Quoting Kenneth Zadeck <zad...@naturalbridge.com>:
if (TREE_CODE (inner) == RSHIFT_EXPR
&& TREE_CODE (TREE_OPERAND (inner, 1)) == INTEGER_CST
&& TREE_INT_CST_HIGH (TREE_OPERAND (inner, 1)) == 0
&& bitnum < TYPE_PRECISION (type)
&& 0 > compare_tree_int (TREE_OPERAND (inner, 1),
bitnum - TYPE_PRECISION (type)))
{
bitnum += TREE_INT_CST_LOW (TREE_OPERAND (inner, 1));
inner = TREE_OPERAND (inner, 0);
}
in particular, in the last stanza of the test
TREE_OPERAND (inner, 1) is a positive number from the second stanza.
bitnum is also always positive and less than the TYPE_PRECISION (type)
from the third stanza,
so bitnum - TYPE_PRECISION (type) is always negative,
Not when you pass it as an "unsigned HOST_WIDE_INT", but then, this
doesn't really make for sane code...
so the compare will always be positive, so this code will never be executed.
... compare will almost always be negative, so this code will be executed,
regardless of the validity of the shift or the bit test being in range.
it is hard to believe that this is what you want.
I see that this code lived previously in expr.c:store_flag_value,
and was modified by a big omnibus patch there:
Mon Mar 6 15:22:29 2000 Richard Kenner <ken...@vlsi1.ultra.nyu.edu>
* expr.c
..
(do_store_flag): Use compare_tree_int.
..
@@ -10204,8 +10204,9 @@ do_store_flag (exp, target, mode, only_c
if (TREE_CODE (inner) == RSHIFT_EXPR
&& TREE_CODE (TREE_OPERAND (inner, 1)) == INTEGER_CST
&& TREE_INT_CST_HIGH (TREE_OPERAND (inner, 1)) == 0
- && (bitnum + TREE_INT_CST_LOW (TREE_OPERAND (inner, 1))
- < TYPE_PRECISION (type)))
+ && bitnum < TYPE_PRECISION (type)
+ && 0 > compare_tree_int (TREE_OPERAND (inner, 1),
+ bitnum - TYPE_PRECISION (type)))
{
bitnum += TREE_INT_CST_LOW (TREE_OPERAND (inner, 1));
inner = TREE_OPERAND (inner, 0);
I suppose that should be "TYPE_PRECISION (type) - bitnum" instead.
