }
 244                                         }
 245                                 }
 246                                 else if (((def->opcode == OP_ADD_IMM) || (def->opcode == OP_LADD_IMM)) && (MONO_IS_LOAD_MEMBASE (ins) || MONO_ARCH_IS_OP_MEMBASE (ins->opcode))) {
 247                                         /* ADD_IMM is created by spill_global_vars */
 248                                         /*
 249                                          * We have to guarantee that def->sreg1 haven't changed since def->dreg
 250                                          * was defined. cfg->frame_reg is assumed to remain constant.
 251                                          */
 252                                         if ((def->sreg1 == cfg->frame_reg) || ((def->next == ins) && (def->dreg != def->sreg1))) {
 253                                                 ins->inst_basereg = def->sreg1;
 254                                                 ins->inst_offset += def->inst_imm;
 255                                         }
 256                                 } else if ((ins->opcode == OP_ISUB_IMM) && (def->opcode == OP_IADD_IMM) && (def->next == ins)) {
 257                                         ins->sreg1 = def->sreg1;
 258                                         ins->inst_imm -= def->inst_imm;
 259                                 } else if ((ins->opcode == OP_IADD_IMM) && (def->opcode == OP_ISUB_IMM) && (def->next == ins)) {
 260                                         ins->sreg1 = def->sreg1;
 261                                         ins->inst_imm -= def->inst_imm;
 262                                 } else if (ins->opcode == OP_STOREI1_MEMBASE_REG &&
 263                                                    (def->opcode == OP_ICONV_TO_U1 || def->opcode == OP_ICONV_TO_I1 || def->opcode == OP_SEXT_I4 || (SIZEOF_REGISTER == 8 && def->opcode == OP_LCONV_TO_U1)) &&
 264                                                    (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg]))) {
 265                                         /* Avoid needless sign extension */
 266                                         ins->sreg1 = def->sreg1;
 267                                 } else if (ins->opcode == OP_STOREI2_MEMBASE_REG &&
 268                                                    (def->opcode == OP_ICONV_TO_U2 || def->opcode == OP_ICONV_TO_I2 || def->opcode == OP_SEXT_I4 || (SIZEOF_REGISTER == 8 && def->opcode == OP_LCONV_TO_I2)) &&
 269                                                    (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg]))) {
 270                                         /* Avoid needless sign extension */
 271                                         ins->sreg1 = def->sreg1;
 272                                 }
 273                         }
 274
 275                         /* Do strength reduction here */
 276                         /* FIXME: Add long/float */
 277                         switch (ins->opcode) {
 278                         case OP_MOVE:
 279                         case OP_XMOVE:
 280                                 if (ins->dreg == ins->sreg1) {
 281                                         MONO_DELETE_INS (bb, ins);
 282                                         spec = INS_INFO (ins->opcode);
 283                                 }
 284                                 break;
 285                         case OP_ADD_IMM:
 286                         case OP_IADD_IMM:
 287                         case OP_SUB_IMM:
 288                         case OP_ISUB_IMM:
 289 #if SIZEOF_REGISTER == 8
 290                         case OP_LADD_IMM:
 291                         case OP_LSUB_IMM:
 292 #endif
 293                                 if (ins->inst_imm == 0) {
 294                                         ins->opcode = OP_MOVE;
 295                                         spec = INS_INFO (ins->opcode);
 296                                 }
 297                                 break;
 298                         case OP_MUL_IMM:
 299                         case OP_IMUL_IMM:
 300 #if SIZEOF_REGISTER == 8
 301                         case OP_LMUL_IMM:
 302 #endif
 303                                 if (ins->inst_imm == 0) {
 304                                         ins->opcode = (ins->opcode == OP_LMUL_IMM) ? OP_I8CONST : OP_ICONST;
 305                                         ins->inst_c0 = 0;
 306                                         ins->sreg1 = -1;
 307                                 } else if (ins->inst_imm == 1) {
 308                                         ins->opcode = OP_MOVE;
 309                                 } else if ((ins->opcode == OP_IMUL_IMM) && (ins->inst_imm == -1)) {
 310                                         ins->opcode = OP_INEG;
 311                                 } else if ((ins->opcode == OP_LMUL_IMM) && (ins->inst_imm == -1)) {
 312                                         ins->opcode = OP_LNEG;
