#define LLVM_SUPPORT_BRANCHPROBABILITY_H
#include "llvm/Support/DataTypes.h"
+#include <algorithm>
+#include <cassert>
+#include <climits>
+#include <numeric>
namespace llvm {
class raw_ostream;
-// This class represents Branch Probability as a non-negative fraction.
+// This class represents Branch Probability as a non-negative fraction that is
+// no greater than 1. It uses a fixed-point-like implementation, in which the
+// denominator is always a constant value (here we use 1<<31 for maximum
+// precision).
class BranchProbability {
-
// Numerator
uint32_t N;
- // Denominator
- uint32_t D;
+ // 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.
+ explicit BranchProbability(uint32_t n) : N(n) {}
public:
- BranchProbability(uint32_t n, uint32_t d);
+ BranchProbability() : N(0) {}
+ 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 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.
+ template <class WeightListIter>
+ static void normalizeEdgeWeights(WeightListIter Begin, WeightListIter End);
uint32_t getNumerator() const { return N; }
- uint32_t getDenominator() const { return D; }
+ static uint32_t getDenominator() { return D; }
// Return (1 - Probability).
- BranchProbability getCompl() {
- return BranchProbability(D - N, D);
- }
+ BranchProbability getCompl() const { return BranchProbability(D - N); }
raw_ostream &print(raw_ostream &OS) const;
void dump() const;
+
+ /// \brief Scale a large integer.
+ ///
+ /// Scales \c Num. Guarantees full precision. Returns the floor of the
+ /// result.
+ ///
+ /// \return \c Num times \c this.
+ uint64_t scale(uint64_t Num) const;
+
+ /// \brief Scale a large integer by the inverse.
+ ///
+ /// Scales \c Num by the inverse of \c this. Guarantees full precision.
+ /// Returns the floor of the result.
+ ///
+ /// \return \c Num divided by \c this.
+ uint64_t scaleByInverse(uint64_t Num) const;
+
+ BranchProbability &operator+=(BranchProbability RHS) {
+ // Saturate the result in case of overflow.
+ N = (uint64_t(N) + RHS.N > D) ? D : N + RHS.N;
+ return *this;
+ }
+
+ BranchProbability &operator-=(BranchProbability RHS) {
+ // Saturate the result in case of underflow.
+ N = N < RHS.N ? 0 : N - RHS.N;
+ return *this;
+ }
+
+ BranchProbability &operator*=(BranchProbability RHS) {
+ N = (static_cast<uint64_t>(N) * RHS.N + D / 2) / D;
+ return *this;
+ }
+
+ BranchProbability operator+(BranchProbability RHS) const {
+ BranchProbability Prob(*this);
+ return Prob += RHS;
+ }
+
+ BranchProbability operator-(BranchProbability RHS) const {
+ BranchProbability Prob(*this);
+ return Prob -= RHS;
+ }
+
+ BranchProbability operator*(BranchProbability RHS) const {
+ BranchProbability Prob(*this);
+ return Prob *= RHS;
+ }
+
+ bool operator==(BranchProbability RHS) const { return N == RHS.N; }
+ bool operator!=(BranchProbability RHS) const { return !(*this == RHS); }
+ bool operator<(BranchProbability RHS) const { return N < RHS.N; }
+ bool operator>(BranchProbability RHS) const { return RHS < *this; }
+ bool operator<=(BranchProbability RHS) const { return !(RHS < *this); }
+ bool operator>=(BranchProbability RHS) const { return !(*this < RHS); }
};
-raw_ostream &operator<<(raw_ostream &OS, const BranchProbability &Prob);
+inline raw_ostream &operator<<(raw_ostream &OS, BranchProbability Prob) {
+ return Prob.print(OS);
+}
+
+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 I = Begin; I != End; ++I)
+ Sum += I->N;
+ assert(Sum > 0);
+ for (auto I = Begin; I != End; ++I)
+ 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);
+ }
+ }
+}
}
projects / oota-llvm.git / blobdiff