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From: "goon.pri.low at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/112657] New: missed optimization: cmove not used with multiple returns Date: Tue, 21 Nov 2023 21:42:59 +0000 [thread overview] Message-ID: <bug-112657-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112657 Bug ID: 112657 Summary: missed optimization: cmove not used with multiple returns Product: gcc Version: 13.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: goon.pri.low at gmail dot com Target Milestone: --- This function int unopt(int c) { if (c == 14) return -9; else return c; } unopt: mov eax, edi cmp edi, 14 je .L4 ret .L4: mov eax, -9 ret Should probably be optimized to: int opt(int c) { if (c == 14) c = -9; return c; } opt: cmp edi, 14 mov eax, -9 cmovne eax, edi ret This seems to only really happen when negative numbers are used, int positive(int c) { if (c == 14) return 9; else return c; } positive: mov eax, edi cmp edi, 14 mov edx, 9 cmove eax, edx ret Though use of positive values still isn't completely optimized (possibly same as https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97968) Also it seems like if the order is reversed: int reverse(int c) { if (c != 14) c = 9120; return c; } reverse: cmp edi, 14 mov edx, 14 mov eax, 9120 cmove eax, edx ret We could use %edi in the cmove and eliminate the 2nd instruction.
next reply other threads:[~2023-11-21 21:42 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-11-21 21:42 goon.pri.low at gmail dot com [this message] 2023-11-21 21:53 ` [Bug target/112657] " pinskia at gcc dot gnu.org 2023-11-21 21:53 ` pinskia at gcc dot gnu.org 2023-11-21 21:59 ` [Bug rtl-optimization/112657] [13/14 Regression] " pinskia at gcc dot gnu.org 2023-11-22 9:16 ` ubizjak at gmail dot com 2023-11-22 9:28 ` ubizjak at gmail dot com 2023-11-22 9:38 ` ubizjak at gmail dot com 2023-11-22 9:46 ` ubizjak at gmail dot com 2023-11-22 10:48 ` rguenth at gcc dot gnu.org 2023-11-22 13:35 ` hubicka at gcc dot gnu.org 2024-03-07 21:01 ` law at gcc dot gnu.org 2024-05-21 9:18 ` [Bug rtl-optimization/112657] [13/14/15 " jakub at gcc dot gnu.org
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