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
