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, *m;
  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         else if (rtype(r0) == RMem) {
 114                 /* eliminate memory operands of
 115                  * the form $foo(%rip, ...)
 116                  */
 117                 m = &fn->mem[r0.val];
 118                 if (req(m->base, R))
 119                 if (m->offset.type == CAddr) {
 120                         n = fn->ncon;
 121                         vgrow(&fn->con, ++fn->ncon);
 122                         fn->con[n] = m->offset;
 123                         m->offset.type = CUndef;
 124                         r0 = newtmp("isel", Kl, fn);
 125                         emit(Oaddr, Kl, r0, CON(n), R);
 126                         m->base = r0;
 127                 }
 128         }
 129         *r = r1;
 130 }
 131
 132 static void
 133 seladdr(Ref *r, ANum *an, Fn *fn)
 134 {
 135         Addr a;
 136         Ref r0;
 137
 138         r0 = *r;
 139         if (rtype(r0) == RTmp) {
 140                 memset(&a, 0, sizeof a);
 141                 if (!amatch(&a, r0, an[r0.val].n, an, fn))
 142                         return;
 143                 if (!req(a.base, R))
 144                 if (a.offset.type == CAddr) {
 145                         /* apple as does not support
 146                          * $foo(%r0, %r1, M); try to
 147                          * rewrite it or bail out if
 148                          * impossible
 149                          */
 150                         if (!req(a.index, R))
 151                                 return;
 152                         else {
 153                                 a.index = a.base;
 154                                 a.scale = 1;
 155                                 a.base = R;
 156                         }
 157                 }
 158                 chuse(r0, -1, fn);
 159                 vgrow(&fn->mem, ++fn->nmem);
 160                 fn->mem[fn->nmem-1] = a;
 161                 chuse(a.base, +1, fn);
 162                 chuse(a.index, +1, fn);
 163                 *r = MEM(fn->nmem-1);
 164         }
 165 }
 166
 167 static int
 168 selcmp(Ref arg[2], int k, Fn *fn)
 169 {
 170         int swap;
 171         Ref r, *iarg;
 172
 173         swap = rtype(arg[0]) == RCon;
 174         if (swap) {
 175                 r = arg[1];
 176                 arg[1] = arg[0];
 177                 arg[0] = r;
 178         }
 179         emit(Oxcmp, k, R, arg[1], arg[0]);
 180         iarg = curi->arg;
 181         if (rtype(arg[0]) == RCon) {
 182                 assert(k == Kl);
 183                 iarg[1] = newtmp("isel", k, fn);
 184                 emit(Ocopy, k, iarg[1], arg[0], R);
 185         }
 186         fixarg(&iarg[0], k, Oxcmp, fn);
 187         fixarg(&iarg[1], k, Oxcmp, fn);
 188         return swap;
 189 }
 190
 191 static void
 192 sel(Ins i, ANum *an, Fn *fn)
 193 {
 194         Ref r0, r1, *iarg;
 195         int x, k, kc;
 196         int64_t sz;
 197         Ins *i0, *i1;
 198
 199         if (rtype(i.to) == RTmp)
 200         if (!isreg(i.to) && !isreg(i.arg[0]) && !isreg(i.arg[1]))
 201         if (fn->tmp[i.to.val].nuse == 0) {
 202                 chuse(i.arg[0], -1, fn);
 203                 chuse(i.arg[1], -1, fn);
 204                 return;
 205         }
 206         i0 = curi;
 207         k = i.cls;
 208         switch (i.op) {
 209         case Odiv:
 210         case Orem:
 211         case Oudiv:
 212         case Ourem:
 213                 if (KBASE(k) == 1)
 214                         goto Emit;
 215                 if (i.op == Odiv || i.op == Oudiv)
 216                         r0 = TMP(RAX), r1 = TMP(RDX);
 217                 else
 218                         r0 = TMP(RDX), r1 = TMP(RAX);
 219                 emit(Ocopy, k, i.to, r0, R);
 220                 emit(Ocopy, k, R, r1, R);
 221                 if (rtype(i.arg[1]) == RCon) {
 222                         /* immediates not allowed for
 223                          * divisions in x86
 224                          */
