tcg/optimize.c

   1 /*
   2  * Optimizations for Tiny Code Generator for QEMU
   3  *
   4  * Copyright (c) 2010 Samsung Electronics.
   5  * Contributed by Kirill Batuzov <batuzovk@ispras.ru>
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a copy
   8  * of this software and associated documentation files (the "Software"), to deal
   9  * in the Software without restriction, including without limitation the rights
  10  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  11  * copies of the Software, and to permit persons to whom the Software is
  12  * furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included in
  15  * all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  18  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  20  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  21  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  22  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  23  * THE SOFTWARE.
  24  */
  25
  26 #include "qemu/osdep.h"
  27 #include "qemu-common.h"
  28 #include "exec/cpu-common.h"
  29 #include "tcg-op.h"
  30
  31 #define CASE_OP_32_64(x)                        \
  32         glue(glue(case INDEX_op_, x), _i32):    \
  33         glue(glue(case INDEX_op_, x), _i64)
  34
  35 struct tcg_temp_info {
  36     bool is_const;
  37     uint16_t prev_copy;
  38     uint16_t next_copy;
  39     tcg_target_ulong val;
  40     tcg_target_ulong mask;
  41 };
  42
  43 static struct tcg_temp_info temps[TCG_MAX_TEMPS];
  44 static TCGTempSet temps_used;
  45
  46 static inline bool temp_is_const(TCGArg arg)
  47 {
  48     return temps[arg].is_const;
  49 }
  50
  51 static inline bool temp_is_copy(TCGArg arg)
  52 {
  53     return temps[arg].next_copy != arg;
  54 }
  55
  56 /* Reset TEMP's state, possibly removing the temp for the list of copies.  */
  57 static void reset_temp(TCGArg temp)
  58 {
  59     temps[temps[temp].next_copy].prev_copy = temps[temp].prev_copy;
  60     temps[temps[temp].prev_copy].next_copy = temps[temp].next_copy;
  61     temps[temp].next_copy = temp;
  62     temps[temp].prev_copy = temp;
  63     temps[temp].is_const = false;
  64     temps[temp].mask = -1;
  65 }
  66
  67 /* Reset all temporaries, given that there are NB_TEMPS of them.  */
  68 static void reset_all_temps(int nb_temps)
  69 {
  70     bitmap_zero(temps_used.l, nb_temps);
  71 }
  72
  73 /* Initialize and activate a temporary.  */
  74 static void init_temp_info(TCGArg temp)
  75 {
  76     if (!test_bit(temp, temps_used.l)) {
  77         temps[temp].next_copy = temp;
  78         temps[temp].prev_copy = temp;
  79         temps[temp].is_const = false;
  80         temps[temp].mask = -1;
  81         set_bit(temp, temps_used.l);
  82     }
  83 }
  84
  85 static int op_bits(TCGOpcode op)
  86 {
  87     const TCGOpDef *def = &tcg_op_defs[op];
  88     return def->flags & TCG_OPF_64BIT ? 64 : 32;
  89 }
  90
  91 static TCGOpcode op_to_mov(TCGOpcode op)
  92 {
  93     switch (op_bits(op)) {
  94     case 32:
  95         return INDEX_op_mov_i32;
  96     case 64:
  97         return INDEX_op_mov_i64;
  98     default:
  99         fprintf(stderr, "op_to_mov: unexpected return value of "
 100                 "function op_bits.\n");
 101         tcg_abort();
 102     }
 103 }
 104
 105 static TCGOpcode op_to_movi(TCGOpcode op)
 106 {
 107     switch (op_bits(op)) {
 108     case 32:
 109         return INDEX_op_movi_i32;
 110     case 64:
 111         return INDEX_op_movi_i64;
 112     default:
 113         fprintf(stderr, "op_to_movi: unexpected return value of "
 114                 "function op_bits.\n");
 115         tcg_abort();
 116     }
 117 }
 118
 119 static TCGArg find_better_copy(TCGContext *s, TCGArg temp)
 120 {
 121     TCGArg i;
 122
 123     /* If this is already a global, we can't do better. */
 124     if (temp < s->nb_globals) {
 125         return temp;
 126     }
 127
 128     /* Search for a global first. */
 129     for (i = temps[temp].next_copy ; i != temp ; i = temps[i].next_copy) {
 130         if (i < s->nb_globals) {
 131             return i;
 132         }
 133     }
 134
 135     /* If it is a temp, search for a temp local. */
 136     if (!s->temps[temp].temp_local) {
 137         for (i = temps[temp].next_copy ; i != temp ; i = temps[i].next_copy) {
 138             if (s->temps[i].temp_local) {
 139                 return i;
 140             }
 141         }
 142     }
 143
 144     /* Failure to find a better representation, return the same temp. */
 145     return temp;
 146 }
 147
 148 static bool temps_are_copies(TCGArg arg1, TCGArg arg2)
 149 {
 150     TCGArg i;
 151
 152     if (arg1 == arg2) {
 153         return true;
 154     }
 155
 156     if (!temp_is_copy(arg1) || !temp_is_copy(arg2)) {
 157         return false;
 158     }
 159
 160     for (i = temps[arg1].next_copy ; i != arg1 ; i = temps[i].next_copy) {
 161         if (i == arg2) {
 162             return true;
 163         }
 164     }
 165
 166     return false;
 167 }
 168
 169 static void tcg_opt_gen_movi(TCGContext *s, TCGOp *op, TCGArg *args,
 170                              TCGArg dst, TCGArg val)
 171 {
 172     TCGOpcode new_op = op_to_movi(op->opc);
 173     tcg_target_ulong mask;
 174
 175     op->opc = new_op;
 176
 177     reset_temp(dst);
 178     temps[dst].is_const = true;
 179     temps[dst].val = val;
 180     mask = val;
