int.c

   1 /* neatcc intermediate code generation */
   2 #include <stdlib.h>
   3 #include <stdio.h>
   4 #include <string.h>
   5 #include "ncc.h"
   6
   7 static struct ic *ic;           /* intermediate code */
   8 static long ic_n, ic_sz;        /* number of instructions in ic[] */
   9 static long iv[NTMPS];          /* operand stack */
  10 static long iv_n;               /* number of values in iv[] */
  11 static long *lab_loc;           /* label locations */
  12 static long lab_n, lab_sz;      /* number of labels in lab_loc[] */
  13 static long lab_last;           /* the last label target */
  14
  15 static int io_num(void);
  16 static int io_mul2(void);
  17 static int io_cmp(void);
  18 static int io_jmp(void);
  19 static int io_addr(void);
  20 static int io_loc(void);
  21 static int io_imm(void);
  22 static int io_call(void);
  23 static void io_deadcode(void);
  24
  25 static void iv_put(long n);
  26
  27 static struct ic *ic_put(long op, long arg1, long arg2, long arg3)
  28 {
  29         struct ic *c;
  30         if (ic_n == ic_sz) {
  31                 ic_sz = MAX(128, ic_sz * 2);
  32                 ic = mextend(ic, ic_n, ic_sz, sizeof(*ic));
  33         }
  34         c = &ic[ic_n++];
  35         c->op = op;
  36         c->a1 = arg1;
  37         c->a2 = arg2;
  38         c->a3 = arg3;
  39         if (op & O_OUT)
  40                 iv_put(ic_n - 1);
  41         return c;
  42 }
  43
  44 static void ic_back(long pos)
  45 {
  46         int i;
  47         for (i = pos; i < ic_n; i++)
  48                 if (ic[i].op & O_CALL)
  49                         free(ic[i].args);
  50         ic_n = pos;
  51 }
  52
  53 static long iv_pop(void)
  54 {
  55         return iv[--iv_n];
  56 }
  57
  58 static long iv_get(int n)
  59 {
  60         return iv[iv_n - n - 1];
  61 }
  62
  63 static void iv_put(long n)
  64 {
  65         iv[iv_n++] = n;
  66 }
  67
  68 static void iv_drop(int n)
  69 {
  70         iv_n = MAX(0, iv_n - n);
  71 }
  72
  73 static void iv_swap(int x, int y)
  74 {
  75         long v = iv[iv_n - x - 1];
  76         iv[iv_n - x - 1] = iv[iv_n - y - 1];
  77         iv[iv_n - y - 1] = v;
  78 }
  79
  80 static void iv_dup(void)
  81 {
  82         iv[iv_n] = iv[iv_n - 1];
  83         iv_n++;
  84 }
  85
  86 void o_num(long n)
  87 {
  88         ic_put(O_MOV | O_NUM, n, 0, 0);
  89 }
  90
  91 void o_local(long id)
  92 {
  93         ic_put(O_MOV | O_LOC, id, 0, 0);
  94 }
  95
  96 void o_sym(char *sym)
  97 {
  98         ic_put(O_MOV | O_SYM, out_sym(sym), 0, 0);
  99 }
 100
 101 void o_tmpdrop(int n)
 102 {
 103         iv_drop(n >= 0 ? n : iv_n);
 104 }
 105
 106 void o_tmpswap(void)
 107 {
 108         iv_swap(0, 1);
 109 }
 110
 111 void o_tmpcopy(void)
 112 {
 113         iv_dup();
 114 }
 115
 116 /* return one if the given value is constant */
 117 static int ic_const(long iv)
 118 {
 119         long oc = O_C(ic[iv].op);
 120         return oc & O_MOV && oc & (O_NUM | O_SYM | O_LOC);
 121 }
 122
 123 /* return one if the given value is a simple load */
 124 static int ic_load(long iv)
 125 {
 126         long oc = O_C(ic[iv].op);
 127         int i;
 128         if (oc & O_LD && oc & (O_NUM | O_SYM | O_LOC)) {
 129                 for (i = iv + 1; i < ic_n; i++)
 130                         if (ic[i].op & O_ST)
 131                                 return 0;
 132                 return 1;
 133         }
 134         return 0;
 135 }
 136
 137 void o_bop(long op)
 138 {
 139         int r1 = iv_pop();
 140         int r2 = iv_pop();
 141         /* load constants as late as possible */
 142         if (opt(1) && ic_const(r2) && !ic_const(r1)) {
