On 05/05/2014 06:11 PM, Jeff Law wrote:
Yes, this is a known issue. There's places where the costing models change the gimple we initially generate and what transformations we apply later.
Well, "known issue" is very subjective. Our developers run into this quite regularly because you get more -Wstrict-overflow warnings on ppc64 and s390x than on x86_64. The GIMPLE on x86_64 contains fewer conditional statements, so the warning does not fire.
Long term we want to push this stuff to a later point in the pipeline, but there's some disagreement over exactly how/when to do that.
Would it be feasible (for someone like me who is not really familiar with GCC internals) to move the BRANCH_COST-dependent bits of fold to an early GIMPLE pass? There's another target dependence related to function pointers which could receive similar treatment.
This wouldn't help with the -Wstrict-overflow issue that prompted my original message, but it would benefit warnings and other analyses performed on early not-fully-optimized GIMPLE.
-- Florian Weimer / Red Hat Product Security Team