 181     if (TCG_TARGET_REG_BITS > 32 && new_op == INDEX_op_movi_i32) {
 182         /* High bits of the destination are now garbage.  */
 183         mask |= ~0xffffffffull;
 184     }
 185     temps[dst].mask = mask;
 186
 187     args[0] = dst;
 188     args[1] = val;
 189 }
 190
 191 static void tcg_opt_gen_mov(TCGContext *s, TCGOp *op, TCGArg *args,
 192                             TCGArg dst, TCGArg src)
 193 {
 194     if (temps_are_copies(dst, src)) {
 195         tcg_op_remove(s, op);
 196         return;
 197     }
 198
 199     TCGOpcode new_op = op_to_mov(op->opc);
 200     tcg_target_ulong mask;
 201
 202     op->opc = new_op;
 203
 204     reset_temp(dst);
 205     mask = temps[src].mask;
 206     if (TCG_TARGET_REG_BITS > 32 && new_op == INDEX_op_mov_i32) {
 207         /* High bits of the destination are now garbage.  */
 208         mask |= ~0xffffffffull;
 209     }
 210     temps[dst].mask = mask;
 211
 212     if (s->temps[src].type == s->temps[dst].type) {
 213         temps[dst].next_copy = temps[src].next_copy;
 214         temps[dst].prev_copy = src;
 215         temps[temps[dst].next_copy].prev_copy = dst;
 216         temps[src].next_copy = dst;
 217         temps[dst].is_const = temps[src].is_const;
 218         temps[dst].val = temps[src].val;
 219     }
 220
 221     args[0] = dst;
 222     args[1] = src;
 223 }
 224
 225 static TCGArg do_constant_folding_2(TCGOpcode op, TCGArg x, TCGArg y)
 226 {
 227     uint64_t l64, h64;
 228
 229     switch (op) {
 230     CASE_OP_32_64(add):
 231         return x + y;
 232
 233     CASE_OP_32_64(sub):
 234         return x - y;
 235
 236     CASE_OP_32_64(mul):
 237         return x * y;
 238
 239     CASE_OP_32_64(and):
 240         return x & y;
 241
 242     CASE_OP_32_64(or):
 243         return x | y;
 244
 245     CASE_OP_32_64(xor):
 246         return x ^ y;
 247
 248     case INDEX_op_shl_i32:
 249         return (uint32_t)x << (y & 31);
 250
 251     case INDEX_op_shl_i64:
 252         return (uint64_t)x << (y & 63);
 253
 254     case INDEX_op_shr_i32:
 255         return (uint32_t)x >> (y & 31);
 256
 257     case INDEX_op_shr_i64:
 258         return (uint64_t)x >> (y & 63);
 259
 260     case INDEX_op_sar_i32:
 261         return (int32_t)x >> (y & 31);
 262
 263     case INDEX_op_sar_i64:
 264         return (int64_t)x >> (y & 63);
 265
 266     case INDEX_op_rotr_i32:
 267         return ror32(x, y & 31);
 268
 269     case INDEX_op_rotr_i64:
 270         return ror64(x, y & 63);
 271
 272     case INDEX_op_rotl_i32:
 273         return rol32(x, y & 31);
 274
 275     case INDEX_op_rotl_i64:
 276         return rol64(x, y & 63);
 277
 278     CASE_OP_32_64(not):
 279         return ~x;
 280
 281     CASE_OP_32_64(neg):
 282         return -x;
 283
 284     CASE_OP_32_64(andc):
 285         return x & ~y;
 286
 287     CASE_OP_32_64(orc):
 288         return x | ~y;
 289
 290     CASE_OP_32_64(eqv):
 291         return ~(x ^ y);
 292
 293     CASE_OP_32_64(nand):
 294         return ~(x & y);
 295
 296     CASE_OP_32_64(nor):
 297         return ~(x | y);
 298
 299     CASE_OP_32_64(ext8s):
 300         return (int8_t)x;
 301
 302     CASE_OP_32_64(ext16s):
 303         return (int16_t)x;
 304
 305     CASE_OP_32_64(ext8u):
 306         return (uint8_t)x;
 307
 308     CASE_OP_32_64(ext16u):
 309         return (uint16_t)x;
 310
 311     case INDEX_op_ext_i32_i64:
 312     case INDEX_op_ext32s_i64:
 313         return (int32_t)x;
 314
 315     case INDEX_op_extu_i32_i64:
 316     case INDEX_op_extrl_i64_i32:
 317     case INDEX_op_ext32u_i64:
 318         return (uint32_t)x;
 319
 320     case INDEX_op_extrh_i64_i32:
 321         return (uint64_t)x >> 32;
 322
 323     case INDEX_op_muluh_i32:
 324         return ((uint64_t)(uint32_t)x * (uint32_t)y) >> 32;
 325     case INDEX_op_mulsh_i32:
 326         return ((int64_t)(int32_t)x * (int32_t)y) >> 32;
 327
 328     case INDEX_op_muluh_i64:
 329         mulu64(&l64, &h64, x, y);
 330         return h64;
 331     case INDEX_op_mulsh_i64:
 332         muls64(&l64, &h64, x, y);
 333         return h64;
 334
 335     case INDEX_op_div_i32:
 336         /* Avoid crashing on divide by zero, otherwise undefined.  */
 337         return (int32_t)x / ((int32_t)y ? : 1);
 338     case INDEX_op_divu_i32:
 339         return (uint32_t)x / ((uint32_t)y ? : 1);
 340     case INDEX_op_div_i64:
 341         return (int64_t)x / ((int64_t)y ? : 1);
 342     case INDEX_op_divu_i64:
 343         return (uint64_t)x / ((uint64_t)y ? : 1);
 344
 345     case INDEX_op_rem_i32:
 346         return (int32_t)x % ((int32_t)y ? : 1);
 347     case INDEX_op_remu_i32:
 348         return (uint32_t)x % ((uint32_t)y ? : 1);
 349     case INDEX_op_rem_i64:
 350         return (int64_t)x % ((int64_t)y ? : 1);
 351     case INDEX_op_remu_i64:
 352         return (uint64_t)x % ((uint64_t)y ? : 1);
 353
 354     default:
 355         fprintf(stderr,
 356                 "Unrecognized operation %d in do_constant_folding.\n", op);
 357         tcg_abort();
 358     }
 359 }
 360
 361 static TCGArg do_constant_folding(TCGOpcode op, TCGArg x, TCGArg y)
 362 {
 363     TCGArg res = do_constant_folding_2(op, x, y);
 364     if (op_bits(op) == 32) {
 365         res = (int32_t)res;
 366     }
 367     return res;
 368 }
 369
 370 static bool do_constant_folding_cond_32(uint32_t x, uint32_t y, TCGCond c)
