On Tue, 18 Nov 2014, Jeff Law wrote: > On 11/18/14 09:57, Tom de Vries wrote: > > Richard, > > > > this (trunk) patch fixes PR62167. > > > > The patch fixes a problem that triggers with the test-case on the 4.8 > > branch, when tail-merge makes a dead type-unsafe load alive. > > > > I'm not able to reproduce this bug on 4.9 and trunk with the same > > test-case. On those branches, the tail-merge already does not happen. > > > > The reason for the difference is as follows: With 4.8 the two phi > > arguments of the phi in the tail block are value-numbered identically: > > ... > > SCC consists of: p_14 > > Value numbering p_14 stmt = p_14 = MEM[(struct head *)_13].first; > > Setting value number of p_14 to p_14 (changed) > > > > SCC consists of: p_15 > > Value numbering p_15 stmt = p_15 = _13->next; > > Setting value number of p_15 to p_14 (changed) > > ... > > > > With 4.9 (and trunk), that's not the case: > > ... > > SCC consists of: p_14 > > Value numbering p_14 stmt = p_14 = MEM[(struct head *)&heads][k.1_9].first; > > Setting value number of p_14 to p_14 (changed) > > > > SCC consists of: p_15 > > Value numbering p_15 stmt = p_15 = _13->next; > > Setting value number of p_15 to p_15 (changed) > > ... > > > > I'm not sure the bug triggers on trunk and 4.9, but I see no reason why > > it could not trigger, so I'd prefer to apply the patch to 4.9 and trunk > > as well. > > > > The patch introduces an xfail for pr51879-12.c. I can follow up with a > > patch to improve upon that, but I think that's better limited to trunk > > only. > > > > Bootstrapped and reg-tested on x86_64/trunk. > So instead of simply disabling for anything with virtual operands, shouldn't > instead we be comparing the virtual operands and alias information? Seems to > me that if we did that properly, this would "just work". Right?
But that would simply use operand_equal_p () .... Richard.
