transform optimization: leave out some convs and use 32bit compare ops, if the upper bits are guaranteed to be clear
transform optimization: leave out some convs and use 32bit compare ops, if the upper bits are guaranteed to be clear

[r22140]

davidgiven/libfirm,killbug2004/libfirm,MatzeB/libfirm,jonashaag/libfirm,MatzeB/libfirm,8l/libfirm,8l/libfirm,8l/libfirm,8l/libfirm,MatzeB/libfirm,MatzeB/libfirm,killbug2004/libfirm,libfirm/libfirm,killbug2004/libfirm,davidgiven/libfirm,libfirm/libfirm,libfirm/libfirm,davidgiven/libfirm,jonashaag/libfirm,killbug2004/libfirm,8l/libfirm,jonashaag/libfirm,libfirm/libfirm,8l/libfirm,MatzeB/libfirm,davidgiven/libfirm,jonashaag/libfirm,killbug2004/libfirm,killbug2004/libfirm,jonashaag/libfirm,MatzeB/libfirm,8l/libfirm,MatzeB/libfirm,davidgiven/libfirm,jonashaag/libfirm,jonashaag/libfirm,libfirm/libfirm,davidgiven/libfirm,killbug2004/libfirm,davidgiven/libfirm