[PATCH v2] fma vs gcc 4.9

[Richard Henderson <rth at twiddle dot net>]

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?


r~

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