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//===-------------- lib/Support/BranchProbability.cpp -----------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements Branch Probability class.
//
//===----------------------------------------------------------------------===//
#include "llvm/Support/BranchProbability.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cmath>
using namespace llvm;
constexpr uint32_t BranchProbability::D;
raw_ostream &BranchProbability::print(raw_ostream &OS) const {
if (isUnknown())
return OS << "?%";
// Get a percentage rounded to two decimal digits. This avoids
// implementation-defined rounding inside printf.
double Percent = rint(((double)N / D) * 100.0 * 100.0) / 100.0;
return OS << format("0x%08" PRIx32 " / 0x%08" PRIx32 " = %.2f%%", N, D,
Percent);
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; }
#endif
BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) {
assert(Denominator > 0 && "Denominator cannot be 0!");
assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
if (Denominator == D)
N = Numerator;
else {
uint64_t Prob64 =
(Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator;
N = static_cast<uint32_t>(Prob64);
}
}
BranchProbability
BranchProbability::getBranchProbability(uint64_t Numerator,
uint64_t Denominator) {
assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
// Scale down Denominator to fit in a 32-bit integer.
int Scale = 0;
while (Denominator > UINT32_MAX) {
Denominator >>= 1;
Scale++;
}
return BranchProbability(Numerator >> Scale, Denominator);
}
// If ConstD is not zero, then replace D by ConstD so that division and modulo
// operations by D can be optimized, in case this function is not inlined by the
// compiler.
template <uint32_t ConstD>
static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
if (ConstD > 0)
D = ConstD;
assert(D && "divide by 0");
// Fast path for multiplying by 1.0.
if (!Num || D == N)
return Num;
// Split Num into upper and lower parts to multiply, then recombine.
uint64_t ProductHigh = (Num >> 32) * N;
uint64_t ProductLow = (Num & UINT32_MAX) * N;
// Split into 32-bit digits.
uint32_t Upper32 = ProductHigh >> 32;
uint32_t Lower32 = ProductLow & UINT32_MAX;
uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
// Carry.
Upper32 += Mid32 < Mid32Partial;
uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
uint64_t UpperQ = Rem / D;
// Check for overflow.
if (UpperQ > UINT32_MAX)
return UINT64_MAX;
Rem = ((Rem % D) << 32) | Lower32;
uint64_t LowerQ = Rem / D;
uint64_t Q = (UpperQ << 32) + LowerQ;
// Check for overflow.
return Q < LowerQ ? UINT64_MAX : Q;
}
uint64_t BranchProbability::scale(uint64_t Num) const {
return ::scale<D>(Num, N, D);
}
uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
return ::scale<0>(Num, D, N);
}
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