 313                                 } else {
 314                                         int power2 = mono_is_power_of_two (ins->inst_imm);
 315                                         if (power2 >= 0) {
 316                                                 ins->opcode = (ins->opcode == OP_MUL_IMM) ? OP_SHL_IMM : ((ins->opcode == OP_LMUL_IMM) ? OP_LSHL_IMM : OP_ISHL_IMM);
 317                                                 ins->inst_imm = power2;
 318                                         }
 319                                 }
 320                                 spec = INS_INFO (ins->opcode);
 321                                 break;
 322                         case OP_IREM_UN_IMM:
 323                         case OP_IDIV_UN_IMM: {
 324                                 int c = ins->inst_imm;
 325                                 int power2 = mono_is_power_of_two (c);
 326
 327                                 if (power2 >= 0) {
 328                                         if (ins->opcode == OP_IREM_UN_IMM) {
 329                                                 ins->opcode = OP_IAND_IMM;
 330                                                 ins->sreg2 = -1;
 331                                                 ins->inst_imm = (1 << power2) - 1;
 332                                         } else if (ins->opcode == OP_IDIV_UN_IMM) {
 333                                                 ins->opcode = OP_ISHR_UN_IMM;
 334                                                 ins->sreg2 = -1;
 335                                                 ins->inst_imm = power2;
 336                                         }
 337                                 }
 338                                 spec = INS_INFO (ins->opcode);
 339                                 break;
 340                         }
 341                         case OP_IDIV_IMM: {
 342                                 int c = ins->inst_imm;
 343                                 int power2 = mono_is_power_of_two (c);
 344                                 MonoInst *tmp1, *tmp2, *tmp3, *tmp4;
 345
 346                                 /* FIXME: Move this elsewhere cause its hard to implement it here */
 347                                 if (power2 == 1) {
 348                                         int r1 = mono_alloc_ireg (cfg);
 349
 350                                         NEW_BIALU_IMM (cfg, tmp1, OP_ISHR_UN_IMM, r1, ins->sreg1, 31);
 351                                         mono_bblock_insert_after_ins (bb, ins, tmp1);
 352                                         NEW_BIALU (cfg, tmp2, OP_IADD, r1, r1, ins->sreg1);
 353                                         mono_bblock_insert_after_ins (bb, tmp1, tmp2);
 354                                         NEW_BIALU_IMM (cfg, tmp3, OP_ISHR_IMM, ins->dreg, r1, 1);
 355                                         mono_bblock_insert_after_ins (bb, tmp2, tmp3);
 356
 357                                         NULLIFY_INS (ins);
 358
 359                                         // We allocated a new vreg, so need to restart
 360                                         goto restart;
 361                                 } else if (power2 > 0) {
 362                                         int r1 = mono_alloc_ireg (cfg);
 363
 364                                         NEW_BIALU_IMM (cfg, tmp1, OP_ISHR_IMM, r1, ins->sreg1, 31);
 365                                         mono_bblock_insert_after_ins (bb, ins, tmp1);
 366                                         NEW_BIALU_IMM (cfg, tmp2, OP_ISHR_UN_IMM, r1, r1, (32 - power2));
 367                                         mono_bblock_insert_after_ins (bb, tmp1, tmp2);
 368                                         NEW_BIALU (cfg, tmp3, OP_IADD, r1, r1, ins->sreg1);
 369                                         mono_bblock_insert_after_ins (bb, tmp2, tmp3);
 370                                         NEW_BIALU_IMM (cfg, tmp4, OP_ISHR_IMM, ins->dreg, r1, power2);
 371                                         mono_bblock_insert_after_ins (bb, tmp3, tmp4);
 372
 373                                         NULLIFY_INS (ins);
 374
 375                                         // We allocated a new vreg, so need to restart
 376                                         goto restart;
 377                                 }
 378                                 break;
 379                         }
 380                         }
 381
 382                         if (spec [MONO_INST_DEST] != ' ') {
 383                                 MonoInst *def = defs [ins->dreg];
 384
 385                                 if (def && (def->opcode == OP_ADD_IMM) && (def->sreg1 == cfg->frame_reg) && (MONO_IS_STORE_MEMBASE (ins))) {
 386                                         /* ADD_IMM is created by spill_global_vars */
 387                                         /* cfg->frame_reg is assumed to remain constant */
