Re: Update x86 ulps for GCC 7 [committed]

Re: Update x86 ulps for GCC 7 [committed]

[Joseph Myers]

On Fri, 8 Sep 2017, Joseph Myers wrote:

> On Mon, 26 Jun 2017, Markus Trippelsdorf wrote:
> 
> > On 2017.06.26 at 10:43 +0000, Joseph Myers wrote:
> > > On Sat, 24 Jun 2017, Markus Trippelsdorf wrote:
> > > 
> > > > On 2017.06.23 at 20:23 +0000, Joseph Myers wrote:
> > > > > Testing with GCC 7 for 32-bit x86 showed some ulps differences,
> > > > > presumably from variation in when values with excess precision get
> > > > > spilled to the stack and so lose that precision.  This patch updates
> > > > > the libm-test-ulps files accordingly.
> > > > 
> > > > For AMD Ryzen x86_64 I need an additional update:
> > > 
> > > Such updates should generally just be committed.  In this case (x86_64, 
> > > not long double) I'm not clear why you'd have ulps variation between 
> > > processors, since excess precision is irrelevant on x86_64 and the x87 
> > > transcendental instructions would only be used for long double.  But it 
> > > could be an fma issue, if $CC $CFLAGS defaults to generating fma 
> > > instructions, as that can cause ulps variation across architectures.
> > 
> > Yes, it should be an fma issue because I used "march=native" (which
> > turns on -mfma).
> > I don't have write access, so it would be nice if somebody could commit
> > the patch for me.
> 
> Now committed.

And also merged to 2.26 branch.

-- 
Joseph S. Myers
joseph@codesourcery.com