 371 {
 372     switch (c) {
 373     case TCG_COND_EQ:
 374         return x == y;
 375     case TCG_COND_NE:
 376         return x != y;
 377     case TCG_COND_LT:
 378         return (int32_t)x < (int32_t)y;
 379     case TCG_COND_GE:
 380         return (int32_t)x >= (int32_t)y;
 381     case TCG_COND_LE:
 382         return (int32_t)x <= (int32_t)y;
 383     case TCG_COND_GT:
 384         return (int32_t)x > (int32_t)y;
 385     case TCG_COND_LTU:
 386         return x < y;
 387     case TCG_COND_GEU:
 388         return x >= y;
 389     case TCG_COND_LEU:
 390         return x <= y;
 391     case TCG_COND_GTU:
 392         return x > y;
 393     default:
 394         tcg_abort();
 395     }
 396 }
 397
 398 static bool do_constant_folding_cond_64(uint64_t x, uint64_t y, TCGCond c)
 399 {
 400     switch (c) {
 401     case TCG_COND_EQ:
 402         return x == y;
 403     case TCG_COND_NE:
 404         return x != y;
 405     case TCG_COND_LT:
 406         return (int64_t)x < (int64_t)y;
 407     case TCG_COND_GE:
 408         return (int64_t)x >= (int64_t)y;
 409     case TCG_COND_LE:
 410         return (int64_t)x <= (int64_t)y;
 411     case TCG_COND_GT:
 412         return (int64_t)x > (int64_t)y;
 413     case TCG_COND_LTU:
 414         return x < y;
 415     case TCG_COND_GEU:
 416         return x >= y;
 417     case TCG_COND_LEU:
 418         return x <= y;
 419     case TCG_COND_GTU:
 420         return x > y;
 421     default:
 422         tcg_abort();
 423     }
 424 }
 425
 426 static bool do_constant_folding_cond_eq(TCGCond c)
 427 {
 428     switch (c) {
 429     case TCG_COND_GT:
 430     case TCG_COND_LTU:
 431     case TCG_COND_LT:
 432     case TCG_COND_GTU:
 433     case TCG_COND_NE:
 434         return 0;
 435     case TCG_COND_GE:
 436     case TCG_COND_GEU:
 437     case TCG_COND_LE:
 438     case TCG_COND_LEU:
 439     case TCG_COND_EQ:
 440         return 1;
 441     default:
 442         tcg_abort();
 443     }
 444 }
 445
 446 /* Return 2 if the condition can't be simplified, and the result
 447    of the condition (0 or 1) if it can */
 448 static TCGArg do_constant_folding_cond(TCGOpcode op, TCGArg x,
 449                                        TCGArg y, TCGCond c)
 450 {
 451     if (temp_is_const(x) && temp_is_const(y)) {
 452         switch (op_bits(op)) {
 453         case 32:
 454             return do_constant_folding_cond_32(temps[x].val, temps[y].val, c);
 455         case 64:
 456             return do_constant_folding_cond_64(temps[x].val, temps[y].val, c);
 457         default:
 458             tcg_abort();
 459         }
 460     } else if (temps_are_copies(x, y)) {
 461         return do_constant_folding_cond_eq(c);
 462     } else if (temp_is_const(y) && temps[y].val == 0) {
 463         switch (c) {
 464         case TCG_COND_LTU:
 465             return 0;
 466         case TCG_COND_GEU:
 467             return 1;
 468         default:
 469             return 2;
 470         }
 471     }
 472     return 2;
 473 }
 474
 475 /* Return 2 if the condition can't be simplified, and the result
 476    of the condition (0 or 1) if it can */
 477 static TCGArg do_constant_folding_cond2(TCGArg *p1, TCGArg *p2, TCGCond c)
 478 {
 479     TCGArg al = p1[0], ah = p1[1];
 480     TCGArg bl = p2[0], bh = p2[1];
 481
 482     if (temp_is_const(bl) && temp_is_const(bh)) {
 483         uint64_t b = ((uint64_t)temps[bh].val << 32) | (uint32_t)temps[bl].val;
 484
 485         if (temp_is_const(al) && temp_is_const(ah)) {
 486             uint64_t a;
 487             a = ((uint64_t)temps[ah].val << 32) | (uint32_t)temps[al].val;
 488             return do_constant_folding_cond_64(a, b, c);
 489         }
 490         if (b == 0) {
 491             switch (c) {
 492             case TCG_COND_LTU:
 493                 return 0;
 494             case TCG_COND_GEU:
 495                 return 1;
 496             default:
 497                 break;
 498             }
 499         }
 500     }
 501     if (temps_are_copies(al, bl) && temps_are_copies(ah, bh)) {
 502         return do_constant_folding_cond_eq(c);
 503     }
 504     return 2;
 505 }
 506
 507 static bool swap_commutative(TCGArg dest, TCGArg *p1, TCGArg *p2)
 508 {
 509     TCGArg a1 = *p1, a2 = *p2;
 510     int sum = 0;
 511     sum += temp_is_const(a1);
 512     sum -= temp_is_const(a2);
 513
 514     /* Prefer the constant in second argument, and then the form
 515        op a, a, b, which is better handled on non-RISC hosts. */
 516     if (sum > 0 || (sum == 0 && dest == a2)) {
 517         *p1 = a2;
 518         *p2 = a1;
 519         return true;
 520     }
 521     return false;
 522 }
 523
 524 static bool swap_commutative2(TCGArg *p1, TCGArg *p2)
 525 {
 526     int sum = 0;
 527     sum += temp_is_const(p1[0]);
 528     sum += temp_is_const(p1[1]);
 529     sum -= temp_is_const(p2[0]);
 530     sum -= temp_is_const(p2[1]);
 531     if (sum > 0) {
 532         TCGArg t;
 533         t = p1[0], p1[0] = p2[0], p2[0] = t;
 534         t = p1[1], p1[1] = p2[1], p2[1] = t;
 535         return true;
 536     }
 537     return false;
 538 }
 539
 540 /* Propagate constants and copies, fold constant expressions. */
 541 void tcg_optimize(TCGContext *s)
 542 {
 543     int oi, oi_next, nb_temps, nb_globals;
 544     TCGArg *prev_mb_args = NULL;
 545
 546     /* Array VALS has an element for each temp.
