(convert_to_integer): Don't pass truncation thru lshift

if shift count >= width of narrower type.  Instead, just use 0.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@2104 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/c-convert.c b/gcc/c-convert.c
index b160fd1..89637cb 100644 (file)
--- a/gcc/c-convert.c
+++ b/gcc/c-convert.c
@@ -187,9 +187,21 @@ convert_to_integer (type, expr)
          /* We can pass truncation down through left shifting
             when the shift count is a nonnegative constant.  */
          if (TREE_CODE (TREE_OPERAND (expr, 1)) == INTEGER_CST
-             && ! tree_int_cst_lt (TREE_OPERAND (expr, 1), integer_zero_node))
-           /* In this case, shifting is like multiplication.  */
-           goto trunc1;
+             && ! tree_int_cst_lt (TREE_OPERAND (expr, 1), integer_zero_node)
+             && TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST)
+           {
+             /* If shift count is less than the width of the truncated type,
+                really shift.  */
+             if (tree_int_cst_lt (TREE_OPERAND (expr, 1), TYPE_SIZE (type)))
+               /* In this case, shifting is like multiplication.  */
+               goto trunc1;
+             else
+               /* If it is >= that width, result is zero.
+                  Handling this with trunc1 would give the wrong result:
+                  (int) ((long long) a << 32) is well defined (as 0)
+                  but (int) a << 32 is undefined and would get a warning.  */
+               return convert_to_integer (type, integer_zero_node);
+           }
          break;
 
        case MAX_EXPR: