amd64/isel.c

   1 #include "all.h"
   2 #include <limits.h>
   3
   4 /* For x86_64, do the following:
   5  *
   6  * - check that constants are used only in
   7  *   places allowed
   8  * - ensure immediates always fit in 32b
   9  * - expose machine register contraints
  10  *   on instructions like division.
  11  * - implement fast locals (the streak of
  12  *   constant allocX in the first basic block)
  13  * - recognize complex addressing modes
  14  *
  15  * Invariant: the use counts that are used
  16  *            in sel() must be sound.  This
  17  *            is not so trivial, maybe the
  18  *            dce should be moved out...
  19  */
  20
  21 typedef struct ANum ANum;
  22
  23 struct ANum {
  24         char n, l, r;
  25         Ins *i;
  26 };
  27
  28 static int amatch(Addr *, Ref, int, ANum *, Fn *);
  29
  30 static int
  31 noimm(Ref r, Fn *fn)
  32 {
  33         int64_t val;
  34
  35         if (rtype(r) != RCon)
  36                 return 0;
  37         switch (fn->con[r.val].type) {
  38         case CAddr:
  39                 /* we only support the 'small'
  40                  * code model of the ABI, this
  41                  * means that we can always
  42                  * address data with 32bits
  43                  */
  44                 return 0;
  45         case CBits:
  46                 val = fn->con[r.val].bits.i;
  47                 return (val < INT32_MIN || val > INT32_MAX);
  48         default:
  49                 die("invalid constant");
  50         }
  51 }
  52
  53 static int
  54 rslot(Ref r, Fn *fn)
  55 {
  56         if (rtype(r) != RTmp)
  57                 return -1;
  58         return fn->tmp[r.val].slot;
  59 }
  60
  61 static void
  62 fixarg(Ref *r, int k, int op, Fn *fn)
  63 {
  64         char buf[32];
  65         Addr a;
  66         Ref r0, r1;
  67         int s, n, cpy, mem;
  68
  69         r1 = r0 = *r;
  70         s = rslot(r0, fn);
  71         cpy = op == Ocopy || op == -1;
  72         mem = isstore(op) || isload(op) || op == Ocall;
  73         if (KBASE(k) == 1 && rtype(r0) == RCon) {
  74                 /* load floating points from memory
  75                  * slots, they can't be used as
  76                  * immediates
  77                  */
  78                 r1 = MEM(fn->nmem);
  79                 vgrow(&fn->mem, ++fn->nmem);
  80                 memset(&a, 0, sizeof a);
  81                 a.offset.type = CAddr;
  82                 a.offset.local = 1;
  83                 n = gasstash(&fn->con[r0.val].bits, KWIDE(k) ? 8 : 4);
  84                 sprintf(buf, "fp%d", n);
  85                 a.offset.label = intern(buf);
  86                 fn->mem[fn->nmem-1] = a;
  87         }
  88         else if (!cpy && k == Kl && noimm(r0, fn)) {
  89                 /* load constants that do not fit in
  90                  * a 32bit signed integer into a
  91                  * long temporary
  92                  */
  93                 r1 = newtmp("isel", Kl, fn);
  94                 emit(Ocopy, Kl, r1, r0, R);
  95         }
  96         else if (s != -1) {
  97                 /* load fast locals' addresses into
  98                  * temporaries right before the
  99                  * instruction
 100                  */
 101                 r1 = newtmp("isel", Kl, fn);
 102                 emit(Oaddr, Kl, r1, SLOT(s), R);
 103         }
 104         else if (!mem && rtype(r0) == RCon
 105         && fn->con[r0.val].type == CAddr) {
 106                 /* apple as does not support 32-bit
 107                  * absolute addressing, use a rip-
 108                  * relative leaq instead
 109                  */
 110                 r1 = newtmp("isel", Kl, fn);
 111                 emit(Oaddr, Kl, r1, r0, R);
 112         }
 113         *r = r1;
 114 }
 115
 116 static void
 117 seladdr(Ref *r, ANum *an, Fn *fn)
 118 {
 119         Addr a;
 120         Ref r0;
 121
 122         r0 = *r;
 123         if (rtype(r0) == RTmp) {
 124                 memset(&a, 0, sizeof a);
 125                 if (!amatch(&a, r0, an[r0.val].n, an, fn))
 126                         return;
 127                 if (!req(a.base, R))
 128                 if (a.offset.type == CAddr) {
 129                         /* apple as does not support
 130                          * $foo(%r0, %r1, M); try to
 131                          * rewrite it or bail out if
