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PtrUseVisitor.h
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1 //===- PtrUseVisitor.h - InstVisitors over a pointers uses ------*- 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 /// \file
11 /// This file provides a collection of visitors which walk the (instruction)
12 /// uses of a pointer. These visitors all provide the same essential behavior
13 /// as an InstVisitor with similar template-based flexibility and
14 /// implementation strategies.
15 ///
16 /// These can be used, for example, to quickly analyze the uses of an alloca,
17 /// global variable, or function argument.
18 ///
19 /// FIXME: Provide a variant which doesn't track offsets and is cheaper.
20 //
21 //===----------------------------------------------------------------------===//
22 
23 #ifndef LLVM_ANALYSIS_PTRUSEVISITOR_H
24 #define LLVM_ANALYSIS_PTRUSEVISITOR_H
25 
26 #include "llvm/ADT/APInt.h"
28 #include "llvm/ADT/SmallPtrSet.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/IR/CallSite.h"
31 #include "llvm/IR/DataLayout.h"
32 #include "llvm/IR/DerivedTypes.h"
33 #include "llvm/IR/InstVisitor.h"
34 #include "llvm/IR/Instruction.h"
35 #include "llvm/IR/Instructions.h"
36 #include "llvm/IR/IntrinsicInst.h"
37 #include "llvm/IR/Intrinsics.h"
38 #include "llvm/IR/Type.h"
39 #include "llvm/IR/Use.h"
40 #include "llvm/IR/User.h"
41 #include "llvm/Support/Casting.h"
42 #include <algorithm>
43 #include <cassert>
44 #include <type_traits>
45 
46 namespace llvm {
47 
48 namespace detail {
49 
50 /// \brief Implementation of non-dependent functionality for \c PtrUseVisitor.
51 ///
52 /// See \c PtrUseVisitor for the public interface and detailed comments about
53 /// usage. This class is just a helper base class which is not templated and
54 /// contains all common code to be shared between different instantiations of
55 /// PtrUseVisitor.
57 public:
58  /// \brief This class provides information about the result of a visit.
59  ///
60  /// After walking all the users (recursively) of a pointer, the basic
61  /// infrastructure records some commonly useful information such as escape
62  /// analysis and whether the visit completed or aborted early.
63  class PtrInfo {
64  public:
65  PtrInfo() : AbortedInfo(nullptr, false), EscapedInfo(nullptr, false) {}
66 
67  /// \brief Reset the pointer info, clearing all state.
68  void reset() {
69  AbortedInfo.setPointer(nullptr);
70  AbortedInfo.setInt(false);
71  EscapedInfo.setPointer(nullptr);
72  EscapedInfo.setInt(false);
73  }
74 
75  /// \brief Did we abort the visit early?
76  bool isAborted() const { return AbortedInfo.getInt(); }
77 
78  /// \brief Is the pointer escaped at some point?
79  bool isEscaped() const { return EscapedInfo.getInt(); }
80 
81  /// \brief Get the instruction causing the visit to abort.
82  /// \returns a pointer to the instruction causing the abort if one is
83  /// available; otherwise returns null.
84  Instruction *getAbortingInst() const { return AbortedInfo.getPointer(); }
85 
86  /// \brief Get the instruction causing the pointer to escape.
87  /// \returns a pointer to the instruction which escapes the pointer if one
88  /// is available; otherwise returns null.
89  Instruction *getEscapingInst() const { return EscapedInfo.getPointer(); }
90 
91  /// \brief Mark the visit as aborted. Intended for use in a void return.
92  /// \param I The instruction which caused the visit to abort, if available.
93  void setAborted(Instruction *I = nullptr) {
94  AbortedInfo.setInt(true);
95  AbortedInfo.setPointer(I);
96  }
97 
98  /// \brief Mark the pointer as escaped. Intended for use in a void return.
99  /// \param I The instruction which escapes the pointer, if available.
100  void setEscaped(Instruction *I = nullptr) {
101  EscapedInfo.setInt(true);
102  EscapedInfo.setPointer(I);
103  }
104 
105  /// \brief Mark the pointer as escaped, and the visit as aborted. Intended
106  /// for use in a void return.
