[PATCH v2] fma vs gcc 4.9

[Joseph S. Myers]

On Wed, 16 Jul 2014, Richard Henderson wrote:

> On 07/16/2014 01:56 PM, Joseph S. Myers wrote:
> > On Thu, 3 Jul 2014, Richard Henderson wrote:
> > 
> >> It seems to me that there's a typo on that exact zero test: a2 should be used,
> >> not m2.  Correct, or have I mis-read the code?
> > 
> > The existing exact zero test seems correct to me.  The conditions for such 
> > an exact zero are that the result of the multiplication is exactly 
> > representable in 53 bits (i.e., m2 == 0, with m1 being the exact result of 
> > the multiplication), and that the result of the addition (of z to the high 
> > part of the multipliation result) is an exact zero (i.e. a1 == 0, which 
> > implies a2 == 0).
> > 
> 
> Thanks.  This second version, then, does not s/m2/a2/, but merely adds the
> appropriate barriers.  It also makes sure that m2 is complete before clearing
> inexact, even though I saw no evidence of it being scheduled after the call.
> 
> Ok?

It seems ldbl-96/s_fma.c, ldbl-96/s_fmal.c and ldbl-128/s_fmal.c could all 
have the same issue and so should have corresponding changes made.

-- 
Joseph S. Myers
joseph@codesourcery.com