path: root/ir/optmem.c

#include "ir.h"
#include <stdlib.h> /* qsort */

static const uchar loadszcls[] = {
   [Oloads8  - Oloads8] = 1|KI32<<4, [Oloadu8  - Oloads8] = 1|KI32<<4,
   [Oloads16 - Oloads8] = 2|KI32<<4, [Oloadu16 - Oloads8] = 2|KI32<<4,
   [Oloads32 - Oloads8] = 4|KI32<<4, [Oloadu32 - Oloads8] = 4|KI32<<4,
   [Oloadi64 - Oloads8] = 8|KI64<<4,
   [Oloadf32 - Oloads8] = 4|KF32<<4,
   [Oloadf64 - Oloads8] = 8|KF64<<4,
};
static const uchar load2ext[] = {
   [Oloads8  - Oloads8] = Oexts8,  [Oloadu8  - Oloads8] = Oextu8,
   [Oloads16 - Oloads8] = Oexts16, [Oloadu16 - Oloads8] = Oextu16,
   [Oloads32 - Oloads8] = Oexts32, [Oloadu32 - Oloads8] = Oextu32,
   [Oloadi64 - Oloads8] = Ocopy,
};
#define loadsz(o) (loadszcls[(o) - Oloads8] & 0xF)
#define loadcls(o) (loadszcls[(o) - Oloads8] >> 4)
#define load2ext(o) (load2ext[(o) - Oloads8])
#define storesz(o) (1 << ((o) - Ostore8))

/* Implements algorithm in 'Simple and Efficient Construction of Static Single Assignment' (Braun et al) */

struct ssabuilder {
   imap_of(union ref *) curdefs; /* map of var to (map of block to def of var) */
   struct bitset *sealed, /* set of sealed blocks */
                 *marked; /* blocks marked, for 'Marker Algorithm' in the paper */
   int lastvisit;
   int nblk;
};

static union ref readvar(struct ssabuilder *, int var, enum irclass, struct block *);

static union ref
deltrivialphis(struct ssabuilder *sb, struct block *blk, union ref phiref)
{
   union ref **pcurdefs;
   int var;
   struct use *use, *uend;
   union ref *args = phitab.p[instrtab[phiref.i].l.i];
   union ref same = {0};

   assert(instrtab[phiref.i].op == Ophi);

   for (int i = 0; i < blk->npred; ++i) {
      if (args[i].bits == same.bits || args[i].bits == phiref.bits) {
         continue; /* unique value or self-reference */
      } if (same.bits != 0) {
         return phiref; /* non-trivial */
      }
      same = args[i];
   }

   if (same.bits == 0)
      same = UNDREF; /* the phi is unreachable or in the start block */

   /* replace uses */
   replcuses(phiref, same);
   imap_each(&sb->curdefs, var, pcurdefs) {
      (void)var;
      for (int i = blk->id; i < sb->nblk; ++i) {
         if ((*pcurdefs)[i].bits == phiref.bits)
            (*pcurdefs)[i] = same;
      }
   }

   /* stops infinite recursion and marks phi for removal */
   instrtab[phiref.i].op = Onop;

   /* recursively try to remove all phi users as they might have become trivial */
Redo:
   for (use = instruse[phiref.i], uend = use + instrnuse[phiref.i]; use < uend; ++use) {
      if (use->u != USERJUMP && instrtab[use->u].op == Ophi && use->u != phiref.i) {
         union ref it = mkref(RTMP, use->u);
         union ref vphi2 = deltrivialphis(sb, use->blk, it);
         if (vphi2.bits != it.bits) {
            same = vphi2;
            /* deletion happened so phiref use may have changed */
            goto Redo;
         }
      }
   }
   deluses(phiref.i);

   return same;
}

static union ref
addphiargs(struct ssabuilder *sb, int var, enum irclass cls, struct block *blk, union ref phiref)
{
   union ref *args = phitab.p[instrtab[phiref.i].l.i];
   for (int i = 0; i < blk->npred; ++i) {
      struct block *pred = blkpred(blk, i);
      args[i] = readvar(sb, var, cls, pred);
      adduse(blk, phiref.i, args[i]);
   }
   instrtab[phiref.i].r.bits = 0;
   return deltrivialphis(sb, blk, phiref);
}

static void
writevar(struct ssabuilder *sb, int var, struct block *blk, union ref val)
{
   union ref **pcurdefs;
   if (!(pcurdefs = imap_get(&sb->curdefs, var))) {
      pcurdefs = imap_set(&sb->curdefs, var, xcalloc(sb->nblk * sizeof(union ref)));
   }
   if (val.t == RTMP) assert(instrtab[val.i].op != Onop);
   (*pcurdefs)[blk->id] = val;
}

