[PATCH, fortran ieee]: PR 88678, Many gfortran.dg/ieee/ieee_X.f90 test cases fail starting with r267465

[Steve Ellcey]

On Thu, 2019-01-31 at 08:46 +0100, Uros Bizjak wrote:
> On Wed, Jan 30, 2019 at 9:51 PM Janne Blomqvist
>
> > This seems to change the only user of support_fpu_trap() that is
> > different from support_fpu_flag(), so with this change one could
> > remove support_fpu_trap() entirely and modify all callers (since
> > it's an internal function it's not used outside libgfortran) to
> > call support_fpu_flag() directly. Otherwise Ok.
> 
> Some targets only support IEEE flags (so, flags in some FP status
> register), but not exceptions (traps) based on these flags that halt
> the program. Currently, fpu-glibc.h assumes that all flags can
> generate exceptions (that is true for the current set of gfortran
> targets), but some future target wants to return 0 from
> support_fpu_trap.
> 
> Uros.

Is this actually true for all existing gfortran targets?  Specifically
I am wondering about Arm and Aarch64.  PR 78314 says that ARM trapping
FPU exceptions are optional.

I am currently seeing gfortran.dg/ieee/ieee_6.f90 fail on my Aarch64
ThunderX box.  I wonder if we should have an Arm/Aarch64 specific
version of the fpu header file (fpu-arm.h) that would use the previous 
version of support_fpu_trap.

Steve Ellcey
sellcey@marvell.com