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From: "aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/103559] Can't optimize away < 0 check on sqrt
Date: Wed, 29 Mar 2023 17:46:09 +0000 [thread overview]
Message-ID: <bug-103559-4-j1bXcECw2e@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-103559-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103559
Aldy Hernandez <aldyh at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |DUPLICATE
CC| |aldyh at gcc dot gnu.org
--- Comment #5 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
(In reply to Jeremy R. from comment #0)
> For a simple invocation of sqrt, gcc inserts a < 0 check to set math errno
> if needed. E.g.
>
> float f(float x) {
> return sqrt(x);
> }
>
> Is generated as
>
> f(float):
> vxorps xmm1, xmm1, xmm1
> vucomiss xmm1, xmm0
> ja .L10
> vsqrtss xmm0, xmm0, xmm0
> ret
> .L10:
> jmp sqrtf
>
>
> Unfortunately, this check is still present when the GCC is able to prove
> that x is non-negative:
>
> float f(float x) {
> if(x < 0) [[unlikely]] {
> __builtin_unreachable();
> } else {
> return sqrt(x);
> }
> }
x could also be a NAN which I *think* the hardware sqrt won't handle, so a
better test would be:
if (x < 0.0 || __builtin_isnan(x)) [[unlikely]]
__builtin_unreachable ();
or perhaps:
if (!__builtin_isgreater(x, 0.0))
Either way, this is a subset of PR91645 so I'm closing it as a duplicate.
*** This bug has been marked as a duplicate of bug 91645 ***
next prev parent reply other threads:[~2023-03-29 17:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-04 20:58 [Bug tree-optimization/103559] New: " llvm at rifkin dot dev
2021-12-04 21:01 ` [Bug tree-optimization/103559] " pinskia at gcc dot gnu.org
2021-12-04 21:34 ` pinskia at gcc dot gnu.org
2021-12-04 21:38 ` pinskia at gcc dot gnu.org
2021-12-04 21:43 ` pinskia at gcc dot gnu.org
2021-12-05 11:38 ` vanyacpp at gmail dot com
2023-03-29 17:46 ` aldyh at gcc dot gnu.org [this message]
2023-03-29 18:34 ` llvm at rifkin dot dev
2023-03-29 18:39 ` jakub at gcc dot gnu.org
2023-03-30 10:40 ` xry111 at gcc dot gnu.org
2023-03-30 10:48 ` jakub at gcc dot gnu.org
2023-03-30 10:53 ` xry111 at gcc dot gnu.org
2023-03-30 11:41 ` jakub at gcc dot gnu.org
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