[PATCH] D30455: [InstCombine] Avoid faulty combines of select-cmp-br

[Bjorn Pettersson via Phabricator via llvm-commits]

bjope added inline comments.


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Comment at: test/Transforms/InstCombine/select-cmp-br.ll:160-168
+define i32 @test6(i32, i1) {
+entry:
+  %2 = select i1 %1, i32 %0, i32 0
+  %3 = icmp eq i32 %2, 0
+  br i1 %3, label %4, label %4
+
+; <label>:2                                      ; preds = %entry, %entry
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spatel wrote:
> Please run 'opt -instnamer' or manually add some names to the test. That makes it easier to see what is happening.
Ok, I tried to just follow the pattern with anonymous names as used in the other tests in this file. But I can definitely add some names to my new test. I guess, in particular, that it is hard to see the connection between "label %4" and "<label>:2".

Btw, do you have any thoughts about how to verify this?
The purpose with this test is to verify that the select-cmp-br rewrite won't trigger. So the checks that I've added actually verifies some other instcombine rewrites that happens instead of select-cmp-br.
I could have added CHECK-NOT checks instead, to only verify that we do not get the faulty pattern that was generated before my correction in replacedSelectWithOperand. The drawback with such a solution is that there are lots of ways to do a faulty optimization and I can not CHECK-NOT all of them. So I preferred to have CHECKs that validates that the transformed code is correct (to a certain degree, similar to other tests in this file...).


https://reviews.llvm.org/D30455