[PATCH] D59916: [CorrelatedValuePropagation][InstCombine] Teach CorrelatedValuePropagation to also mark sub as no wrap and use that in InstCombine to fold icmp+sub.

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

Can you please split off the InstCombine change into a separate revision?



================
Comment at: llvm/test/Transforms/InstCombine/icmp-sub.ll:3
+
+define i64 @test_icmp_sub_elide(i64 %offset) {
+; CHECK-LABEL: @test_icmp_sub_elide
----------------
For the instcombine tests it's enough to just check the sub+icmp folding to true/false, such as:

```
define i1 @test(i64 %x) {
  %y = sub nuw i64 10, %x
  %z = icmp ult i64 %y, 3
  ret i1 %z
}
```

Instead we'd want to test more variations here, in particular: Both nuw and nsw should be covered. Cases where the subtraction overflows should be covered. And I believe this transform also needs to be guarded based on the signedness of the predicate -- i.e. you can't do it if you have sub nsw and ult, so we'd want to test such combinations as well.

Test checks can be generated using `utils/update_test_checks.py`.


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D59916