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From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/104376] New: Failure to optimize clz equivalent to clz Date: Fri, 04 Feb 2022 01:10:30 +0000 [thread overview] Message-ID: <bug-104376-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104376 Bug ID: 104376 Summary: Failure to optimize clz equivalent to clz Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: gabravier at gmail dot com Target Milestone: --- #include <stdint.h> uint32_t countLeadingZeros32(uint32_t x) { if (x == 0) return 32; return (31 - __builtin_clz(x)) ^ 31; } On x86, with `-mlzcnt`, GCC outputs this: countLeadingZeros32(unsigned int): mov eax, 32 test edi, edi je .L1 mov eax, 31 lzcnt edi, edi sub eax, edi xor eax, 31 .L1: ret LLVM instead outputs this: countLeadingZeros32(unsigned int): lzcnt eax, edi ret
next reply other threads:[~2022-02-04 1:10 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-02-04 1:10 gabravier at gmail dot com [this message] 2022-02-04 4:26 ` [Bug tree-optimization/104376] " pinskia at gcc dot gnu.org 2022-02-04 4:27 ` pinskia at gcc dot gnu.org 2022-02-04 7:01 ` pinskia at gcc dot gnu.org 2022-02-09 6:10 ` pinskia at gcc dot gnu.org 2022-02-09 7:40 ` pinskia at gcc dot gnu.org 2023-05-06 21:23 ` pinskia at gcc dot gnu.org 2023-10-15 18:58 ` pinskia at gcc dot gnu.org 2023-10-15 19:21 ` pinskia at gcc dot gnu.org 2023-10-24 11:17 ` cvs-commit at gcc dot gnu.org 2023-10-24 11:20 ` pinskia at gcc dot gnu.org
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