 132                          * impossible
 133                          */
 134                         if (!req(a.index, R))
 135                                 return;
 136                         else {
 137                                 a.index = a.base;
 138                                 a.scale = 1;
 139                                 a.base = R;
 140                         }
 141                 }
 142                 chuse(r0, -1, fn);
 143                 vgrow(&fn->mem, ++fn->nmem);
 144                 fn->mem[fn->nmem-1] = a;
 145                 chuse(a.base, +1, fn);
 146                 chuse(a.index, +1, fn);
 147                 *r = MEM(fn->nmem-1);
 148         }
 149 }
 150
 151 static int
 152 selcmp(Ref arg[2], int k, Fn *fn)
 153 {
 154         int swap;
 155         Ref r, *iarg;
 156
 157         swap = rtype(arg[0]) == RCon;
 158         if (swap) {
 159                 r = arg[1];
 160                 arg[1] = arg[0];
 161                 arg[0] = r;
 162         }
 163         emit(Oxcmp, k, R, arg[1], arg[0]);
 164         iarg = curi->arg;
 165         if (rtype(arg[0]) == RCon) {
 166                 assert(k == Kl);
 167                 iarg[1] = newtmp("isel", k, fn);
 168                 emit(Ocopy, k, iarg[1], arg[0], R);
 169         }
 170         fixarg(&iarg[0], k, Oxcmp, fn);
 171         fixarg(&iarg[1], k, Oxcmp, fn);
 172         return swap;
 173 }
 174
 175 static void
 176 sel(Ins i, ANum *an, Fn *fn)
 177 {
 178         Ref r0, r1, *iarg;
 179         int x, k, kc;
 180         int64_t sz;
 181         Ins *i0, *i1;
 182
 183         if (rtype(i.to) == RTmp)
 184         if (!isreg(i.to) && !isreg(i.arg[0]) && !isreg(i.arg[1]))
 185         if (fn->tmp[i.to.val].nuse == 0) {
 186                 chuse(i.arg[0], -1, fn);
 187                 chuse(i.arg[1], -1, fn);
 188                 return;
 189         }
 190         i0 = curi;
 191         k = i.cls;
 192         switch (i.op) {
 193         case Odiv:
 194         case Orem:
 195         case Oudiv:
 196         case Ourem:
 197                 if (KBASE(k) == 1)
 198                         goto Emit;
 199                 if (i.op == Odiv || i.op == Oudiv)
 200                         r0 = TMP(RAX), r1 = TMP(RDX);
 201                 else
 202                         r0 = TMP(RDX), r1 = TMP(RAX);
 203                 emit(Ocopy, k, i.to, r0, R);
 204                 emit(Ocopy, k, R, r1, R);
 205                 if (rtype(i.arg[1]) == RCon) {
 206                         /* immediates not allowed for
 207                          * divisions in x86
 208                          */
 209                         r0 = newtmp("isel", k, fn);
 210                 } else
 211                         r0 = i.arg[1];
 212                 if (fn->tmp[r0.val].slot != -1)
 213                         err("unlikely argument %%%s in %s",
 214                                 fn->tmp[r0.val].name, optab[i.op].name);
 215                 if (i.op == Odiv || i.op == Orem) {
 216                         emit(Oxidiv, k, R, r0, R);
 217                         emit(Osign, k, TMP(RDX), TMP(RAX), R);
 218                 } else {
 219                         emit(Oxdiv, k, R, r0, R);
 220                         emit(Ocopy, k, TMP(RDX), CON_Z, R);
 221                 }
 222                 emit(Ocopy, k, TMP(RAX), i.arg[0], R);
 223                 fixarg(&curi->arg[0], k, Ocopy, fn);
 224                 if (rtype(i.arg[1]) == RCon)
 225                         emit(Ocopy, k, r0, i.arg[1], R);
 226                 break;
 227         case Osar:
 228         case Oshr:
 229         case Oshl:
 230                 if (rtype(i.arg[1]) == RCon)
 231                         goto Emit;
 232                 r0 = i.arg[1];
 233                 i.arg[1] = TMP(RCX);
 234                 emit(Ocopy, Kw, R, TMP(RCX), R);
 235                 emiti(i);
 236                 emit(Ocopy, Kw, TMP(RCX), r0, R);
 237                 break;
 238         case Onop:
 239                 break;
 240         case Ostored:
 241         case Ostores:
 242         case Ostorel:
 243         case Ostorew:
 244         case Ostoreh:
 245         case Ostoreb:
 246                 if (rtype(i.arg[0]) == RCon) {
 247                         if (i.op == Ostored)
 248                                 i.op = Ostorel;
 249                         if (i.op == Ostores)
 250                                 i.op = Ostorew;
