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From: "spamandnoise at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/100137] [10/11 Regression] -Warray-bounds
 false positive on varying offset plus negative
Date: Mon, 19 Apr 2021 16:56:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100137

--- Comment #4 from Moritz Beutel <spamandnoise at gmail dot com> ---
Interesting. I had figured that the test case could probably be reduced
further, but I didn't try because the bug appeared so brittle. Slightly
changing seemingly unrelated details made it vanish:

-----
// line 10:
        if ( _size !=3D 0 && _data =3D=3D nullptr ) throw 42;  // bug
        //if ( _size !=3D 0 && _data =3D=3D nullptr ) throw 42;  // no bug

// line 23:
size_t string_length( char const * ptr, size_t max =3D (size_t) -1 )  // bug
size_t string_length( char const * ptr, size_t max =3D (size_t) -2 )  // no=
 bug

// line 26:
    while ( len < max && ptr[len] )  // bug
    while ( ptr[len] )  // no bug

-----

Link for experimentation: https://gcc.godbolt.org/z/af8P7v64T=