https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63464
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Created attachment 33658 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33658&action=edit gcc5-pr63464.patch Updated patch for the switchconv, this time checking rtx costs. As for reassoc, the problem I see is that this kind of optimization needs to split basic blocks, as left shift by negative or >= word bit size is undefined behavior, so the expected generated code is probably jump around the left shift. I think reassoc pass is not prepared to see splitting of basic blocks, nor adding new PHI nodes etc. In the: int foo (int x) { return x == 1 || x == 2 || x == 4 || x == 6 || x == 15 || x == 17; } case we actually have 2 basic blocks and there is no other test ored in in either of the basic blocks, so we could perform it even without creating a new bb, but I'd say that very often we will not be that lucky.
