new simplcfg pass

Useful for ifopt to match more
often. Empty blocks are fused
and conditional jumps on empty
blocks with the same successor
(and no phis in the successor)
are collapsed.
This commit is contained in:
Quentin Carbonneaux 2026-01-13 18:15:01 +01:00
parent c6336557da
commit e8365dd0a2
3 changed files with 123 additions and 0 deletions

1
all.h
View File

@ -560,6 +560,7 @@ void simpljmp(Fn *);
int reaches(Fn *, Blk *, Blk *);
int reachesnotvia(Fn *, Blk *, Blk *, Blk *);
int ifgraph(Blk *, Blk **, Blk **, Blk **);
void simplcfg(Fn *);
/* mem.c */
void promote(Fn *);

121
cfg.c
View File

@ -441,3 +441,124 @@ ifgraph(Blk *ifb, Blk **pthenb, Blk **pelseb, Blk **pjoinb)
*pjoinb = s1->s1;
return 1;
}
typedef struct Jmp Jmp;
struct Jmp {
int type;
Ref arg;
Blk *s1, *s2;
};
static int
jmpeq(Jmp *a, Jmp *b)
{
return a->type == b->type && req(a->arg, b->arg)
&& a->s1 == b->s1 && a->s2 == b->s2;
}
static int
jmpnophi(Jmp *j)
{
if (j->s1 && j->s1->phi)
return 0;
if (j->s2 && j->s2->phi)
return 0;
return 1;
}
/* require cfg rpo, breaks use */
void
simplcfg(Fn *fn)
{
Ins cpy, *i;
Blk *b, *bb, **pb;
Jmp *jmp, *j, *jj;
Phi *p;
int *empty, done;
uint n;
if (debug['C']) {
fprintf(stderr, "\n> Before CFG simplification:\n");
printfn(fn, stderr);
}
cpy = (Ins){.op = Ocopy};
for (b=fn->start; b; b=b->link)
if (b->npred == 1) {
bb = b->pred[0];
for (p=b->phi; p; p=p->link) {
cpy.cls = p->cls;
cpy.to = p->to;
cpy.arg[0] = phiarg(p, bb);
addins(&bb->ins, &bb->nins, &cpy);
}
b->phi = 0;
}
jmp = emalloc(fn->nblk * sizeof jmp[0]);
empty = emalloc(fn->nblk * sizeof empty[0]);
for (b=fn->start; b; b=b->link) {
jmp[b->id].type = b->jmp.type;
jmp[b->id].arg = b->jmp.arg;
jmp[b->id].s1 = b->s1;
jmp[b->id].s2 = b->s2;
empty[b->id] = !b->phi;
for (i=b->ins; i<&b->ins[b->nins]; i++)
if (i->op != Onop || i->op != Odbgloc) {
empty[b->id] = 0;
break;
}
}
do {
done = 1;
for (b=fn->start; b; b=b->link) {
if (b->id == -1u)
continue;
j = &jmp[b->id];
if (j->type == Jjmp && j->s1->npred == 1) {
assert(!j->s1->phi);
addbins(&b->ins, &b->nins, j->s1);
empty[b->id] &= empty[j->s1->id];
jj = &jmp[j->s1->id];
pb = (Blk*[]){jj->s1, jj->s2, 0};
for (; (bb=*pb); pb++)
for (p=bb->phi; p; p=p->link) {
n = phiargn(p, j->s1);
p->blk[n] = b;
}
j->s1->id = -1u;
*j = *jj;
done = 0;
}
else if (j->type == Jjnz
&& empty[j->s1->id] && empty[j->s2->id]
&& jmpeq(&jmp[j->s1->id], &jmp[j->s2->id])
&& jmpnophi(&jmp[j->s1->id])) {
*j = jmp[j->s1->id];
done = 0;
}
}
} while (!done);
for (b=fn->start; b; b=b->link)
if (b->id != -1u) {
j = &jmp[b->id];
b->jmp.type = j->type;
b->jmp.arg = j->arg;
b->s1 = j->s1;
b->s2 = j->s2;
assert(!j->s1 || j->s1->id != -1u);
assert(!j->s2 || j->s2->id != -1u);
}
fillcfg(fn);
free(empty);
free(jmp);
if (debug['C']) {
fprintf(stderr, "\n> After CFG simplification:\n");
printfn(fn, stderr);
}
}

1
main.c
View File

@ -77,6 +77,7 @@ func(Fn *fn)
ssacheck(fn);
gvn(fn);
fillcfg(fn);
simplcfg(fn);
filluse(fn);
filldom(fn);
gcm(fn);