 225                         r0 = newtmp("isel", k, fn);
 226                 } else
 227                         r0 = i.arg[1];
 228                 if (fn->tmp[r0.val].slot != -1)
 229                         err("unlikely argument %%%s in %s",
 230                                 fn->tmp[r0.val].name, optab[i.op].name);
 231                 if (i.op == Odiv || i.op == Orem) {
 232                         emit(Oxidiv, k, R, r0, R);
 233                         emit(Osign, k, TMP(RDX), TMP(RAX), R);
 234                 } else {
 235                         emit(Oxdiv, k, R, r0, R);
 236                         emit(Ocopy, k, TMP(RDX), CON_Z, R);
 237                 }
 238                 emit(Ocopy, k, TMP(RAX), i.arg[0], R);
 239                 fixarg(&curi->arg[0], k, Ocopy, fn);
 240                 if (rtype(i.arg[1]) == RCon)
 241                         emit(Ocopy, k, r0, i.arg[1], R);
 242                 break;
 243         case Osar:
 244         case Oshr:
 245         case Oshl:
 246                 if (rtype(i.arg[1]) == RCon)
 247                         goto Emit;
 248                 r0 = i.arg[1];
 249                 i.arg[1] = TMP(RCX);
 250                 emit(Ocopy, Kw, R, TMP(RCX), R);
 251                 emiti(i);
 252                 emit(Ocopy, Kw, TMP(RCX), r0, R);
 253                 break;
 254         case Onop:
 255                 break;
 256         case Ostored:
 257         case Ostores:
 258         case Ostorel:
 259         case Ostorew:
 260         case Ostoreh:
 261         case Ostoreb:
 262                 if (rtype(i.arg[0]) == RCon) {
 263                         if (i.op == Ostored)
 264                                 i.op = Ostorel;
 265                         if (i.op == Ostores)
 266                                 i.op = Ostorew;
 267                 }
 268                 seladdr(&i.arg[1], an, fn);
 269                 goto Emit;
 270         case_Oload:
 271                 seladdr(&i.arg[0], an, fn);
 272                 goto Emit;
 273         case Ocall:
 274         case Osalloc:
 275         case Ocopy:
 276         case Oadd:
 277         case Osub:
 278         case Omul:
 279         case Oand:
 280         case Oor:
 281         case Oxor:
 282         case Oxtest:
 283         case Ostosi:
 284         case Odtosi:
 285         case Oswtof:
 286         case Osltof:
 287         case Oexts:
 288         case Otruncd:
 289         case Ocast:
 290         case_OExt:
 291 Emit:
 292                 emiti(i);
 293                 iarg = curi->arg; /* fixarg() can change curi */
 294                 fixarg(&iarg[0], argcls(&i, 0), i.op, fn);
 295                 fixarg(&iarg[1], argcls(&i, 1), i.op, fn);
 296                 break;
 297         case Oalloc:
 298         case Oalloc+1:
 299         case Oalloc+2: /* == Oalloc1 */
 300                 /* we need to make sure
 301                  * the stack remains aligned
 302                  * (rsp = 0) mod 16
 303                  */
 304                 fn->dynalloc = 1;
 305                 if (rtype(i.arg[0]) == RCon) {
 306                         sz = fn->con[i.arg[0].val].bits.i;
 307                         if (sz < 0 || sz >= INT_MAX-15)
 308                                 err("invalid alloc size %"PRId64, sz);
 309                         sz = (sz + 15)  & -16;
 310                         emit(Osalloc, Kl, i.to, getcon(sz, fn), R);
 311                 } else {
 312                         /* r0 = (i.arg[0] + 15) & -16 */
 313                         r0 = newtmp("isel", Kl, fn);
 314                         r1 = newtmp("isel", Kl, fn);
 315                         emit(Osalloc, Kl, i.to, r0, R);
 316                         emit(Oand, Kl, r0, r1, getcon(-16, fn));
 317                         emit(Oadd, Kl, r1, i.arg[0], getcon(15, fn));
 318                         if (fn->tmp[i.arg[0].val].slot != -1)
 319                                 err("unlikely argument %%%s in %s",
 320                                         fn->tmp[i.arg[0].val].name, optab[i.op].name);
