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  * Copyright 2011 Xamarin, Inc (http://www.xamarin.com)
  13  */
  14
  15
  16 #include <string.h>
  17 #include <stdio.h>
  18 #ifdef HAVE_ALLOCA_H
  19 #include <alloca.h>
  20 #endif
  21
  22 #include <mono/metadata/debug-helpers.h>
  23 #include <mono/metadata/mempool.h>
  24 #include <mono/metadata/opcodes.h>
  25 #include "mini.h"
  26 #include "ir-emit.h"
  27
  28 #ifndef MONO_ARCH_IS_OP_MEMBASE
  29 #define MONO_ARCH_IS_OP_MEMBASE(opcode) FALSE
  30 #endif
  31
  32 static inline MonoBitSet*
  33 mono_bitset_mp_new_noinit (MonoMemPool *mp,  guint32 max_size)
  34 {
  35         int size = mono_bitset_alloc_size (max_size, 0);
  36         gpointer mem;
  37
  38         mem = mono_mempool_alloc (mp, size);
  39         return mono_bitset_mem_new (mem, max_size, MONO_BITSET_DONT_FREE);
  40 }
  41
  42 /*
  43  * mono_local_cprop:
  44  *
  45  *  A combined local copy and constant propagation pass.
  46  */
  47 void
  48 mono_local_cprop (MonoCompile *cfg)
  49 {
  50         MonoBasicBlock *bb;
  51         MonoInst **defs;
  52         gint32 *def_index;
  53         int max;
  54
  55 restart:
  56
  57         max = cfg->next_vreg;
  58         defs = mono_mempool_alloc (cfg->mempool, sizeof (MonoInst*) * (cfg->next_vreg + 1));
  59         def_index = mono_mempool_alloc (cfg->mempool, sizeof (guint32) * (cfg->next_vreg + 1));
  60
  61         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
  62                 MonoInst *ins;
  63                 int ins_index;
  64                 int last_call_index;
  65
  66                 /* Manually init the defs entries used by the bblock */
  67                 MONO_BB_FOR_EACH_INS (bb, ins) {
  68                         int sregs [MONO_MAX_SRC_REGS];
  69                         int num_sregs, i;
  70
  71                         if ((ins->dreg != -1) && (ins->dreg < max)) {
  72                                 defs [ins->dreg] = NULL;
  73 #if SIZEOF_REGISTER == 4
  74                                 defs [ins->dreg + 1] = NULL;
  75 #endif
  76                         }
  77
  78                         num_sregs = mono_inst_get_src_registers (ins, sregs);
  79                         for (i = 0; i < num_sregs; ++i) {
  80                                 int sreg = sregs [i];
  81                                 if (sreg < max) {
  82                                         defs [sreg] = NULL;
  83 #if SIZEOF_REGISTER == 4
  84                                         defs [sreg + 1] = NULL;
  85 #endif
  86                                 }
  87                         }
  88                 }
  89
  90                 ins_index = 0;
  91                 last_call_index = -1;
  92                 MONO_BB_FOR_EACH_INS (bb, ins) {
  93                         const char *spec = INS_INFO (ins->opcode);
  94                         int regtype, srcindex, sreg;
  95                         int num_sregs;
  96                         int sregs [MONO_MAX_SRC_REGS];
  97
  98                         if (ins->opcode == OP_NOP) {
  99                                 MONO_DELETE_INS (bb, ins);
 100                                 continue;
 101                         }
 102
 103                         g_assert (ins->opcode > MONO_CEE_LAST);
 104
 105                         /* FIXME: Optimize this */
 106                         if (ins->opcode == OP_LDADDR) {
 107                                 MonoInst *var = ins->inst_p0;
 108
 109                                 defs [var->dreg] = NULL;
 110                                 /*
 111                                 if (!MONO_TYPE_ISSTRUCT (var->inst_vtype))
 112                                         break;
 113                                 */
 114                         }
 115
 116                         if (MONO_IS_STORE_MEMBASE (ins)) {
 117                                 sreg = ins->dreg;
 118                                 regtype = 'i';
 119
 120                                 if ((regtype == 'i') && (sreg != -1) && defs [sreg]) {
 121                                         MonoInst *def = defs [sreg];
 122
 123                                         if ((def->opcode == OP_MOVE) && (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg])) && !vreg_is_volatile (cfg, def->sreg1)) {
 124                                                 int vreg = def->sreg1;
 125                                                 if (cfg->verbose_level > 2) printf ("CCOPY: R%d -> R%d\n", sreg, vreg);
 126                                                 ins->dreg = vreg;
 127                                         }
 128                                 }
 129                         }
 130
 131                         num_sregs = mono_inst_get_src_registers (ins, sregs);
 132                         for (srcindex = 0; srcindex < num_sregs; ++srcindex) {
 133                                 MonoInst *def;
 134                                 int nregs;
 135
 136                                 nregs = mono_inst_get_src_registers (ins, sregs);
 137
 138                                 regtype = spec [MONO_INST_SRC1 + srcindex];
 139                                 sreg = sregs [srcindex];
 140
 141                                 if ((regtype == ' ') || (sreg == -1) || (!defs [sreg]))
 142                                         continue;
 143
 144                                 def = defs [sreg];
 145
 146                                 /* Copy propagation */
 147                                 /*
 148                                  * The first check makes sure the source of the copy did not change since
 149                                  * the copy was made.
