https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123262
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2025-12-29
Component|target |middle-end
--- Comment #2 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Kang-Che Sung from comment #0)
> This is more of an optimization feature request than a bug, but I believe
> these patterns for "subtract and overflow check" are common, and GCC missing
> these could be annoying (at least to me).
There is nothing that target-dependent code can do here. Middle-end does not
detect
.SUB_OVERFLOW that would generate optimal code.
This variant is detected as .SUB_OVERFLOW:
--cut here--
unsigned foo (unsigned x, unsigned y)
{
unsigned d = x - y;
if (d > x)
return 0x123;
return d;
}
--cut here--
... but these ones are not:
--cut here--
unsigned bar (unsigned x, unsigned y)
{
unsigned d = x - y;
if (x - y > x)
return 0x123;
return d;
}
unsigned baz (unsigned x, unsigned y)
{
unsigned d = x - y;
if (x < y)
return 0x123;
return d;
}
--cut here--
Confirmed as middle-end PR.