 251                 }
 252                 seladdr(&i.arg[1], an, fn);
 253                 goto Emit;
 254         case_Oload:
 255                 seladdr(&i.arg[0], an, fn);
 256                 goto Emit;
 257         case Ocall:
 258         case Osalloc:
 259         case Ocopy:
 260         case Oadd:
 261         case Osub:
 262         case Omul:
 263         case Oand:
 264         case Oor:
 265         case Oxor:
 266         case Oxtest:
 267         case Ostosi:
 268         case Odtosi:
 269         case Oswtof:
 270         case Osltof:
 271         case Oexts:
 272         case Otruncd:
 273         case Ocast:
 274         case_OExt:
 275 Emit:
 276                 emiti(i);
 277                 iarg = curi->arg; /* fixarg() can change curi */
 278                 fixarg(&iarg[0], argcls(&i, 0), i.op, fn);
 279                 fixarg(&iarg[1], argcls(&i, 1), i.op, fn);
 280                 break;
 281         case Oalloc:
 282         case Oalloc+1:
 283         case Oalloc+2: /* == Oalloc1 */
 284                 /* we need to make sure
 285                  * the stack remains aligned
 286                  * (rsp = 0) mod 16
 287                  */
 288                 fn->dynalloc = 1;
 289                 if (rtype(i.arg[0]) == RCon) {
 290                         sz = fn->con[i.arg[0].val].bits.i;
 291                         if (sz < 0 || sz >= INT_MAX-15)
 292                                 err("invalid alloc size %"PRId64, sz);
 293                         sz = (sz + 15)  & -16;
 294                         emit(Osalloc, Kl, i.to, getcon(sz, fn), R);
 295                 } else {
 296                         /* r0 = (i.arg[0] + 15) & -16 */
 297                         r0 = newtmp("isel", Kl, fn);
 298                         r1 = newtmp("isel", Kl, fn);
 299                         emit(Osalloc, Kl, i.to, r0, R);
 300                         emit(Oand, Kl, r0, r1, getcon(-16, fn));
 301                         emit(Oadd, Kl, r1, i.arg[0], getcon(15, fn));
 302                         if (fn->tmp[i.arg[0].val].slot != -1)
 303                                 err("unlikely argument %%%s in %s",
 304                                         fn->tmp[i.arg[0].val].name, optab[i.op].name);
 305                 }
 306                 break;
 307         default:
 308                 if (isext(i.op))
 309                         goto case_OExt;
 310                 if (isload(i.op))
 311                         goto case_Oload;
 312                 if (iscmp(i.op, &kc, &x)) {
 313                         emit(Oflag+x, k, i.to, R, R);
 314                         i1 = curi;
 315                         if (selcmp(i.arg, kc, fn))
 316                                 i1->op = Oflag + cmpop(x);
 317                         break;
 318                 }
 319                 die("unknown instruction %s", optab[i.op].name);
 320         }
 321
 322         while (i0 > curi && --i0) {
 323                 assert(rslot(i0->arg[0], fn) == -1);
 324                 assert(rslot(i0->arg[1], fn) == -1);
 325         }
 326 }
 327
 328 static Ins *
 329 flagi(Ins *i0, Ins *i)
 330 {
 331         while (i>i0) {
 332                 i--;
 333                 if (amd64_op[i->op].zflag)
 334                         return i;
 335                 if (amd64_op[i->op].lflag)
 336                         continue;
 337                 return 0;
 338         }
 339         return 0;
 340 }
 341
 342 static void
 343 seljmp(Blk *b, Fn *fn)
 344 {
 345         Ref r;
 346         int c, k;
 347         Ins *fi;
 348         Tmp *t;
 349
 350         if (b->jmp.type == Jret0 || b->jmp.type == Jjmp)
 351                 return;
 352         assert(b->jmp.type == Jjnz);
 353         r = b->jmp.arg;
 354         t = &fn->tmp[r.val];
 355         b->jmp.arg = R;
 356         assert(!req(r, R) && rtype(r) != RCon);
 357         if (b->s1 == b->s2) {
 358                 chuse(r, -1, fn);
 359                 b->jmp.type = Jjmp;
 360                 b->s2 = 0;
 361                 return;
 362         }
 363         fi = flagi(b->ins, &b->ins[b->nins]);
 364         if (!fi || !req(fi->to, r)) {
 365                 selcmp((Ref[2]){r, CON_Z}, Kw, fn); /* todo, long jnz */
 366                 b->jmp.type = Jjf + Cine;
 367         }
 368         else if (iscmp(fi->op, &k, &c)) {
 369                 if (t->nuse == 1) {
 370                         if (selcmp(fi->arg, k, fn))
