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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/109866] New: Sometimes using sub/test instead
 just test
Date: Mon, 15 May 2023 18:44:19 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109866

            Bug ID: 109866
           Summary: Sometimes using sub/test instead just test
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
int g(void); int h(void); int t(void);
int f(int a, int b)
{
  int c =3D a - b;
  if(c =3D=3D 0)
    return g();
  if (c > 0)
    return h();
  return t();
}
```
This is reduced from bzip2 in spec 2006, though I am not so sure any more.
On x86_64 GCC produces:
```
        subl    %esi, %edi
        testl   %edi, %edi
        je      .L5
        jle     .L3
        jmp     h()
.L3:
        jmp     t()
.L5:
        jmp     g()
```
But GCC should produce (likes clang/LLVM does):
```
        cmpl    %esi, %edi
        je      .L5
        jle     .L3
        jmp     h()
.L3:
        jmp     t()
.L5:
        jmp     g()
```

Note a similar thing happens with aarch64 target too.=