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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/97690] New: (cond ? 2 : 0) is not optimized to int(cond) << 1 Date: Tue, 03 Nov 2020 10:28:49 +0000 [thread overview] Message-ID: <bug-97690-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97690 Bug ID: 97690 Summary: (cond ? 2 : 0) is not optimized to int(cond) << 1 Product: gcc Version: 11.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: redi at gcc dot gnu.org Target Milestone: --- enum E { init=0, active=1, done=2 }; int f(bool d) { return d ? done : init; } int g(bool d) { return int(d) << 1; } The first function is more readable and less fragile (in case the order of bits is changed) but GCC produces larger code for it. For x86_64 with -O3: f(bool): xor eax, eax test dil, dil setne al add eax, eax ret g(bool): movzx eax, dil add eax, eax ret And for x86_64 -Os: f(bool): neg dil sbb eax, eax and eax, 2 ret g(bool): movzx eax, dil add eax, eax ret Clang produces the same code for both functions at all optimization levels: f(bool): # @f(bool) lea eax, [rdi + rdi] ret g(bool): # @g(bool) lea eax, [rdi + rdi] ret
next reply other threads:[~2020-11-03 10:28 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-11-03 10:28 redi at gcc dot gnu.org [this message] 2020-11-03 10:30 ` [Bug tree-optimization/97690] " redi at gcc dot gnu.org 2020-11-03 10:37 ` redi at gcc dot gnu.org 2020-11-03 12:55 ` rguenth at gcc dot gnu.org 2020-11-03 17:32 ` jakub at gcc dot gnu.org 2020-11-04 11:15 ` cvs-commit at gcc dot gnu.org 2021-05-24 7:12 ` pinskia at gcc dot gnu.org 2021-06-01 20:50 ` pinskia at gcc dot gnu.org
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