Let += and -= operators in BranchProbability have saturation behaviors.

[oota-llvm.git] / include / llvm / Support / BranchProbability.h

diff --git a/include/llvm/Support/BranchProbability.h b/include/llvm/Support/BranchProbability.h
index f204777066e9be5b0dfd2b3eff63822884e512b7..1ca94ca3196fc50b372e10712a6404eac853cdf1 100644 (file)
--- a/include/llvm/Support/BranchProbability.h
+++ b/include/llvm/Support/BranchProbability.h
@@ -34,6 +34,7 @@ class BranchProbability {
 
   // Denominator, which is a constant value.
   static const uint32_t D = 1u << 31;
+  static const uint32_t UnknownN = UINT32_MAX;
 
   // Construct a BranchProbability with only numerator assuming the denominator
   // is 1<<31. For internal use only.
@@ -44,17 +45,20 @@ public:
   BranchProbability(uint32_t Numerator, uint32_t Denominator);
 
   bool isZero() const { return N == 0; }
+  bool isUnknown() const { return N == UnknownN; }
 
   static BranchProbability getZero() { return BranchProbability(0); }
   static BranchProbability getOne() { return BranchProbability(D); }
+  static BranchProbability getUnknown() { return BranchProbability(UnknownN); }
   // Create a BranchProbability object with the given numerator and 1<<31
   // as denominator.
   static BranchProbability getRaw(uint32_t N) { return BranchProbability(N); }
 
   // Normalize given probabilties so that the sum of them becomes approximate
   // one.
-  template <class ProbabilityList>
-  static void normalizeProbabilities(ProbabilityList &Probs);
+  template <class ProbabilityIter>
+  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.
@@ -88,16 +92,14 @@ public:
   uint64_t scaleByInverse(uint64_t Num) const;
 
   BranchProbability &operator+=(BranchProbability RHS) {
-    assert(N <= D - RHS.N &&
-           "The sum of branch probabilities should not exceed one!");
-    N += RHS.N;
+    // Saturate the result in case of overflow.
+    N = (uint64_t(N) + RHS.N > D) ? D : N + RHS.N;
     return *this;
   }
 
   BranchProbability &operator-=(BranchProbability RHS) {
-    assert(N >= RHS.N &&
-           "Can only subtract a smaller probability from a larger one!");
-    N -= RHS.N;
+    // Saturate the result in case of underflow.
+    N = N < RHS.N ? 0 : N - RHS.N;
     return *this;
   }
 
@@ -133,14 +135,22 @@ inline raw_ostream &operator<<(raw_ostream &OS, BranchProbability Prob) {
   return Prob.print(OS);
 }
 
-template <class ProbabilityList>
-void BranchProbability::normalizeProbabilities(ProbabilityList &Probs) {
+inline BranchProbability operator/(BranchProbability LHS, uint32_t RHS) {
+  return BranchProbability::getRaw(LHS.getNumerator() / RHS);
+}
+
+template <class ProbabilityIter>
+void BranchProbability::normalizeProbabilities(ProbabilityIter Begin,
+                                               ProbabilityIter End) {
+  if (Begin == End)
+    return;
+
   uint64_t Sum = 0;
-  for (auto Prob : Probs)
-    Sum += Prob.N;
+  for (auto I = Begin; I != End; ++I)
+    Sum += I->N;
   assert(Sum > 0);
-  for (auto &Prob : Probs)
-    Prob.N = (Prob.N * uint64_t(D) + Sum / 2) / Sum;
+  for (auto I = Begin; I != End; ++I)
+    I->N = (I->N * uint64_t(D) + Sum / 2) / Sum;
 }
 
 template <class WeightListIter>