https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106902
--- Comment #21 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Alexander Monakov from comment #20) > I missed it the first time around, but placing PAREN_EXPR around the > complete expression won't work: nothing will prevent GCC from duplicating > evaluations of the sub-expressions, and then randomly forming FMAs like > here. It would just bury this class of bugs deeper. Hmm, true. > Now that we are in stage1, can we make some kind of progress here? Is there > any buy-in for: > > 1. Implementing fp-contract=on via GENERIC folding? > 2. Defaulting to fp-contract=on instead of fp-contract=fast under -std=gnu*? > 3. Enabling fp-contract=fast under -ffast-math? Sounds reasonable. Though I wouldn't use GENERIC folding but instead some folding-like code in c-family/ that for example would get invoked by genericization or via the gimplification hook? If we'd add GENERIC folding in fold-const.cc or match.pd the chance is that it will pick up FMAs "late".
