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//====--------------- lib/Support/BlockFrequency.cpp -----------*- C++ -*-====//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements Block Frequency class.
//
//===----------------------------------------------------------------------===//
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/BlockFrequency.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
using namespace llvm;
/// Multiply FREQ by N and store result in W array.
static void mult96bit(uint64_t freq, uint32_t N, uint32_t W[3]) {
uint64_t u0 = freq & UINT32_MAX;
uint64_t u1 = freq >> 32;
// Represent 96-bit value as W[2]:W[1]:W[0];
uint64_t t = u0 * N;
uint64_t k = t >> 32;
W[0] = t;
t = u1 * N + k;
W[1] = t;
W[2] = t >> 32;
}
/// Divide 96-bit value stored in W[2]:W[1]:W[0] by D. Since our word size is a
/// 32 bit unsigned integer, we can use a short division algorithm.
static uint64_t divrem96bit(uint32_t W[3], uint32_t D, uint32_t *Rout) {
// We assume that W[2] is non-zero since if W[2] is not then the user should
// just use hardware division.
assert(W[2] && "This routine assumes that W[2] is non-zero since if W[2] is "
"zero, the caller should just use 64/32 hardware.");
uint32_t Q[3] = { 0, 0, 0 };
// The generalized short division algorithm sets i to m + n - 1, where n is
// the number of words in the divisior and m is the number of words by which
// the divident exceeds the divisor (i.e. m + n == the length of the dividend
// in words). Due to our assumption that W[2] is non-zero, we know that the
// dividend is of length 3 implying since n is 1 that m = 2. Thus we set i to
// m + n - 1 = 2 + 1 - 1 = 2.
uint32_t R = 0;
for (int i = 2; i >= 0; --i) {
uint64_t PartialD = uint64_t(R) << 32 | W[i];
if (PartialD == 0) {
Q[i] = 0;
R = 0;
} else if (PartialD < D) {
Q[i] = 0;
R = uint32_t(PartialD);
} else if (PartialD == D) {
Q[i] = 1;
R = 0;
} else {
Q[i] = uint32_t(PartialD / D);
R = uint32_t(PartialD - (Q[i] * D));
}
}
// If Q[2] is non-zero, then we overflowed.
uint64_t Result;
if (Q[2]) {
Result = UINT64_MAX;
R = D;
} else {
// Form the final uint64_t result, avoiding endianness issues.
Result = uint64_t(Q[0]) | (uint64_t(Q[1]) << 32);
}
if (Rout)
*Rout = R;
return Result;
}
uint32_t BlockFrequency::scale(uint32_t N, uint32_t D) {
assert(D != 0 && "Division by zero");
// Calculate Frequency * N.
uint64_t MulLo = (Frequency & UINT32_MAX) * N;
uint64_t MulHi = (Frequency >> 32) * N;
uint64_t MulRes = (MulHi << 32) + MulLo;
// If the product fits in 64 bits, just use built-in division.
if (MulHi <= UINT32_MAX && MulRes >= MulLo) {
Frequency = MulRes / D;
return MulRes % D;
}
// Product overflowed, use 96-bit operations.
// 96-bit value represented as W[2]:W[1]:W[0].
uint32_t W[3];
uint32_t R;
mult96bit(Frequency, N, W);
Frequency = divrem96bit(W, D, &R);
return R;
}
BlockFrequency &BlockFrequency::operator*=(const BranchProbability &Prob) {
scale(Prob.getNumerator(), Prob.getDenominator());
return *this;
}
const BlockFrequency
BlockFrequency::operator*(const BranchProbability &Prob) const {
BlockFrequency Freq(Frequency);
Freq *= Prob;
return Freq;
}
BlockFrequency &BlockFrequency::operator/=(const BranchProbability &Prob) {
scale(Prob.getDenominator(), Prob.getNumerator());
return *this;
}
BlockFrequency BlockFrequency::operator/(const BranchProbability &Prob) const {
BlockFrequency Freq(Frequency);
Freq /= Prob;
return Freq;
}
BlockFrequency &BlockFrequency::operator+=(const BlockFrequency &Freq) {
uint64_t Before = Freq.Frequency;
Frequency += Freq.Frequency;
// If overflow, set frequency to the maximum value.
if (Frequency < Before)
Frequency = UINT64_MAX;
return *this;
}
const BlockFrequency
BlockFrequency::operator+(const BlockFrequency &Prob) const {
BlockFrequency Freq(Frequency);
Freq += Prob;
return Freq;
}
uint32_t BlockFrequency::scale(const BranchProbability &Prob) {
return scale(Prob.getNumerator(), Prob.getDenominator());
}
void BlockFrequency::print(raw_ostream &OS) const {
// Convert fixed-point number to decimal.
OS << Frequency / getEntryFrequency() << ".";
uint64_t Rem = Frequency % getEntryFrequency();
uint64_t Eps = 1;
do {
Rem *= 10;
Eps *= 10;
OS << Rem / getEntryFrequency();
Rem = Rem % getEntryFrequency();
} while (Rem >= Eps/2);
}
namespace llvm {
raw_ostream &operator<<(raw_ostream &OS, const BlockFrequency &Freq) {
Freq.print(OS);
return OS;
}
}
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