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                         int sregs [MONO_MAX_SRC_REGS];
  68                         int num_sregs, i;
  69
  70                         if ((ins->dreg != -1) && (ins->dreg < max)) {
  71                                 defs [ins->dreg] = NULL;
  72 #if SIZEOF_REGISTER == 4
  73                                 defs [ins->dreg + 1] = NULL;
  74 #endif
  75                         }
  76
  77                         num_sregs = mono_inst_get_src_registers (ins, sregs);
  78                         for (i = 0; i < num_sregs; ++i) {
  79                                 int sreg = sregs [i];
  80                                 if (sreg < max) {
  81                                         defs [sreg] = NULL;
  82 #if SIZEOF_REGISTER == 4
  83                                         defs [sreg + 1] = NULL;
  84 #endif
  85                                 }
  86                         }
  87                 }
  88
  89                 ins_index = 0;
  90                 last_call_index = -1;
  91                 MONO_BB_FOR_EACH_INS (bb, ins) {
  92                         const char *spec = INS_INFO (ins->opcode);
  93                         int regtype, srcindex, sreg;
  94                         int num_sregs;
  95                         int sregs [MONO_MAX_SRC_REGS];
  96
  97                         if (ins->opcode == OP_NOP) {
  98                                 MONO_DELETE_INS (bb, ins);
  99                                 continue;
 100                         }
 101
 102                         g_assert (ins->opcode > MONO_CEE_LAST);
 103
 104                         /* FIXME: Optimize this */
 105                         if (ins->opcode == OP_LDADDR) {
 106                                 MonoInst *var = ins->inst_p0;
 107
 108                                 defs [var->dreg] = NULL;
 109                                 /*
 110                                 if (!MONO_TYPE_ISSTRUCT (var->inst_vtype))
 111                                         break;
 112                                 */
 113                         }
 114
 115                         if (MONO_IS_STORE_MEMBASE (ins)) {
 116                                 sreg = ins->dreg;
 117                                 regtype = 'i';
 118
 119                                 if ((regtype == 'i') && (sreg != -1) && defs [sreg]) {
 120                                         MonoInst *def = defs [sreg];
 121
 122                                         if ((def->opcode == OP_MOVE) && (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg])) && !vreg_is_volatile (cfg, def->sreg1)) {
 123                                                 int vreg = def->sreg1;
 124                                                 if (cfg->verbose_level > 2) printf ("CCOPY: R%d -> R%d\n", sreg, vreg);
 125                                                 ins->dreg = vreg;
 126                                         }
 127                                 }
 128                         }
 129
 130                         num_sregs = mono_inst_get_src_registers (ins, sregs);
 131                         for (srcindex = 0; srcindex < num_sregs; ++srcindex) {
 132                                 MonoInst *def;
 133
 134                                 regtype = spec [MONO_INST_SRC1 + srcindex];
 135                                 sreg = sregs [srcindex];
 136
 137                                 if ((regtype == ' ') || (sreg == -1) || (!defs [sreg]))
 138                                         continue;
 139
 140                                 def = defs [sreg];
 141
 142                                 /* Copy propagation */
 143                                 /*
 144                                  * The first check makes sure the source of the copy did not change since
 145                                  * the copy was made.
 146                                  * The second check avoids volatile variables.
 147                                  * The third check avoids copy propagating local vregs through a call,
 148                                  * since the lvreg will be spilled
 149                                  * The fourth check avoids copy propagating a vreg in cases where
 150                                  * it would be eliminated anyway by reverse copy propagation later,
 151                                  * because propagating it would create another use for it, thus making
 152                                  * it impossible to use reverse copy propagation.
 153                                  */
 154                                 /* Enabling this for floats trips up the fp stack */
 155                                 /*
 156                                  * Enabling this for floats on amd64 seems to cause a failure in
 157                                  * basic-math.cs, most likely because it gets rid of some r8->r4
 158                                  * conversions.