 143                 ic_put(ic[r2].op, ic[r2].a1, ic[r2].a2, ic[r2].a3);
 144                 r2 = iv_pop();
 145         }
 146         ic_put(op, r2, r1, 0);
 147         if (opt(1))
 148                 io_num() && io_mul2() && io_addr() && io_imm();
 149 }
 150
 151 void o_uop(long op)
 152 {
 153         int r1 = iv_pop();
 154         ic_put(op, r1, 0, 0);
 155         if (opt(1))
 156                 io_num() && io_cmp();
 157 }
 158
 159 void o_assign(long bt)
 160 {
 161         int rv = iv_pop();
 162         int lv = iv_pop();
 163         /* load constants as late as possible */
 164         if (opt(1) && (ic_const(lv) || ic_load(lv))) {
 165                 ic_put(ic[lv].op, ic[lv].a1, ic[lv].a2, ic[lv].a3);
 166                 lv = iv_pop();
 167         }
 168         ic_put(O_MK(O_ST | O_NUM, bt), rv, lv, 0);
 169         iv_put(rv);
 170         if (opt(1))
 171                 io_loc();
 172 }
 173
 174 void o_deref(long bt)
 175 {
 176         int r1 = iv_pop();
 177         ic_put(O_MK(O_LD | O_NUM, bt), r1, 0, 0);
 178         if (opt(1))
 179                 io_loc();
 180 }
 181
 182 void o_cast(long bt)
 183 {
 184         if (T_SZ(bt) != ULNG) {
 185                 int r1 = iv_pop();
 186                 ic_put(O_MK(O_MOV, bt), r1, 0, 0);
 187                 if (opt(1))
 188                         io_num();
 189         }
 190 }
 191
 192 void o_memcpy(void)
 193 {
 194         int r2 = iv_pop();
 195         int r1 = iv_pop();
 196         int r0 = iv_pop();
 197         ic_put(O_MCPY, r0, r1, r2);
 198 }
 199
 200 void o_memset(void)
 201 {
 202         int r2 = iv_pop();
 203         int r1 = iv_pop();
 204         int r0 = iv_pop();
 205         ic_put(O_MSET, r0, r1, r2);
 206 }
 207
 208 void o_call(int argc, int ret)
 209 {
 210         struct ic *c;
 211         long *args = malloc(argc * sizeof(c->args[0]));
 212         int r1, i;
 213         for (i = argc - 1; i >= 0; --i)
 214                 args[i] = iv_pop();
 215         for (i = argc - 1; i >= 0; --i) {
 216                 int iv = args[i];
 217                 /* load constants as late as possible */
 218                 if (opt(1) && (ic_const(iv) || ic_load(iv))) {
 219                         ic_put(ic[iv].op, ic[iv].a1, ic[iv].a2, ic[iv].a3);
 220                         args[i] = iv_pop();
 221                 }
 222         }
 223         r1 = iv_pop();
 224         c = ic_put(O_CALL, r1, 0, argc);
 225         c->args = args;
 226         iv_drop(ret == 0);
 227         if (opt(1))
 228                 io_call();
 229 }
 230
 231 void o_ret(int ret)
 232 {
 233         if (!ret)
 234                 o_num(0);
 235         ic_put(O_RET, iv_pop(), 0, 0);
 236 }
 237
 238 void o_label(long id)
 239 {
 240         while (id >= lab_sz) {
 241                 lab_sz = MAX(128, lab_sz * 2);
 242                 lab_loc = mextend(lab_loc, lab_n, lab_sz, sizeof(*lab_loc));
 243         }
 244         while (lab_n <= id)
 245                 lab_loc[lab_n++] = -1;
 246         lab_loc[id] = ic_n;
 247         lab_last = ic_n;
 248 }
 249
 250 void o_jmp(long id)
 251 {
 252         ic_put(O_JMP, 0, 0, id);
 253 }
 254
 255 void o_jz(long id)
 256 {
 257         ic_put(O_JZ, iv_pop(), 0, id);
 258         if (opt(1))
 259                 io_jmp();
 260 }
 261
 262 int o_popnum(long *n)
 263 {
 264         if (ic_num(ic, iv_get(0), n))
 265                 return 1;
 266         iv_drop(1);
 267         return 0;
 268 }
 269
 270 int o_popsym(long *sym, long *off)
 271 {
 272         if (ic_sym(ic, iv_get(0), sym, off))
 273                 return 1;
 274         iv_drop(1);
 275         return 0;
