[ctxprof][nfc] Move profile annotator to Analysis (#135871)

This moves the utility that propagates counter values such that we can reuse it elsewhere. Specifically, in a subsequent patch, it'll be used to guide ICP: we need to prioritize promoting indirect calls that dominate larger portions of the dynamic instruction count. We can compare them based on the dynamic count of IR instructions, and we can get that early with this counter propagation logic.

The patch is mostly a move of the existing logic, with a pimpl - style implementation to hide all the current complexity.

Author: mtrofin

llvm/include/llvm/Analysis/CtxProfAnalysis.h

@@ -157,6 +157,34 @@ class CtxProfAnalysisPrinterPass
   const PrintMode Mode;
 };
 
+/// Utility that propagates counter values to each basic block and to each edge
+/// when a basic block has more than one outgoing edge, using an adaptation of
+/// PGOUseFunc::populateCounters.
+// FIXME(mtrofin): look into factoring the code to share one implementation.
+class ProfileAnnotatorImpl;
+class ProfileAnnotator {
+  std::unique_ptr<ProfileAnnotatorImpl> PImpl;
+
+public:
+  ProfileAnnotator(const Function &F, ArrayRef<uint64_t> RawCounters);
+  uint64_t getBBCount(const BasicBlock &BB) const;
+
+  // Finds the true and false counts for the given select instruction. Returns
+  // false if the select doesn't have instrumentation or if the count of the
+  // parent BB is 0.
+  bool getSelectInstrProfile(SelectInst &SI, uint64_t &TrueCount,
+                             uint64_t &FalseCount) const;
+  // Clears Profile and populates it with the edge weights, in the same order as
+  // they need to appear in the MD_prof metadata. Also computes the max of those
+  // weights an returns it in MaxCount. Returs false if:
+  //   - the BB has less than 2 successors
+  //   - the counts are 0
+  bool getOutgoingBranchWeights(BasicBlock &BB,
+                                SmallVectorImpl<uint64_t> &Profile,
+                                uint64_t &MaxCount) const;
+  ~ProfileAnnotator();
+};
+
 /// Assign a GUID to functions as metadata. GUID calculation takes linkage into
 /// account, which may change especially through and after thinlto. By
 /// pre-computing and assigning as metadata, this mechanism is resilient to such