 371                                 c = cmpop(c);
 372                         *fi = (Ins){.op = Onop};
 373                 }
 374                 b->jmp.type = Jjf + c;
 375         }
 376         else if (fi->op == Oand && t->nuse == 1
 377              && (rtype(fi->arg[0]) == RTmp ||
 378                  rtype(fi->arg[1]) == RTmp)) {
 379                 fi->op = Oxtest;
 380                 fi->to = R;
 381                 b->jmp.type = Jjf + Cine;
 382                 if (rtype(fi->arg[1]) == RCon) {
 383                         r = fi->arg[1];
 384                         fi->arg[1] = fi->arg[0];
 385                         fi->arg[0] = r;
 386                 }
 387         }
 388         else {
 389                 /* since flags are not tracked in liveness,
 390                  * the result of the flag-setting instruction
 391                  * has to be marked as live
 392                  */
 393                 if (t->nuse == 1)
 394                         emit(Ocopy, Kw, R, r, R);
 395                 b->jmp.type = Jjf + Cine;
 396         }
 397 }
 398
 399 static int
 400 aref(Ref r, ANum *ai)
 401 {
 402         switch (rtype(r)) {
 403         case RCon:
 404                 return 2;
 405         case RTmp:
 406                 return ai[r.val].n;
 407         default:
 408                 die("constant or temporary expected");
 409         }
 410 }
 411
 412 static int
 413 ascale(Ref r, Con *con)
 414 {
 415         int64_t n;
 416
 417         if (rtype(r) != RCon)
 418                 return 0;
 419         if (con[r.val].type != CBits)
 420                 return 0;
 421         n = con[r.val].bits.i;
 422         return n == 1 || n == 2 || n == 4 || n == 8;
 423 }
 424
 425 static void
 426 anumber(ANum *ai, Blk *b, Con *con)
 427 {
 428         /* This should be made obsolete by a proper
 429          * reassoc pass.
 430          *
 431          * Rules:
 432          *
 433          *   RTmp(_) -> 0    tmp
 434          *   ( RTmp(_) -> 1    slot )
 435          *   RCon(_) -> 2    con
 436          *   0 * 2   -> 3    s * i (when constant is 1,2,4,8)
 437          */
 438         static char add[10][10] = {
 439                 [2] [2] = 2,              /* folding */
 440                 [2] [4] = 4, [4] [2] = 4,
 441                 [2] [6] = 6, [6] [2] = 6,
 442                 [2] [7] = 7, [7] [2] = 7,
 443                 [0] [2] = 4, [2] [0] = 4, /* 4: o + b */
 444                 [0] [0] = 5,              /* 5: b + s * i */
 445                 [0] [3] = 5, [3] [0] = 5,
 446                 [2] [3] = 6, [3] [2] = 6, /* 6: o + s * i */
 447                 [2] [5] = 7, [5] [2] = 7, /* 7: o + b + s * i */
 448                 [0] [6] = 7, [6] [0] = 7,
 449                 [4] [3] = 7, [3] [4] = 7,
 450         };
 451         int a, a1, a2, n1, n2, t1, t2;
 452         Ins *i;
 453
 454         for (i=b->ins; i<&b->ins[b->nins]; i++) {
 455                 if (rtype(i->to) == RTmp)
 456                         ai[i->to.val].i = i;
 457                 if (i->op != Oadd && i->op != Omul)
 458                         continue;
 459                 a1 = aref(i->arg[0], ai);
 460                 a2 = aref(i->arg[1], ai);
 461                 t1 = a1 != 1 && a1 != 2;
 462                 t2 = a2 != 1 && a2 != 2;
 463                 if (i->op == Oadd) {
 464                         a = add[n1 = a1][n2 = a2];
 465                         if (t1 && a < add[0][a2])
 466                                 a = add[n1 = 0][n2 = a2];
 467                         if (t2 && a < add[a1][0])
 468                                 a = add[n1 = a1][n2 = 0];
 469                         if (t1 && t2 && a < add[0][0])
 470                                 a = add[n1 = 0][n2 = 0];
 471                 } else {
 472                         n1 = n2 = a = 0;
 473                         if (ascale(i->arg[0], con) && t2)
 474                                 a = 3, n1 = 2, n2 = 0;
 475                         if (t1 && ascale(i->arg[1], con))
 476                                 a = 3, n1 = 0, n2 = 2;
 477                 }
 478                 ai[i->to.val].n = a;
 479                 ai[i->to.val].l = n1;
 480                 ai[i->to.val].r = n2;
 481         }
 482 }
 483
 484 static int
 485 amatch(Addr *a, Ref r, int n, ANum *ai, Fn *fn)
 486 {
 487         Ins *i;
 488         int nl, nr, t, s;
 489         Ref al, ar;
 490
 491         if (rtype(r) == RCon) {