 276 }
 277
 278 long o_mark(void)
 279 {
 280         return ic_n;
 281 }
 282
 283 void o_back(long mark)
 284 {
 285         ic_back(mark);
 286 }
 287
 288 void ic_get(struct ic **c, long *n)
 289 {
 290         int i;
 291         if (!ic_n || ~ic[ic_n - 1].op & O_RET || lab_last == ic_n)
 292                 o_ret(0);
 293         for (i = 0; i < ic_n; i++)      /* filling branch targets */
 294                 if (ic[i].op & O_JXX)
 295                         ic[i].a3 = lab_loc[ic[i].a3];
 296         io_deadcode();                  /* removing dead code */
 297         *c = ic;
 298         *n = ic_n;
 299         ic = NULL;
 300         ic_n = 0;
 301         ic_sz = 0;
 302         iv_n = 0;
 303         free(lab_loc);
 304         lab_loc = NULL;
 305         lab_n = 0;
 306         lab_sz = 0;
 307         lab_last = 0;
 308 }
 309
 310 void ic_free(struct ic *ic)
 311 {
 312         if (ic->op & O_CALL)
 313                 free(ic->args);
 314 }
 315
 316 /* intermediate code queries */
 317
 318 static long cb(long op, long a, long b)
 319 {
 320         switch (O_C(op)) {
 321         case O_ADD:
 322                 return a + b;
 323         case O_SUB:
 324                 return a - b;
 325         case O_AND:
 326                 return a & b;
 327         case O_OR:
 328                 return a | b;
 329         case O_XOR:
 330                 return a ^ b;
 331         case O_MUL:
 332                 return a * b;
 333         case O_DIV:
 334                 return a / b;
 335         case O_MOD:
 336                 return a % b;
 337         case O_SHL:
 338                 return a << b;
 339         case O_SHR:
 340                 return O_T(op) & T_MSIGN ? a >> b : (unsigned long) a >> b;
 341         case O_LT:
 342                 return a < b;
 343         case O_GT:
 344                 return a > b;
 345         case O_LE:
 346                 return a <= b;
 347         case O_GE:
 348                 return a >= b;
 349         case O_EQ:
 350                 return a == b;
 351         case O_NE:
 352                 return a != b;
 353         }
 354         return 0;
 355 }
 356
 357 static long cu(int op, long i)
 358 {
 359         switch (O_C(op)) {
 360         case O_NEG:
 361                 return -i;
 362         case O_NOT:
 363                 return ~i;
 364         case O_LNOT:
 365                 return !i;
 366         }
 367         return 0;
 368 }
 369
 370 static long c_cast(long n, unsigned bt)
 371 {
 372         if (!(bt & T_MSIGN) && T_SZ(bt) != ULNG)
 373                 n &= ((1l << (long) (T_SZ(bt) * 8)) - 1);
 374         if (bt & T_MSIGN && T_SZ(bt) != ULNG &&
 375                                 n > (1l << (T_SZ(bt) * 8 - 1)))
 376                 n = -((1l << (T_SZ(bt) * 8)) - n);
 377         return n;
 378 }
 379
 380 int ic_num(struct ic *ic, long iv, long *n)
 381 {
 382         long n1, n2;
 383         long oc = O_C(ic[iv].op);
 384         long bt = O_T(ic[iv].op);
 385         if (oc & O_MOV && oc & O_NUM) {
 386                 *n = ic[iv].a1;
 387                 return 0;
 388         }
 389         if (oc & O_BOP) {
 390                 if (ic_num(ic, ic[iv].a1, &n1))
 391                         return 1;
 392                 if (ic_num(ic, ic[iv].a2, &n2))
 393                         return 1;
 394                 *n = cb(ic[iv].op, n1, n2);
 395                 return 0;
 396         }
 397         if (oc & O_UOP) {
 398                 if (ic_num(ic, ic[iv].a1, &n1))
 399                         return 1;
 400                 *n = cu(ic[iv].op, n1);
 401                 return 0;
 402         }
