[Bug tree-optimization/114797] New: Missed optimization : fail to merge memset with unrelated clobber

[Bug tree-optimization/114797] New: Missed optimization : fail to merge memset with unrelated clobber

[xxs_chy at outlook dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114797

            Bug ID: 114797
           Summary: Missed optimization : fail to merge memset with
                    unrelated clobber
           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/E581jvaPs

Code like:
```
void src(char* config){
    char stack[208];
    memset(stack, 0, 184);
    *config = 0;
    memset(stack + 184, 0, 8);
    use(stack);
}
```

can be transformed to

```
void tgt(char* config){
    char stack[208];
    memset(stack, 0, 192);
    *config = 0;
    use(stack);
}
```

GCC doesn't merge them even both memsets overlap:
https://godbolt.org/z/ffc6b8zqs

[Bug tree-optimization/114797] Missed optimization : fail to merge memset with unrelated clobber

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114797

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC does not even merge without an unrelated clobber yet.

*** This bug has been marked as a duplicate of bug 49872 ***

[Bug tree-optimization/114797] Missed optimization : fail to merge memset with unrelated clobber

[xxs_chy at outlook dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114797

--- Comment #2 from XChy <xxs_chy at outlook dot com> ---
It looks like for completely overlapped memset, it's merged:
https://godbolt.org/z/4r7Eqr1Ee
With clobber, that's not the case: https://godbolt.org/z/8jhaEbKqo

[Bug tree-optimization/114797] Missed optimization : fail to merge memset with unrelated clobber

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114797

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to XChy from comment #2)
> It looks like for completely overlapped memset, it's merged:
> https://godbolt.org/z/4r7Eqr1Ee
> With clobber, that's not the case: https://godbolt.org/z/8jhaEbKqo

Yes for the secondary memset that is completely overlapping can be removed.