 150                                  * The second check avoids volatile variables.
 151                                  * The third check avoids copy propagating local vregs through a call,
 152                                  * since the lvreg will be spilled
 153                                  * The fourth check avoids copy propagating a vreg in cases where
 154                                  * it would be eliminated anyway by reverse copy propagation later,
 155                                  * because propagating it would create another use for it, thus making
 156                                  * it impossible to use reverse copy propagation.
 157                                  */
 158                                 /* Enabling this for floats trips up the fp stack */
 159                                 /*
 160                                  * Enabling this for floats on amd64 seems to cause a failure in
 161                                  * basic-math.cs, most likely because it gets rid of some r8->r4
 162                                  * conversions.
 163                                  */
 164                                 if (MONO_IS_MOVE (def) &&
 165                                         (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg])) &&
 166                                         !vreg_is_volatile (cfg, def->sreg1) &&
 167                                         /* This avoids propagating local vregs across calls */
 168                                         ((get_vreg_to_inst (cfg, def->sreg1) || !defs [def->sreg1] || (def_index [def->sreg1] >= last_call_index) || (def->opcode == OP_VMOVE))) &&
 169                                         !(defs [def->sreg1] && defs [def->sreg1]->next == def) &&
 170                                         (!MONO_ARCH_USE_FPSTACK || (def->opcode != OP_FMOVE)) &&
 171                                         (def->opcode != OP_FMOVE)) {
 172                                         int vreg = def->sreg1;
 173
 174                                         if (cfg->verbose_level > 2) printf ("CCOPY/2: R%d -> R%d\n", sreg, vreg);
 175                                         sregs [srcindex] = vreg;
 176                                         mono_inst_set_src_registers (ins, sregs);
 177
 178                                         /* Allow further iterations */
 179                                         srcindex = -1;
 180                                         continue;
 181                                 }
 182
 183                                 /* Constant propagation */
 184                                 /* FIXME: Make is_inst_imm a macro */
 185                                 /* FIXME: Make is_inst_imm take an opcode argument */
 186                                 /* is_inst_imm is only needed for binops */
 187                                 if ((((def->opcode == OP_ICONST) || ((sizeof (gpointer) == 8) && (def->opcode == OP_I8CONST))) &&
 188                                          (((srcindex == 0) && (ins->sreg2 == -1)) || mono_arch_is_inst_imm (def->inst_c0))) ||
 189                                         (!MONO_ARCH_USE_FPSTACK && (def->opcode == OP_R8CONST))) {
 190                                         guint32 opcode2;
 191
 192                                         /* srcindex == 1 -> binop, ins->sreg2 == -1 -> unop */
 193                                         if ((srcindex == 1) && (ins->sreg1 != -1) && defs [ins->sreg1] && (defs [ins->sreg1]->opcode == OP_ICONST) && defs [ins->sreg2]) {
 194                                                 /* Both arguments are constants, perform cfold */
 195                                                 mono_constant_fold_ins (cfg, ins, defs [ins->sreg1], defs [ins->sreg2], TRUE);
 196                                         } else if ((srcindex == 0) && (ins->sreg2 != -1) && defs [ins->sreg2]) {
 197                                                 /* Arg 1 is constant, swap arguments if possible */
 198                                                 int opcode = ins->opcode;
 199                                                 mono_constant_fold_ins (cfg, ins, defs [ins->sreg1], defs [ins->sreg2], TRUE);
 200                                                 if (ins->opcode != opcode) {
