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 
21 void BranchProbability::print(raw_ostream &OS) const {
22   OS << N << " / " << D << " = " << format("%g%%", ((double)N / D) * 100.0);
23 }
24 
25 void BranchProbability::dump() const {
26   dbgs() << *this << '\n';
27 }
28 
29 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
30   assert(D && "divide by 0");
31 
32   // Fast path for multiplying by 1.0.
33   if (!Num || D == N)
34     return Num;
35 
36   // Split Num into upper and lower parts to multiply, then recombine.
37   uint64_t ProductHigh = (Num >> 32) * N;
38   uint64_t ProductLow = (Num & UINT32_MAX) * N;
39 
40   // Split into 32-bit digits.
41   uint32_t Upper32 = ProductHigh >> 32;
42   uint32_t Lower32 = ProductLow & UINT32_MAX;
43   uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
44   uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
45 
46   // Carry.
47   Upper32 += Mid32 < Mid32Partial;
48 
49   // Check for overflow.
50   if (Upper32 >= D)
51     return UINT64_MAX;
52 
53   uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
54   uint64_t UpperQ = Rem / D;
55 
56   // Check for overflow.
57   if (UpperQ > UINT32_MAX)
58     return UINT64_MAX;
59 
60   Rem = ((Rem % D) << 32) | Lower32;
61   uint64_t LowerQ = Rem / D;
62   uint64_t Q = (UpperQ << 32) + LowerQ;
63 
64   // Check for overflow.
65   return Q < LowerQ ? UINT64_MAX : Q;
66 }
67 
68 uint64_t BranchProbability::scale(uint64_t Num) const {
69   return ::scale(Num, N, D);
70 }
71 
72 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
73   return ::scale(Num, D, N);
74 }
75 
76 namespace llvm {
77 
78 raw_ostream &operator<<(raw_ostream &OS, const BranchProbability &Prob) {
79   Prob.print(OS);
80   return OS;
81 }
82 
83 }
84