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* [Bug target/100874] New: [12 Regression] slight missed optimization with min<a,CST>-CST on aarch64
@ 2021-06-02  9:32 pinskia at gcc dot gnu.org
  2021-06-02  9:33 ` [Bug target/100874] " pinskia at gcc dot gnu.org
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-06-02  9:32 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100874

            Bug ID: 100874
           Summary: [12 Regression] slight missed optimization with
                    min<a,CST>-CST on aarch64
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64-*-*

Take:
int f(int a) { return a < 4 ? a - 4 : 0; }
int f1(int a) { int x = a - 4; if (a < 4) return x; return 0; }
int f2(int a) { int t = a < 4 ? a : 4; return t - 4; }

In GCC 11, we produce:
f(int):
        mov     w1, 4
        cmp     w0, w1
        csel    w0, w0, w1, le
        sub     w0, w0, #4
        ret
f1(int):
        subs    w0, w0, 4
        csel    w0, w0, wzr, lt
        ret
f2(int):
        mov     w1, 4
        cmp     w0, w1
        csel    w0, w0, w1, le
        sub     w0, w0, #4
        ret

On the trunk all three give the same code gen (due to PHI-OPT being improved)
but of what f and f2 used to give.
All three should produce what f1 had produed instead.
This is gcc.target/aarch64/subs_compare_2.c

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2022-02-15 18:15 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-06-02  9:32 [Bug target/100874] New: [12 Regression] slight missed optimization with min<a,CST>-CST on aarch64 pinskia at gcc dot gnu.org
2021-06-02  9:33 ` [Bug target/100874] " pinskia at gcc dot gnu.org
2021-06-02  9:35 ` pinskia at gcc dot gnu.org
2021-06-02  9:39 ` pinskia at gcc dot gnu.org
2022-02-15 18:10 ` [Bug target/100874] [12 Regression] slight missed optimization with min<a,CST>-CST on aarch64 (subs_compare_2.c) cvs-commit at gcc dot gnu.org
2022-02-15 18:15 ` rsandifo at gcc dot gnu.org

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