 403         if (oc & O_MOV && !(oc & (O_NUM | O_LOC | O_SYM))) {
 404                 if (ic_num(ic, ic[iv].a1, &n1))
 405                         return 1;
 406                 *n = c_cast(n1, bt);
 407                 return 0;
 408         }
 409         return 1;
 410 }
 411
 412 int ic_sym(struct ic *ic, long iv, long *sym, long *off)
 413 {
 414         long n;
 415         long oc = O_C(ic[iv].op);
 416         if (oc & O_MOV && oc & O_SYM) {
 417                 *sym = ic[iv].a1;
 418                 *off = ic[iv].a2;
 419                 return 0;
 420         }
 421         if (oc == O_ADD) {
 422                 if ((ic_sym(ic, ic[iv].a1, sym, off) ||
 423                                 ic_num(ic, ic[iv].a2, &n)) &&
 424                         (ic_sym(ic, ic[iv].a2, sym, off) ||
 425                                 ic_num(ic, ic[iv].a1, &n)))
 426                         return 1;
 427                 *off += n;
 428                 return 0;
 429         }
 430         if (oc == O_SUB) {
 431                 if (ic_sym(ic, ic[iv].a1, sym, off) ||
 432                                 ic_num(ic, ic[iv].a2, &n))
 433                         return 1;
 434                 *off -= n;
 435                 return 0;
 436         }
 437         return 1;
 438 }
 439
 440 static int ic_off(struct ic *ic, long iv, long *base_iv, long *off)
 441 {
 442         long n;
 443         long oc = O_C(ic[iv].op);
 444         if (oc == (O_ADD | O_NUM)) {
 445                 *base_iv = ic[iv].a1;
 446                 *off = ic[iv].a2;
 447                 return 0;
 448         }
 449         if (oc == (O_SUB | O_NUM)) {
 450                 *base_iv = ic[iv].a1;
 451                 *off = -ic[iv].a2;
 452                 return 0;
 453         }
 454         if (oc == O_ADD) {
 455                 if ((ic_off(ic, ic[iv].a1, base_iv, off) ||
 456                                 ic_num(ic, ic[iv].a2, &n)) &&
 457                         (ic_off(ic, ic[iv].a2, base_iv, off) ||
 458                                 ic_num(ic, ic[iv].a1, &n)))
 459                         return 1;
 460                 *off += n;
 461                 return 0;
 462         }
 463         if (oc == O_SUB) {
 464                 if (ic_off(ic, ic[iv].a1, base_iv, off) ||
 465                                 ic_num(ic, ic[iv].a2, &n))
 466                         return 1;
 467                 *off -= n;
 468                 return 0;
 469         }
 470         *base_iv = iv;
 471         *off = 0;
 472         return 0;
 473 }
 474
 475 /* number of register arguments */
 476 int ic_regcnt(struct ic *ic)
 477 {
 478         long o = ic->op;
 479         if (o & O_BOP)
 480                 return o & (O_NUM | O_SYM | O_LOC) ? 1 : 2;
 481         if (o & O_UOP)
 482                 return o & (O_NUM | O_SYM | O_LOC) ? 0 : 1;
 483         if (o & O_CALL)
 484                 return o & (O_NUM | O_SYM | O_LOC) ? 0 : 1;
 485         if (o & O_MOV)
 486                 return o & (O_NUM | O_SYM | O_LOC) ? 0 : 1;
 487         if (o & O_MEM)
 488                 return 3;
 489         if (o & O_JMP)
 490                 return 0;
 491         if (o & O_JZ)
 492                 return 1;
 493         if (o & O_JCC)
 494                 return o & (O_NUM | O_SYM | O_LOC) ? 1 : 2;
 495         if (o & O_RET)
 496                 return 1;
 497         if (o & O_LD)
 498                 return ((o & O_NUM) != 0);
 499         if (o & O_ST)
 500                 return 1 + ((o & O_NUM) != 0);
 501         return 0;
 502 }
 503
 504 /*
 505  * The returned array indicates the last instruction in
 506  * which the value produced by each instruction is used.
