re PR tree-optimization/27364 (VRP miscompiles some unsigned math)

	PR tree-optimization/27364
	* tree-vrp.c (vrp_int_const_binop): Fix detection of overflow from
	multiply expressions.

	* gcc.c-torture/execute/pr27364.c: New test.

From-SVN: r113481

gcc/ChangeLog

+2006-05-02  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/27364
+	* tree-vrp.c (vrp_int_const_binop): Fix detection of overflow from
+	multiply expressions.
+
 2006-05-02  Tom Tromey  <tromey@redhat.com>
 
 	* tree-flow-inline.h (op_iter_init_phiuse): Fixed typo.

gcc/testsuite/ChangeLog

+2006-05-02  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/27364
+	* gcc.c-torture/execute/pr27364.c: New test.
+
 2006-05-02  Mark Mitchell  <mark@codesourcery.com>
 
 	PR c++/27309

gcc/testsuite/gcc.c-torture/execute/pr27364.c

+int f(unsigned number_of_digits_to_use)
+{
+  if (number_of_digits_to_use >1294)
+    return 0;
+  return (number_of_digits_to_use * 3321928 / 1000000 + 1) /16;
+}
+
+int main(void)
+{
+  if (f(11) != 2)
+    __builtin_abort ();
+  exit (0);
+}

gcc/tree-vrp.c

@@ -1191,17 +1191,39 @@ vrp_int_const_binop (enum tree_code code, tree val1, tree val2)
   if (TYPE_UNSIGNED (TREE_TYPE (val1)))
     {
       int checkz = compare_values (res, val1);
+      bool overflow = false;
 
       /* Ensure that res = val1 [+*] val2 >= val1
          or that res = val1 - val2 <= val1.  */
-      if (((code == PLUS_EXPR || code == MULT_EXPR)
+      if ((code == PLUS_EXPR
 	   && !(checkz == 1 || checkz == 0))
           || (code == MINUS_EXPR
 	      && !(checkz == 0 || checkz == -1)))
 	{
+	  overflow = true;
+	}
+      /* Checking for multiplication overflow is done by dividing the
+	 output of the multiplication by the first input of the
+	 multiplication.  If the result of that division operation is
+	 not equal to the second input of the multiplication, then the
+	 multiplication overflowed.  */
+      else if (code == MULT_EXPR && !integer_zerop (val1))
+	{
+	  tree tmp = int_const_binop (TRUNC_DIV_EXPR,
+				      TYPE_MAX_VALUE (TREE_TYPE (val1)),
+				      val1, 0);
+	  int check = compare_values (tmp, val2);
+
+	  if (check != 0)
+	    overflow = true;
+	}
+
+      if (overflow)
+	{
 	  res = copy_node (res);
 	  TREE_OVERFLOW (res) = 1;
 	}
+
     }
   else if (TREE_OVERFLOW (res)
 	   && !TREE_OVERFLOW (val1)