[Bug tree-optimization/78529] [7 Regression] gcc.c-torture/execute/builtins/strcat-chk.c failed with lto/O2

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78529

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The cmp %rax, %rax is just a missed optimization, because we manage to optimize
it only so late that nothing cleans it up afterwards.  We could optimize this
away already in GIMPLE, e.g. for SCCVN use the same VN for return value of
pass-through builtin as the corresponding argument (if we don't do that
already).
That doesn't explain the failure.