On Tue, 12 Sep 2017, Alexander Monakov wrote: > > * Make -fno-trapping-math the default - another obvious one. From the docs: > > "Compile code assuming that floating-point operations cannot generate > > user-visible traps." > > There isn't a lot of code that actually uses user-visible traps (if any - > > many CPUs don't even support user traps as it's an optional IEEE > > feature). > > So assuming trapping math by default is way too conservative since there > > is > > no obvious benefit to users. > > OTOH -O options are understood to _never_ sacrifice standards compliance, with > the exception of -Ofast. I believe that's an important property to keep.
ISO C allows the FENV_ACCESS pragma to be OFF by default (we don't support the standard pragmas, but FENV_ACCESS ON is equivalent to a stricter version of -frounding-math -ftrapping-math). Thus, this is not a standards compliance issue (unlike various parts of -ffast-math that break IEEE 754 semantics even with FENV_ACCESS OFF). And since -fno-rounding-math is the default, the default is already a form of FENV_ACCESS OFF. I don't think any -O implication of -fno-trapping-math was proposed; the proposal was about the default (independent of -O options). -- Joseph S. Myers jos...@codesourcery.com
