[llvm] [LV] Fix emission of debug message in legality check (PR #101924)

[Ramkumar Ramachandra via llvm-commits]

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@@ -1441,10 +1441,12 @@ bool LoopVectorizationLegality::canVectorize(bool UseVPlanNativePath) {
   // Check whether the loop-related control flow in the loop nest is expected by
   // vectorizer.
   if (!canVectorizeLoopNestCFG(TheLoop, UseVPlanNativePath)) {
-    if (DoExtraAnalysis)
+    if (DoExtraAnalysis) {
+      LLVM_DEBUG(dbgs() << "LV legality check failed: loop nest");
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artagnon wrote:

Perhaps possible to check this message as well? Shouldn't the debug message start with an "LV: " prefix for uniformity?

https://github.com/llvm/llvm-project/pull/101924