 159                                  */
 160                                 if (MONO_IS_MOVE (def) &&
 161                                         (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg])) &&
 162                                         !vreg_is_volatile (cfg, def->sreg1) &&
 163                                         /* This avoids propagating local vregs across calls */
 164                                         ((get_vreg_to_inst (cfg, def->sreg1) || !defs [def->sreg1] || (def_index [def->sreg1] >= last_call_index) || (def->opcode == OP_VMOVE))) &&
 165                                         !(defs [def->sreg1] && defs [def->sreg1]->next == def) &&
 166                                         (!MONO_ARCH_USE_FPSTACK || (def->opcode != OP_FMOVE)) &&
 167                                         (def->opcode != OP_FMOVE)) {
 168                                         int vreg = def->sreg1;
 169
 170                                         if (cfg->verbose_level > 2) printf ("CCOPY/2: R%d -> R%d\n", sreg, vreg);
 171                                         sregs [srcindex] = vreg;
 172                                         mono_inst_set_src_registers (ins, sregs);
 173
 174                                         /* Allow further iterations */
 175                                         srcindex = -1;
 176                                         continue;
 177                                 }
 178
 179                                 /* Constant propagation */
 180                                 /* FIXME: Make is_inst_imm a macro */
 181                                 /* FIXME: Make is_inst_imm take an opcode argument */
 182                                 /* is_inst_imm is only needed for binops */
 183                                 if ((((def->opcode == OP_ICONST) || ((sizeof (gpointer) == 8) && (def->opcode == OP_I8CONST))) &&
 184                                          (((srcindex == 0) && (ins->sreg2 == -1)) || mono_arch_is_inst_imm (def->inst_c0))) ||
 185                                         (!MONO_ARCH_USE_FPSTACK && (def->opcode == OP_R8CONST))) {
 186                                         guint32 opcode2;
 187
 188                                         /* srcindex == 1 -> binop, ins->sreg2 == -1 -> unop */
 189                                         if ((srcindex == 1) && (ins->sreg1 != -1) && defs [ins->sreg1] && (defs [ins->sreg1]->opcode == OP_ICONST) && defs [ins->sreg2]) {
 190                                                 /* Both arguments are constants, perform cfold */
 191                                                 mono_constant_fold_ins (cfg, ins, defs [ins->sreg1], defs [ins->sreg2], TRUE);
 192                                         } else if ((srcindex == 0) && (ins->sreg2 != -1) && defs [ins->sreg2]) {
 193                                                 /* Arg 1 is constant, swap arguments if possible */
 194                                                 int opcode = ins->opcode;
 195                                                 mono_constant_fold_ins (cfg, ins, defs [ins->sreg1], defs [ins->sreg2], TRUE);
 196                                                 if (ins->opcode != opcode) {
 197                                                         /* Allow further iterations */
 198                                                         srcindex = -1;
 199                                                         continue;
 200                                                 }
 201                                         } else if ((srcindex == 0) && (ins->sreg2 == -1)) {
 202                                                 /* Constant unop, perform cfold */
 203                                                 mono_constant_fold_ins (cfg, ins, defs [ins->sreg1], NULL, TRUE);
 204                                         }
 205
 206                                         opcode2 = mono_op_to_op_imm (ins->opcode);
 207                                         if ((opcode2 != -1) && mono_arch_is_inst_imm (def->inst_c0) && ((srcindex == 1) || (ins->sreg2 == -1))) {
 208                                                 ins->opcode = opcode2;
 209                                                 if ((def->opcode == OP_I8CONST) && (sizeof (gpointer) == 4)) {
 210                                                         ins->inst_ls_word = def->inst_ls_word;
 211                                                         ins->inst_ms_word = def->inst_ms_word;
 212                                                 } else {
 213                                                         ins->inst_imm = def->inst_c0;
 214                                                 }
