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

[prathamesh3492 at gcc dot gnu.org]

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

--- Comment #9 from prathamesh3492 at gcc dot gnu.org ---
(In reply to Richard Biener from comment #6)
> (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.
Hi Richard,
It seems strcat-chk.c depends on lib/chk.c and lib/main.c.
For lib/chk.c, I verified that there is no difference in .optimized dump
and slim .dfinish dump with and without patch on aarch64-none-elf.
lib/main.c just contains definitions of main() which calls main_test() and
link_error(), so didn't check that.

Thanks,
Prathamesh
> 
> > Thanks,
> > Prathamesh