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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/111762] New: `(a | 3) ^ 1` and `(a & ~1) | 2` should produce the same code Date: Tue, 10 Oct 2023 19:25:22 +0000 [thread overview] Message-ID: <bug-111762-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111762 Bug ID: 111762 Summary: `(a | 3) ^ 1` and `(a & ~1) | 2` should produce the same code Product: gcc Version: 14.0 Status: UNCONFIRMED Keywords: internal-improvement Severity: enhancement Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: pinskia at gcc dot gnu.org Target Milestone: --- Take: ``` int f(int in) { in = in | 3; in = in ^ 1; return in; } int f1(int in) { in = (in & ~(unsigned long)1); in = in | 2; return in; } ``` These 2 functions produce the same result but the code generated is different. I noticed this while writing the patch for PR 111282 and noticing that `gcc.dg/tree-ssa/and-1.c` testcase now fails (test needs to be fixed). LLVM/clang looks like canonicalizes to f1. I suspect xor is harder to optimize when dealing with reassociation so doing f1 is better.
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