 215                                                 sregs [srcindex] = -1;
 216                                                 mono_inst_set_src_registers (ins, sregs);
 217
 218                                                 if ((opcode2 == OP_VOIDCALL) || (opcode2 == OP_CALL) || (opcode2 == OP_LCALL) || (opcode2 == OP_FCALL))
 219                                                         ((MonoCallInst*)ins)->fptr = (gpointer)ins->inst_imm;
 220
 221                                                 /* Allow further iterations */
 222                                                 srcindex = -1;
 223                                                 continue;
 224                                         }
 225                                         else {
 226                                                 /* Special cases */
 227 #if defined(TARGET_X86) || defined(TARGET_AMD64)
 228                                                 if ((ins->opcode == OP_X86_LEA) && (srcindex == 1)) {
 229 #if SIZEOF_REGISTER == 8
 230                                                         /* FIXME: Use OP_PADD_IMM when the new JIT is done */
 231                                                         ins->opcode = OP_LADD_IMM;
 232 #else
 233                                                         ins->opcode = OP_ADD_IMM;
 234 #endif
 235                                                         ins->inst_imm += def->inst_c0 << ins->backend.shift_amount;
 236                                                         ins->sreg2 = -1;
 237                                                 }
 238 #endif
 239                                                 opcode2 = mono_load_membase_to_load_mem (ins->opcode);
 240                                                 if ((srcindex == 0) && (opcode2 != -1) && mono_arch_is_inst_imm (def->inst_c0)) {
 241                                                         ins->opcode = opcode2;
 242                                                         ins->inst_imm = def->inst_c0 + ins->inst_offset;
 243                                                         ins->sreg1 = -1;
 244                                                 }
 245                                         }
 246                                 }
 247                                 else if (((def->opcode == OP_ADD_IMM) || (def->opcode == OP_LADD_IMM)) && (MONO_IS_LOAD_MEMBASE (ins) || MONO_ARCH_IS_OP_MEMBASE (ins->opcode))) {
 248                                         /* ADD_IMM is created by spill_global_vars */
 249                                         /*
 250                                          * We have to guarantee that def->sreg1 haven't changed since def->dreg
 251                                          * was defined. cfg->frame_reg is assumed to remain constant.
 252                                          */
 253                                         if ((def->sreg1 == cfg->frame_reg) || ((def->next == ins) && (def->dreg != def->sreg1))) {
 254                                                 ins->inst_basereg = def->sreg1;
 255                                                 ins->inst_offset += def->inst_imm;
 256                                         }
 257                                 } else if ((ins->opcode == OP_ISUB_IMM) && (def->opcode == OP_IADD_IMM) && (def->next == ins) && (def->dreg != def->sreg1)) {
 258                                         ins->sreg1 = def->sreg1;
 259                                         ins->inst_imm -= def->inst_imm;
 260                                 } else if ((ins->opcode == OP_IADD_IMM) && (def->opcode == OP_ISUB_IMM) && (def->next == ins) && (def->dreg != def->sreg1)) {
 261                                         ins->sreg1 = def->sreg1;
 262                                         ins->inst_imm -= def->inst_imm;
 263                                 } else if (ins->opcode == OP_STOREI1_MEMBASE_REG &&
 264                                                    (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)) &&
 265                                                    (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg]))) {
 266                                         /* Avoid needless sign extension */
 267                                         ins->sreg1 = def->sreg1;
 268                                 } else if (ins->opcode == OP_STOREI2_MEMBASE_REG &&
 269                                                    (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)) &&
 270                                                    (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg]))) {
 271                                         /* Avoid needless sign extension */
 272                                         ins->sreg1 = def->sreg1;
