[Bug fortran/31120] ICE with integer_exponentiation_1.f90 and -ffast-math

[fxcoudert at gcc dot gnu dot org]

------- Comment #3 from fxcoudert at gcc dot gnu dot org  2007-03-14 12:31 -------
Here's a patch that should make the code in gfc_conv_cst_int_power() work in
all cases:

Index: trans-expr.c
===================================================================
--- trans-expr.c        (revision 122912)
+++ trans-expr.c        (working copy)
@@ -634,7 +634,7 @@
 /* Recursive function to expand the power operator. The temporary 
    values are put in tmpvar. The function returns tmpvar[1] ** n.  */
 static tree
-gfc_conv_powi (gfc_se * se, int n, tree * tmpvar)
+gfc_conv_powi (gfc_se * se, unsigned HOST_WIDE_INT n, tree * tmpvar)
 {
   tree op0;
   tree op1;
@@ -681,15 +681,25 @@
   tree tmp;
   tree type;
   tree vartmp[POWI_TABLE_SIZE];
-  int n;
+  HOST_WIDE_INT m;
+  unsigned HOST_WIDE_INT n;
   int sgn;

+  /* If exponent is too large, we won't expand it anyway, so don't bother
+     with large integer values.  */
+  if (!double_int_fits_in_shwi_p (TREE_INT_CST (rhs)))
+    return 0;
+
+  m = double_int_to_shwi (TREE_INT_CST (rhs));
+  /* There's no ABS for HOST_WIDE_INT, so here we go. It also takes care
+     of the asymmetric range of the integer type.  */
+  n = (unsigned HOST_WIDE_INT) (m < 0 ? -m : m);
+  
   type = TREE_TYPE (lhs);
-  n = abs (TREE_INT_CST_LOW (rhs));
   sgn = tree_int_cst_sgn (rhs);

-  if (((FLOAT_TYPE_P (type) && !flag_unsafe_math_optimizations) ||
optimize_siz
e)
-      && (n > 2 || n < -1))
+  if (((FLOAT_TYPE_P (type) && !flag_unsafe_math_optimizations)
+       || optimize_size) && (m > 2 || m < -1))
     return 0;

   /* rhs == 0  */
@@ -698,6 +708,7 @@
       se->expr = gfc_build_const (type, integer_one_node);
       return 1;
     }
+
   /* If rhs < 0 and lhs is an integer, the result is -1, 0 or 1.  */
   if ((sgn == -1) && (TREE_CODE (type) == INTEGER_TYPE))
     {


It's regtesting right now. The following should now be done:
  * write a testcase, using both kind=4 and 8 integers as exponents, and
testing difficult cases (huge(),-huge(),-huge()-1, etc.); the testcase should
also check constant vs. non-constant results, to make sure the testcase run
isn't rendered useless by constant folding
  * the code generated should be manually checked in the above-mentionned
difficult cases (huge(), -huge(), ...)

If nobody does it before the week-end, I'll do it then (but won't have time
before that). And Dominique, I would appreciate if you could test the patch on
ppc-darwin7.


-- 

fxcoudert at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |fxcoudert at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
           Keywords|                            |patch
   Last reconfirmed|2007-03-10 12:15:25         |2007-03-14 12:31:35
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31120