 547        If this temp holds a constant then its value is kept in VALS' element.
 548        If this temp is a copy of other ones then the other copies are
 549        available through the doubly linked circular list. */
 550
 551     nb_temps = s->nb_temps;
 552     nb_globals = s->nb_globals;
 553     reset_all_temps(nb_temps);
 554
 555     for (oi = s->gen_op_buf[0].next; oi != 0; oi = oi_next) {
 556         tcg_target_ulong mask, partmask, affected;
 557         int nb_oargs, nb_iargs, i;
 558         TCGArg tmp;
 559
 560         TCGOp * const op = &s->gen_op_buf[oi];
 561         TCGArg * const args = &s->gen_opparam_buf[op->args];
 562         TCGOpcode opc = op->opc;
 563         const TCGOpDef *def = &tcg_op_defs[opc];
 564
 565         oi_next = op->next;
 566
 567         /* Count the arguments, and initialize the temps that are
 568            going to be used */
 569         if (opc == INDEX_op_call) {
 570             nb_oargs = op->callo;
 571             nb_iargs = op->calli;
 572             for (i = 0; i < nb_oargs + nb_iargs; i++) {
 573                 tmp = args[i];
 574                 if (tmp != TCG_CALL_DUMMY_ARG) {
 575                     init_temp_info(tmp);
 576                 }
 577             }
 578         } else {
 579             nb_oargs = def->nb_oargs;
 580             nb_iargs = def->nb_iargs;
 581             for (i = 0; i < nb_oargs + nb_iargs; i++) {
 582                 init_temp_info(args[i]);
 583             }
 584         }
 585
 586         /* Do copy propagation */
 587         for (i = nb_oargs; i < nb_oargs + nb_iargs; i++) {
 588             if (temp_is_copy(args[i])) {
 589                 args[i] = find_better_copy(s, args[i]);
 590             }
 591         }
 592
 593         /* For commutative operations make constant second argument */
 594         switch (opc) {
 595         CASE_OP_32_64(add):
 596         CASE_OP_32_64(mul):
 597         CASE_OP_32_64(and):
 598         CASE_OP_32_64(or):
 599         CASE_OP_32_64(xor):
 600         CASE_OP_32_64(eqv):
 601         CASE_OP_32_64(nand):
 602         CASE_OP_32_64(nor):
 603         CASE_OP_32_64(muluh):
 604         CASE_OP_32_64(mulsh):
 605             swap_commutative(args[0], &args[1], &args[2]);
 606             break;
 607         CASE_OP_32_64(brcond):
 608             if (swap_commutative(-1, &args[0], &args[1])) {
 609                 args[2] = tcg_swap_cond(args[2]);
 610             }
 611             break;
 612         CASE_OP_32_64(setcond):
 613             if (swap_commutative(args[0], &args[1], &args[2])) {
 614                 args[3] = tcg_swap_cond(args[3]);
 615             }
 616             break;
 617         CASE_OP_32_64(movcond):
 618             if (swap_commutative(-1, &args[1], &args[2])) {
 619                 args[5] = tcg_swap_cond(args[5]);
 620             }
 621             /* For movcond, we canonicalize the "false" input reg to match
 622                the destination reg so that the tcg backend can implement
 623                a "move if true" operation.  */
 624             if (swap_commutative(args[0], &args[4], &args[3])) {
 625                 args[5] = tcg_invert_cond(args[5]);
 626             }
 627             break;
 628         CASE_OP_32_64(add2):
 629             swap_commutative(args[0], &args[2], &args[4]);
 630             swap_commutative(args[1], &args[3], &args[5]);
 631             break;
 632         CASE_OP_32_64(mulu2):
 633         CASE_OP_32_64(muls2):
 634             swap_commutative(args[0], &args[2], &args[3]);
 635             break;
 636         case INDEX_op_brcond2_i32:
 637             if (swap_commutative2(&args[0], &args[2])) {
 638                 args[4] = tcg_swap_cond(args[4]);
 639             }
 640             break;
 641         case INDEX_op_setcond2_i32:
 642             if (swap_commutative2(&args[1], &args[3])) {
 643                 args[5] = tcg_swap_cond(args[5]);
 644             }
 645             break;
 646         default:
 647             break;
 648         }
 649
 650         /* Simplify expressions for "shift/rot r, 0, a => movi r, 0",
 651            and "sub r, 0, a => neg r, a" case.  */
 652         switch (opc) {
 653         CASE_OP_32_64(shl):
 654         CASE_OP_32_64(shr):
 655         CASE_OP_32_64(sar):
 656         CASE_OP_32_64(rotl):
 657         CASE_OP_32_64(rotr):
 658             if (temp_is_const(args[1]) && temps[args[1]].val == 0) {
 659                 tcg_opt_gen_movi(s, op, args, args[0], 0);
 660                 continue;
 661             }
 662             break;
 663         CASE_OP_32_64(sub):
 664             {
 665                 TCGOpcode neg_op;
 666                 bool have_neg;
 667
 668                 if (temp_is_const(args[2])) {
 669                     /* Proceed with possible constant folding. */
 670                     break;
 671                 }
 672                 if (opc == INDEX_op_sub_i32) {
 673                     neg_op = INDEX_op_neg_i32;
 674                     have_neg = TCG_TARGET_HAS_neg_i32;
 675                 } else {
 676                     neg_op = INDEX_op_neg_i64;
 677                     have_neg = TCG_TARGET_HAS_neg_i64;
 678                 }
 679                 if (!have_neg) {
 680                     break;
 681                 }
 682                 if (temp_is_const(args[1]) && temps[args[1]].val == 0) {
 683                     op->opc = neg_op;
 684                     reset_temp(args[0]);
 685                     args[1] = args[2];
 686                     continue;
 687                 }
 688             }
 689             break;
 690         CASE_OP_32_64(xor):
 691         CASE_OP_32_64(nand):
 692             if (!temp_is_const(args[1])
 693                 && temp_is_const(args[2]) && temps[args[2]].val == -1) {
 694                 i = 1;
 695                 goto try_not;
 696             }
 697             break;
 698         CASE_OP_32_64(nor):
 699             if (!temp_is_const(args[1])
 700                 && temp_is_const(args[2]) && temps[args[2]].val == 0) {
 701                 i = 1;
 702                 goto try_not;
 703             }
 704             break;
 705         CASE_OP_32_64(andc):
 706             if (!temp_is_const(args[2])
 707                 && temp_is_const(args[1]) && temps[args[1]].val == -1) {
 708                 i = 2;
