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?