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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/110598] [14 Regression] wrong code on llvm-14.0.6 due to memcmp being miscompiled Date: Wed, 12 Jul 2023 13:13:13 +0000 [thread overview] Message-ID: <bug-110598-4-O5Gfd55xSs@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-110598-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110598 --- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>: https://gcc.gnu.org/g:d2c18b4a16f9e1a6ed271ec1efaf94533d1c4a94 commit r14-2465-gd2c18b4a16f9e1a6ed271ec1efaf94533d1c4a94 Author: Roger Sayle <roger@nextmovesoftware.com> Date: Wed Jul 12 14:12:34 2023 +0100 PR target/110598: Fix rega = 0; rega ^= rega regression in i386.md This patch fixes the regression PR target/110598 caused by my recent addition of a peephole2. The intention of that optimization was to simplify zeroing a register, followed by an IOR, XOR or PLUS operation on it into a move, or as described in the comment: ;; Peephole2 rega = 0; rega op= regb into rega = regb. The issue is that I'd failed to consider the (rare and unusual) case, where regb is rega, where the transformation leads to the incorrect "rega = rega", when it should be "rega = 0". The minimal fix is to add a !reg_mentioned_p check to the recent peephole2. In addition to resolving the regression, I've added a second peephole2 to optimize the problematic case above, which contains a false dependency and is therefore tricky to optimize elsewhere. This is an improvement over GCC 13, for example, that generates the redundant: xorl %edx, %edx xorq %rdx, %rdx 2023-07-12 Roger Sayle <roger@nextmovesoftware.com> gcc/ChangeLog PR target/110598 * config/i386/i386.md (peephole2): Check !reg_mentioned_p when optimizing rega = 0; rega op= regb for op in [XOR,IOR,PLUS]. (peephole2): Simplify rega = 0; rega op= rega cases. gcc/testsuite/ChangeLog PR target/110598 * gcc.target/i386/pr110598.c: New test case.
next prev parent reply other threads:[~2023-07-12 13:13 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-07-08 17:00 [Bug c++/110598] New: [14 Regression] wrong code on llvm-14.0.6 slyfox at gcc dot gnu.org 2023-07-08 17:32 ` [Bug target/110598] [14 Regression] wrong code on llvm-14.0.6 due to memcmp being miscompiled pinskia at gcc dot gnu.org 2023-07-08 17:41 ` pinskia at gcc dot gnu.org 2023-07-08 20:31 ` slyfox at gcc dot gnu.org 2023-07-09 22:34 ` roger at nextmovesoftware dot com 2023-07-12 13:13 ` cvs-commit at gcc dot gnu.org [this message] 2023-07-12 16:15 ` slyfox at gcc dot gnu.org 2023-07-12 19:42 ` roger at nextmovesoftware dot com
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