 273                                 }
 274                         }
 275
 276                         /* Do strength reduction here */
 277                         /* FIXME: Add long/float */
 278                         switch (ins->opcode) {
 279                         case OP_MOVE:
 280                         case OP_XMOVE:
 281                                 if (ins->dreg == ins->sreg1) {
 282                                         MONO_DELETE_INS (bb, ins);
 283                                         spec = INS_INFO (ins->opcode);
 284                                 }
 285                                 break;
 286                         case OP_ADD_IMM:
 287                         case OP_IADD_IMM:
 288                         case OP_SUB_IMM:
 289                         case OP_ISUB_IMM:
 290 #if SIZEOF_REGISTER == 8
 291                         case OP_LADD_IMM:
 292                         case OP_LSUB_IMM:
 293 #endif
 294                                 if (ins->inst_imm == 0) {
 295                                         ins->opcode = OP_MOVE;
 296                                         spec = INS_INFO (ins->opcode);
 297                                 }
 298                                 break;
 299                         case OP_MUL_IMM:
 300                         case OP_IMUL_IMM:
 301 #if SIZEOF_REGISTER == 8
 302                         case OP_LMUL_IMM:
 303 #endif
 304                                 if (ins->inst_imm == 0) {
 305                                         ins->opcode = (ins->opcode == OP_LMUL_IMM) ? OP_I8CONST : OP_ICONST;
 306                                         ins->inst_c0 = 0;
 307                                         ins->sreg1 = -1;
 308                                 } else if (ins->inst_imm == 1) {
 309                                         ins->opcode = OP_MOVE;
 310                                 } else if ((ins->opcode == OP_IMUL_IMM) && (ins->inst_imm == -1)) {
 311                                         ins->opcode = OP_INEG;
 312                                 } else if ((ins->opcode == OP_LMUL_IMM) && (ins->inst_imm == -1)) {
 313                                         ins->opcode = OP_LNEG;
 314                                 } else {
 315                                         int power2 = mono_is_power_of_two (ins->inst_imm);
 316                                         if (power2 >= 0) {
 317                                                 ins->opcode = (ins->opcode == OP_MUL_IMM) ? OP_SHL_IMM : ((ins->opcode == OP_LMUL_IMM) ? OP_LSHL_IMM : OP_ISHL_IMM);
 318                                                 ins->inst_imm = power2;
 319                                         }
 320                                 }
 321                                 spec = INS_INFO (ins->opcode);
 322                                 break;
 323                         case OP_IREM_UN_IMM:
 324                         case OP_IDIV_UN_IMM: {
 325                                 int c = ins->inst_imm;
 326                                 int power2 = mono_is_power_of_two (c);
 327
 328                                 if (power2 >= 0) {
 329                                         if (ins->opcode == OP_IREM_UN_IMM) {
 330                                                 ins->opcode = OP_IAND_IMM;
 331                                                 ins->sreg2 = -1;
 332                                                 ins->inst_imm = (1 << power2) - 1;
 333                                         } else if (ins->opcode == OP_IDIV_UN_IMM) {
 334                                                 ins->opcode = OP_ISHR_UN_IMM;
 335                                                 ins->sreg2 = -1;
 336                                                 ins->inst_imm = power2;
 337                                         }
 338                                 }
 339                                 spec = INS_INFO (ins->opcode);
 340                                 break;
 341                         }
 342                         case OP_IDIV_IMM: {
 343                                 int c = ins->inst_imm;
 344                                 int power2 = mono_is_power_of_two (c);
 345                                 MonoInst *tmp1, *tmp2, *tmp3, *tmp4;
 346
 347                                 /* FIXME: Move this elsewhere cause its hard to implement it here */
 348                                 if (power2 == 1) {
 349                                         int r1 = mono_alloc_ireg (cfg);
 350
 351                                         NEW_BIALU_IMM (cfg, tmp1, OP_ISHR_UN_IMM, r1, ins->sreg1, 31);
 352                                         mono_bblock_insert_after_ins (bb, ins, tmp1);