 321                 }
 322                 break;
 323         default:
 324                 if (isext(i.op))
 325                         goto case_OExt;
 326                 if (isload(i.op))
 327                         goto case_Oload;
 328                 if (iscmp(i.op, &kc, &x)) {
 329                         emit(Oflag+x, k, i.to, R, R);
 330                         i1 = curi;
 331                         if (selcmp(i.arg, kc, fn))
 332                                 i1->op = Oflag + cmpop(x);
 333                         break;
 334                 }
 335                 die("unknown instruction %s", optab[i.op].name);
 336         }
 337
 338         while (i0 > curi && --i0) {
 339                 assert(rslot(i0->arg[0], fn) == -1);
 340                 assert(rslot(i0->arg[1], fn) == -1);
 341         }
 342 }
 343
 344 static Ins *
 345 flagi(Ins *i0, Ins *i)
 346 {
 347         while (i>i0) {
 348                 i--;
 349                 if (amd64_op[i->op].zflag)
 350                         return i;
 351                 if (amd64_op[i->op].lflag)
 352                         continue;
 353                 return 0;
 354         }
 355         return 0;
 356 }
 357
 358 static void
 359 seljmp(Blk *b, Fn *fn)
 360 {
 361         Ref r;
 362         int c, k;
 363         Ins *fi;
 364         Tmp *t;
 365
 366         if (b->jmp.type == Jret0 || b->jmp.type == Jjmp)
 367                 return;
 368         assert(b->jmp.type == Jjnz);
 369         r = b->jmp.arg;
 370         t = &fn->tmp[r.val];
 371         b->jmp.arg = R;
 372         assert(!req(r, R) && rtype(r) != RCon);
 373         if (b->s1 == b->s2) {
 374                 chuse(r, -1, fn);
 375                 b->jmp.type = Jjmp;
 376                 b->s2 = 0;
 377                 return;
 378         }
 379         fi = flagi(b->ins, &b->ins[b->nins]);
 380         if (!fi || !req(fi->to, r)) {
 381                 selcmp((Ref[2]){r, CON_Z}, Kw, fn); /* todo, long jnz */
 382                 b->jmp.type = Jjf + Cine;
 383         }
 384         else if (iscmp(fi->op, &k, &c)) {
 385                 if (t->nuse == 1) {
 386                         if (selcmp(fi->arg, k, fn))
 387                                 c = cmpop(c);
 388                         *fi = (Ins){.op = Onop};
 389                 }
 390                 b->jmp.type = Jjf + c;
 391         }
 392         else if (fi->op == Oand && t->nuse == 1
 393              && (rtype(fi->arg[0]) == RTmp ||
 394                  rtype(fi->arg[1]) == RTmp)) {
 395                 fi->op = Oxtest;
 396                 fi->to = R;
 397                 b->jmp.type = Jjf + Cine;
 398                 if (rtype(fi->arg[1]) == RCon) {
 399                         r = fi->arg[1];
 400                         fi->arg[1] = fi->arg[0];
 401                         fi->arg[0] = r;
 402                 }
 403         }
 404         else {
 405                 /* since flags are not tracked in liveness,
 406                  * the result of the flag-setting instruction
 407                  * has to be marked as live
 408                  */
 409                 if (t->nuse == 1)
 410                         emit(Ocopy, Kw, R, r, R);
 411                 b->jmp.type = Jjf + Cine;
 412         }
 413 }
 414
 415 static int
 416 aref(Ref r, ANum *ai)
 417 {
 418         switch (rtype(r)) {
 419         case RCon:
 420                 return 2;
 421         case RTmp:
 422                 return ai[r.val].n;
 423         default:
 424                 die("constant or temporary expected");
 425         }
 426 }
 427
 428 static int
 429 ascale(Ref r, Con *con)
 430 {
 431         int64_t n;
 432
 433         if (rtype(r) != RCon)
 434                 return 0;
 435         if (con[r.val].type != CBits)
 436                 return 0;
 437         n = con[r.val].bits.i;
 438         return n == 1 || n == 2 || n == 4 || n == 8;
 439 }
 440
 441 static void
 442 anumber(ANum *ai, Blk *b, Con *con)
 443 {
 444         /* This should be made obsolete by a proper
 445          * reassoc pass.
