https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78529
--- Comment #5 from prathamesh3492 at gcc dot gnu.org --- (In reply to Jakub Jelinek from comment #4) > 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. Hmm yes, but I don't understand why should this patch cause the test to fail. The patch makes following two separate changes: a) to make gimple_stmt_nonzero_warnv_p (stmt) return true, if stmt is function-call, and the function returns one of it's argument and that argument is non-null. However this change doesn't make any difference to the .evrp (and .optimized) dumps for strcat-chk.c because the patch expects SSA_VAR_P (arg) to be true, and the argument is MEM_REF. b) The other change was to modify attribute of string builtins like STRCAT, STRNCAT, etc. from ATTR_NOTHROW_NONNULL_LEAF to ATTR_RET1_NOTHROW_NONNULL_LEAF, which resulted in above code-gen difference, but as you mention it's a missed optimization and not incorrect. I would be grateful for suggestions on how to proceed. Thanks, Prathamesh