 353                                         NEW_BIALU (cfg, tmp2, OP_IADD, r1, r1, ins->sreg1);
 354                                         mono_bblock_insert_after_ins (bb, tmp1, tmp2);
 355                                         NEW_BIALU_IMM (cfg, tmp3, OP_ISHR_IMM, ins->dreg, r1, 1);
 356                                         mono_bblock_insert_after_ins (bb, tmp2, tmp3);
 357
 358                                         NULLIFY_INS (ins);
 359
 360                                         // We allocated a new vreg, so need to restart
 361                                         goto restart;
 362                                 } else if (power2 > 0) {
 363                                         int r1 = mono_alloc_ireg (cfg);
 364
 365                                         NEW_BIALU_IMM (cfg, tmp1, OP_ISHR_IMM, r1, ins->sreg1, 31);
 366                                         mono_bblock_insert_after_ins (bb, ins, tmp1);
 367                                         NEW_BIALU_IMM (cfg, tmp2, OP_ISHR_UN_IMM, r1, r1, (32 - power2));
 368                                         mono_bblock_insert_after_ins (bb, tmp1, tmp2);
 369                                         NEW_BIALU (cfg, tmp3, OP_IADD, r1, r1, ins->sreg1);
 370                                         mono_bblock_insert_after_ins (bb, tmp2, tmp3);
 371                                         NEW_BIALU_IMM (cfg, tmp4, OP_ISHR_IMM, ins->dreg, r1, power2);
 372                                         mono_bblock_insert_after_ins (bb, tmp3, tmp4);
 373
 374                                         NULLIFY_INS (ins);
 375
 376                                         // We allocated a new vreg, so need to restart
 377                                         goto restart;
 378                                 }
 379                                 break;
 380                         }
 381                         }
 382
 383                         if (spec [MONO_INST_DEST] != ' ') {
 384                                 MonoInst *def = defs [ins->dreg];
 385
 386                                 if (def && (def->opcode == OP_ADD_IMM) && (def->sreg1 == cfg->frame_reg) && (MONO_IS_STORE_MEMBASE (ins))) {
 387                                         /* ADD_IMM is created by spill_global_vars */
 388                                         /* cfg->frame_reg is assumed to remain constant */
 389                                         ins->inst_destbasereg = def->sreg1;
 390                                         ins->inst_offset += def->inst_imm;
 391                                 }
 392                         }
 393
 394                         if ((spec [MONO_INST_DEST] != ' ') && !MONO_IS_STORE_MEMBASE (ins) && !vreg_is_volatile (cfg, ins->dreg)) {
 395                                 defs [ins->dreg] = ins;
 396                                 def_index [ins->dreg] = ins_index;
 397                         }
 398
 399                         if (MONO_IS_CALL (ins))
 400                                 last_call_index = ins_index;
 401
 402                         ins_index ++;
 403                 }
 404         }
 405 }
 406
 407 static inline gboolean
 408 reg_is_softreg_no_fpstack (int reg, const char spec)
 409 {
 410         return (spec == 'i' && reg >= MONO_MAX_IREGS)
 411                 || ((spec == 'f' && reg >= MONO_MAX_FREGS) && !MONO_ARCH_USE_FPSTACK)
 412 #ifdef MONO_ARCH_SIMD_INTRINSICS
 413                 || (spec == 'x' && reg >= MONO_MAX_XREGS)
 414 #endif
 415                 || (spec == 'v');
 416 }
 417
 418 static inline gboolean
 419 reg_is_softreg (int reg, const char spec)
 420 {
 421         return (spec == 'i' && reg >= MONO_MAX_IREGS)
 422                 || (spec == 'f' && reg >= MONO_MAX_FREGS)
 423 #ifdef MONO_ARCH_SIMD_INTRINSICS
 424                 || (spec == 'x' && reg >= MONO_MAX_XREGS)
 425 #endif
 426                 || (spec == 'v');
 427 }
 428
 429 static inline gboolean
 430 mono_is_simd_accessor (MonoInst *ins)
 431 {
 432         switch (ins->opcode) {
 433 #ifdef MONO_ARCH_SIMD_INTRINSICS
 434         case OP_INSERT_I1:
 435         case OP_INSERT_I2:
 436         case OP_INSERT_I4:
 437         case OP_INSERT_I8:
 438         case OP_INSERT_R4:
 439         case OP_INSERT_R8:
 440
 441         case OP_INSERTX_U1_SLOW:
 442         case OP_INSERTX_I4_SLOW:
 443         case OP_INSERTX_R4_SLOW:
 444         case OP_INSERTX_R8_SLOW:
 445         case OP_INSERTX_I8_SLOW:
 446                 return TRUE;
 447 #endif
 448         default:
 449                 return FALSE;
 450         }
 451 }
 452
 453 /**
 454  * mono_local_deadce:
 455  *
 456  *   Get rid of the dead assignments to local vregs like the ones created by the
 457  * copyprop pass.
