On Fri, Nov 8, 2013 at 5:02 PM, Jeff Law <l...@redhat.com> wrote:
> On 11/08/13 07:45, Steven Bosscher wrote:
>>
>> On Fri, Nov 8, 2013 at 3:40 PM, Joern Rennecke
>> <joern.renne...@embecosm.com> wrote:
>>>
>>> bootstrapped / regtested on i686-pc-linux-gnu.
>>
>>
>> Not a very elaborate description of the patch, eh? :-)
>>
>> This is IMHO not OK without at least an explanation of why the
>> comparison of two const_ints is not folded. Better yet would be to fix
>> that underlying problem. We should not present such non-sense to the
>> RTL parts of the middle end.
> Agreed.
In this case it's fold-all-builtins folding a strlen call with a
PHI <"foo", "bar"> argument. IMHO not presenting RTL with such
non-sense is best achieved by not letting TER do constant propagation
(because it doesn't "fold" the result). We can never rule out such
stray non-propagated constants, so that makes expand more robust
(and hopes for RTL CCP).
Index: gcc/tree-ssa-ter.c
===================================================================
--- gcc/tree-ssa-ter.c (revision 204664)
+++ gcc/tree-ssa-ter.c (working copy)
@@ -438,6 +439,12 @@ ter_is_replaceable_p (gimple stmt)
&& !is_gimple_val (gimple_assign_rhs1 (stmt)))
return false;
+ /* Do not propagate "modeless" constants - we may end up
confusing the RTL
+ expanders. Leave the optimization to RTL CCP. */
+ if (gimple_assign_single_p (stmt)
+ && CONSTANT_CLASS_P (gimple_assign_rhs1 (stmt)))
+ return false;
+
return true;
}
return false;
does that make sense? I'll test it then.
Thanks,
Richard.
> jeff
>
