Re: [fortran, patch] Add Fortran 2003 IEEE intrinsic modules

[Uros Bizjak <ubizjak at gmail dot com>]

Hello!

> 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.

Uros.