(expand_expr, case MINUS_EXPR): Properly handle case when the NEGATE

overflows.

From-SVN: r8648

diff --git a/gcc/expr.c b/gcc/expr.c
index 6634811174438f5eddaf3d892287e4fb12c41a56..fc6223e9a73393004e47b13a7f76d080f8f3f1f1 100644 (file)
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -5239,10 +5239,29 @@ expand_expr (exp, target, tmode, modifier)
       /* Convert A - const to A + (-const).  */
       if (TREE_CODE (TREE_OPERAND (exp, 1)) == INTEGER_CST)
        {
-         exp = build (PLUS_EXPR, type, TREE_OPERAND (exp, 0),
-                      fold (build1 (NEGATE_EXPR, type,
-                                    TREE_OPERAND (exp, 1))));
-         goto plus_expr;
+         tree negated = fold (build1 (NEGATE_EXPR, type,
+                                      TREE_OPERAND (exp, 1)));
+
+         /* Deal with the case where we can't negate the constant
+            in TYPE.  */
+         if (TREE_UNSIGNED (type) || TREE_OVERFLOW (negated))
+           {
+             tree newtype = signed_type (type);
+             tree newop0 = convert (newtype, TREE_OPERAND (exp, 0));
+             tree newop1 = convert (newtype, TREE_OPERAND (exp, 1));
+             tree newneg = fold (build1 (NEGATE_EXPR, newtype, newop1));
+
+             if (! TREE_OVERFLOW (newneg))
+               return expand_expr (convert (type, 
+                                            build (PLUS_EXPR, newtype,
+                                                   newop0, newneg)),
+                                   target, tmode, modifier);
+           }
+         else
+           {
+             exp = build (PLUS_EXPR, type, TREE_OPERAND (exp, 0), negated);
+             goto plus_expr;
+           }
        }
       this_optab = sub_optab;
       goto binop;