https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78529
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to prathamesh3492 from comment #5) > (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. > As I said, look at the additional sources involved, like execute/builtins/lib/chk.c, and the effect on those. > Thanks, > Prathamesh
