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From: "bugdal at aerifal dot cx" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/107107] New: Wrong codegen from TBAA when stores to distinct same-mode types are collapsed?
Date: Fri, 30 Sep 2022 21:34:15 +0000 [thread overview]
Message-ID: <bug-107107-4@http.gcc.gnu.org/bugzilla/> (raw)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107107
Bug ID: 107107
Summary: Wrong codegen from TBAA when stores to distinct
same-mode types are collapsed?
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: bugdal at aerifal dot cx
Target Milestone: ---
Created attachment 53646
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53646&action=edit
original test case by supercat
The attached test case is from user supercat on Stack Overflow (original
source:
https://stackoverflow.com/questions/42178179/will-casting-around-sockaddr-storage-and-sockaddr-in-break-strict-aliasing/42178347?noredirect=1#comment130509588_42178347,
https://godbolt.org/z/83v4ssrn4) and demonstrates wrong TBAA apparently
assuming an object of type long long was not modified after the code path
modifying it was collapsed with a different code path performing the
modification via an lvalue of type long.
On 64-bit targets, the test program outputs 1/2 with optimization levels that
enable -fstrict-aliasing. The expected output is 2/2. Using
-fno-strict-aliasing fixes it.
I have not checked this myself, but according to others who have looked at the
test case, the regression came between GCC 4.7 and 4.8.
next reply other threads:[~2022-09-30 21:34 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-30 21:34 bugdal at aerifal dot cx [this message]
2022-10-01 2:25 ` [Bug middle-end/107107] " bugdal at aerifal dot cx
2022-10-01 2:59 ` pinskia at gcc dot gnu.org
2022-10-01 3:02 ` pinskia at gcc dot gnu.org
2022-10-01 3:05 ` [Bug tree-optimization/107107] [10/11/12/13 Regression] " pinskia at gcc dot gnu.org
2022-10-01 3:05 ` pinskia at gcc dot gnu.org
2022-10-01 17:08 ` amonakov at gcc dot gnu.org
2022-10-01 20:01 ` bugdal at aerifal dot cx
2022-10-06 9:02 ` rguenth at gcc dot gnu.org
2022-10-06 9:22 ` rguenth at gcc dot gnu.org
2022-10-06 10:07 ` cvs-commit at gcc dot gnu.org
2022-10-06 10:08 ` [Bug tree-optimization/107107] [10/11/12 " rguenth at gcc dot gnu.org
2022-10-17 13:10 ` cvs-commit at gcc dot gnu.org
2022-12-12 16:33 ` [Bug tree-optimization/107107] [10/11 " cvs-commit at gcc dot gnu.org
2023-01-26 13:05 ` [Bug tree-optimization/107107] [10 " cvs-commit at gcc dot gnu.org
2023-01-26 13:06 ` rguenth at gcc dot gnu.org
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