lib/IR/Use.cpp

   1 //===-- Use.cpp - Implement the Use class ---------------------------------===//
   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 #include "llvm/IR/Use.h"
  11 #include "llvm/IR/User.h"
  12 #include "llvm/IR/Value.h"
  13 #include <new>
  14
  15 namespace llvm {
  16
  17 void Use::swap(Use &RHS) {
  18   if (Val == RHS.Val)
  19     return;
  20
  21   if (Val)
  22     removeFromList();
  23
  24   Value *OldVal = Val;
  25   if (RHS.Val) {
  26     RHS.removeFromList();
  27     Val = RHS.Val;
  28     Val->addUse(*this);
  29   } else {
  30     Val = nullptr;
  31   }
  32
  33   if (OldVal) {
  34     RHS.Val = OldVal;
  35     RHS.Val->addUse(RHS);
  36   } else {
  37     RHS.Val = nullptr;
  38   }
  39 }
  40
  41 User *Use::getUser() const {
  42   const Use *End = getImpliedUser();
  43   const UserRef *ref = reinterpret_cast<const UserRef *>(End);
  44   return ref->getInt() ? ref->getPointer()
  45                        : reinterpret_cast<User *>(const_cast<Use *>(End));
  46 }
  47
  48 unsigned Use::getOperandNo() const {
  49   return this - getUser()->op_begin();
  50 }
  51
  52 // Sets up the waymarking algorithm's tags for a series of Uses. See the
  53 // algorithm details here:
  54 //
  55 //   http://www.llvm.org/docs/ProgrammersManual.html#the-waymarking-algorithm
  56 //
  57 Use *Use::initTags(Use *const Start, Use *Stop) {
  58   ptrdiff_t Done = 0;
  59   while (Done < 20) {
  60     if (Start == Stop--)
  61       return Start;
  62     static const PrevPtrTag tags[20] = {
  63         fullStopTag,  oneDigitTag,  stopTag,      oneDigitTag, oneDigitTag,
  64         stopTag,      zeroDigitTag, oneDigitTag,  oneDigitTag, stopTag,
  65         zeroDigitTag, oneDigitTag,  zeroDigitTag, oneDigitTag, stopTag,
  66         oneDigitTag,  oneDigitTag,  oneDigitTag,  oneDigitTag, stopTag};
  67     new (Stop) Use(tags[Done++]);
  68   }
  69
  70   ptrdiff_t Count = Done;
  71   while (Start != Stop) {
  72     --Stop;
  73     if (!Count) {
  74       new (Stop) Use(stopTag);
  75       ++Done;
  76       Count = Done;
  77     } else {
  78       new (Stop) Use(PrevPtrTag(Count & 1));
  79       Count >>= 1;
  80       ++Done;
  81     }
  82   }
  83
  84   return Start;
  85 }
  86
  87 void Use::zap(Use *Start, const Use *Stop, bool del) {
  88   while (Start != Stop)
  89     (--Stop)->~Use();
  90   if (del)
  91     ::operator delete(Start);
  92 }
  93
  94 const Use *Use::getImpliedUser() const {
  95   const Use *Current = this;
  96
  97   while (true) {
  98     unsigned Tag = (Current++)->Prev.getInt();
  99     switch (Tag) {
 100     case zeroDigitTag:
 101     case oneDigitTag:
 102       continue;
 103
 104     case stopTag: {
 105       ++Current;
 106       ptrdiff_t Offset = 1;
 107       while (true) {
 108         unsigned Tag = Current->Prev.getInt();
 109         switch (Tag) {
 110         case zeroDigitTag:
 111         case oneDigitTag:
 112           ++Current;
 113           Offset = (Offset << 1) + Tag;
 114           continue;
 115         default:
 116           return Current + Offset;
 117         }
 118       }
 119     }
 120
 121     case fullStopTag:
 122       return Current;
 123     }
 124   }
 125 }
 126
 127 } // End llvm namespace