Jakub Jelinek <ja...@redhat.com> writes: > On Tue, Oct 14, 2014 at 11:23:22AM -0600, Jeff Law wrote: >> On 10/14/14 10:02, Jakub Jelinek wrote: >> >When hacking on range reassoc opt, I've noticed we can emit >> >code with undefined behavior even when there wasn't one originally, >> >in particular for: >> > (X - 43U) <= 3U || (X - 75U) <= 3U >> > and this loop can transform that into >> > ((X - 43U) & ~(75U - 43U)) <= 3U. */ >> >we actually don't transform it to what the comment says, but >> > ((X - 43) & ~(75U - 43U)) <= 3U >> >i.e. the initial subtraction can be performed in signed type, >> >if in here X is e.g. INT_MIN or INT_MIN + 42, the subtraction >> >at gimple level would be UB (not caught by -fsanitize=undefined, >> >because that is handled much earlier). >> > >> >Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? >> > >> >2014-10-14 Jakub Jelinek <ja...@redhat.com> >> > >> > * tree-ssa-reassoc.c (optimize_range_tests_diff): Perform >> > MINUS_EXPR in unsigned type to avoid undefined behavior. >> Any chance this fixes: >> >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63302 > > No. For that I have right now: > - if (tree_log2 (lowxor) < 0) > + if (wi::popcount (wi::to_widest (lowxor)) != 1) > in my tree, though supposedly: > if (wi::popcount (wi::zext (wi::to_widest (lowxor), TYPE_PRECISION > (TREE_TYPE (lowxor)))) != 1) > might be better, as without zext it will supposedly > not say popcount is 1 for smaller precision signed minimum values. > My wide-int-fu is limited, so if there is a better way to do this, I'm all > ears.
Sorry for the very late reply, but just: if (wi::popcount (lowxor) != 1) should do what you want. Thanks, Richard
