[BPI] Replace weights by probabilities in BPI.

This patch removes all weight-related interfaces from BPI and replace
them by probability versions. With this patch, we won't use edge weight
anymore in either IR or MC passes. Edge probabilitiy is a better
representation in terms of CFG update and validation.


Differential revision: http://reviews.llvm.org/D15519 

llvm-svn: 256263

llvm/include/llvm/Analysis/BranchProbabilityInfo.h

@@ -84,36 +84,14 @@ class BranchProbabilityInfo {
   raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src,
                                     const BasicBlock *Dst) const;
 
-  /// \brief Get the raw edge weight calculated for the edge.
+  /// \brief Set the raw edge probability for the given edge.
   ///
-  /// This returns the raw edge weight. It is guaranteed to fall between 1 and
-  /// UINT32_MAX. Note that the raw edge weight is not meaningful in isolation.
-  /// This interface should be very carefully, and primarily by routines that
-  /// are updating the analysis by later calling setEdgeWeight.
-  uint32_t getEdgeWeight(const BasicBlock *Src,
-                         unsigned IndexInSuccessors) const;
-
-  /// \brief Get the raw edge weight calculated for the block pair.
-  ///
-  /// This returns the sum of all raw edge weights from Src to Dst.
-  /// It is guaranteed to fall between 1 and UINT32_MAX.
-  uint32_t getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const;
-
-  uint32_t getEdgeWeight(const BasicBlock *Src,
-                         succ_const_iterator Dst) const;
-
-  /// \brief Set the raw edge weight for a given edge.
-  ///
-  /// This allows a pass to explicitly set the edge weight for an edge. It can
-  /// be used when updating the CFG to update and preserve the branch
+  /// This allows a pass to explicitly set the edge probability for an edge. It
+  /// can be used when updating the CFG to update and preserve the branch
   /// probability information. Read the implementation of how these edge
-  /// weights are calculated carefully before using!
-  void setEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors,
-                     uint32_t Weight);
-
-  static uint32_t getBranchWeightStackProtector(bool IsLikely) {
-    return IsLikely ? (1u << 20) - 1 : 1;
-  }
+  /// probabilities are calculated carefully before using!
+  void setEdgeProbability(const BasicBlock *Src, unsigned IndexInSuccessors,
+                          BranchProbability Prob);
 
   static BranchProbability getBranchProbStackProtector(bool IsLikely) {
     static const BranchProbability LikelyProb((1u << 20) - 1, 1u << 20);
@@ -135,7 +113,7 @@ class BranchProbabilityInfo {
   // weight to just "inherit" the non-zero weight of an adjacent successor.
   static const uint32_t DEFAULT_WEIGHT = 16;
 
-  DenseMap<Edge, uint32_t> Weights;
+  DenseMap<Edge, BranchProbability> Probs;
 
   /// \brief Track the last function we run over for printing.
   Function *LastF;
@@ -146,9 +124,6 @@ class BranchProbabilityInfo {
   /// \brief Track the set of blocks that always lead to a cold call.
   SmallPtrSet<BasicBlock *, 16> PostDominatedByColdCall;
 
-  /// \brief Get sum of the block successors' weights.
-  uint32_t getSumForBlock(const BasicBlock *BB) const;
-
   bool calcUnreachableHeuristics(BasicBlock *BB);
   bool calcMetadataWeights(BasicBlock *BB);
   bool calcColdCallHeuristics(BasicBlock *BB);

llvm/include/llvm/Support/BranchProbability.h

@@ -63,11 +63,6 @@ class BranchProbability {
   static void normalizeProbabilities(ProbabilityIter Begin,
                                      ProbabilityIter End);
 
-  // Normalize a list of weights by scaling them down so that the sum of them
-  // doesn't exceed UINT32_MAX.
-  template <class WeightListIter>
-  static void normalizeEdgeWeights(WeightListIter Begin, WeightListIter End);
-
   uint32_t getNumerator() const { return N; }
   static uint32_t getDenominator() { return D; }
 
@@ -219,49 +214,6 @@ void BranchProbability::normalizeProbabilities(ProbabilityIter Begin,
     I->N = (I->N * uint64_t(D) + Sum / 2) / Sum;
 }
 
-template <class WeightListIter>
-void BranchProbability::normalizeEdgeWeights(WeightListIter Begin,
-                                             WeightListIter End) {
-  // First we compute the sum with 64-bits of precision.
-  uint64_t Sum = std::accumulate(Begin, End, uint64_t(0));
-
-  if (Sum > UINT32_MAX) {
-    // Compute the scale necessary to cause the weights to fit, and re-sum with
-    // that scale applied.
-    assert(Sum / UINT32_MAX < UINT32_MAX &&
-           "The sum of weights exceeds UINT32_MAX^2!");
-    uint32_t Scale = Sum / UINT32_MAX + 1;
-    for (auto I = Begin; I != End; ++I)
-      *I /= Scale;
-    Sum = std::accumulate(Begin, End, uint64_t(0));
-  }
-
-  // Eliminate zero weights.
-  auto ZeroWeightNum = std::count(Begin, End, 0u);
-  if (ZeroWeightNum > 0) {
-    // If all weights are zeros, replace them by 1.
-    if (Sum == 0)
-      std::fill(Begin, End, 1u);
-    else {
-      // We are converting zeros into ones, and here we need to make sure that
-      // after this the sum won't exceed UINT32_MAX.
-      if (Sum + ZeroWeightNum > UINT32_MAX) {
-        for (auto I = Begin; I != End; ++I)
-          *I /= 2;
-        ZeroWeightNum = std::count(Begin, End, 0u);
-        Sum = std::accumulate(Begin, End, uint64_t(0));
-      }
-      // Scale up non-zero weights and turn zero weights into ones.
-      uint64_t ScalingFactor = (UINT32_MAX - ZeroWeightNum) / Sum;
-      assert(ScalingFactor >= 1);
-      if (ScalingFactor > 1)
-        for (auto I = Begin; I != End; ++I)
-          *I *= ScalingFactor;
-      std::replace(Begin, End, 0u, 1u);
-    }
-  }
-}
-
 }
 
 #endif