[llvm-bugs] [Bug 28833] strlen (s) == 0 not folded when return type is casted to unsigned

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28833

David Majnemer <david.majnemer at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |david.majnemer at gmail.com
         Resolution|---                         |INVALID

--- Comment #1 from David Majnemer <david.majnemer at gmail.com> ---
It is not correct to transform ((unsigned)__builtin_strlen(s)) == 0 into *s ==
0.

The unsigned cast is masking out the high half of the strlen result.

For example, if __builtin_strlen comes out to 1ULL << 32 then
(unsigned)__builtin_strlen is zero but *s isn't 0.

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