 507  */
 508 long *ic_lastuse(struct ic *ic, long ic_n)
 509 {
 510         long *luse = calloc(ic_n, sizeof(luse[0]));
 511         int i, j;
 512         for (i = ic_n - 1; i >= 0; --i) {
 513                 int n = ic_regcnt(ic + i);
 514                 if (!luse[i])
 515                         if (!(ic[i].op & O_OUT) || ic[i].op & O_CALL)
 516                                 luse[i] = -1;
 517                 if (!luse[i])
 518                         continue;
 519                 if (n >= 1 && !luse[ic[i].a1])
 520                         luse[ic[i].a1] = i;
 521                 if (n >= 2 && !luse[ic[i].a2])
 522                         luse[ic[i].a2] = i;
 523                 if (n >= 3 && !luse[ic[i].a3])
 524                         luse[ic[i].a3] = i;
 525                 if (ic[i].op & O_CALL)
 526                         for (j = 0; j < ic[i].a3; j++)
 527                                 if (!luse[ic[i].args[j]])
 528                                         luse[ic[i].args[j]] = i;
 529         }
 530         return luse;
 531 }
 532
 533 /* intermediate code optimisations */
 534
 535 /* constant folding */
 536 static int io_num(void)
 537 {
 538         long n;
 539         if (!ic_num(ic, iv_get(0), &n)) {
 540                 iv_drop(1);
 541                 o_num(n);
 542                 return 0;
 543         }
 544         return 1;
 545 }
 546
 547 static int log2a(unsigned long n)
 548 {
 549         int i = 0;
 550         for (i = 0; i < LONGSZ * 8; i++)
 551                 if (n & (1u << i))
 552                         break;
 553         if (i == LONGSZ * 8 || !(n >> (i + 1)))
 554                 return i;
 555         return -1;
 556 }
 557
 558 static long iv_num(long n)
 559 {
 560         o_num(n);
 561         return iv_pop();
 562 }
 563
 564 /* optimised multiplication operations for powers of two */
 565 static int io_mul2(void)
 566 {
 567         long iv = iv_get(0);
 568         long n, p;
 569         long r1, r2;
 570         long oc = O_C(ic[iv].op);
 571         long bt = O_T(ic[iv].op);
 572         if (!(oc & O_MUL))
 573                 return 1;
 574         if (oc == O_MUL && !ic_num(ic, ic[iv].a1, &n)) {
 575                 long t = ic[iv].a1;
 576                 ic[iv].a1 = ic[iv].a2;
 577                 ic[iv].a2 = t;
 578         }
 579         if (ic_num(ic, ic[iv].a2, &n))
 580                 return 1;
 581         p = log2a(n);
 582         if (n && p < 0)
 583                 return 1;
 584         if (oc == O_MUL) {
 585                 iv_drop(1);
 586                 if (n == 1) {
 587                         iv_put(ic[iv].a1);
 588                         return 0;
 589                 }
 590                 if (n == 0) {
 591                         o_num(0);
 592                         return 0;
 593                 }
 594                 r2 = iv_num(p);
 595                 ic_put(O_MK(O_SHL, ULNG), ic[iv].a1, r2, 0);
 596                 return 0;
 597         }
 598         if (oc == O_DIV && ~bt & T_MSIGN) {
 599                 iv_drop(1);
 600                 if (n == 1) {
 601                         iv_put(ic[iv].a1);
 602                         return 0;
 603                 }
 604                 r2 = iv_num(p);
 605                 ic_put(O_MK(O_SHR, ULNG), ic[iv].a1, r2, 0);
 606                 return 0;
 607         }
 608         if (oc == O_MOD && ~bt & T_MSIGN) {
 609                 iv_drop(1);
 610                 if (n == 1) {
 611                         o_num(0);
 612                         return 0;
 613                 }
 614                 r2 = iv_num(LONGSZ * 8 - p);
 615                 ic_put(O_MK(O_SHL, ULNG), ic[iv].a1, r2, 0);
 616                 r1 = iv_pop();
 617                 r2 = iv_num(LONGSZ * 8 - p);
 618                 ic_put(O_MK(O_SHR, ULNG), r1, r2, 0);
 619                 return 0;
 620         }
 621         return 1;
 622 }
 623
 624 /* optimise comparison */
 625 static int io_cmp(void)
 626 {
