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annotate lib/Support/BranchProbability.cpp @ 77:54457678186b

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LLVM 3.6
author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Mon, 08 Sep 2014 22:06:00 +0900
parents 95c75e76d11b
children afa8332a0e37
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1 //===-------------- lib/Support/BranchProbability.cpp -----------*- C++ -*-===//
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2 //
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3 // The LLVM Compiler Infrastructure
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4 //
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5 // This file is distributed under the University of Illinois Open Source
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6 // License. See LICENSE.TXT for details.
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7 //
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8 //===----------------------------------------------------------------------===//
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9 //
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10 // This file implements Branch Probability class.
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11 //
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12 //===----------------------------------------------------------------------===//
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13
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14 #include "llvm/Support/BranchProbability.h"
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15 #include "llvm/Support/Debug.h"
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16 #include "llvm/Support/Format.h"
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17 #include "llvm/Support/raw_ostream.h"
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18
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19 using namespace llvm;
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21 raw_ostream &BranchProbability::print(raw_ostream &OS) const {
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22 return OS << N << " / " << D << " = "
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23 << format("%g%%", ((double)N / D) * 100.0);
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24 }
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25
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26 void BranchProbability::dump() const { print(dbgs()) << '\n'; }
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27
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28 static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) {
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29 assert(D && "divide by 0");
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30
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31 // Fast path for multiplying by 1.0.
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32 if (!Num || D == N)
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33 return Num;
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34
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35 // Split Num into upper and lower parts to multiply, then recombine.
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36 uint64_t ProductHigh = (Num >> 32) * N;
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37 uint64_t ProductLow = (Num & UINT32_MAX) * N;
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38
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39 // Split into 32-bit digits.
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40 uint32_t Upper32 = ProductHigh >> 32;
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41 uint32_t Lower32 = ProductLow & UINT32_MAX;
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42 uint32_t Mid32Partial = ProductHigh & UINT32_MAX;
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43 uint32_t Mid32 = Mid32Partial + (ProductLow >> 32);
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44
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45 // Carry.
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46 Upper32 += Mid32 < Mid32Partial;
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47
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48 // Check for overflow.
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49 if (Upper32 >= D)
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50 return UINT64_MAX;
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51
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52 uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32;
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53 uint64_t UpperQ = Rem / D;
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54
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55 // Check for overflow.
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56 if (UpperQ > UINT32_MAX)
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57 return UINT64_MAX;
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58
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59 Rem = ((Rem % D) << 32) | Lower32;
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60 uint64_t LowerQ = Rem / D;
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61 uint64_t Q = (UpperQ << 32) + LowerQ;
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62
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63 // Check for overflow.
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64 return Q < LowerQ ? UINT64_MAX : Q;
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65 }
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67 uint64_t BranchProbability::scale(uint64_t Num) const {
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68 return ::scale(Num, N, D);
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69 }
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71 uint64_t BranchProbability::scaleByInverse(uint64_t Num) const {
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72 return ::scale(Num, D, N);
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73 }