On Mon, 18 Sep 2023, Alexander Monakov wrote:
>
> On Mon, 18 Sep 2023, Florian Weimer wrote:
>
> > Okay, you meant “changing the result” as in “changing the result in a
> > permitted way”. Sorry, was confused. So this is a bad example all
> > around. Are there better ones (that don't involve
On Mon, 18 Sep 2023, Florian Weimer wrote:
> Okay, you meant “changing the result” as in “changing the result in a
> permitted way”. Sorry, was confused. So this is a bad example all
> around. Are there better ones (that don't involve FMA)?
If you're looking for something similar to your ori
* Alexander Monakov:
>> > Contracting 'x + x - x' to fma(x, 2, -x) would be fine.
>>
>> It still changes the result, doesn't it?
>
> I don't follow. I doesn't change the result for infinities (produces
> a NaN). It changes the result when x is so large that 'x + x' is
> not representable (exponen
On Mon, 18 Sep 2023, Martin Uecker wrote:
> > The hardest part would be popping the pragma state when leaving a block,
> > which didn't seem difficult (at least for C).
>
> It is fairly restricted where it can appear, it essentially operates
> on the level of compound statements (!= blocks).
Am Montag, dem 18.09.2023 um 14:43 +0300 schrieb Alexander Monakov:
> On Mon, 18 Sep 2023, Jakub Jelinek wrote:
>
> > Perhaps we should add some initial hammer approach for the pragma, like
> > if you ever use the pragma to turn it somewhere off, it is turned off
> > globally, or ditto per functio
On Mon, 18 Sep 2023, Florian Weimer via Gcc wrote:
> But the contraction would still be valid after an isfinite check
> (something that ranger might catch these days), or with with
> -ffinite-math-only in general. Right?
Nope, still not valid for negative zero ('x + x - x' would yield
positive
On Mon, 18 Sep 2023, Jakub Jelinek wrote:
> Perhaps we should add some initial hammer approach for the pragma, like
> if you ever use the pragma to turn it somewhere off, it is turned off
> globally, or ditto per function. Might be far easier than trying to
> make it precise that contraction is
* Richard Biener:
>> How much numerical code is compatible with that? For example, David
>> Goldberg's What Every Computer Scientist Should Know About
>> Floating-Point Arithmetic (revised) contains this sentence:
>>
>> | A language definition that does not require parentheses to be honored
>> |
* Alexander Monakov:
> On Mon, 18 Sep 2023, Florian Weimer via Gcc wrote:
>
>> x - x is different because replacing it with 0 doesn't seem to be a
>> valid contraction because it's incorrect for NaNs. x + x - x seems to
>> be different in this regard, but in our implementation, there might be a
>
On Mon, Sep 18, 2023 at 01:26:54PM +0200, Martin Uecker wrote:
> > I think that changing the default to =standard without -ffast-math is
> > reasonable.
> > IIRC the standard allows such default if it's indicated, so it doesn't
> > require
> > =off anywhere.
>
> The C standard requires a pragma t
Am Montag, dem 18.09.2023 um 10:06 +0200 schrieb Richard Biener via Gcc:
> On Mon, Sep 18, 2023 at 9:51 AM Alexander Monakov wrote:
> >
> > Hi Florian,
> >
> > On Thu, 14 Sep 2023, Alexander Monakov wrote:
> >
> > >
> > > On Thu, 14 Sep 2023, Florian Weimer via Gcc wrote:
> > >
> > > > While
On Mon, 18 Sep 2023, Florian Weimer via Gcc wrote:
> x - x is different because replacing it with 0 doesn't seem to be a
> valid contraction because it's incorrect for NaNs. x + x - x seems to
> be different in this regard, but in our implementation, there might be a
> quirk about sNaNs and qNa
On Mon, Sep 18, 2023 at 12:10 PM Florian Weimer wrote:
>
> * Richard Biener:
>
> >> > > GCC contraction behavior is rather inconsistent. It does not contract
> >> > > x
> >> > > + x - x without -ffast-math, for example, although I believe it would
> >> > > be
> >> > > permissible under the rule
* Richard Biener:
>> > > GCC contraction behavior is rather inconsistent. It does not contract x
>> > > + x - x without -ffast-math, for example, although I believe it would be
>> > > permissible under the rules that enable FMA contraction. This whole
>
> Is that really just x + x - x? We curre
On Mon, Sep 18, 2023 at 9:51 AM Alexander Monakov wrote:
>
> Hi Florian,
>
> On Thu, 14 Sep 2023, Alexander Monakov wrote:
>
> >
> > On Thu, 14 Sep 2023, Florian Weimer via Gcc wrote:
> >
> > > While rebuilding CentOS Stream with -march=x86-64-v3, I rediscovered
> > > several packages had test sui
Hi Florian,
On Thu, 14 Sep 2023, Alexander Monakov wrote:
>
> On Thu, 14 Sep 2023, Florian Weimer via Gcc wrote:
>
> > While rebuilding CentOS Stream with -march=x86-64-v3, I rediscovered
> > several packages had test suite failures because x86-64 suddenly gained
> > FMA support. I say “redisc
On Thu, 14 Sep 2023, Florian Weimer via Gcc wrote:
> While rebuilding CentOS Stream with -march=x86-64-v3, I rediscovered
> several packages had test suite failures because x86-64 suddenly gained
> FMA support. I say “rediscovered” because these issues were already
> visible on other architectu
While rebuilding CentOS Stream with -march=x86-64-v3, I rediscovered
several packages had test suite failures because x86-64 suddenly gained
FMA support. I say “rediscovered” because these issues were already
visible on other architectures with FMA.
So far, our package/architecture maintainers ha
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