1 //===-------------- lib/Support/BranchProbability.cpp -----------*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements Branch Probability class.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/Support/BranchProbability.h"
15 #include "llvm/Config/llvm-config.h"
16 #include "llvm/Support/Debug.h"
17 #include "llvm/Support/Format.h"
18 #include "llvm/Support/raw_ostream.h"
19 #include <cassert>
20
21 using namespace llvm;
22
23 const uint32_t BranchProbability::D;
24
print(raw_ostream & OS) const25 raw_ostream &BranchProbability::print(raw_ostream &OS) const {
26 if (isUnknown())
27 return OS << "?%";
28
29 // Get a percentage rounded to two decimal digits. This avoids
30 // implementation-defined rounding inside printf.
31 double Percent = rint(((double)N / D) * 100.0 * 100.0) / 100.0;
32 return OS << format("0x%08" PRIx32 " / 0x%08" PRIx32 " = %.2f%%", N, D,
33 Percent);
34 }
35
36 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
dump() const37 LLVM_DUMP_METHOD void BranchProbability::dump() const { print(dbgs()) << '\n'; }
38 #endif
39
BranchProbability(uint32_t Numerator,uint32_t Denominator)40 BranchProbability::BranchProbability(uint32_t Numerator, uint32_t Denominator) {
41 assert(Denominator > 0 && "Denominator cannot be 0!");
42 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
43 if (Denominator == D)
44 N = Numerator;
45 else {
46 uint64_t Prob64 =
47 (Numerator * static_cast<uint64_t>(D) + Denominator / 2) / Denominator;
48 N = static_cast<uint32_t>(Prob64);
49 }
50 }
51
52 BranchProbability
getBranchProbability(uint64_t Numerator,uint64_t Denominator)53 BranchProbability::getBranchProbability(uint64_t Numerator,
54 uint64_t Denominator) {
55 assert(Numerator <= Denominator && "Probability cannot be bigger than 1!");
56 // Scale down Denominator to fit in a 32-bit integer.
57 int Scale = 0;
58 while (Denominator > UINT32_MAX) {
59 Denominator >>= 1;
60 Scale++;
61 }
62 return BranchProbability(Numerator >> Scale, Denominator);
63 }
64
65 // If ConstD is not zero, then replace D by ConstD so that division and modulo
66 // operations by D can be optimized, in case this function is not inlined by the
67 // compiler.
68 template <uint32_t ConstD>
scale(uint64_t Num,uint32_t N,uint32_t D)69 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
70 if (ConstD > 0)
71 D = ConstD;
72
73 assert(D && "divide by 0");
74
75 // Fast path for multiplying by 1.0.
76 if (!Num || D == N)
77 return Num;
78
79 // Split Num into upper and lower parts to multiply, then recombine.
80 uint64_t ProductHigh = (Num >> 32) * N;
81 uint64_t ProductLow = (Num & UINT32_MAX) * N;
82
83 // Split into 32-bit digits.
84 uint32_t Upper32 = ProductHigh >> 32;
85 uint32_t Lower32 = ProductLow & UINT32_MAX;
86 uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
87 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
88
89 // Carry.
90 Upper32 += Mid32 < Mid32Partial;
91
92 // Check for overflow.
93 if (Upper32 >= D)
94 return UINT64_MAX;
95
96 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
97 uint64_t UpperQ = Rem / D;
98
99 // Check for overflow.
100 if (UpperQ > UINT32_MAX)
101 return UINT64_MAX;
102
103 Rem = ((Rem % D) << 32) | Lower32;
104 uint64_t LowerQ = Rem / D;
105 uint64_t Q = (UpperQ << 32) + LowerQ;
106
107 // Check for overflow.
108 return Q < LowerQ ? UINT64_MAX : Q;
109 }
110
scale(uint64_t Num) const111 uint64_t BranchProbability::scale(uint64_t Num) const {
112 return ::scale<D>(Num, N, D);
113 }
114
scaleByInverse(uint64_t Num) const115 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
116 return ::scale<0>(Num, D, N);
117 }
118