 709                 goto try_not;
 710             }
 711             break;
 712         CASE_OP_32_64(orc):
 713         CASE_OP_32_64(eqv):
 714             if (!temp_is_const(args[2])
 715                 && temp_is_const(args[1]) && temps[args[1]].val == 0) {
 716                 i = 2;
 717                 goto try_not;
 718             }
 719             break;
 720         try_not:
 721             {
 722                 TCGOpcode not_op;
 723                 bool have_not;
 724
 725                 if (def->flags & TCG_OPF_64BIT) {
 726                     not_op = INDEX_op_not_i64;
 727                     have_not = TCG_TARGET_HAS_not_i64;
 728                 } else {
 729                     not_op = INDEX_op_not_i32;
 730                     have_not = TCG_TARGET_HAS_not_i32;
 731                 }
 732                 if (!have_not) {
 733                     break;
 734                 }
 735                 op->opc = not_op;
 736                 reset_temp(args[0]);
 737                 args[1] = args[i];
 738                 continue;
 739             }
 740         default:
 741             break;
 742         }
 743
 744         /* Simplify expression for "op r, a, const => mov r, a" cases */
 745         switch (opc) {
 746         CASE_OP_32_64(add):
 747         CASE_OP_32_64(sub):
 748         CASE_OP_32_64(shl):
 749         CASE_OP_32_64(shr):
 750         CASE_OP_32_64(sar):
 751         CASE_OP_32_64(rotl):
 752         CASE_OP_32_64(rotr):
 753         CASE_OP_32_64(or):
 754         CASE_OP_32_64(xor):
 755         CASE_OP_32_64(andc):
 756             if (!temp_is_const(args[1])
 757                 && temp_is_const(args[2]) && temps[args[2]].val == 0) {
 758                 tcg_opt_gen_mov(s, op, args, args[0], args[1]);
 759                 continue;
 760             }
 761             break;
 762         CASE_OP_32_64(and):
 763         CASE_OP_32_64(orc):
 764         CASE_OP_32_64(eqv):
 765             if (!temp_is_const(args[1])
 766                 && temp_is_const(args[2]) && temps[args[2]].val == -1) {
 767                 tcg_opt_gen_mov(s, op, args, args[0], args[1]);
 768                 continue;
 769             }
 770             break;
 771         default:
 772             break;
 773         }
 774
 775         /* Simplify using known-zero bits. Currently only ops with a single
 776            output argument is supported. */
 777         mask = -1;
 778         affected = -1;
 779         switch (opc) {
 780         CASE_OP_32_64(ext8s):
 781             if ((temps[args[1]].mask & 0x80) != 0) {
 782                 break;
 783             }
 784         CASE_OP_32_64(ext8u):
 785             mask = 0xff;
 786             goto and_const;
 787         CASE_OP_32_64(ext16s):
 788             if ((temps[args[1]].mask & 0x8000) != 0) {
 789                 break;
 790             }
 791         CASE_OP_32_64(ext16u):
 792             mask = 0xffff;
 793             goto and_const;
 794         case INDEX_op_ext32s_i64:
 795             if ((temps[args[1]].mask & 0x80000000) != 0) {
 796                 break;
 797             }
 798         case INDEX_op_ext32u_i64:
 799             mask = 0xffffffffU;
 800             goto and_const;
 801
 802         CASE_OP_32_64(and):
 803             mask = temps[args[2]].mask;
 804             if (temp_is_const(args[2])) {
 805         and_const:
 806                 affected = temps[args[1]].mask & ~mask;
 807             }
 808             mask = temps[args[1]].mask & mask;
 809             break;
 810
 811         case INDEX_op_ext_i32_i64:
 812             if ((temps[args[1]].mask & 0x80000000) != 0) {
 813                 break;
 814             }
 815         case INDEX_op_extu_i32_i64:
 816             /* We do not compute affected as it is a size changing op.  */
 817             mask = (uint32_t)temps[args[1]].mask;
 818             break;
 819
 820         CASE_OP_32_64(andc):
 821             /* Known-zeros does not imply known-ones.  Therefore unless
 822                args[2] is constant, we can't infer anything from it.  */
 823             if (temp_is_const(args[2])) {
 824                 mask = ~temps[args[2]].mask;
 825                 goto and_const;
 826             }
 827             /* But we certainly know nothing outside args[1] may be set. */
 828             mask = temps[args[1]].mask;
 829             break;
 830
 831         case INDEX_op_sar_i32:
 832             if (temp_is_const(args[2])) {
 833                 tmp = temps[args[2]].val & 31;
 834                 mask = (int32_t)temps[args[1]].mask >> tmp;
 835             }
 836             break;
 837         case INDEX_op_sar_i64:
 838             if (temp_is_const(args[2])) {
 839                 tmp = temps[args[2]].val & 63;
 840                 mask = (int64_t)temps[args[1]].mask >> tmp;
 841             }
 842             break;
 843
 844         case INDEX_op_shr_i32:
 845             if (temp_is_const(args[2])) {
 846                 tmp = temps[args[2]].val & 31;
 847                 mask = (uint32_t)temps[args[1]].mask >> tmp;
 848             }
 849             break;
 850         case INDEX_op_shr_i64:
 851             if (temp_is_const(args[2])) {
 852                 tmp = temps[args[2]].val & 63;
 853                 mask = (uint64_t)temps[args[1]].mask >> tmp;
 854             }
 855             break;
 856
 857         case INDEX_op_extrl_i64_i32:
 858             mask = (uint32_t)temps[args[1]].mask;
 859             break;
 860         case INDEX_op_extrh_i64_i32:
 861             mask = (uint64_t)temps[args[1]].mask >> 32;
 862             break;
 863
 864         CASE_OP_32_64(shl):
 865             if (temp_is_const(args[2])) {
 866                 tmp = temps[args[2]].val & (TCG_TARGET_REG_BITS - 1);
 867                 mask = temps[args[1]].mask << tmp;
 868             }
 869             break;
 870
 871         CASE_OP_32_64(neg):
 872             /* Set to 1 all bits to the left of the rightmost.  */
 873             mask = -(temps[args[1]].mask & -temps[args[1]].mask);
 874             break;
 875
 876         CASE_OP_32_64(deposit):
 877             mask = deposit64(temps[args[1]].mask, args[3], args[4],
 878                              temps[args[2]].mask);
 879             break;
 880
 881         CASE_OP_32_64(or):
 882         CASE_OP_32_64(xor):