enum { RPENDINGPHI = 7 };
static union ref
readvarrec(struct ssabuilder *sb, int var, enum irclass cls, struct block *blk)
{
   union ref val;
   assert(blk->npred > 0);
   if (!bstest(sb->sealed, blk->id)) { /* unsealed block */
      /* add pending phi */
      val = insertphi(blk, cls);
      instrtab[val.i].r = mkref(RPENDINGPHI, var);
   } else if (blk->npred == 1) { /* trivial case when block has a single predecessor */
      val = readvar(sb, var, cls, blkpred(blk, 0));
   } else if (!bstest(sb->marked, blk->id)) {
      /* Marker Algorithm to optimize the common case where a control flow join doesn't
       * need a phi function for the variable: mark the block in case we recursively reach
       * it again, collect defs from predecessors, only create a phi if they differ.
       * This avoids creating temporary trivial phi functions in acyclic data flow
       */
      bsset(sb->marked, blk->id);
      for (int i = 0; i < blk->npred; ++i) {
         struct block *pred = blkpred(blk, i);
         union ref it = readvar(sb, var, cls, pred);
         if (!bstest(sb->marked, blk->id)) {
            /* recursion reached this blk again, use its phi */
            union ref **pcurdefs = imap_get(&sb->curdefs, var);
            /* must have called writevar */
            assert(*pcurdefs && (*pcurdefs)[blk->id].bits);
            return (*pcurdefs)[blk->id];
         }
         if (i == 0) val = it;
         else if (it.bits != val.bits) /* found a different definition, must add phi */
            goto AddPhi;
      }
      bsclr(sb->marked, blk->id);
   } else { /* reached block while recursing */
   AddPhi:
      val = insertphi(blk, cls);
      writevar(sb, var, blk, val);
      val = addphiargs(sb, var, cls, blk, val);
      bsclr(sb->marked, blk->id);
      return val;
   }
   writevar(sb, var, blk, val);
   return val;
}

static union ref
readvar(struct ssabuilder *sb, int var, enum irclass cls, struct block *blk)
{
   union ref **pcurdefs;
   if ((pcurdefs = imap_get(&sb->curdefs, var)) && (*pcurdefs)[blk->id].bits)
      return (*pcurdefs)[blk->id];
   if (blk->npred == 0) /* entry block, var is read before being written to */
      return UNDREF;
   return readvarrec(sb, var, cls, blk);
}

static bool
trysealrec(struct ssabuilder *sb, struct block *blk)
{
Recur:
   if (bstest(sb->sealed, blk->id)) return 1;
   if (blk->id > sb->lastvisit) return 0;
   markvisited(blk);
   for (int i = 0; i < blk->npred; ++i) {
      struct block *p = blkpred(blk, i);
      if (wasvisited(p)) continue;
      if (p->id > sb->lastvisit) return 0;
   }

   bsset(sb->sealed, blk->id);
   for (int i = 0; i < blk->phi.n; ++i) {
      struct instr *ins = &instrtab[blk->phi.p[i]];
      if (ins->r.t == RPENDINGPHI)
         addphiargs(sb, ins->r.i, ins->cls, blk, mkref(RTMP, blk->phi.p[i]));
   }
   if (blk->s1 && !blk->s2) {
      blk = blk->s1;
      goto Recur;
   } else if (blk->s1 && blk->s2) {
      trysealrec(sb, blk->s1);
      blk = blk->s2;
      goto Recur;
   }
   return 1;
}

static void
tryseal(struct ssabuilder *sb, struct block *blk)
{
   startbbvisit();
   trysealrec(sb, blk);
}

static int
blkfindins(struct block *blk, int ins)
{
   for (int i = 0; i < blk->phi.n; ++i)
      if (blk->phi.p[i] == ins) return -1;
   for (int i = 0; i < blk->ins.n; ++i)
      if (blk->ins.p[i] == ins) return i;
   assert(0 && "ins not in blk");
}

static int
cmpuse(const void *a, const void *b)
{
   const struct use *ua = a, *ub = b;
   struct block *blk = ua->blk;
   if (ua->blk != ub->blk) return ua->blk->id - ub->blk->id;
   if (ua->u == USERJUMP) return ub->u != USERJUMP;
   if (ub->u == USERJUMP) return -(ua->u != USERJUMP);
   return blkfindins(blk, ua->u) - blkfindins(blk, ub->u);
}