 458  */
 459 void
 460 mono_local_deadce (MonoCompile *cfg)
 461 {
 462         MonoBasicBlock *bb;
 463         MonoInst *ins, *prev;
 464         MonoBitSet *used, *defined;
 465
 466         //mono_print_code (cfg, "BEFORE LOCAL-DEADCE");
 467
 468         /*
 469          * Assignments to global vregs can't be eliminated so this pass must come
 470          * after the handle_global_vregs () pass.
 471          */
 472
 473         used = mono_bitset_mp_new_noinit (cfg->mempool, cfg->next_vreg + 1);
 474         defined = mono_bitset_mp_new_noinit (cfg->mempool, cfg->next_vreg + 1);
 475
 476         /* First pass: collect liveness info */
 477         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
 478                 /* Manually init the defs entries used by the bblock */
 479                 MONO_BB_FOR_EACH_INS (bb, ins) {
 480                         const char *spec = INS_INFO (ins->opcode);
 481                         int sregs [MONO_MAX_SRC_REGS];
 482                         int num_sregs, i;
 483
 484                         if (spec [MONO_INST_DEST] != ' ') {
 485                                 mono_bitset_clear_fast (used, ins->dreg);
 486                                 mono_bitset_clear_fast (defined, ins->dreg);
 487 #if SIZEOF_REGISTER == 4
 488                                 /* Regpairs */
 489                                 mono_bitset_clear_fast (used, ins->dreg + 1);
 490                                 mono_bitset_clear_fast (defined, ins->dreg + 1);
 491 #endif
 492                         }
 493                         num_sregs = mono_inst_get_src_registers (ins, sregs);
 494                         for (i = 0; i < num_sregs; ++i) {
 495                                 mono_bitset_clear_fast (used, sregs [i]);
 496 #if SIZEOF_REGISTER == 4
 497                                 mono_bitset_clear_fast (used, sregs [i] + 1);
 498 #endif
 499                         }
 500                 }
 501
 502                 /*
 503                  * Make a reverse pass over the instruction list
 504                  */
 505                 MONO_BB_FOR_EACH_INS_REVERSE_SAFE (bb, prev, ins) {
 506                         const char *spec = INS_INFO (ins->opcode);
 507                         int sregs [MONO_MAX_SRC_REGS];
 508                         int num_sregs, i;
 509
 510                         if (ins->opcode == OP_NOP) {
 511                                 MONO_DELETE_INS (bb, ins);
 512                                 continue;
 513                         }
 514
 515                         g_assert (ins->opcode > MONO_CEE_LAST);
 516
 517                         if (MONO_IS_NON_FP_MOVE (ins) && ins->prev) {
 518                                 MonoInst *def;
 519                                 const char *spec2;
 520
 521                                 def = ins->prev;
 522                                 while (def->prev && (def->opcode == OP_NOP))
 523                                         def = def->prev;
 524                                 spec2 = INS_INFO (def->opcode);
 525
 526                                 /*
 527                                  * Perform a limited kind of reverse copy propagation, i.e.
