On Sat, 2022-02-05 at 08:21 +0100, Richard Biener via Gcc-patches wrote:
>
>
> > Am 05.02.2022 um 00:08 schrieb Jakub Jelinek via Gcc-patches
> > <gcc-patches@gcc.gnu.org>:
> >
> > Hi!
> >
> > The recent PR95115 change to punt in const_binop on folding operation
> > with non-NaN operands into NaN if flag_trapping_math broke the following
> > testcase, because the x * 0.0 simplification punts just if
> > x maybe a NaN (because NaN * 0.0 is NaN not 0.0) or if one of the operands
> > could be negative zero. But Inf * 0.0 or -Inf * 0.0 is also NaN, not
> > 0.0, so when NaNs are honored we need to punt for possible infinities too.
Sorry for the trouble, but some warning here: even with this patch
applied, Python would still need to replace inf * 0.0 with nan("") or
something. Now with folding for inf * 0.0 disabled, the multiplication
will be evaluated at runtime and raise FE_INVALID, which is likely
unwanted by Python. However, raising FE_INVALID is the correct behavior
no matter if we like or dislike it...
> > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk
> > and 11/10 where the PR95115 change has been unfortunately backported to
> > as well?
As there may be many packages (unfortunately) using the nasty "inf *
0.0" pattern to get NaN, maybe we should just revert the PR95115 change
for 11/10, apply PR104389 patch for trunk, and announce the behavior
change in gcc-12/changes.html?
--
Xi Ruoyao <xry...@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University