 883             mask = temps[args[1]].mask | temps[args[2]].mask;
 884             break;
 885
 886         CASE_OP_32_64(setcond):
 887         case INDEX_op_setcond2_i32:
 888             mask = 1;
 889             break;
 890
 891         CASE_OP_32_64(movcond):
 892             mask = temps[args[3]].mask | temps[args[4]].mask;
 893             break;
 894
 895         CASE_OP_32_64(ld8u):
 896             mask = 0xff;
 897             break;
 898         CASE_OP_32_64(ld16u):
 899             mask = 0xffff;
 900             break;
 901         case INDEX_op_ld32u_i64:
 902             mask = 0xffffffffu;
 903             break;
 904
 905         CASE_OP_32_64(qemu_ld):
 906             {
 907                 TCGMemOpIdx oi = args[nb_oargs + nb_iargs];
 908                 TCGMemOp mop = get_memop(oi);
 909                 if (!(mop & MO_SIGN)) {
 910                     mask = (2ULL << ((8 << (mop & MO_SIZE)) - 1)) - 1;
 911                 }
 912             }
 913             break;
 914
 915         default:
 916             break;
 917         }
 918
 919         /* 32-bit ops generate 32-bit results.  For the result is zero test
 920            below, we can ignore high bits, but for further optimizations we
 921            need to record that the high bits contain garbage.  */
 922         partmask = mask;
 923         if (!(def->flags & TCG_OPF_64BIT)) {
 924             mask |= ~(tcg_target_ulong)0xffffffffu;
 925             partmask &= 0xffffffffu;
 926             affected &= 0xffffffffu;
 927         }
 928
 929         if (partmask == 0) {
 930             tcg_debug_assert(nb_oargs == 1);
 931             tcg_opt_gen_movi(s, op, args, args[0], 0);
 932             continue;
 933         }
 934         if (affected == 0) {
 935             tcg_debug_assert(nb_oargs == 1);
 936             tcg_opt_gen_mov(s, op, args, args[0], args[1]);
 937             continue;
 938         }
 939
 940         /* Simplify expression for "op r, a, 0 => movi r, 0" cases */
 941         switch (opc) {
 942         CASE_OP_32_64(and):
 943         CASE_OP_32_64(mul):
 944         CASE_OP_32_64(muluh):
 945         CASE_OP_32_64(mulsh):
 946             if ((temp_is_const(args[2]) && temps[args[2]].val == 0)) {
 947                 tcg_opt_gen_movi(s, op, args, args[0], 0);
 948                 continue;
 949             }
 950             break;
 951         default:
 952             break;
 953         }
 954
 955         /* Simplify expression for "op r, a, a => mov r, a" cases */
 956         switch (opc) {
 957         CASE_OP_32_64(or):
 958         CASE_OP_32_64(and):
 959             if (temps_are_copies(args[1], args[2])) {
 960                 tcg_opt_gen_mov(s, op, args, args[0], args[1]);
 961                 continue;
 962             }
 963             break;
 964         default:
 965             break;
 966         }
 967
 968         /* Simplify expression for "op r, a, a => movi r, 0" cases */
 969         switch (opc) {
 970         CASE_OP_32_64(andc):
 971         CASE_OP_32_64(sub):
 972         CASE_OP_32_64(xor):
 973             if (temps_are_copies(args[1], args[2])) {
 974                 tcg_opt_gen_movi(s, op, args, args[0], 0);
 975                 continue;
 976             }
 977             break;
 978         default:
 979             break;
 980         }
 981
 982         /* Propagate constants through copy operations and do constant
 983            folding.  Constants will be substituted to arguments by register
 984            allocator where needed and possible.  Also detect copies. */
 985         switch (opc) {
 986         CASE_OP_32_64(mov):
 987             tcg_opt_gen_mov(s, op, args, args[0], args[1]);
 988             break;
 989         CASE_OP_32_64(movi):
 990             tcg_opt_gen_movi(s, op, args, args[0], args[1]);
 991             break;
 992
 993         CASE_OP_32_64(not):
 994         CASE_OP_32_64(neg):
 995         CASE_OP_32_64(ext8s):
 996         CASE_OP_32_64(ext8u):
 997         CASE_OP_32_64(ext16s):
 998         CASE_OP_32_64(ext16u):
 999         case INDEX_op_ext32s_i64:
1000         case INDEX_op_ext32u_i64:
1001         case INDEX_op_ext_i32_i64:
1002         case INDEX_op_extu_i32_i64:
1003         case INDEX_op_extrl_i64_i32:
1004         case INDEX_op_extrh_i64_i32:
1005             if (temp_is_const(args[1])) {
1006                 tmp = do_constant_folding(opc, temps[args[1]].val, 0);
1007                 tcg_opt_gen_movi(s, op, args, args[0], tmp);
1008                 break;
1009             }
1010             goto do_default;
1011
1012         CASE_OP_32_64(add):
1013         CASE_OP_32_64(sub):
1014         CASE_OP_32_64(mul):
1015         CASE_OP_32_64(or):
1016         CASE_OP_32_64(and):
1017         CASE_OP_32_64(xor):
1018         CASE_OP_32_64(shl):
1019         CASE_OP_32_64(shr):
1020         CASE_OP_32_64(sar):
1021         CASE_OP_32_64(rotl):
1022         CASE_OP_32_64(rotr):
1023         CASE_OP_32_64(andc):
1024         CASE_OP_32_64(orc):
1025         CASE_OP_32_64(eqv):
1026         CASE_OP_32_64(nand):
1027         CASE_OP_32_64(nor):
1028         CASE_OP_32_64(muluh):
1029         CASE_OP_32_64(mulsh):
1030         CASE_OP_32_64(div):
1031         CASE_OP_32_64(divu):
1032         CASE_OP_32_64(rem):
1033         CASE_OP_32_64(remu):
1034             if (temp_is_const(args[1]) && temp_is_const(args[2])) {
1035                 tmp = do_constant_folding(opc, temps[args[1]].val,
1036                                           temps[args[2]].val);
1037                 tcg_opt_gen_movi(s, op, args, args[0], tmp);
1038                 break;
1039             }
1040             goto do_default;
1041
1042         CASE_OP_32_64(deposit):
1043             if (temp_is_const(args[1]) && temp_is_const(args[2])) {
1044                 tmp = deposit64(temps[args[1]].val, args[3], args[4],
1045                                 temps[args[2]].val);
1046                 tcg_opt_gen_movi(s, op, args, args[0], tmp);
1047                 break;
1048             }
1049             goto do_default;
1050
1051         CASE_OP_32_64(setcond):
1052             tmp = do_constant_folding_cond(opc, args[1], args[2], args[3]);
1053             if (tmp != 2) {
1054                 tcg_opt_gen_movi(s, op, args, args[0], tmp);
1055                 break;
1056             }