 201                                                         /* Allow further iterations */
 202                                                         srcindex = -1;
 203                                                         continue;
 204                                                 }
 205                                         } else if ((srcindex == 0) && (ins->sreg2 == -1)) {
 206                                                 /* Constant unop, perform cfold */
 207                                                 mono_constant_fold_ins (cfg, ins, defs [ins->sreg1], NULL, TRUE);
 208                                         }
 209
 210                                         opcode2 = mono_op_to_op_imm (ins->opcode);
 211                                         if ((opcode2 != -1) && mono_arch_is_inst_imm (def->inst_c0) && ((srcindex == 1) || (ins->sreg2 == -1))) {
 212                                                 ins->opcode = opcode2;
 213                                                 if ((def->opcode == OP_I8CONST) && (sizeof (gpointer) == 4)) {
 214                                                         ins->inst_ls_word = def->inst_ls_word;
 215                                                         ins->inst_ms_word = def->inst_ms_word;
 216                                                 } else {
 217                                                         ins->inst_imm = def->inst_c0;
 218                                                 }
 219                                                 sregs [srcindex] = -1;
 220                                                 mono_inst_set_src_registers (ins, sregs);
 221
 222                                                 if ((opcode2 == OP_VOIDCALL) || (opcode2 == OP_CALL) || (opcode2 == OP_LCALL) || (opcode2 == OP_FCALL))
 223                                                         ((MonoCallInst*)ins)->fptr = (gpointer)ins->inst_imm;
 224
 225                                                 /* Allow further iterations */
 226                                                 srcindex = -1;
 227                                                 continue;
 228                                         }
 229                                         else {
 230                                                 /* Special cases */
 231 #if defined(TARGET_X86) || defined(TARGET_AMD64)
 232                                                 if ((ins->opcode == OP_X86_LEA) && (srcindex == 1)) {
 233 #if SIZEOF_REGISTER == 8
 234                                                         /* FIXME: Use OP_PADD_IMM when the new JIT is done */
 235                                                         ins->opcode = OP_LADD_IMM;
 236 #else
 237                                                         ins->opcode = OP_ADD_IMM;
 238 #endif
 239                                                         ins->inst_imm += def->inst_c0 << ins->backend.shift_amount;
 240                                                         ins->sreg2 = -1;
 241                                                 }
 242 #endif
 243                                                 opcode2 = mono_load_membase_to_load_mem (ins->opcode);
 244                                                 if ((srcindex == 0) && (opcode2 != -1) && mono_arch_is_inst_imm (def->inst_c0)) {
 245                                                         ins->opcode = opcode2;
 246                                                         ins->inst_imm = def->inst_c0 + ins->inst_offset;
 247                                                         ins->sreg1 = -1;
 248                                                 }
 249                                         }
 250                                 }
 251                                 else if (((def->opcode == OP_ADD_IMM) || (def->opcode == OP_LADD_IMM)) && (MONO_IS_LOAD_MEMBASE (ins) || MONO_ARCH_IS_OP_MEMBASE (ins->opcode))) {
 252                                         /* ADD_IMM is created by spill_global_vars */
 253                                         /*
 254                                          * We have to guarantee that def->sreg1 haven't changed since def->dreg
 255                                          * was defined. cfg->frame_reg is assumed to remain constant.
