1 //===-------------- lib/Support/BranchProbability.cpp -----------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements Branch Probability class.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "llvm/Support/BranchProbability.h"
14 #include "llvm/Config/llvm-config.h"
15 #include "llvm/Support/Debug.h"
16 #include "llvm/Support/Format.h"
17 #include "llvm/Support/raw_ostream.h"
18 #include <cassert>
19
20 using namespace llvm;
21
22 const uint32_t BranchProbability::D;
23
print(raw_ostream & OS) const24 raw_ostream &BranchProbability::print(raw_ostream &OS) const {
25 if (isUnknown())
26 return OS << "?%";
27
28 // Get a percentage rounded to two decimal digits. This avoids
29 // implementation-defined rounding inside printf.
30 double Percent = rint(((double)N / D) * 100.0 * 100.0) / 100.0;
31 return OS << format("0x%08" PRIx32 " / 0x%08" PRIx32 " = %.2f%%", N, D,
32 Percent);
33 }
34
35 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
dump() const36 LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; }
37 #endif
38
BranchProbability(uint32_t Numerator,uint32_t Denominator)39 BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) {
40 assert(Denominator > 0 && "Denominator cannot be 0!");
41 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
42 if (Denominator == D)
43 N = Numerator;
44 else {
45 uint64_t Prob64 =
46 (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator;
47 N = static_cast<uint32_t>(Prob64);
48 }
49 }
50
51 BranchProbability
getBranchProbability(uint64_t Numerator,uint64_t Denominator)52 BranchProbability::getBranchProbability(uint64_t Numerator,
53 uint64_t Denominator) {
54 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
55 // Scale down Denominator to fit in a 32-bit integer.
56 int Scale = 0;
57 while (Denominator > UINT32_MAX) {
58 Denominator >>= 1;
59 Scale++;
60 }
61 return BranchProbability(Numerator >> Scale, Denominator);
62 }
63
64 // If ConstD is not zero, then replace D by ConstD so that division and modulo
65 // operations by D can be optimized, in case this function is not inlined by the
66 // compiler.
67 template <uint32_t ConstD>
scale(uint64_t Num,uint32_t N,uint32_t D)68 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
69 if (ConstD > 0)
70 D = ConstD;
71
72 assert(D && "divide by 0");
73
74 // Fast path for multiplying by 1.0.
75 if (!Num || D == N)
76 return Num;
77
78 // Split Num into upper and lower parts to multiply, then recombine.
79 uint64_t ProductHigh = (Num >> 32) * N;
80 uint64_t ProductLow = (Num & UINT32_MAX) * N;
81
82 // Split into 32-bit digits.
83 uint32_t Upper32 = ProductHigh >> 32;
84 uint32_t Lower32 = ProductLow & UINT32_MAX;
85 uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
86 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
87
88 // Carry.
89 Upper32 += Mid32 < Mid32Partial;
90
91 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
92 uint64_t UpperQ = Rem / D;
93
94 // Check for overflow.
95 if (UpperQ > UINT32_MAX)
96 return UINT64_MAX;
97
98 Rem = ((Rem % D) << 32) | Lower32;
99 uint64_t LowerQ = Rem / D;
100 uint64_t Q = (UpperQ << 32) + LowerQ;
101
102 // Check for overflow.
103 return Q < LowerQ ? UINT64_MAX : Q;
104 }
105
scale(uint64_t Num) const106 uint64_t BranchProbability::scale(uint64_t Num) const {
107 return ::scale<D>(Num, N, D);
108 }
109
scaleByInverse(uint64_t Num) const110 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
111 return ::scale<0>(Num, D, N);
112 }
113