[llvm-dev] Default FPENV state

[Hal Finkel via llvm-dev]

Hi, Dinar,

You should assume that FPU exceptions are not enabled. LLVM does not 
(currently) support them. That having been said, in this particular 
case, the output is also different if a NaN is produced (i.e. it 
produces a NaN and not a -1), and so I'd think you can only do this 
transformations when the call has the nnan flag (e.g. because the code 
was compiled with -ffinite-math-only).

  -Hal

On 06/14/2017 05:06 AM, Dinar Temirbulatov wrote:
> Hi,
> We are interesting in expanding some vector operations directly in the
> IR form as constants https://reviews.llvm.org/D33406,
> for example: _mm256_cmp_ps("any input", "any input", _CMP_TRUE_UQ)
> should produce -1, -1, -1, ... vector, but for some values for example
> "1.00 -nan" if FPU exceptions were enabled this operation triggers the
> exception. Here is the question: Should we assume that FPENV was
> initialized with FE_ALL_EXCEPT by default or we could rely for example
> on "-fno-trapping-math" flag or we could completely ignore the FPU
> exception issue(see https://bugs.llvm.org/show_bug.cgi?id=6050)?
>
>                  Thanks, Dinar.

-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory