(fold, case MULT_EXPR): If arg is an unsigned CEIL_DIV_EXPR, convert

to TRUNC_DIV_EXPR of a PLUS_EXPR in some cases.

From-SVN: r7744

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index fc611902aa4d9036d39dcf0ee0d98822b836cf25..15509a3f07ae2567a0f7447e2024584c38affba6 100644 (file)
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -3751,6 +3751,24 @@ fold (expr)
              && operand_equal_p (TREE_OPERAND (arg0, 1), arg1, 0))
            return TREE_OPERAND (arg0, 0);
 
+         /* If we have ((A / C1) * C2) with C1 and C2 constant,
+            C2 >= C1, and the division an unsigned CEIL_DIV_EXPR,
+            we know that the addition that's part of the CEIL_DIV_EXPR
+            cannot overflow while the generic CEIL_DIV_EXPR does not.
+            So convert it into a TRUNC_DIV_EXPR of an add.  */
+         if (TREE_CODE (arg0) == CEIL_DIV_EXPR && TREE_UNSIGNED (type)
+             && TREE_CODE (arg1) == INTEGER_CST
+             && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST
+             && ! tree_int_cst_lt (arg1, TREE_OPERAND (arg0, 1)))
+           return
+             build (MULT_EXPR, type,
+                    build (TRUNC_DIV_EXPR, type,
+                           build (PLUS_EXPR, type,
+                                  TREE_OPERAND (TREE_OPERAND (arg0, 0), 0)),
+                           const_binop (MINUS_EXPR, TREE_OPERAND (arg0, 1),
+                                        integer_one_node, 0)),
+                    arg1);
+                                
          /* (a * (1 << b)) is (a << b)  */
          if (TREE_CODE (arg1) == LSHIFT_EXPR
              && integer_onep (TREE_OPERAND (arg1, 0)))