 528                                  * transform B <- FOO; A <- B into A <- FOO
 529                                  * This isn't copyprop, not deadce, but it can only be performed
 530                                  * after handle_global_vregs () has run.
 531                                  */
 532                                 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]) && !mono_is_simd_accessor (def)) {
 533                                         if (cfg->verbose_level > 2) {
 534                                                 printf ("\tReverse copyprop in BB%d on ", bb->block_num);
 535                                                 mono_print_ins (ins);
 536                                         }
 537
 538                                         def->dreg = ins->dreg;
 539                                         MONO_DELETE_INS (bb, ins);
 540                                         spec = INS_INFO (ins->opcode);
 541                                 }
 542                         }
 543
 544                         /* Enabling this on x86 could screw up the fp stack */
 545                         if (reg_is_softreg_no_fpstack (ins->dreg, spec [MONO_INST_DEST])) {
 546                                 /*
 547                                  * Assignments to global vregs can only be eliminated if there is another
 548                                  * assignment to the same vreg later in the same bblock.
 549                                  */
 550                                 if (!mono_bitset_test_fast (used, ins->dreg) &&
 551                                         (!get_vreg_to_inst (cfg, ins->dreg) || (!bb->extended && !vreg_is_volatile (cfg, ins->dreg) && mono_bitset_test_fast (defined, ins->dreg))) &&
 552                                         MONO_INS_HAS_NO_SIDE_EFFECT (ins)) {
 553                                         /* Happens with CMOV instructions */
 554                                         if (ins->prev && ins->prev->opcode == OP_ICOMPARE_IMM) {
 555                                                 MonoInst *prev = ins->prev;
 556                                                 /*
 557                                                  * Can't use DELETE_INS since that would interfere with the
 558                                                  * FOR_EACH_INS loop.
 559                                                  */
 560                                                 NULLIFY_INS (prev);
 561                                         }
 562                                         //printf ("DEADCE: "); mono_print_ins (ins);
 563                                         MONO_DELETE_INS (bb, ins);
 564                                         spec = INS_INFO (ins->opcode);
 565                                 }
 566
 567                                 if (spec [MONO_INST_DEST] != ' ')
 568                                         mono_bitset_clear_fast (used, ins->dreg);
 569                         }
 570
 571                         if (spec [MONO_INST_DEST] != ' ')
 572                                 mono_bitset_set_fast (defined, ins->dreg);
 573                         num_sregs = mono_inst_get_src_registers (ins, sregs);
 574                         for (i = 0; i < num_sregs; ++i)
 575                                 mono_bitset_set_fast (used, sregs [i]);
 576                         if (MONO_IS_STORE_MEMBASE (ins))
 577                                 mono_bitset_set_fast (used, ins->dreg);
 578
 579                         if (MONO_IS_CALL (ins)) {
 580                                 MonoCallInst *call = (MonoCallInst*)ins;
 581                                 GSList *l;
 582
 583                                 if (call->out_ireg_args) {
 584                                         for (l = call->out_ireg_args; l; l = l->next) {
 585                                                 guint32 regpair, reg;
 586
 587                                                 regpair = (guint32)(gssize)(l->data);
 588                                                 reg = regpair & 0xffffff;
 589
 590                                                 mono_bitset_set_fast (used, reg);
 591                                         }
 592                                 }
 593
 594                                 if (call->out_freg_args) {
 595                                         for (l = call->out_freg_args; l; l = l->next) {
 596                                                 guint32 regpair, reg;
 597
 598                                                 regpair = (guint32)(gssize)(l->data);
 599                                                 reg = regpair & 0xffffff;
 600
 601                                                 mono_bitset_set_fast (used, reg);
 602                                         }
 603                                 }
 604                         }
 605                 }
 606         }
 607
 608         //mono_print_code (cfg, "AFTER LOCAL-DEADCE");
 609 }