[llvm] [VPlan] Use BlockFrequencyInfo in getPredBlockCostDivisor (PR #158690)

[Luke Lau via llvm-commits]

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@@ -1729,6 +1722,11 @@ class LoopVectorizationCostModel {
   /// Interface to emit optimization remarks.
   OptimizationRemarkEmitter *ORE;
 
+  /// A function to lazily fetch BlockFrequencyInfo. This avoids computing it
+  /// unless necessary, e.g. when the loop isn't legal to vectorize or when
+  /// there is no predication.
+  std::function<BlockFrequencyInfo *()> GetBFI;
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lukel97 wrote:

We would also need to plumb through the FunctionAnalysisManager to fetch the BFI, which doesn't seem right. Although I took a look at what other passes do e.g. FunctionSpecialization.cpp and they also seem to just pass through a std::function, albeit they return a reference. So I've updated it return a reference too in 296797f804bc48c34ba23e3ffbc2ef2bdd6e451d

https://github.com/llvm/llvm-project/pull/158690