On 11/3/16, Jakub Jelinek <ja...@redhat.com> wrote: > On Thu, Nov 03, 2016 at 09:27:55AM -0400, Jason Merrill wrote: >> On Thu, Nov 3, 2016 at 7:24 AM, Marek Polacek <pola...@redhat.com> wrote: >> > On Tue, Nov 01, 2016 at 02:53:58PM +0100, Jakub Jelinek wrote: >> >> On Tue, Nov 01, 2016 at 09:41:20AM -0400, Jason Merrill wrote: >> >> > On Tue, Oct 25, 2016 at 9:59 AM, Marek Polacek <pola...@redhat.com> >> >> > wrote: >> >> > > On Mon, Oct 24, 2016 at 04:10:21PM +0200, Marek Polacek wrote: >> >> > >> On Thu, Oct 20, 2016 at 12:28:36PM +0200, Marek Polacek wrote: >> >> > >> > I found a problem with this patch--we can't call >> >> > >> > do_warn_duplicated_branches in >> >> > >> > build_conditional_expr, because that way the C++-specific codes >> >> > >> > might leak into >> >> > >> > the hasher. Instead, I should use operand_equal_p, I think. >> >> > >> > Let me rework >> >> > >> > that part of the patch. >> >> > >> >> > Hmm, is there a reason not to use operand_equal_p for >> >> > do_warn_duplicated_branches as well? I'm concerned about hash >> >> > collisions leading to false positives. >> >> >> >> If the hashing function is iterative_hash_expr / inchash::add_expr, >> >> then >> >> that is supposed to pair together with operand_equal_p, we even have >> >> checking verification of that. >> >> Yes, but there could still be hash collisions; we can't guarantee that >> everything that compares unequal also hashes unequal. > > Right, after h0 == h1 is missing && operand_equal_p (thenb, elseb, 0) > or so (the exact last operand needs to be figured out). > OEP_ONLY_CONST is certainly wrong, we want the same VAR_DECLs to mean the > same thing. 0 is a tiny bit better, but still it will give up on e.g. pure > and other calls. OEP_PURE_SAME is tiny bit better than that, but still > calls with the same arguments to the same function will not be considered > equal, plus likely operand_equal_p doesn't handle STATEMENT_LIST etc. > So maybe we need another OEP_* mode for this. > > Jakub >
Pinging this conversation for the new year. Any chances of -Wduplicated-branches making it in in time for GCC 7? Thanks, Eric