 256                                          */
 257                                         if ((def->sreg1 == cfg->frame_reg) || ((def->next == ins) && (def->dreg != def->sreg1))) {
 258                                                 ins->inst_basereg = def->sreg1;
 259                                                 ins->inst_offset += def->inst_imm;
 260                                         }
 261                                 } else if ((ins->opcode == OP_ISUB_IMM) && (def->opcode == OP_IADD_IMM) && (def->next == ins) && (def->dreg != def->sreg1)) {
 262                                         ins->sreg1 = def->sreg1;
 263                                         ins->inst_imm -= def->inst_imm;
 264                                 } else if ((ins->opcode == OP_IADD_IMM) && (def->opcode == OP_ISUB_IMM) && (def->next == ins) && (def->dreg != def->sreg1)) {
 265                                         ins->sreg1 = def->sreg1;
 266                                         ins->inst_imm -= def->inst_imm;
 267                                 } else if (ins->opcode == OP_STOREI1_MEMBASE_REG &&
 268                                                    (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)) &&
 269                                                    (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg]))) {
 270                                         /* Avoid needless sign extension */
 271                                         ins->sreg1 = def->sreg1;
 272                                 } else if (ins->opcode == OP_STOREI2_MEMBASE_REG &&
 273                                                    (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)) &&
 274                                                    (!defs [def->sreg1] || (def_index [def->sreg1] < def_index [sreg]))) {
 275                                         /* Avoid needless sign extension */
 276                                         ins->sreg1 = def->sreg1;
 277                                 }
 278                         }
 279
 280                         /* Do strength reduction here */
 281                         /* FIXME: Add long/float */
 282                         switch (ins->opcode) {
 283                         case OP_MOVE:
 284                         case OP_XMOVE:
 285                                 if (ins->dreg == ins->sreg1) {
 286                                         MONO_DELETE_INS (bb, ins);
 287                                         spec = INS_INFO (ins->opcode);
 288                                 }
 289                                 break;
 290                         case OP_ADD_IMM:
 291                         case OP_IADD_IMM:
 292                         case OP_SUB_IMM:
 293                         case OP_ISUB_IMM:
 294 #if SIZEOF_REGISTER == 8
 295                         case OP_LADD_IMM:
 296                         case OP_LSUB_IMM:
 297 #endif
 298                                 if (ins->inst_imm == 0) {
 299                                         ins->opcode = OP_MOVE;
 300                                         spec = INS_INFO (ins->opcode);
 301                                 }
 302                                 break;
 303                         case OP_MUL_IMM:
 304                         case OP_IMUL_IMM:
 305 #if SIZEOF_REGISTER == 8
 306                         case OP_LMUL_IMM:
 307 #endif
 308                                 if (ins->inst_imm == 0) {
 309                                         ins->opcode = (ins->opcode == OP_LMUL_IMM) ? OP_I8CONST : OP_ICONST;
 310                                         ins->inst_c0 = 0;
 311                                         ins->sreg1 = -1;
 312                                 } else if (ins->inst_imm == 1) {
 313                                         ins->opcode = OP_MOVE;
 314                                 } else if ((ins->opcode == OP_IMUL_IMM) && (ins->inst_imm == -1)) {
 315                                         ins->opcode = OP_INEG;
 316                                 } else if ((ins->opcode == OP_LMUL_IMM) && (ins->inst_imm == -1)) {
 317                                         ins->opcode = OP_LNEG;
 318                                 } else {
 319                                         int power2 = mono_is_power_of_two (ins->inst_imm);
 320                                         if (power2 >= 0) {
 321                                                 ins->opcode = (ins->opcode == OP_MUL_IMM) ? OP_SHL_IMM : ((ins->opcode == OP_LMUL_IMM) ? OP_LSHL_IMM : OP_ISHL_IMM);
 322                                                 ins->inst_imm = power2;
 323                                         }
 324                                 }
 325                                 spec = INS_INFO (ins->opcode);
 326                                 break;
 327                         case OP_IREM_UN_IMM:
