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From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/105328] New: [x86] Failure to optimize out test instruction after add Date: Thu, 21 Apr 2022 07:32:34 +0000 [thread overview] Message-ID: <bug-105328-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105328 Bug ID: 105328 Summary: [x86] Failure to optimize out test instruction after add 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 f1(); void f2(); void f3(); void g(int b, int c) { int a = b + c; if (a > 0) f1(); else if (a < 0) f2(); else f3(); } With -O3, GCC outputs this: g(int, int): add edi, esi test edi, edi jg .L5 je .L3 jmp f2() .L3: jmp f3() .L5: jmp f1() LLVM instead outputs this: g(int, int): add edi, esi jle .LBB0_1 jmp f1()@PLT # TAILCALL .LBB0_1: js .LBB0_4 jmp f3()@PLT # TAILCALL .LBB0_4: jmp f2()@PLT # TAILCALL It appears like the `test` instruction can be removed (I assume without having to change anything about which functions get called on branchless paths and things like that). I'm not completely sure about this, considering how complex x86 performance can sometimes be, but I'd think removing that instruction should be beneficial everywhere.
next reply other threads:[~2022-04-21 7:32 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-04-21 7:32 gabravier at gmail dot com [this message] 2022-11-02 22:30 ` [Bug target/105328] " pinskia at gcc dot gnu.org
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