 627         long iv = iv_get(0);
 628         long cmp = ic[iv].a1;
 629         if (O_C(ic[iv].op) == O_LNOT && ic[cmp].op & O_CMP) {
 630                 iv_drop(1);
 631                 ic[cmp].op ^= 1;
 632                 iv_put(cmp);
 633                 return 0;
 634         }
 635         return 1;
 636 }
 637
 638 /* optimise branch instructions after comparison */
 639 static int io_jmp(void)
 640 {
 641         struct ic *c = &ic[ic_n - 1];
 642         long oc = O_C(c->op);
 643         if (oc & O_JZ && O_C(ic[c->a1].op) == O_LNOT) {
 644                 c->a1 = ic[c->a1].a1;
 645                 c->op ^= 1;
 646                 return 0;
 647         }
 648         if (oc & O_JZ && O_C(ic[c->a1].op) & O_CMP) {
 649                 long cop = (ic[c->a1].op & ~O_CMP) | O_JCC;
 650                 c->op = O_C(c->op) == O_JZ ? cop ^ 1 : cop;
 651                 c->a2 = ic[c->a1].a2;
 652                 c->a1 = ic[c->a1].a1;
 653                 return 0;
 654         }
 655         return 1;
 656 }
 657
 658 /* optimise accessing locals or symbols with an offset */
 659 static int io_addr(void)
 660 {
 661         long iv, off;
 662         if (ic_off(ic, iv_get(0), &iv, &off) || iv == iv_get(0))
 663                 return 1;
 664         if (ic[iv].op & O_MOV && ic[iv].op & O_LOC) {
 665                 iv_drop(1);
 666                 ic_put(O_MOV | O_LOC, ic[iv].a1, ic[iv].a2 + off, 0);
 667                 return 0;
 668         }
 669         if (ic[iv].op & O_MOV && ic[iv].op & O_SYM) {
 670                 iv_drop(1);
 671                 ic_put(O_MOV | O_SYM, ic[iv].a1, ic[iv].a2 + off, 0);
 672                 return 0;
 673         }
 674         return 1;
 675 }
 676
 677 static int imm_ok(long op, long n, int arg)
 678 {
 679         long m[5];
 680         if (i_reg(op | O_NUM, m + 0, m + 1, m + 2, m + 3, m + 4))
 681                 return 0;
 682         return i_imm(m[arg], n);
 683 }
 684
 685 /* optimise loading and storing locals */
 686 static int io_loc(void)
 687 {
 688         struct ic *c = &ic[ic_n - 1];
 689         long iv, off;
 690         if (c->op & O_LD && c->op & O_NUM) {
 691                 if (ic_off(ic, c->a1, &iv, &off))
 692                         return 1;
 693                 if (ic[iv].op & O_MOV && ic[iv].op & O_LOC) {
 694                         c->op = (c->op & ~O_NUM) | O_LOC;
 695                         c->a1 = ic[iv].a1;
 696                         c->a2 += ic[iv].a2 + off;
 697                         return 0;
 698                 }
 699                 if (imm_ok(c->op, off, 2)) {
 700                         c->a1 = iv;
 701                         c->a2 += off;
 702                 }
 703                 return 0;
 704         }
 705         if (c->op & O_ST && c->op & O_NUM) {
 706                 if (ic_off(ic, c->a2, &iv, &off))
 707                         return 1;
 708                 if (ic[iv].op & O_MOV && ic[iv].op & O_LOC) {
 709                         c->op = (c->op & ~O_NUM) | O_LOC;
 710                         c->a2 = ic[iv].a1;
 711                         c->a3 += ic[iv].a2 + off;
 712                         return 0;
 713                 }
 714                 if (imm_ok(c->op, off, 3)) {
 715                         c->a2 = iv;
 716                         c->a3 += off;
 717                 }
 718                 return 0;
 719         }
 720         return 1;
 721 }
 722
 723 /* use instruction immediates */
 724 static int io_imm(void)
 725 {
 726         struct ic *c = &ic[ic_n - 1];
 727         long oc = O_C(c->op);
 728         long n;
 729         if (oc & (O_NUM | O_LOC | O_SYM))
 730                 return 1;
 731         if (oc == O_ADD || oc == O_MUL || oc == O_AND || oc == O_OR ||
 732                         oc == O_XOR || oc == O_EQ || oc == O_NE) {
 733                 if (!ic_num(ic, c->a1, &n)) {
 734                         long t = c->a1;
 735                         c->a1 = c->a2;
 736                         c->a2 = t;