 328                         case OP_IDIV_UN_IMM: {
 329                                 int c = ins->inst_imm;
 330                                 int power2 = mono_is_power_of_two (c);
 331
 332                                 if (power2 >= 0) {
 333                                         if (ins->opcode == OP_IREM_UN_IMM) {
 334                                                 ins->opcode = OP_IAND_IMM;
 335                                                 ins->sreg2 = -1;
 336                                                 ins->inst_imm = (1 << power2) - 1;
 337                                         } else if (ins->opcode == OP_IDIV_UN_IMM) {
 338                                                 ins->opcode = OP_ISHR_UN_IMM;
 339                                                 ins->sreg2 = -1;
 340                                                 ins->inst_imm = power2;
 341                                         }
 342                                 }
 343                                 spec = INS_INFO (ins->opcode);
 344                                 break;
 345                         }
 346                         case OP_IDIV_IMM: {
 347                                 int c = ins->inst_imm;
 348                                 int power2 = mono_is_power_of_two (c);
 349                                 MonoInst *tmp1, *tmp2, *tmp3, *tmp4;
 350
 351                                 /* FIXME: Move this elsewhere cause its hard to implement it here */
 352                                 if (power2 == 1) {
 353                                         int r1 = mono_alloc_ireg (cfg);
 354
 355                                         NEW_BIALU_IMM (cfg, tmp1, OP_ISHR_UN_IMM, r1, ins->sreg1, 31);
 356                                         mono_bblock_insert_after_ins (bb, ins, tmp1);
 357                                         NEW_BIALU (cfg, tmp2, OP_IADD, r1, r1, ins->sreg1);
 358                                         mono_bblock_insert_after_ins (bb, tmp1, tmp2);
 359                                         NEW_BIALU_IMM (cfg, tmp3, OP_ISHR_IMM, ins->dreg, r1, 1);
 360                                         mono_bblock_insert_after_ins (bb, tmp2, tmp3);
 361
 362                                         NULLIFY_INS (ins);
 363
 364                                         // We allocated a new vreg, so need to restart
 365                                         goto restart;
 366                                 } else if (power2 > 0) {
 367                                         int r1 = mono_alloc_ireg (cfg);
 368
 369                                         NEW_BIALU_IMM (cfg, tmp1, OP_ISHR_IMM, r1, ins->sreg1, 31);
 370                                         mono_bblock_insert_after_ins (bb, ins, tmp1);
 371                                         NEW_BIALU_IMM (cfg, tmp2, OP_ISHR_UN_IMM, r1, r1, (32 - power2));
 372                                         mono_bblock_insert_after_ins (bb, tmp1, tmp2);
 373                                         NEW_BIALU (cfg, tmp3, OP_IADD, r1, r1, ins->sreg1);
 374                                         mono_bblock_insert_after_ins (bb, tmp2, tmp3);
 375                                         NEW_BIALU_IMM (cfg, tmp4, OP_ISHR_IMM, ins->dreg, r1, power2);
 376                                         mono_bblock_insert_after_ins (bb, tmp3, tmp4);
 377
 378                                         NULLIFY_INS (ins);
 379
 380                                         // We allocated a new vreg, so need to restart
 381                                         goto restart;
 382                                 }
 383                                 break;
 384                         }
 385                         }
 386
 387                         if (spec [MONO_INST_DEST] != ' ') {
 388                                 MonoInst *def = defs [ins->dreg];
 389
 390                                 if (def && (def->opcode == OP_ADD_IMM) && (def->sreg1 == cfg->frame_reg) && (MONO_IS_STORE_MEMBASE (ins))) {
 391                                         /* ADD_IMM is created by spill_global_vars */
 392                                         /* cfg->frame_reg is assumed to remain constant */
 393                                         ins->inst_destbasereg = def->sreg1;
 394                                         ins->inst_offset += def->inst_imm;
 395                                 }
 396                         }
 397
 398                         if ((spec [MONO_INST_DEST] != ' ') && !MONO_IS_STORE_MEMBASE (ins) && !vreg_is_volatile (cfg, ins->dreg)) {
 399                                 defs [ins->dreg] = ins;
 400                                 def_index [ins->dreg] = ins_index;
 401                         }
 402
 403                         if (MONO_IS_CALL (ins))
 404                                 last_call_index = ins_index;
 405