/* require use, blkid; keeps use */
void
mem2reg(struct function *fn)
{
   static struct bitset bsbuf[2][4];
   struct ssabuilder sb = { .nblk = fn->nblk };
   struct block *blk;

   if (fn->nblk <= 64 * arraylength(bsbuf[0])) {
      sb.sealed = bsbuf[0];
      sb.marked = bsbuf[1];
      memset(bsbuf[0], 0, BSSIZE(fn->nblk) * sizeof *bsbuf[0]);
      memset(bsbuf[1], 0, BSSIZE(fn->nblk) * sizeof *bsbuf[1]);
   } else {
      sb.sealed = xcalloc(BSSIZE(fn->nblk) * sizeof *sb.sealed);
      sb.marked = xcalloc(BSSIZE(fn->nblk) * sizeof *sb.marked);
   }

   sortrpo(fn);
   blk = fn->entry;

   do {
      for (int i = 0; i < blk->ins.n; ++i) {
         struct use *use, *uend;
         enum irclass k = 0;
         int sz = 0, ndef = 0;
         enum op ext = Ocopy;
         int var = blk->ins.p[i];
         struct instr *ins = &instrtab[var];
         
         if (!oisalloca(ins->op)) continue;
         uend = instruse[var] + instrnuse[var];
         for (use = instruse[var]; use < uend; ++use) {
            struct instr *m;
            
            if (use->u == USERJUMP) goto Next;
            m = &instrtab[use->u];
            if (oisload(m->op) && (!sz || sz == loadsz(m->op))) {
               sz = loadsz(m->op);
               k = loadcls(m->op);
               if (sz < 4) ext = load2ext(m->op);
               continue;
            }
            if (oisstore(m->op) && m->l.bits == mkref(RTMP, var).bits
            && (!sz || sz == storesz(m->op))) {
               sz = storesz(m->op);
               ++ndef;
               continue;
            }
            goto Next;
         }
         if (!ndef) /* slot is read from but never written to */
            goto Next;
         
         qsort(instruse[var], instrnuse[var], sizeof *instruse[var], cmpuse);
         for (use = instruse[var]; use < uend; ++use) {
            struct instr *m = &instrtab[use->u];

            if (oisstore(m->op)) {
               writevar(&sb, var, use->blk, m->r);
               *m = mkinstr(Onop,0,);
            } else if (oisload(m->op)) {
               union ref val = readvar(&sb, var, k = m->cls, use->blk);
               if (!val.bits) { /* var is used uninitialized */
                  /* TODO emit diagnostic */
                  /* load some garbage */
                  *m = mkinstr(kisflt(k) ? Oloadf32 + (k==KF64) : Oloads8+ilog2(sz)*2,
                               k, mkref(RREG, mctarg->bpr));
               } else {
                  adduse(use->blk, use->u, val);
                  if (isintcon(val) && ext != Ocopy) {
                     vlong x = intconval(val);
                     switch (ext) {
                     case Oexts8:  x = (schar)x; break;
                     case Oextu8:  x = (uchar)x; break;
                     case Oexts16: x = (short)x; break;
                     case Oextu16: x = (ushort)x; break;
                     case Oexts32: x = (int)x; break;
                     case Oextu32: x = (uint)x; break;
                     default: assert(0);
                     }
                     val = mkintcon(k, x);
                     ext = Ocopy;
                  }
                  *m = mkinstr(ext, k, val);
               }
            }
         }
         /* remove alloca */
         delinstr(blk, i--);
         
      Next:;
      }

      assert(sb.lastvisit == blk->id);
      ++sb.lastvisit;
      tryseal(&sb, blk);
   } while ((blk = blk->lnext) != fn->entry);

   do {
      /* remove phis marked for deletion */
      for (int i = 0; i < blk->phi.n; ++i)
         if (instrtab[blk->phi.p[i]].op == Onop)
            delphi(blk, i--);
   } while ((blk = blk->lnext) != fn->entry);

   if (sb.sealed != bsbuf[0]) {
      free(sb.sealed);
      free(sb.marked);
   }

   for (int i = 0; i < sb.curdefs.mb.N; ++i)
      if (bstest(sb.curdefs.mb.bs, i))
         free(sb.curdefs.v[i]);
   imap_free(&sb.curdefs);
   if (ccopt.dbg.m) {
      bfmt(ccopt.dbgout, "<< After mem2reg >>\n");
      irdump(fn);
   }
}


/* vim:set ts=3 sw=3 expandtab: */