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From: "xxs_chy at outlook dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114704] New: Missed optimization : eliminate
 store if the value is known in all predecessors
Date: Fri, 12 Apr 2024 14:32:53 +0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114704

            Bug ID: 114704
           Summary: Missed optimization : eliminate store if the value is
                    known in all predecessors
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xxs_chy at outlook dot com
  Target Milestone: ---

Godbolt link: https://godbolt.org/z/KEeGTM49E

For code like:
```
void src(int *p){
    if(*p =3D=3D 0)
        goto then;
    else {
        dummy();
        if(*p =3D=3D 0)
            goto then;
        else
            return;
    }

then:
    *p =3D 0; // *p is already 0, it's dead now
}

```
In then basic block, *p is known to be 0 in all predecessors, thus the store
"*p =3D 0" is redundant.=