https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118974
Tamar Christina <tnfchris at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2025-02-21
--- Comment #1 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Confirmed, I had submitted a patch for this a few years ago but it never got a
review/help I requested
https://patchwork.sourceware.org/project/gcc/patch/zjw6svuwbaxlp...@arm.com/
I was stuck on being able to do this in RTL because the problem is that the
sequence in gimple is
b = a > 0
if (c != 0)
break
and so the cbranch expansion doesn't always see the actual comparison being
done.
And if you try to match them up in RTL it becomes very complicated as the patch
above showed.
I've been thinking about it again, but this time I'd instead change it so that
expand gives the comparison as the operation to cbranch. This removes the
complication of trying to match an SVE and Adv. SIMD compare into one.
But this can only be done if the target supports more than 0 as the second
operand.
because e.g. MVE can do c != 0, but not b1 > b2, where they're both predicates.
Also:
cmpgt p14.s, p7/z, z28.s, #0
ptest p15, p14.b
b.none .L3
should be:
cmpgt p14.s, p7/z, z28.s, #0
b.none .L3
we don't need the ptest since we only use b.none or b.any and the size of the
predicate of the ptest is smaller than the original.
This however is a general problem with SVE codegen in GCC and not cbranch
related. The CC elimination pass needs to be expanded here, I think Richard was
playing with extending it to do this.
