[Bug tree-optimization/96758] [10/11 Regression] strncmp miscompiles as memcmp since r10-3920-g27c14dbc6b01d5b7

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96758

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-08-24
      Known to work|                            |9.3.0
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org,
                   |                            |msebor at gcc dot gnu.org
     Ever confirmed|0                           |1
           Keywords|                            |wrong-code
            Summary|strncmp miscompiles as      |[10/11 Regression] strncmp
                   |memcmp                      |miscompiles as memcmp since
                   |                            |r10-3920-g27c14dbc6b01d5b7
      Known to fail|                            |10.2.0, 11.0
             Status|UNCONFIRMED                 |NEW
           Priority|P3                          |P1

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Thank you for the report. It really started with r10-3920-g27c14dbc6b01d5b7.

Slightly modified test-case:

$ cat pr96758.c
int main(int argc, char *argv[]) {
    const char *s = argc > 0 ? "a" : "b";
    char x[5];
    char y[5] = "a\0a";
    __builtin_memcpy(x, y, sizeof(y));
    if (__builtin_strncmp(x, s, 4) != 0)
      __builtin_abort ();
    return 0;
}