[PATCH] D152684: [ConstraintElimination] Handle non-equality predicates

[Florian Hahn via Phabricator via llvm-commits]

fhahn added inline comments.


================
Comment at: llvm/lib/Transforms/Scalar/ConstraintElimination.cpp:455
+      IsNe = true;
+      Pred = CmpInst::ICMP_ULE;
+    }
----------------
I think this is not correct, as this effectively means we will be adding `Op0 <= Op1` to the constraint system as fact for `Op0 != Op1` at the moment. To start with, it would be good to only support `NE` predicates for solving, not when adding facts.


A test case that shows the issue is below. Would be good to have similar variants with UGE/UGT/ULT and signed variants.

```
define i1 @assume(i64 %a, i64 %b, i64 %c) {
  %1 = icmp ne i64 %a, %b
  tail call void @llvm.assume(i1 %1)
  %r = icmp ule i64 %a, %b
  ret i1 %r
}
```


================
Comment at: llvm/test/Transforms/ConstraintElimination/ne.ll:298
+
+define i1 @assume_b_plus_1_ult_a(i64 %a, i64 %b) {
+; CHECK-LABEL: @assume_b_plus_1_ult_a(
----------------
please add the additional test coverage separately. It would also be good to use names for the various values (instead of numbers) so they are easier to modify/play with.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D152684/new/

https://reviews.llvm.org/D152684