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/Support/Debug.h"
16 #include "llvm/Support/Format.h"
17 #include "llvm/Support/raw_ostream.h"
18
19 using namespace llvm;
20
print(raw_ostream & OS) const21 raw_ostream &BranchProbability::print(raw_ostream &OS) const {
22 return OS << N << " / " << D << " = "
23 << format("%g%%", ((double)N / D) * 100.0);
24 }
25
dump() const26 void BranchProbability::dump() const { print(dbgs()) << '\n'; }
27
scale(uint64_t Num,uint32_t N,uint32_t D)28 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
29 assert(D && "divide by 0");
30
31 // Fast path for multiplying by 1.0.
32 if (!Num || D == N)
33 return Num;
34
35 // Split Num into upper and lower parts to multiply, then recombine.
36 uint64_t ProductHigh = (Num >> 32) * N;
37 uint64_t ProductLow = (Num & UINT32_MAX) * N;
38
39 // Split into 32-bit digits.
40 uint32_t Upper32 = ProductHigh >> 32;
41 uint32_t Lower32 = ProductLow & UINT32_MAX;
42 uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
43 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
44
45 // Carry.
46 Upper32 += Mid32 < Mid32Partial;
47
48 // Check for overflow.
49 if (Upper32 >= D)
50 return UINT64_MAX;
51
52 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
53 uint64_t UpperQ = Rem / D;
54
55 // Check for overflow.
56 if (UpperQ > UINT32_MAX)
57 return UINT64_MAX;
58
59 Rem = ((Rem % D) << 32) | Lower32;
60 uint64_t LowerQ = Rem / D;
61 uint64_t Q = (UpperQ << 32) + LowerQ;
62
63 // Check for overflow.
64 return Q < LowerQ ? UINT64_MAX : Q;
65 }
66
scale(uint64_t Num) const67 uint64_t BranchProbability::scale(uint64_t Num) const {
68 return ::scale(Num, N, D);
69 }
70
scaleByInverse(uint64_t Num) const71 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
72 return ::scale(Num, D, N);
73 }
74