*** empty log message ***

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@997 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/combine.c b/gcc/combine.c
index 8db1fb9..044a413 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -3687,11 +3687,16 @@ expand_compound_operation (x)
     case ZERO_EXTEND:
       unsignedp = 1;
     case SIGN_EXTEND:
-      /* If we somehow managed to end up with (sign/zero_extend (const_int x)),
-        just return the CONST_INT.  We can't know how much masking to do
-        in that case.  */
+      /* We can't necessarily use a const_int for a multiword mode;
+        it depends on implicitly extending the value.
+        Since we don't know the right way to extend it,
+        we can't tell whether the implicit way is right.
+
+        Even for a mode that is no wider than a const_int,
+        we can't win, because we need to sign extend one of its bits through
+        the rest of it, and we don't know which bit.  */
       if (GET_CODE (XEXP (x, 0)) == CONST_INT)
-       return XEXP (x, 0);
+       return x;
 
       if (! FAKE_EXTEND_SAFE_P (GET_MODE (XEXP (x, 0)), XEXP (x, 0)))
        return x;