[llvm] [LoopInterchange] Improve profitability check for vectorization (PR #133672)

[Ryotaro Kasuga via llvm-commits]

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@@ -103,3 +103,135 @@ for.i.inc:
 exit:
   ret void
 }
+
+; Check that the below loops are exchanged to allow innermost loop
+; vectorization. We cannot vectorize the j-loop because it has a lexically
+; backward dependency, but the i-loop can be vectorized because all the
+; loop-carried dependencies are lexically forward.
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kasuga-fj wrote:

I meant to continue with something like this (which I should have written): Therefore, interchanging the loops could help `LoopVectorize`.

(But that also means we don’t know whether the loop will actually be vectorized…)

https://github.com/llvm/llvm-project/pull/133672