On October 14, 2014 6:02:19 PM CEST, Jakub Jelinek <ja...@redhat.com> wrote: >Hi! > >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?
OK. Thanks, Richard. >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. > >--- gcc/tree-ssa-reassoc.c.jj 2014-10-13 17:54:33.000000000 +0200 >+++ gcc/tree-ssa-reassoc.c 2014-10-13 17:58:07.312705218 +0200 >@@ -2250,8 +2250,13 @@ optimize_range_tests_diff (enum tree_cod > if (tree_log2 (tem1) < 0) > return false; > >+ type = unsigned_type_for (type); >+ tem1 = fold_convert (type, tem1); >+ tem2 = fold_convert (type, tem2); >+ lowi = fold_convert (type, lowi); > mask = fold_build1 (BIT_NOT_EXPR, type, tem1); >- tem1 = fold_binary (MINUS_EXPR, type, rangei->exp, lowi); >+ tem1 = fold_binary (MINUS_EXPR, type, >+ fold_convert (type, rangei->exp), lowi); > tem1 = fold_build2 (BIT_AND_EXPR, type, tem1, mask); > lowj = build_int_cst (type, 0); > if (update_range_test (rangei, rangej, 1, opcode, ops, tem1, > > Jakub