 388                                         ins->inst_destbasereg = def->sreg1;
 389                                         ins->inst_offset += def->inst_imm;
 390                                 }
 391                         }
 392
 393                         if ((spec [MONO_INST_DEST] != ' ') && !MONO_IS_STORE_MEMBASE (ins) && !vreg_is_volatile (cfg, ins->dreg)) {
 394                                 defs [ins->dreg] = ins;
 395                                 def_index [ins->dreg] = ins_index;
 396                         }
 397
 398                         if (MONO_IS_CALL (ins))
 399                                 last_call_index = ins_index;
 400
 401                         ins_index ++;
 402                 }
 403         }
 404 }
 405
 406 static inline gboolean
 407 reg_is_softreg_no_fpstack (int reg, const char spec)
 408 {
 409         return (spec == 'i' && reg > MONO_MAX_IREGS)
 410                 || ((spec == 'f' && reg > MONO_MAX_FREGS) && !MONO_ARCH_USE_FPSTACK)
 411 #ifdef MONO_ARCH_SIMD_INTRINSICS
 412                 || (spec == 'x' && reg > MONO_MAX_XREGS)
 413 #endif
 414                 || (spec == 'v');
 415 }
 416
 417 static inline gboolean
 418 reg_is_softreg (int reg, const char spec)
 419 {
 420         return (spec == 'i' && reg > MONO_MAX_IREGS)
 421                 || (spec == 'f' && reg > MONO_MAX_FREGS)
 422 #ifdef MONO_ARCH_SIMD_INTRINSICS
 423                 || (spec == 'x' && reg > MONO_MAX_XREGS)
 424 #endif
 425                 || (spec == 'v');
 426 }
 427
 428 /**
 429  * mono_local_deadce:
 430  *
 431  *   Get rid of the dead assignments to local vregs like the ones created by the
 432  * copyprop pass.
 433  */
 434 void
 435 mono_local_deadce (MonoCompile *cfg)
 436 {
 437         MonoBasicBlock *bb;
 438         MonoInst *ins, *prev;
 439         MonoBitSet *used, *defined;
 440
 441         //mono_print_code (cfg, "BEFORE LOCAL-DEADCE");
 442
 443         /*
 444          * Assignments to global vregs can't be eliminated so this pass must come
 445          * after the handle_global_vregs () pass.
 446          */
 447
 448         used = mono_bitset_mp_new_noinit (cfg->mempool, cfg->next_vreg + 1);
 449         defined = mono_bitset_mp_new_noinit (cfg->mempool, cfg->next_vreg + 1);
 450
 451         /* First pass: collect liveness info */
 452         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
 453                 /* Manually init the defs entries used by the bblock */
 454                 MONO_BB_FOR_EACH_INS (bb, ins) {
 455                         const char *spec = INS_INFO (ins->opcode);
 456
 457                         if (spec [MONO_INST_DEST] != ' ') {
 458                                 mono_bitset_clear_fast (used, ins->dreg);
 459                                 mono_bitset_clear_fast (defined, ins->dreg);
 460 #if SIZEOF_REGISTER == 4
 461                                 /* Regpairs */
 462                                 mono_bitset_clear_fast (used, ins->dreg + 1);
 463                                 mono_bitset_clear_fast (defined, ins->dreg + 1);
 464 #endif
 465                         }
 466                         if (spec [MONO_INST_SRC1] != ' ') {
 467                                 mono_bitset_clear_fast (used, ins->sreg1);
 468 #if SIZEOF_REGISTER == 4
 469                                 mono_bitset_clear_fast (used, ins->sreg1 + 1);
 470 #endif
 471                         }
 472                         if (spec [MONO_INST_SRC2] != ' ') {
 473                                 mono_bitset_clear_fast (used, ins->sreg2);
 474 #if SIZEOF_REGISTER == 4
 475                                 mono_bitset_clear_fast (used, ins->sreg2 + 1);
 476 #endif
 477                         }
 478                 }
 479
 480                 /*
 481                  * Make a reverse pass over the instruction list
 482                  */
 483                 MONO_BB_FOR_EACH_INS_REVERSE_SAFE (bb, prev, ins) {
 484                         const char *spec = INS_INFO (ins->opcode);
 485
 486                         if (ins->opcode == OP_NOP) {
 487                                 MONO_DELETE_INS (bb, ins);
 488                                 continue;
 489                         }
 490
 491                         g_assert (ins->opcode > MONO_CEE_LAST);
 492
 493                         if (MONO_IS_NON_FP_MOVE (ins) && ins->prev) {
 494                                 MonoInst *def;
 495                                 const char *spec2;
 496
 497                                 def = ins->prev;
 498                                 while (def->prev && (def->opcode == OP_NOP))
 499                                         def = def->prev;
 500                                 spec2 = INS_INFO (def->opcode);
 501
 502                                 /*
 503                                  * Perform a limited kind of reverse copy propagation, i.e.