 446          *
 447          * Rules:
 448          *
 449          *   RTmp(_) -> 0    tmp
 450          *   ( RTmp(_) -> 1    slot )
 451          *   RCon(_) -> 2    con
 452          *   0 * 2   -> 3    s * i (when constant is 1,2,4,8)
 453          */
 454         static char add[10][10] = {
 455                 [2] [2] = 2,              /* folding */
 456                 [2] [4] = 4, [4] [2] = 4,
 457                 [2] [6] = 6, [6] [2] = 6,
 458                 [2] [7] = 7, [7] [2] = 7,
 459                 [0] [2] = 4, [2] [0] = 4, /* 4: o + b */
 460                 [0] [0] = 5,              /* 5: b + s * i */
 461                 [0] [3] = 5, [3] [0] = 5,
 462                 [2] [3] = 6, [3] [2] = 6, /* 6: o + s * i */
 463                 [2] [5] = 7, [5] [2] = 7, /* 7: o + b + s * i */
 464                 [0] [6] = 7, [6] [0] = 7,
 465                 [4] [3] = 7, [3] [4] = 7,
 466         };
 467         int a, a1, a2, n1, n2, t1, t2;
 468         Ins *i;
 469
 470         for (i=b->ins; i<&b->ins[b->nins]; i++) {
 471                 if (rtype(i->to) == RTmp)
 472                         ai[i->to.val].i = i;
 473                 if (i->op != Oadd && i->op != Omul)
 474                         continue;
 475                 a1 = aref(i->arg[0], ai);
 476                 a2 = aref(i->arg[1], ai);
 477                 t1 = a1 != 1 && a1 != 2;
 478                 t2 = a2 != 1 && a2 != 2;
 479                 if (i->op == Oadd) {
 480                         a = add[n1 = a1][n2 = a2];
 481                         if (t1 && a < add[0][a2])
 482                                 a = add[n1 = 0][n2 = a2];
 483                         if (t2 && a < add[a1][0])
 484                                 a = add[n1 = a1][n2 = 0];
 485                         if (t1 && t2 && a < add[0][0])
 486                                 a = add[n1 = 0][n2 = 0];
 487                 } else {
 488                         n1 = n2 = a = 0;
 489                         if (ascale(i->arg[0], con) && t2)
 490                                 a = 3, n1 = 2, n2 = 0;
 491                         if (t1 && ascale(i->arg[1], con))
 492                                 a = 3, n1 = 0, n2 = 2;
 493                 }
 494                 ai[i->to.val].n = a;
 495                 ai[i->to.val].l = n1;
 496                 ai[i->to.val].r = n2;
 497         }
 498 }
 499
 500 static int
 501 amatch(Addr *a, Ref r, int n, ANum *ai, Fn *fn)
 502 {
 503         Ins *i;
 504         int nl, nr, t, s;
 505         Ref al, ar;
 506
 507         if (rtype(r) == RCon) {
 508                 addcon(&a->offset, &fn->con[r.val]);
 509                 return 1;
 510         }
 511         assert(rtype(r) == RTmp);
 512         i = ai[r.val].i;
 513         nl = ai[r.val].l;
 514         nr = ai[r.val].r;
 515         if (i) {
 516                 if (nl > nr) {
 517                         al = i->arg[1];
 518                         ar = i->arg[0];
 519                         t = nl, nl = nr, nr = t;
 520                 } else {
 521                         al = i->arg[0];
 522                         ar = i->arg[1];
 523                 }
 524         }
 525         switch (n) {
 526         case 3: /* s * i */
 527                 a->index = al;
 528                 a->scale = fn->con[ar.val].bits.i;
 529                 return 0;
 530         case 5: /* b + s * i */
 531                 switch (nr) {
 532                 case 0:
 533                         if (fn->tmp[ar.val].slot != -1) {
 534                                 al = i->arg[1];
