LLVM 17.0.0git
BranchProbability.cpp
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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
14#include "llvm/Config/llvm-config.h"
15#include "llvm/Support/Debug.h"
16#include "llvm/Support/Format.h"
18#include <cassert>
19#include <cmath>
20
21using namespace llvm;
22
23constexpr uint32_t BranchProbability::D;
24
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)
38#endif
39
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
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.
68template <uint32_t ConstD>
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 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
93 uint64_t UpperQ = Rem / D;
94
95 // Check for overflow.
96 if (UpperQ > UINT32_MAX)
97 return UINT64_MAX;
98
99 Rem = ((Rem % D) << 32) | Lower32;
100 uint64_t LowerQ = Rem / D;
101 uint64_t Q = (UpperQ << 32) + LowerQ;
102
103 // Check for overflow.
104 return Q < LowerQ ? UINT64_MAX : Q;
105}
106
108 return ::scale<D>(Num, N, D);
109}
110
112 return ::scale<0>(Num, D, N);
113}
static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D)
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
#define LLVM_DUMP_METHOD
Mark debug helper function definitions like dump() that should not be stripped from debug builds.
Definition: Compiler.h:492
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
static BranchProbability getBranchProbability(uint64_t Numerator, uint64_t Denominator)
raw_ostream & print(raw_ostream &OS) const
uint64_t scaleByInverse(uint64_t Num) const
Scale a large integer by the inverse.
uint64_t scale(uint64_t Num) const
Scale a large integer.
This class implements an extremely fast bulk output stream that can only output to a stream.
Definition: raw_ostream.h:52
#define UINT64_MAX
Definition: DataTypes.h:77
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
format_object< Ts... > format(const char *Fmt, const Ts &... Vals)
These are helper functions used to produce formatted output.
Definition: Format.h:124
#define N