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From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/100931] New: [x86-64] Failure to optimize 2 32-bit stores converted to a 64-bit store into using movabs instead of loading from a constant Date: Sun, 06 Jun 2021 14:07:12 +0000 [thread overview] Message-ID: <bug-100931-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100931 Bug ID: 100931 Summary: [x86-64] Failure to optimize 2 32-bit stores converted to a 64-bit store into using movabs instead of loading from a constant Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: gabravier at gmail dot com Target Milestone: --- void g(int *p) { *p = 2; p[1] = 2; } void h(long long *p) { *p = 0x200000002; } g compiles to this on GCC on plenty of architectures: g(int*): mov rax, QWORD PTR .LC0[rip] mov QWORD PTR [rdi], rax ret .LC0: .long 2 .long 2 h is equivalent to g (non-withstanding aliasing) and instead compiles to this: h(long long*): movabs rax, 8589934594 mov QWORD PTR [rdi], rax ret g has been compiled differently from h since GCC 10. I'm somewhat doubtful about filing this bug actually, I personally think that h will be faster and that g is simply a regression from GCC 9, but I can't really be sure there isn't some architecture-specific reasoning to use a separate constant, especially since this transformation seems to only occur on specific architectures (generic, core2, nehalem, westmere, sandybridge, ivybridge, haswell, broadwell, znver1, znver2 and znver3)
next reply other threads:[~2021-06-06 14:07 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-06 14:07 gabravier at gmail dot com [this message] 2021-06-06 20:21 ` [Bug target/100931] " pinskia at gcc dot gnu.org 2021-06-07 3:24 ` crazylht at gmail dot com 2021-06-07 10:27 ` rguenth at gcc dot gnu.org 2021-06-07 10:40 ` gabravier at gmail dot com
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