 492                 addcon(&a->offset, &fn->con[r.val]);
 493                 return 1;
 494         }
 495         assert(rtype(r) == RTmp);
 496         i = ai[r.val].i;
 497         nl = ai[r.val].l;
 498         nr = ai[r.val].r;
 499         if (i) {
 500                 if (nl > nr) {
 501                         al = i->arg[1];
 502                         ar = i->arg[0];
 503                         t = nl, nl = nr, nr = t;
 504                 } else {
 505                         al = i->arg[0];
 506                         ar = i->arg[1];
 507                 }
 508         }
 509         switch (n) {
 510         case 3: /* s * i */
 511                 a->index = al;
 512                 a->scale = fn->con[ar.val].bits.i;
 513                 return 0;
 514         case 5: /* b + s * i */
 515                 switch (nr) {
 516                 case 0:
 517                         if (fn->tmp[ar.val].slot != -1) {
 518                                 al = i->arg[1];
 519                                 ar = i->arg[0];
 520                         }
 521                         a->index = ar;
 522                         a->scale = 1;
 523                         break;
 524                 case 3:
 525                         amatch(a, ar, nr, ai, fn);
 526                         break;
 527                 }
 528                 r = al;
 529                 /* fall through */
 530         case 0:
 531                 s = fn->tmp[r.val].slot;
 532                 if (s != -1)
 533                         r = SLOT(s);
 534                 a->base = r;
 535                 return n || s != -1;
 536         case 2: /* constants */
 537         case 4: /* o + b */
 538         case 6: /* o + s * i */
 539         case 7: /* o + b + s * i */
 540                 amatch(a, ar, nr, ai, fn);
 541                 amatch(a, al, nl, ai, fn);
 542                 return 1;
 543         default:
 544                 die("unreachable");
 545         }
 546 }
 547
 548 /* instruction selection
 549  * requires use counts (as given by parsing)
 550  */
 551 void
 552 amd64_isel(Fn *fn)
 553 {
 554         Blk *b, **sb;
 555         Ins *i;
 556         Phi *p;
 557         uint a;
 558         int n, al;
 559         int64_t sz;
 560         ANum *ainfo;
 561
 562         /* assign slots to fast allocs */
 563         b = fn->start;
 564         /* specific to NAlign == 3 */ /* or change n=4 and sz /= 4 below */
 565         for (al=Oalloc, n=4; al<=Oalloc1; al++, n*=2)
 566                 for (i=b->ins; i<&b->ins[b->nins]; i++)
 567                         if (i->op == al) {
 568                                 if (rtype(i->arg[0]) != RCon)
 569                                         break;
 570                                 sz = fn->con[i->arg[0].val].bits.i;
 571                                 if (sz < 0 || sz >= INT_MAX-15)
 572                                         err("invalid alloc size %"PRId64, sz);
 573                                 sz = (sz + n-1) & -n;
 574                                 sz /= 4;
 575                                 fn->tmp[i->to.val].slot = fn->slot;
 576                                 fn->slot += sz;
 577                                 *i = (Ins){.op = Onop};
 578                         }
 579
 580         /* process basic blocks */
 581         n = fn->ntmp;
 582         ainfo = emalloc(n * sizeof ainfo[0]);
 583         for (b=fn->start; b; b=b->link) {
 584                 curi = &insb[NIns];
 585                 for (sb=(Blk*[3]){b->s1, b->s2, 0}; *sb; sb++)
 586                         for (p=(*sb)->phi; p; p=p->link) {
 587                                 for (a=0; p->blk[a] != b; a++)
 588                                         assert(a+1 < p->narg);
 589                                 fixarg(&p->arg[a], p->cls, -1, fn);
 590                         }
 591                 memset(ainfo, 0, n * sizeof ainfo[0]);
 592                 anumber(ainfo, b, fn->con);
 593                 seljmp(b, fn);
 594                 for (i=&b->ins[b->nins]; i!=b->ins;)
 595                         sel(*--i, ainfo, fn);
 596                 b->nins = &insb[NIns] - curi;
 597                 idup(&b->ins, curi, b->nins);
 598         }
 599         free(ainfo);
 600
 601         if (debug['I']) {
 602                 fprintf(stderr, "\n> After instruction selection:\n");
 603                 printfn(fn, stderr);
 604         }
 605 }