 737                 }
 738         }
 739         if (oc == O_LT || oc == O_GE || oc == O_LE || oc == O_GT) {
 740                 if (!ic_num(ic, c->a1, &n)) {
 741                         int t = c->a1;
 742                         c->a1 = c->a2;
 743                         c->a2 = t;
 744                         c->op ^= 1;
 745                 }
 746         }
 747         if (oc & O_JCC && !ic_num(ic, c->a1, &n)) {
 748                 int t = c->a1;
 749                 c->a1 = c->a2;
 750                 c->a2 = t;
 751                 c->op ^= 1;
 752         }
 753         if (oc & O_JCC && !ic_num(ic, c->a2, &n) && imm_ok(c->op, n, 1)) {
 754                 c->op |= O_NUM;
 755                 c->a2 = n;
 756                 return 0;
 757         }
 758         if (!(oc & O_BOP) || ic_num(ic, c->a2, &n))
 759                 return 1;
 760         if ((oc == O_ADD || oc == O_SUB || oc & O_SHL) && n == 0) {
 761                 iv_drop(1);
 762                 iv_put(c->a1);
 763                 return 0;
 764         }
 765         if (imm_ok(c->op, n, 2)) {
 766                 c->op |= O_NUM;
 767                 c->a2 = n;
 768                 return 0;
 769         }
 770         return 1;
 771 }
 772
 773 /* calling symbols */
 774 static int io_call(void)
 775 {
 776         struct ic *c = &ic[ic_n - 1];
 777         long sym, off;
 778         if (c->op & O_CALL && !ic_sym(ic, c->a1, &sym, &off) && !off) {
 779                 c->op |= O_SYM;
 780                 c->a1 = sym;
 781                 return 0;
 782         }
 783         return 1;
 784 }
 785
 786 /* remove dead code */
 787 static void io_deadcode(void)
 788 {
 789         char *live;
 790         long *nidx;
 791         long src = 0, dst = 0;
 792         int i, j;
 793         /* liveness analysis */
 794         live = calloc(ic_n, sizeof(live[0]));
 795         for (i = ic_n - 1; i >= 0; i--) {
 796                 int n = ic_regcnt(ic + i);
 797                 if (!(ic[i].op & O_OUT) || ic[i].op & O_CALL)
 798                         live[i] = 1;
 799                 if (!live[i])
 800                         continue;
 801                 if (n >= 1)
 802                         live[ic[i].a1] = 1;
 803                 if (n >= 2)
 804                         live[ic[i].a2] = 1;
 805                 if (n >= 3)
 806                         live[ic[i].a3] = 1;
 807                 if (ic[i].op & O_CALL)
 808                         for (j = 0; j < ic[i].a3; j++)
 809                                 live[ic[i].args[j]] = 1;
 810         }
 811         /* the new indices of intermediate instructions */
 812         nidx = calloc(ic_n, sizeof(nidx[0]));
 813         while (src < ic_n) {
 814                 while (src < ic_n && !live[src]) {
 815                         nidx[src] = dst;
 816                         ic_free(&ic[src++]);
 817                 }
 818                 if (src < ic_n) {
 819                         nidx[src] = dst;
 820                         if (src != dst)
 821                                 memcpy(ic + dst, ic + src, sizeof(ic[src]));
 822                         src++;
 823                         dst++;
 824                 }
 825         }
 826         ic_n = dst;
 827         /* adjusting arguments and branch targets */
 828         for (i = 0; i < ic_n; i++) {
 829                 int n = ic_regcnt(ic + i);
 830                 if (n >= 1)
 831                         ic[i].a1 = nidx[ic[i].a1];
 832                 if (n >= 2)
 833                         ic[i].a2 = nidx[ic[i].a2];
 834                 if (n >= 3)
 835                         ic[i].a3 = nidx[ic[i].a3];
 836                 if (ic[i].op & O_JXX)
 837                         ic[i].a3 = nidx[ic[i].a3];
 838                 if (ic[i].op & O_CALL)
 839                         for (j = 0; j < ic[i].a3; j++)
 840                                 ic[i].args[j] = nidx[ic[i].args[j]];
 841         }
 842         free(live);
 843         free(nidx);
 844 }