 406                         ins_index ++;
 407                 }
 408         }
 409 }
 410
 411 static inline gboolean
 412 reg_is_softreg_no_fpstack (int reg, const char spec)
 413 {
 414         return (spec == 'i' && reg >= MONO_MAX_IREGS)
 415                 || ((spec == 'f' && reg >= MONO_MAX_FREGS) && !MONO_ARCH_USE_FPSTACK)
 416 #ifdef MONO_ARCH_SIMD_INTRINSICS
 417                 || (spec == 'x' && reg >= MONO_MAX_XREGS)
 418 #endif
 419                 || (spec == 'v');
 420 }
 421
 422 static inline gboolean
 423 reg_is_softreg (int reg, const char spec)
 424 {
 425         return (spec == 'i' && reg >= MONO_MAX_IREGS)
 426                 || (spec == 'f' && reg >= MONO_MAX_FREGS)
 427 #ifdef MONO_ARCH_SIMD_INTRINSICS
 428                 || (spec == 'x' && reg >= MONO_MAX_XREGS)
 429 #endif
 430                 || (spec == 'v');
 431 }
 432
 433 static inline gboolean
 434 mono_is_simd_accessor (MonoInst *ins)
 435 {
 436         switch (ins->opcode) {
 437 #ifdef MONO_ARCH_SIMD_INTRINSICS
 438         case OP_INSERT_I1:
 439         case OP_INSERT_I2:
 440         case OP_INSERT_I4:
 441         case OP_INSERT_I8:
 442         case OP_INSERT_R4:
 443         case OP_INSERT_R8:
 444
 445         case OP_INSERTX_U1_SLOW:
 446         case OP_INSERTX_I4_SLOW:
 447         case OP_INSERTX_R4_SLOW:
 448         case OP_INSERTX_R8_SLOW:
 449         case OP_INSERTX_I8_SLOW:
 450                 return TRUE;
 451 #endif
 452         default:
 453                 return FALSE;
 454         }
 455 }
 456
 457 /**
 458  * mono_local_deadce:
 459  *
 460  *   Get rid of the dead assignments to local vregs like the ones created by the
 461  * copyprop pass.
 462  */
 463 void
 464 mono_local_deadce (MonoCompile *cfg)
 465 {
 466         MonoBasicBlock *bb;
 467         MonoInst *ins, *prev;
 468         MonoBitSet *used, *defined;
 469
 470         //mono_print_code (cfg, "BEFORE LOCAL-DEADCE");
 471
 472         /*
 473          * Assignments to global vregs can't be eliminated so this pass must come
 474          * after the handle_global_vregs () pass.
 475          */
 476
 477         used = mono_bitset_mp_new_noinit (cfg->mempool, cfg->next_vreg + 1);
 478         defined = mono_bitset_mp_new_noinit (cfg->mempool, cfg->next_vreg + 1);
 479
 480         /* First pass: collect liveness info */
 481         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
 482                 /* Manually init the defs entries used by the bblock */
 483                 MONO_BB_FOR_EACH_INS (bb, ins) {
 484                         const char *spec = INS_INFO (ins->opcode);
 485                         int sregs [MONO_MAX_SRC_REGS];
 486                         int num_sregs, i;
 487
 488                         if (spec [MONO_INST_DEST] != ' ') {
 489                                 mono_bitset_clear_fast (used, ins->dreg);
 490                                 mono_bitset_clear_fast (defined, ins->dreg);
 491 #if SIZEOF_REGISTER == 4
 492                                 /* Regpairs */
 493                                 mono_bitset_clear_fast (used, ins->dreg + 1);
 494                                 mono_bitset_clear_fast (defined, ins->dreg + 1);
 495 #endif
 496                         }
 497                         num_sregs = mono_inst_get_src_registers (ins, sregs);
 498                         for (i = 0; i < num_sregs; ++i) {
 499                                 mono_bitset_clear_fast (used, sregs [i]);
 500 #if SIZEOF_REGISTER == 4
 501                                 mono_bitset_clear_fast (used, sregs [i] + 1);
 502 #endif
 503                         }
 504                 }
 505
 506                 /*
 507                  * Make a reverse pass over the instruction list
 508                  */
 509                 MONO_BB_FOR_EACH_INS_REVERSE_SAFE (bb, prev, ins) {
 510                         const char *spec = INS_INFO (ins->opcode);
 511                         int sregs [MONO_MAX_SRC_REGS];
 512                         int num_sregs, i;
 513
 514                         if (ins->opcode == OP_NOP) {
 515                                 MONO_DELETE_INS (bb, ins);
 516                                 continue;
 517                         }
 518
 519                         g_assert (ins->opcode > MONO_CEE_LAST);
 520
 521                         if (MONO_IS_NON_FP_MOVE (ins) && ins->prev) {
 522                                 MonoInst *def;
 523                                 const char *spec2;
 524
 525                                 def = ins->prev;
 526                                 while (def->prev && (def->opcode == OP_NOP))
 527                                         def = def->prev;
 528                                 spec2 = INS_INFO (def->opcode);
 529
 530                                 /*
 531                                  * Perform a limited kind of reverse copy propagation, i.e.
