lib/IR/Use.cpp

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