 535                                 ar = i->arg[0];
 536                         }
 537                         a->index = ar;
 538                         a->scale = 1;
 539                         break;
 540                 case 3:
 541                         amatch(a, ar, nr, ai, fn);
 542                         break;
 543                 }
 544                 r = al;
 545                 /* fall through */
 546         case 0:
 547                 s = fn->tmp[r.val].slot;
 548                 if (s != -1)
 549                         r = SLOT(s);
 550                 a->base = r;
 551                 return n || s != -1;
 552         case 2: /* constants */
 553         case 4: /* o + b */
 554         case 6: /* o + s * i */
 555         case 7: /* o + b + s * i */
 556                 amatch(a, ar, nr, ai, fn);
 557                 amatch(a, al, nl, ai, fn);
 558                 return 1;
 559         default:
 560                 die("unreachable");
 561         }
 562 }
 563
 564 /* instruction selection
 565  * requires use counts (as given by parsing)
 566  */
 567 void
 568 amd64_isel(Fn *fn)
 569 {
 570         Blk *b, **sb;
 571         Ins *i;
 572         Phi *p;
 573         uint a;
 574         int n, al;
 575         int64_t sz;
 576         ANum *ainfo;
 577
 578         /* assign slots to fast allocs */
 579         b = fn->start;
 580         /* specific to NAlign == 3 */ /* or change n=4 and sz /= 4 below */
 581         for (al=Oalloc, n=4; al<=Oalloc1; al++, n*=2)
 582                 for (i=b->ins; i<&b->ins[b->nins]; i++)
 583                         if (i->op == al) {
 584                                 if (rtype(i->arg[0]) != RCon)
 585                                         break;
 586                                 sz = fn->con[i->arg[0].val].bits.i;
 587                                 if (sz < 0 || sz >= INT_MAX-15)
 588                                         err("invalid alloc size %"PRId64, sz);
 589                                 sz = (sz + n-1) & -n;
 590                                 sz /= 4;
 591                                 if (sz > INT_MAX - fn->slot)
 592                                         die("alloc too large");
 593                                 fn->tmp[i->to.val].slot = fn->slot;
 594                                 fn->slot += sz;
 595                                 *i = (Ins){.op = Onop};
 596                         }
 597
 598         /* process basic blocks */
 599         n = fn->ntmp;
 600         ainfo = emalloc(n * sizeof ainfo[0]);
 601         for (b=fn->start; b; b=b->link) {
 602                 curi = &insb[NIns];
 603                 for (sb=(Blk*[3]){b->s1, b->s2, 0}; *sb; sb++)
 604                         for (p=(*sb)->phi; p; p=p->link) {
 605                                 for (a=0; p->blk[a] != b; a++)
 606                                         assert(a+1 < p->narg);
 607                                 fixarg(&p->arg[a], p->cls, -1, fn);
 608                         }
 609                 memset(ainfo, 0, n * sizeof ainfo[0]);
 610                 anumber(ainfo, b, fn->con);
 611                 seljmp(b, fn);
 612                 for (i=&b->ins[b->nins]; i!=b->ins;)
 613                         sel(*--i, ainfo, fn);
 614                 b->nins = &insb[NIns] - curi;
 615                 idup(&b->ins, curi, b->nins);
 616         }
 617         free(ainfo);
 618
 619         if (debug['I']) {
 620                 fprintf(stderr, "\n> After instruction selection:\n");
 621                 printfn(fn, stderr);
 622         }
 623 }