[llvm] r303387 - [InstCombine] add more tests for xor-of-icmps; NFC

[Davide Italiano via llvm-commits]

On Thu, May 18, 2017 at 3:47 PM, Sanjay Patel via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: spatel
> Date: Thu May 18 17:47:57 2017
> New Revision: 303387
>
> URL: http://llvm.org/viewvc/llvm-project?rev=303387&view=rev
> Log:
> [InstCombine] add more tests for xor-of-icmps; NFC
>
> Modified:
>     llvm/trunk/test/Transforms/InstCombine/set.ll
>
> Modified: llvm/trunk/test/Transforms/InstCombine/set.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/set.ll?rev=303387&r1=303386&r2=303387&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/set.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/set.ll Thu May 18 17:47:57 2017
> @@ -175,6 +175,36 @@ define i1 @xor_of_icmps(i64 %a) {
>    ret i1 %xor
>  }
>
> +; FIXME: This is also equivalent to the previous test.
> +
> +define i1 @xor_of_icmps_commute(i64 %a) {
> +; CHECK-LABEL: @xor_of_icmps_commute(
> +; CHECK-NEXT:    [[B:%.*]] = icmp sgt i64 %a, 0
> +; CHECK-NEXT:    [[C:%.*]] = icmp eq i64 %a, 1
> +; CHECK-NEXT:    [[XOR:%.*]] = xor i1 [[B]], [[C]]
> +; CHECK-NEXT:    ret i1 [[XOR]]
> +;
> +  %b = icmp sgt i64 %a, 0
> +  %c = icmp eq i64 %a, 1
> +  %xor = xor i1 %b, %c
> +  ret i1 %xor
> +}
> +
> +; FIXME: This is (a != 5).
> +
> +define i1 @xor_of_icmps_folds_more(i64 %a) {
> +; CHECK-LABEL: @xor_of_icmps_folds_more(
> +; CHECK-NEXT:    [[B:%.*]] = icmp sgt i64 %a, 4
> +; CHECK-NEXT:    [[C:%.*]] = icmp slt i64 %a, 6
> +; CHECK-NEXT:    [[XOR:%.*]] = xor i1 [[B]], [[C]]
> +; CHECK-NEXT:    ret i1 [[XOR]]
> +;

You can start from having these in `-instcombine`, but these (and
other tests) seems like a VRP problem to me. I haven't studied this
carefully, but I wonder why we don't catch these. Have you tried to
evaluate why our VRP pass doesn't handle these?

--
Davide