 532                                  * transform B <- FOO; A <- B into A <- FOO
 533                                  * This isn't copyprop, not deadce, but it can only be performed
 534                                  * after handle_global_vregs () has run.
 535                                  */
 536                                 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)) {
 537                                         if (cfg->verbose_level > 2) {
 538                                                 printf ("\tReverse copyprop in BB%d on ", bb->block_num);
 539                                                 mono_print_ins (ins);
 540                                         }
 541
 542                                         def->dreg = ins->dreg;
 543                                         MONO_DELETE_INS (bb, ins);
 544                                         spec = INS_INFO (ins->opcode);
 545                                 }
 546                         }
 547
 548                         /* Enabling this on x86 could screw up the fp stack */
 549                         if (reg_is_softreg_no_fpstack (ins->dreg, spec [MONO_INST_DEST])) {
 550                                 /*
 551                                  * Assignments to global vregs can only be eliminated if there is another
 552                                  * assignment to the same vreg later in the same bblock.
 553                                  */
 554                                 if (!mono_bitset_test_fast (used, ins->dreg) &&
 555                                         (!get_vreg_to_inst (cfg, ins->dreg) || (!bb->extended && !vreg_is_volatile (cfg, ins->dreg) && mono_bitset_test_fast (defined, ins->dreg))) &&
 556                                         MONO_INS_HAS_NO_SIDE_EFFECT (ins)) {
 557                                         /* Happens with CMOV instructions */
 558                                         if (ins->prev && ins->prev->opcode == OP_ICOMPARE_IMM) {
 559                                                 MonoInst *prev = ins->prev;
 560                                                 /*
 561                                                  * Can't use DELETE_INS since that would interfere with the
 562                                                  * FOR_EACH_INS loop.
 563                                                  */
 564                                                 NULLIFY_INS (prev);
 565                                         }
 566                                         //printf ("DEADCE: "); mono_print_ins (ins);
 567                                         MONO_DELETE_INS (bb, ins);
 568                                         spec = INS_INFO (ins->opcode);
 569                                 }
 570
 571                                 if (spec [MONO_INST_DEST] != ' ')
 572                                         mono_bitset_clear_fast (used, ins->dreg);
 573                         }
 574
 575                         if (spec [MONO_INST_DEST] != ' ')
 576                                 mono_bitset_set_fast (defined, ins->dreg);
 577                         num_sregs = mono_inst_get_src_registers (ins, sregs);
 578                         for (i = 0; i < num_sregs; ++i)
 579                                 mono_bitset_set_fast (used, sregs [i]);
 580                         if (MONO_IS_STORE_MEMBASE (ins))
 581                                 mono_bitset_set_fast (used, ins->dreg);
 582
 583                         if (MONO_IS_CALL (ins)) {
 584                                 MonoCallInst *call = (MonoCallInst*)ins;
 585                                 GSList *l;
 586
 587                                 if (call->out_ireg_args) {
 588                                         for (l = call->out_ireg_args; l; l = l->next) {
 589                                                 guint32 regpair, reg;
 590
 591                                                 regpair = (guint32)(gssize)(l->data);
 592                                                 reg = regpair & 0xffffff;
 593
 594                                                 mono_bitset_set_fast (used, reg);
 595                                         }
 596                                 }
 597
 598                                 if (call->out_freg_args) {
 599                                         for (l = call->out_freg_args; l; l = l->next) {
 600                                                 guint32 regpair, reg;
 601
 602                                                 regpair = (guint32)(gssize)(l->data);
 603                                                 reg = regpair & 0xffffff;
 604
 605                                                 mono_bitset_set_fast (used, reg);
 606                                         }
 607                                 }
 608                         }
 609                 }
 610         }
 611
 612         //mono_print_code (cfg, "AFTER LOCAL-DEADCE");
 613 }