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From: "wschmidt at linux dot ibm.com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/95737] PPC: Unnecessary extsw after negative less than
Date: Sun, 21 Jun 2020 15:35:40 +0000 [thread overview]
Message-ID: <bug-95737-4-G8lSdjTgm3@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-95737-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95737
--- Comment #4 from wschmidt at linux dot ibm.com ---
On 6/19/20 12:43 PM, jens.seifert at de dot ibm.com wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95737
>
> Jens Seifert <jens.seifert at de dot ibm.com> changed:
>
> What |Removed |Added
> ----------------------------------------------------------------------------
> Status|RESOLVED |UNCONFIRMED
> Resolution|DUPLICATE |---
>
> --- Comment #3 from Jens Seifert <jens.seifert at de dot ibm.com> ---
> This is different as the extsw also happens if the result gets used e.g.
> followed by a andc, which is my case. I obviously oversimplified the sample. It
> has nothing to do with function result and ABI requirements. gcc assume that
> the result of -(a < b) implemented by subfc, subfe is signed 32-bit. But the
> result is already 64-bit.
>
> unsigned long long branchlesconditional(unsigned long long a, unsigned long
> long b, unsigned long long c)
> {
> unsigned long long mask = -(a < b);
> return c &~ mask;
> }
>
> results in
>
> _Z20branchlesconditionalyyy:
> .LFB1:
> .cfi_startproc
> subfc 4,4,3
> subfe 3,3,3
> not 3,3
> extsw 3,3
> and 3,3,5
> blr
>
> expected
> subfc
> subfe
> andc
>
Thanks for verifying, Jens!
next prev parent reply other threads:[~2020-06-21 15:35 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-18 8:10 [Bug target/95737] New: " jens.seifert at de dot ibm.com
2020-06-19 16:40 ` [Bug target/95737] " wschmidt at gcc dot gnu.org
2020-06-19 16:42 ` wschmidt at gcc dot gnu.org
2020-06-19 17:43 ` jens.seifert at de dot ibm.com
2020-06-21 15:35 ` wschmidt at linux dot ibm.com [this message]
2020-06-21 16:30 ` segher at gcc dot gnu.org
2022-01-06 5:39 ` guihaoc at gcc dot gnu.org
2022-01-13 12:19 ` segher at gcc dot gnu.org
2022-01-13 16:34 ` segher at gcc dot gnu.org
2022-01-14 9:16 ` guihaoc at gcc dot gnu.org
2022-05-18 5:24 ` cvs-commit at gcc dot gnu.org
2022-07-29 2:52 ` guihaoc at gcc dot gnu.org
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