1057             goto do_default;
1058
1059         CASE_OP_32_64(brcond):
1060             tmp = do_constant_folding_cond(opc, args[0], args[1], args[2]);
1061             if (tmp != 2) {
1062                 if (tmp) {
1063                     reset_all_temps(nb_temps);
1064                     op->opc = INDEX_op_br;
1065                     args[0] = args[3];
1066                 } else {
1067                     tcg_op_remove(s, op);
1068                 }
1069                 break;
1070             }
1071             goto do_default;
1072
1073         CASE_OP_32_64(movcond):
1074             tmp = do_constant_folding_cond(opc, args[1], args[2], args[5]);
1075             if (tmp != 2) {
1076                 tcg_opt_gen_mov(s, op, args, args[0], args[4-tmp]);
1077                 break;
1078             }
1079             goto do_default;
1080
1081         case INDEX_op_add2_i32:
1082         case INDEX_op_sub2_i32:
1083             if (temp_is_const(args[2]) && temp_is_const(args[3])
1084                 && temp_is_const(args[4]) && temp_is_const(args[5])) {
1085                 uint32_t al = temps[args[2]].val;
1086                 uint32_t ah = temps[args[3]].val;
1087                 uint32_t bl = temps[args[4]].val;
1088                 uint32_t bh = temps[args[5]].val;
1089                 uint64_t a = ((uint64_t)ah << 32) | al;
1090                 uint64_t b = ((uint64_t)bh << 32) | bl;
1091                 TCGArg rl, rh;
1092                 TCGOp *op2 = tcg_op_insert_before(s, op, INDEX_op_movi_i32, 2);
1093                 TCGArg *args2 = &s->gen_opparam_buf[op2->args];
1094
1095                 if (opc == INDEX_op_add2_i32) {
1096                     a += b;
1097                 } else {
1098                     a -= b;
1099                 }
1100
1101                 rl = args[0];
1102                 rh = args[1];
1103                 tcg_opt_gen_movi(s, op, args, rl, (int32_t)a);
1104                 tcg_opt_gen_movi(s, op2, args2, rh, (int32_t)(a >> 32));
1105
1106                 /* We've done all we need to do with the movi.  Skip it.  */
1107                 oi_next = op2->next;
1108                 break;
1109             }
1110             goto do_default;
1111
1112         case INDEX_op_mulu2_i32:
1113             if (temp_is_const(args[2]) && temp_is_const(args[3])) {
1114                 uint32_t a = temps[args[2]].val;
1115                 uint32_t b = temps[args[3]].val;
1116                 uint64_t r = (uint64_t)a * b;
1117                 TCGArg rl, rh;
1118                 TCGOp *op2 = tcg_op_insert_before(s, op, INDEX_op_movi_i32, 2);
1119                 TCGArg *args2 = &s->gen_opparam_buf[op2->args];
1120
1121                 rl = args[0];
1122                 rh = args[1];
1123                 tcg_opt_gen_movi(s, op, args, rl, (int32_t)r);
1124                 tcg_opt_gen_movi(s, op2, args2, rh, (int32_t)(r >> 32));
1125
1126                 /* We've done all we need to do with the movi.  Skip it.  */
1127                 oi_next = op2->next;
1128                 break;
1129             }
1130             goto do_default;
1131
1132         case INDEX_op_brcond2_i32:
1133             tmp = do_constant_folding_cond2(&args[0], &args[2], args[4]);
1134             if (tmp != 2) {
1135                 if (tmp) {
1136             do_brcond_true:
1137                     reset_all_temps(nb_temps);
1138                     op->opc = INDEX_op_br;
1139                     args[0] = args[5];
1140                 } else {
1141             do_brcond_false:
1142                     tcg_op_remove(s, op);
1143                 }
1144             } else if ((args[4] == TCG_COND_LT || args[4] == TCG_COND_GE)
1145                        && temp_is_const(args[2]) && temps[args[2]].val == 0
1146                        && temp_is_const(args[3]) && temps[args[3]].val == 0) {
1147                 /* Simplify LT/GE comparisons vs zero to a single compare
1148                    vs the high word of the input.  */
1149             do_brcond_high:
1150                 reset_all_temps(nb_temps);
1151                 op->opc = INDEX_op_brcond_i32;
1152                 args[0] = args[1];
1153                 args[1] = args[3];
1154                 args[2] = args[4];
1155                 args[3] = args[5];
1156             } else if (args[4] == TCG_COND_EQ) {
1157                 /* Simplify EQ comparisons where one of the pairs
1158                    can be simplified.  */
1159                 tmp = do_constant_folding_cond(INDEX_op_brcond_i32,
1160                                                args[0], args[2], TCG_COND_EQ);
1161                 if (tmp == 0) {
1162                     goto do_brcond_false;
1163                 } else if (tmp == 1) {
1164                     goto do_brcond_high;
1165                 }
1166                 tmp = do_constant_folding_cond(INDEX_op_brcond_i32,
1167                                                args[1], args[3], TCG_COND_EQ);
1168                 if (tmp == 0) {
1169                     goto do_brcond_false;
1170                 } else if (tmp != 1) {
1171                     goto do_default;
1172                 }
1173             do_brcond_low:
1174                 reset_all_temps(nb_temps);
1175                 op->opc = INDEX_op_brcond_i32;
1176                 args[1] = args[2];
1177                 args[2] = args[4];
1178                 args[3] = args[5];
1179             } else if (args[4] == TCG_COND_NE) {
1180                 /* Simplify NE comparisons where one of the pairs
1181                    can be simplified.  */
1182                 tmp = do_constant_folding_cond(INDEX_op_brcond_i32,
1183                                                args[0], args[2], TCG_COND_NE);
1184                 if (tmp == 0) {
1185                     goto do_brcond_high;
1186                 } else if (tmp == 1) {
1187                     goto do_brcond_true;
1188                 }
1189                 tmp = do_constant_folding_cond(INDEX_op_brcond_i32,
1190                                                args[1], args[3], TCG_COND_NE);
1191                 if (tmp == 0) {
1192                     goto do_brcond_low;
1193                 } else if (tmp == 1) {
1194                     goto do_brcond_true;
1195                 }
1196                 goto do_default;
1197             } else {
1198                 goto do_default;
