ColdBlockInfo: overhaul the analysis

Author: kavon

include/swift/SILOptimizer/Analysis/ColdBlockInfo.h

@@ -15,6 +15,7 @@
 
 #include "llvm/ADT/DenseMap.h"
 #include "swift/SIL/SILValue.h"
+#include <bitset>
 
 namespace swift {
 class DominanceAnalysis;
@@ -29,47 +30,45 @@ class ColdBlockInfo {
   DominanceAnalysis *DA;
   PostDominanceAnalysis *PDA;
 
-  /// Each block in this map has been determined to be either cold or hot.
-  llvm::DenseMap<const SILBasicBlock*, bool> ColdBlockMap;
-
-  // This is a cache and shouldn't be copied around.
-  ColdBlockInfo(const ColdBlockInfo &) = delete;
-  ColdBlockInfo &operator=(const ColdBlockInfo &) = delete;
-
-  /// Tri-value return code for checking branch hints.
-  enum BranchHint : unsigned {
-    None,
-    LikelyTrue,
-    LikelyFalse
+  // Represents the temperatures of edges flowing into a block.
+  //
+  //         T = "top" -- both warm and cold edges
+  //        /  \
+  //     Warm  Cold
+  //        \  /
+  //         B = "bottom" -- neither warm or cold edges
+  struct State {
+    // Each state kind, as an integer, is its position in any bit vectors.
+    enum Temperature {
+      Warm = 0,
+      Cold = 1
+    };
+
+    // Number of states, excluding Top or Bottom, in this flow problem.
+    static constexpr unsigned NumStates = 2;
   };
 
-  enum {
-    RecursionDepthLimit = 3
-  };
+  using Energy = std::bitset<State::NumStates>;
+  static std::string toString(Energy e);
 
-  // \returns none if there is no known temperature for the block.
-  std::optional<bool> queryIsCold(const SILBasicBlock *BB);
+  /// Each block in this map has been determined to be cold and/or warm.
+  llvm::DenseMap<const SILBasicBlock*, Energy> EnergyMap;
+  bool changedMap = false;
 
-  BranchHint getBranchHint(SILValue Cond, int recursionDepth);
-
-  bool isSlowPath(const SILBasicBlock *FromBB, const SILBasicBlock *ToBB,
-                  int recursionDepth);
+  // This is a cache and shouldn't be copied around.
+  ColdBlockInfo(const ColdBlockInfo &) = delete;
+  ColdBlockInfo &operator=(const ColdBlockInfo &) = delete;
+  LLVM_DUMP_METHOD void dump() const;
 
-  bool isCold(const SILBasicBlock *BB,
-              int recursionDepth);
+  void resetToCold(const SILBasicBlock *BB);
+  void set(const SILBasicBlock *BB, State::Temperature temp);
 
 public:
   ColdBlockInfo(DominanceAnalysis *DA, PostDominanceAnalysis *PDA);
 
-  /// Pre-seed the info with information starting at the exits of the function.
-  /// Recommended prior to querying if blocks are cold in a function.
-  void analyzeExits(SILFunction *Fn);
-
-  bool isSlowPath(const SILBasicBlock *FromBB, const SILBasicBlock *ToBB) {
-    return isSlowPath(FromBB, ToBB, 0);
-  }
+  void analyze(SILFunction *F);
 
-  bool isCold(const SILBasicBlock *BB) { return isCold(BB, 0); }
+  bool isCold(const SILBasicBlock *BB) const;
 };
 } // end namespace swift
 

include/swift/SILOptimizer/Utils/PerformanceInlinerUtils.h

@@ -429,7 +429,7 @@ class ShortestPathAnalysis {
       return;
 
     BlockInfoStorage.resize(numBlocks);
-    CBI.analyzeExits(F);
+    CBI.analyze(F);
 
     // First step: compute the length of the blocks.
     unsigned BlockIdx = 0;