> Does it look OK?
No.
If I understand your code correctly, there's essentially the same code
as you have a bit above that:
/* If the constant is one less than a power of two, this might be
representable by an extraction even if no shift is present.
If it doesn't end up being a ZERO_EXTEND, we will ignore it unless
we are in a COMPARE. */
else if ((i = exact_log2 (INTVAL (XEXP (x, 1)) + 1)) >= 0)
new_rtx = make_extraction (mode,
make_compound_operation (XEXP (x, 0),
next_code),
0, NULL_RTX, i, 1, 0, in_code == COMPARE);
So you need to understand why your code "fires" and it doesn't.