 504                                  * transform B <- FOO; A <- B into A <- FOO
 505                                  * This isn't copyprop, not deadce, but it can only be performed
 506                                  * after handle_global_vregs () has run.
 507                                  */
 508                                 if (!get_vreg_to_inst (cfg, ins->sreg1) && (spec2 [MONO_INST_DEST] != ' ') && (def->dreg == ins->sreg1) && !mono_bitset_test_fast (used, ins->sreg1) && !MONO_IS_STORE_MEMBASE (def) && reg_is_softreg (ins->sreg1, spec [MONO_INST_DEST])) {
 509                                         if (cfg->verbose_level > 2) {
 510                                                 printf ("\tReverse copyprop in BB%d on ", bb->block_num);
 511                                                 mono_print_ins (ins);
 512                                         }
 513
 514                                         def->dreg = ins->dreg;
 515                                         MONO_DELETE_INS (bb, ins);
 516                                         spec = INS_INFO (ins->opcode);
 517                                 }
 518                         }
 519
 520                         /* Enabling this on x86 could screw up the fp stack */
 521                         if (reg_is_softreg_no_fpstack (ins->dreg, spec [MONO_INST_DEST])) {
 522                                 /*
 523                                  * Assignments to global vregs can only be eliminated if there is another
 524                                  * assignment to the same vreg later in the same bblock.
 525                                  */
 526                                 if (!mono_bitset_test_fast (used, ins->dreg) &&
 527                                         (!get_vreg_to_inst (cfg, ins->dreg) || (!bb->extended && !vreg_is_volatile (cfg, ins->dreg) && mono_bitset_test_fast (defined, ins->dreg))) &&
 528                                         MONO_INS_HAS_NO_SIDE_EFFECT (ins)) {
 529                                         /* Happens with CMOV instructions */
 530                                         if (ins->prev && ins->prev->opcode == OP_ICOMPARE_IMM) {
 531                                                 MonoInst *prev = ins->prev;
 532                                                 /*
 533                                                  * Can't use DELETE_INS since that would interfere with the
 534                                                  * FOR_EACH_INS loop.
 535                                                  */
 536                                                 NULLIFY_INS (prev);
 537                                         }
 538                                         //printf ("DEADCE: "); mono_print_ins (ins);
 539                                         MONO_DELETE_INS (bb, ins);
 540                                         spec = INS_INFO (ins->opcode);
 541                                 }
 542
 543                                 if (spec [MONO_INST_DEST] != ' ')
 544                                         mono_bitset_clear_fast (used, ins->dreg);
 545                         }
 546
 547                         if (spec [MONO_INST_DEST] != ' ')
 548                                 mono_bitset_set_fast (defined, ins->dreg);
 549                         if (spec [MONO_INST_SRC1] != ' ')
 550                                 mono_bitset_set_fast (used, ins->sreg1);
 551                         if (spec [MONO_INST_SRC2] != ' ')
 552                                 mono_bitset_set_fast (used, ins->sreg2);
 553                         if (MONO_IS_STORE_MEMBASE (ins))
 554                                 mono_bitset_set_fast (used, ins->dreg);
 555
 556                         if (MONO_IS_CALL (ins)) {
 557                                 MonoCallInst *call = (MonoCallInst*)ins;
 558                                 GSList *l;
 559
 560                                 if (call->out_ireg_args) {
 561                                         for (l = call->out_ireg_args; l; l = l->next) {
 562                                                 guint32 regpair, reg;
 563
 564                                                 regpair = (guint32)(gssize)(l->data);
 565                                                 reg = regpair & 0xffffff;
 566
 567                                                 mono_bitset_set_fast (used, reg);
 568                                         }
 569                                 }
 570
 571                                 if (call->out_freg_args) {
 572                                         for (l = call->out_freg_args; l; l = l->next) {
 573                                                 guint32 regpair, reg;
 574
 575                                                 regpair = (guint32)(gssize)(l->data);
 576                                                 reg = regpair & 0xffffff;
 577
 578                                                 mono_bitset_set_fast (used, reg);
 579                                         }
 580                                 }
 581                         }
 582                 }
 583         }
 584
 585         //mono_print_code (cfg, "AFTER LOCAL-DEADCE");
 586 }