1 //===-- User.cpp - Implement the User 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/User.h"
10 #include "llvm/IR/Constant.h"
11 #include "llvm/IR/GlobalValue.h"
12 #include "llvm/IR/IntrinsicInst.h"
13 
14 namespace llvm {
15 class BasicBlock;
16 
17 //===----------------------------------------------------------------------===//
18 //                                 User Class
19 //===----------------------------------------------------------------------===//
20 
21 void User::replaceUsesOfWith(Value *From, Value *To) {
22   if (From == To) return;   // Duh what?
23 
24   assert((!isa<Constant>(this) || isa<GlobalValue>(this)) &&
25          "Cannot call User::replaceUsesOfWith on a constant!");
26 
27   for (unsigned i = 0, E = getNumOperands(); i != E; ++i)
28     if (getOperand(i) == From) {  // Is This operand is pointing to oldval?
29       // The side effects of this setOperand call include linking to
30       // "To", adding "this" to the uses list of To, and
31       // most importantly, removing "this" from the use list of "From".
32       setOperand(i, To);
33     }
34 }
35 
36 //===----------------------------------------------------------------------===//
37 //                         User allocHungoffUses Implementation
38 //===----------------------------------------------------------------------===//
39 
40 void User::allocHungoffUses(unsigned N, bool IsPhi) {
41   assert(HasHungOffUses && "alloc must have hung off uses");
42 
43   static_assert(alignof(Use) >= alignof(BasicBlock *),
44                 "Alignment is insufficient for 'hung-off-uses' pieces");
45 
46   // Allocate the array of Uses
47   size_t size = N * sizeof(Use);
48   if (IsPhi)
49     size += N * sizeof(BasicBlock *);
50   Use *Begin = static_cast<Use*>(::operator new(size));
51   Use *End = Begin + N;
52   setOperandList(Begin);
53   for (; Begin != End; Begin++)
54     new (Begin) Use(this);
55 }
56 
57 void User::growHungoffUses(unsigned NewNumUses, bool IsPhi) {
58   assert(HasHungOffUses && "realloc must have hung off uses");
59 
60   unsigned OldNumUses = getNumOperands();
61 
62   // We don't support shrinking the number of uses.  We wouldn't have enough
63   // space to copy the old uses in to the new space.
64   assert(NewNumUses > OldNumUses && "realloc must grow num uses");
65 
66   Use *OldOps = getOperandList();
67   allocHungoffUses(NewNumUses, IsPhi);
68   Use *NewOps = getOperandList();
69 
70   // Now copy from the old operands list to the new one.
71   std::copy(OldOps, OldOps + OldNumUses, NewOps);
72 
73   // If this is a Phi, then we need to copy the BB pointers too.
74   if (IsPhi) {
75     auto *OldPtr = reinterpret_cast<char *>(OldOps + OldNumUses);
76     auto *NewPtr = reinterpret_cast<char *>(NewOps + NewNumUses);
77     std::copy(OldPtr, OldPtr + (OldNumUses * sizeof(BasicBlock *)), NewPtr);
78   }
79   Use::zap(OldOps, OldOps + OldNumUses, true);
80 }
81 
82 
83 // This is a private struct used by `User` to track the co-allocated descriptor
84 // section.
