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Re: RFC: Improving GCC8 default option settings
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
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