[polly] [Polly] Retain vectorization for fallback loop when RTC is false (PR #165525)

[Michael Kruse via llvm-commits]

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@@ -282,9 +273,22 @@ static bool generateCode(Scop &S, IslAstInfo &AI, LoopInfo &LI,
   } else {
     NodeBuilder.addParameters(S.getContext().release());
     Value *RTC = NodeBuilder.createRTC(AI.getRunCondition().release());
-
     Builder.GetInsertBlock()->getTerminator()->setOperand(0, RTC);
 
+    auto *CI = dyn_cast<ConstantInt>(RTC);
+    // The code below annotates the "llvm.loop.vectorize.enable" to false
+    // for the code flow taken when RTCs fail. Because we don't want the
+    // Loop Vectorizer to come in later and vectorize the original fall back
+    // loop when Polly is enabled. This also prevent's multiple loop versions
+    // created by Polly with Loop Vectorizer. Also don't do this when Polly's
+    // RTC value is false, as we are left with only one version of Loop.
----------------
Meinersbur wrote:

> This also prevent's multiple loop versions created by Polly with Loop Vectorizer

I don't understand this part. Do you mean the loop versioning that LoopVectorize does in addition to the one Polly already did?

```suggestion
    // loop when Polly is enabled. This also prevent's multiple loop versions
    // created by Polly with Loop Vectorizer. Also don't do this when Polly's
    // RTC value is false (which may be the result of code generation having failed), as we are left with only one version of Loop.
```
Some additional info

https://github.com/llvm/llvm-project/pull/165525