85 struct DescriptorInfo {
86   intptr_t SizeInBytes;
87 };
88 
89 ArrayRef<const uint8_t> User::getDescriptor() const {
90   auto MutableARef = const_cast<User *>(this)->getDescriptor();
91   return {MutableARef.begin(), MutableARef.end()};
92 }
93 
94 MutableArrayRef<uint8_t> User::getDescriptor() {
95   assert(HasDescriptor && "Don't call otherwise!");
96   assert(!HasHungOffUses && "Invariant!");
97 
98   auto *DI = reinterpret_cast<DescriptorInfo *>(getIntrusiveOperands()) - 1;
99   assert(DI->SizeInBytes != 0 && "Should not have had a descriptor otherwise!");
100 
101   return MutableArrayRef<uint8_t>(
102       reinterpret_cast<uint8_t *>(DI) - DI->SizeInBytes, DI->SizeInBytes);
103 }
104 
105 bool User::isDroppable() const {
106   if (const auto *Intr = dyn_cast<IntrinsicInst>(this))
107     return Intr->getIntrinsicID() == Intrinsic::assume;
108   return false;
109 }
110 
111 //===----------------------------------------------------------------------===//
112 //                         User operator new Implementations
113 //===----------------------------------------------------------------------===//
114 
115 void *User::allocateFixedOperandUser(size_t Size, unsigned Us,
116                                      unsigned DescBytes) {
117   assert(Us < (1u << NumUserOperandsBits) && "Too many operands");
118 
119   static_assert(sizeof(DescriptorInfo) % sizeof(void *) == 0, "Required below");
120 
121   unsigned DescBytesToAllocate =
122       DescBytes == 0 ? 0 : (DescBytes + sizeof(DescriptorInfo));
123   assert(DescBytesToAllocate % sizeof(void *) == 0 &&
124          "We need this to satisfy alignment constraints for Uses");
125 
126   uint8_t *Storage = static_cast<uint8_t *>(
127       ::operator new(Size + sizeof(Use) * Us + DescBytesToAllocate));
128   Use *Start = reinterpret_cast<Use *>(Storage + DescBytesToAllocate);
129   Use *End = Start + Us;
130   User *Obj = reinterpret_cast<User*>(End);
131   Obj->NumUserOperands = Us;
132   Obj->HasHungOffUses = false;
133   Obj->HasDescriptor = DescBytes != 0;
134   for (; Start != End; Start++)
135     new (Start) Use(Obj);
136 
137   if (DescBytes != 0) {
138     auto *DescInfo = reinterpret_cast<DescriptorInfo *>(Storage + DescBytes);
139     DescInfo->SizeInBytes = DescBytes;
140   }
141 
142   return Obj;
143 }
144 
145 void *User::operator new(size_t Size, unsigned Us) {
146   return allocateFixedOperandUser(Size, Us, 0);
147 }
148 
149 void *User::operator new(size_t Size, unsigned Us, unsigned DescBytes) {
150   return allocateFixedOperandUser(Size, Us, DescBytes);
151 }
152 
153 void *User::operator new(size_t Size) {
154   // Allocate space for a single Use*
155   void *Storage = ::operator new(Size + sizeof(Use *));
156   Use **HungOffOperandList = static_cast<Use **>(Storage);
157   User *Obj = reinterpret_cast<User *>(HungOffOperandList + 1);
158   Obj->NumUserOperands = 0;
159   Obj->HasHungOffUses = true;
160   Obj->HasDescriptor = false;
161   *HungOffOperandList = nullptr;
162   return Obj;
163 }
164 
165 //===----------------------------------------------------------------------===//
166 //                         User operator delete Implementation
167 //===----------------------------------------------------------------------===//
168 
169 // Repress memory sanitization, due to use-after-destroy by operator
170 // delete. Bug report 24578 identifies this issue.
171 LLVM_NO_SANITIZE_MEMORY_ATTRIBUTE void User::operator delete(void *Usr) {
172   // Hung off uses use a single Use* before the User, while other subclasses
173   // use a Use[] allocated prior to the user.
174   User *Obj = static_cast<User *>(Usr);
175   if (Obj->HasHungOffUses) {
176     assert(!Obj->HasDescriptor && "not supported!");
177 
178     Use **HungOffOperandList = static_cast<Use **>(Usr) - 1;
179     // drop the hung off uses.
180     Use::zap(*HungOffOperandList, *HungOffOperandList + Obj->NumUserOperands,
181              /* Delete */ true);
182     ::operator delete(HungOffOperandList);
183   } else if (Obj->HasDescriptor) {
184     Use *UseBegin = static_cast<Use *>(Usr) - Obj->NumUserOperands;
185     Use::zap(UseBegin, UseBegin + Obj->NumUserOperands, /* Delete */ false);
186 
187     auto *DI = reinterpret_cast<DescriptorInfo *>(UseBegin) - 1;
188     uint8_t *Storage = reinterpret_cast<uint8_t *>(DI) - DI->SizeInBytes;
189     ::operator delete(Storage);
190   } else {
191     Use *Storage = static_cast<Use *>(Usr) - Obj->NumUserOperands;
192     Use::zap(Storage, Storage + Obj->NumUserOperands,
193              /* Delete */ false);
194     ::operator delete(Storage);
195   }
196 }
197 
198 } // namespace llvm
199