On Tue, 13 Feb 2018, Marc Glisse wrote: > On Tue, 13 Feb 2018, Richard Biener wrote: > > > On February 13, 2018 6:51:29 PM GMT+01:00, Jakub Jelinek <ja...@redhat.com> > > wrote: > > > Hi! > > > > > > On the following testcase, we recurse infinitely, because > > > we have float re-association enabled, but also rounding-math, so > > > we try to optimize (cst1 + cst2) + cst3 as (cst2 + cst3) + cst1 > > > but (cst2 + cst3) doesn't simplify and we try again and optimize > > > it as (cst3 + cst1) + cst2 and then (cst1 + cst2) + cst3 and so on > > > forever. If @0 is not a CONSTANT_CLASS_P, there is not a problem, > > > if it is, the code just checks if we can actually simplify the > > > operation between cst2 and cst3 into a constant. > > > > Is there a reason to try simplifying at all for constant @0? > > Yes. cst2+cst3 might simplify (the operation happens to be exact and not > require rounding), which leaves us with only one addition instead of 2. > > On the other hand, mixing -frounding-math with reassociation seems strange to > me, and likely not worth optimizing for.
./cc1 -quiet t.c -O -frounding-math -fassociative-math cc1: warning: -fassociative-math disabled; other options take precedence So _maybe_ we should disable these patterns for !flag_associative_math when dealing with FP? Richard.
