re PR middle-end/77436 (Incorrect constant result for summing loop inserted)

2016-09-01  Richard Biener  <rguenther@suse.de>

	PR middle-end/77436
	* tree-chrec.c (tree_fold_binomial): Use widest_int, properly
	check whether the result fits the desired result type.

	* gcc.dg/torture/pr77436.c: New testcase.

From-SVN: r239937

gcc/ChangeLog

+2016-09-01  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/77436
+	* tree-chrec.c (tree_fold_binomial): Use widest_int, properly
+	check whether the result fits the desired result type.
+
 2016-09-01  Nathan Sidwell  <nathan@acm.org>
 
 	* config/nvptx/nvptx.md (cbranch<mode>4): Op 2 can be const.

gcc/testsuite/ChangeLog

+2016-09-01  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/77436
+	* gcc.dg/torture/pr77436.c: New testcase.
+
 2016-09-01  Senthil Kumar Selvaraj  <senthil_kumar.selvaraj@atmel.com>
 
 	* gcc.dg/pr64252.c: Require int32plus.

gcc/testsuite/gcc.dg/torture/pr77436.c

+/* { dg-do run } */
+
+int main()
+{
+  unsigned short sum = 0;
+  for (short x = -(__SHRT_MAX__ -1); x <= (__SHRT_MAX__ -1); x++)
+    sum += x;
+  if (sum != 0)
+    __builtin_abort ();
+  return 0;
+}

gcc/tree-chrec.c

@@ -490,7 +490,6 @@ tree_fold_binomial (tree type, tree n, unsigned int k)
 {
   bool overflow;
   unsigned int i;
-  tree res;
 
   /* Handle the most frequent cases.  */
   if (k == 0)
@@ -498,18 +497,20 @@ tree_fold_binomial (tree type, tree n, unsigned int k)
   if (k == 1)
     return fold_convert (type, n);
 
+  widest_int num = wi::to_widest (n);
+
   /* Check that k <= n.  */
-  if (wi::ltu_p (n, k))
+  if (wi::ltu_p (num, k))
     return NULL_TREE;
 
   /* Denominator = 2.  */
-  wide_int denom = wi::two (TYPE_PRECISION (TREE_TYPE (n)));
+  widest_int denom = 2;
 
   /* Index = Numerator-1.  */
-  wide_int idx = wi::sub (n, 1);
+  widest_int idx = num - 1;
 
   /* Numerator = Numerator*Index = n*(n-1).  */
-  wide_int num = wi::smul (n, idx, &overflow);
+  num = wi::smul (num, idx, &overflow);
   if (overflow)
     return NULL_TREE;
 
@@ -528,9 +529,10 @@ tree_fold_binomial (tree type, tree n, unsigned int k)
     }
 
   /* Result = Numerator / Denominator.  */
-  wide_int di_res = wi::udiv_trunc (num, denom);
-  res = wide_int_to_tree (type, di_res);
-  return int_fits_type_p (res, type) ? res : NULL_TREE;
+  num = wi::udiv_trunc (num, denom);
+  if (! wi::fits_to_tree_p (num, type))
+    return NULL_TREE;
+  return wide_int_to_tree (type, num);
 }
 
 /* Helper function.  Use the Newton's interpolating formula for