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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109960] New: [10/11/12/13/14 Regression]
 missing combining of `(a&1) != 0 || (a&2)!=0` into `(a&3)!=0`
Date: Thu, 25 May 2023 00:40:12 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109960

            Bug ID: 109960
           Summary: [10/11/12/13/14 Regression] missing combining of
                    `(a&1) !=3D 0 || (a&2)!=3D0` into `(a&3)!=3D0`
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take the following C++ code (reduced from stmt_can_terminate_bb_p):
```
static inline bool f1(unsigned *a)
{
        return (*a&1);
}
static inline bool f2(unsigned *a)
{
        return (*a&2);
}

bool f(int c, unsigned *a)
{
  if (c)
    return 0;
  return f2(a) || f1(a) ;
}
```

At -O1 we can produce:
```
        movl    $0, %eax
        testl   %edi, %edi
        jne     .L1
        testb   $3, (%rsi)
        setne   %al
.L1:
        ret
```
But at -O2 we get:
        xorl    %eax, %eax
        testl   %edi, %edi
        jne     .L1
        movl    (%rsi), %edx
        movl    %edx, %eax
        andl    $1, %eax
        andl    $2, %edx
        movl    $1, %edx
        cmovne  %edx, %eax
.L1:
        ret

Which is just so much worse.
This started in GCC 9.=