commit 0db06dad63e02b619671bfb3dd25fc92c0856319
parent 674901b71834739cccf3f8665833dc125d1172b7
Author: Quentin Carbonneaux <quentin@c9x.me>
Date: Mon, 21 Nov 2022 11:29:22 +0100
recognize some phis as copies
The copy elimination pass is not
complete. This patch improves
things a bit, but I think we still
have quite a bit of incompleteness.
We now consistently mark phis with
all arguments identical as copies.
Previously, they were inconsistently
eliminated by phisimpl(). An example
where they were not eliminated is
the following:
@blk2
%a = phi @blk0 %x, @blk1 %x
jnz ?, @blk3, @blk4
@blk3
%b = copy %x
@blk4
%c = phi @blk2 %a, @blk3 %b
In this example, neither %c nor %a
were marked as copies of %x because,
when phisimpl() is called, the copy
information for %b is not available.
The incompleteness is still present
and can be observed by modifying
the example above so that %a takes
a copy of %x through a back-edge.
Then, phisimpl()'s lack of copy
information about %b will prevent
optimization.
Diffstat:
| M | copy.c | | | 21 | +++++++++++++++------ |
1 file changed, 15 insertions(+), 6 deletions(-)
diff --git a/copy.c b/copy.c
@@ -134,8 +134,8 @@ copy(Fn *fn)
Phi *p, **pp;
Ins *i;
Blk *b;
- uint n, a;
- Ref *cpy, r;
+ uint n, a, eq;
+ Ref *cpy, r, r1;
int t;
bsinit(ts, fn->ntmp);
@@ -150,13 +150,22 @@ copy(Fn *fn)
assert(rtype(p->to) == RTmp);
if (!req(cpy[p->to.val], R))
continue;
+ eq = 0;
r = R;
for (a=0; a<p->narg; a++)
- if (p->blk[a]->id < n)
- r = copyof(p->arg[a], cpy);
+ if (p->blk[a]->id < n) {
+ r1 = copyof(p->arg[a], cpy);
+ if (req(r, R) || req(r1, r))
+ eq++;
+ r = r1;
+ }
assert(!req(r, R));
- cpy[p->to.val] = p->to;
- phisimpl(p, r, cpy, &stk, ts, as, fn);
+ if (eq == p->narg)
+ cpy[p->to.val] = r;
+ else {
+ cpy[p->to.val] = p->to;
+ phisimpl(p, r, cpy, &stk, ts, as, fn);
+ }
}
for (i=b->ins; i<&b->ins[b->nins]; i++) {
assert(rtype(i->to) <= RTmp);
