On Thu, Oct 13, 2011 at 2:23 PM, Richard Kenner <ken...@vlsi1.ultra.nyu.edu> wrote: >> 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. > >
It is because mask 0xffffffff is optimized to 0xfffffffc by keeping track of non-zero bits in registers and the above code doesn't take that into account. -- H.J.