1199             }
1200             break;
1201
1202         case INDEX_op_setcond2_i32:
1203             tmp = do_constant_folding_cond2(&args[1], &args[3], args[5]);
1204             if (tmp != 2) {
1205             do_setcond_const:
1206                 tcg_opt_gen_movi(s, op, args, args[0], tmp);
1207             } else if ((args[5] == TCG_COND_LT || args[5] == TCG_COND_GE)
1208                        && temp_is_const(args[3]) && temps[args[3]].val == 0
1209                        && temp_is_const(args[4]) && temps[args[4]].val == 0) {
1210                 /* Simplify LT/GE comparisons vs zero to a single compare
1211                    vs the high word of the input.  */
1212             do_setcond_high:
1213                 reset_temp(args[0]);
1214                 temps[args[0]].mask = 1;
1215                 op->opc = INDEX_op_setcond_i32;
1216                 args[1] = args[2];
1217                 args[2] = args[4];
1218                 args[3] = args[5];
1219             } else if (args[5] == TCG_COND_EQ) {
1220                 /* Simplify EQ comparisons where one of the pairs
1221                    can be simplified.  */
1222                 tmp = do_constant_folding_cond(INDEX_op_setcond_i32,
1223                                                args[1], args[3], TCG_COND_EQ);
1224                 if (tmp == 0) {
1225                     goto do_setcond_const;
1226                 } else if (tmp == 1) {
1227                     goto do_setcond_high;
1228                 }
1229                 tmp = do_constant_folding_cond(INDEX_op_setcond_i32,
1230                                                args[2], args[4], TCG_COND_EQ);
1231                 if (tmp == 0) {
1232                     goto do_setcond_high;
1233                 } else if (tmp != 1) {
1234                     goto do_default;
1235                 }
1236             do_setcond_low:
1237                 reset_temp(args[0]);
1238                 temps[args[0]].mask = 1;
1239                 op->opc = INDEX_op_setcond_i32;
1240                 args[2] = args[3];
1241                 args[3] = args[5];
1242             } else if (args[5] == TCG_COND_NE) {
1243                 /* Simplify NE comparisons where one of the pairs
1244                    can be simplified.  */
1245                 tmp = do_constant_folding_cond(INDEX_op_setcond_i32,
1246                                                args[1], args[3], TCG_COND_NE);
1247                 if (tmp == 0) {
1248                     goto do_setcond_high;
1249                 } else if (tmp == 1) {
1250                     goto do_setcond_const;
1251                 }
1252                 tmp = do_constant_folding_cond(INDEX_op_setcond_i32,
1253                                                args[2], args[4], TCG_COND_NE);
1254                 if (tmp == 0) {
1255                     goto do_setcond_low;
1256                 } else if (tmp == 1) {
1257                     goto do_setcond_const;
1258                 }
1259                 goto do_default;
1260             } else {
1261                 goto do_default;
1262             }
1263             break;
1264
1265         case INDEX_op_call:
1266             if (!(args[nb_oargs + nb_iargs + 1]
1267                   & (TCG_CALL_NO_READ_GLOBALS | TCG_CALL_NO_WRITE_GLOBALS))) {
1268                 for (i = 0; i < nb_globals; i++) {
1269                     if (test_bit(i, temps_used.l)) {
1270                         reset_temp(i);
1271                     }
1272                 }
1273             }
1274             goto do_reset_output;
1275
1276         default:
1277         do_default:
1278             /* Default case: we know nothing about operation (or were unable
1279                to compute the operation result) so no propagation is done.
1280                We trash everything if the operation is the end of a basic
1281                block, otherwise we only trash the output args.  "mask" is
1282                the non-zero bits mask for the first output arg.  */
1283             if (def->flags & TCG_OPF_BB_END) {
1284                 reset_all_temps(nb_temps);
1285             } else {
1286         do_reset_output:
1287                 for (i = 0; i < nb_oargs; i++) {
1288                     reset_temp(args[i]);
1289                     /* Save the corresponding known-zero bits mask for the
1290                        first output argument (only one supported so far). */
1291                     if (i == 0) {
1292                         temps[args[i]].mask = mask;
1293                     }
1294                 }
1295             }
1296             break;
1297         }
1298
1299         /* Eliminate duplicate and redundant fence instructions.  */
1300         if (prev_mb_args) {
1301             switch (opc) {
1302             case INDEX_op_mb:
1303                 /* Merge two barriers of the same type into one,
1304                  * or a weaker barrier into a stronger one,
1305                  * or two weaker barriers into a stronger one.
1306                  *   mb X; mb Y => mb X|Y
1307                  *   mb; strl => mb; st
1308                  *   ldaq; mb => ld; mb
1309                  *   ldaq; strl => ld; mb; st
1310                  * Other combinations are also merged into a strong
1311                  * barrier.  This is stricter than specified but for
1312                  * the purposes of TCG is better than not optimizing.
1313                  */
1314                 prev_mb_args[0] |= args[0];
1315                 tcg_op_remove(s, op);
1316                 break;
1317
1318             default:
1319                 /* Opcodes that end the block stop the optimization.  */
1320                 if ((def->flags & TCG_OPF_BB_END) == 0) {
1321                     break;
1322                 }
1323                 /* fallthru */
1324             case INDEX_op_qemu_ld_i32:
1325             case INDEX_op_qemu_ld_i64:
1326             case INDEX_op_qemu_st_i32:
1327             case INDEX_op_qemu_st_i64:
1328             case INDEX_op_call:
1329                 /* Opcodes that touch guest memory stop the optimization.  */
1330                 prev_mb_args = NULL;
1331                 break;
1332             }
1333         } else if (opc == INDEX_op_mb) {
1334             prev_mb_args = args;
1335         }
1336     }
1337 }