On Thu, Nov 21, 2013 at 1:19 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
>> Here’s my patch submission for adding IEEE intrinsic modules (following
>> Fortran 2003 and 2008
>> standards) to gfortran. It implements the item 1, and part of item 2, of my
>> initial plan [1]. All the
>> IEEE modules, types, named constants, procedures are defined and fully
>> working. The patch
>> comes of course with plenty of testcases, and I can add some more if you can
>> think of things I’ve
>> forgotten. I’ve bootstrapped and regtested the patch on:
>
> __asm__ __volatile__ ("fnclex\n\tfldcw\t%0" : : "m" (cw));
>
> @@ -136,16 +165,54 @@ set_fpu (void)
> __asm__ __volatile__ ("%vstmxcsr\t%0" : "=m" (cw_sse));
>
> /* The SSE exception masks are shifted by 7 bits. */
> - cw_sse |= _FPU_MASK_ALL << 7;
> - cw_sse &= ~(excepts << 7);
> -
> - /* Clear stalled exception flags. */
> - cw_sse &= ~_FPU_EX_ALL;
>
> You have to clear stalled SSE exceptions here. Their flags are in LSB
> bits, so their position is different than the position of exception
> mask bits in the control word.
>
> + /* Change the flags. This is tricky on 387 (unlike SSE), because we have
> + FNSTSW but no FLDSW instruction. */
> + __asm__ __volatile__ ("fnstenv\t%0" : "=m" (*&temp));
> +
> + temp.__status_word &= ~exc_clr;
> + temp.__status_word |= exc_set;
> +
> + __asm__ __volatile__ ("fldenv\t%0" : : "m" (*&temp));
>
> Why do you need "*&" here?
>
> fldenv will also trigger exceptions with set flags on the next x87 FP insn ...
>
> + __asm__ __volatile__ ("%vstmxcsr\t%0" : "=m" (cw_sse));
> +
> + cw_sse &= ~exc_clr;
> + cw_sse |= exc_set;
> +
> + __asm__ __volatile__ ("%vldmxcsr\t%0" : : "m" (cw_sse));
>
> ... and ldmxcsr won't trigger exceptions, neither with SSE insn.
> Please see Intel documentation on FP exceptions.
Also, it is not clear to me, if the intention of the function is to
throw an exception? in this case, you should look at the code in
config/x86/fenv.c from libatomic (or config/i386/sfp-exceptions.c from
libgcc) for how exceptions should be generated.
Uros.