107  /// \param I The instruction which both escapes the pointer and aborts the
108  /// visit, if available.
109  void setEscapedAndAborted(Instruction *I = nullptr) {
110  setEscaped(I);
111  setAborted(I);
112  }
113 
114  private:
115  PointerIntPair<Instruction *, 1, bool> AbortedInfo, EscapedInfo;
116  };
117 
118 protected:
119  const DataLayout &DL;
120 
121  /// \name Visitation infrastructure
122  /// @{
123 
124  /// \brief The info collected about the pointer being visited thus far.
126 
127  /// \brief A struct of the data needed to visit a particular use.
128  ///
129  /// This is used to maintain a worklist fo to-visit uses. This is used to
130  /// make the visit be iterative rather than recursive.
131  struct UseToVisit {
133 
136  };
137 
138  /// \brief The worklist of to-visit uses.
140 
141  /// \brief A set of visited uses to break cycles in unreachable code.
143 
144  /// @}
145 
146  /// \name Per-visit state
147  /// This state is reset for each instruction visited.
148  /// @{
149 
150  /// \brief The use currently being visited.
151  Use *U;
152 
153  /// \brief True if we have a known constant offset for the use currently
154  /// being visited.
156 
157  /// \brief The constant offset of the use if that is known.
159 
160  /// @}
161 
162  /// Note that the constructor is protected because this class must be a base
163  /// class, we can't create instances directly of this class.
164  PtrUseVisitorBase(const DataLayout &DL) : DL(DL) {}
165 
166  /// \brief Enqueue the users of this instruction in the visit worklist.
167  ///
168  /// This will visit the users with the same offset of the current visit
169  /// (including an unknown offset if that is the current state).
170  void enqueueUsers(Instruction &I);
171 
172  /// \brief Walk the operands of a GEP and adjust the offset as appropriate.
173  ///
174  /// This routine does the heavy lifting of the pointer walk by computing
175  /// offsets and looking through GEPs.
177 };
178 
179 } // end namespace detail
180 
181 /// \brief A base class for visitors over the uses of a pointer value.
182 ///
183 /// Once constructed, a user can call \c visit on a pointer value, and this
184 /// will walk its uses and visit each instruction using an InstVisitor. It also
185 /// provides visit methods which will recurse through any pointer-to-pointer
186 /// transformations such as GEPs and bitcasts.
187 ///
188 /// During the visit, the current Use* being visited is available to the
189 /// subclass, as well as the current offset from the original base pointer if
190 /// known.
191 ///
192 /// The recursive visit of uses is accomplished with a worklist, so the only
193 /// ordering guarantee is that an instruction is visited before any uses of it
194 /// are visited. Note that this does *not* mean before any of its users are
195 /// visited! This is because users can be visited multiple times due to
196 /// multiple, different uses of pointers derived from the same base.
197 ///
198 /// A particular Use will only be visited once, but a User may be visited
199 /// multiple times, once per Use. This visits may notably have different
200 /// offsets.
201 ///
202 /// All visit methods on the underlying InstVisitor return a boolean. This
203 /// return short-circuits the visit, stopping it immediately.
204 ///
205 /// FIXME: Generalize this for all values rather than just instructions.
206 template <typename DerivedT>
207 class PtrUseVisitor : protected InstVisitor<DerivedT>,
209  friend class InstVisitor<DerivedT>;
210 
211  using Base = InstVisitor<DerivedT>;
212 
213 public:
215  static_assert(std::is_base_of<PtrUseVisitor, DerivedT>::value,
216  "Must pass the derived type to this template!");
217  }
218 
219  /// \brief Recursively visit the uses of the given pointer.
220  /// \returns An info struct about the pointer. See \c PtrInfo for details.
222  // This must be a pointer type. Get an integer type suitable to hold
223  // offsets on this pointer.
224  // FIXME: Support a vector of pointers.
225  assert(I.getType()->isPointerTy());
226  IntegerType *IntPtrTy = cast<IntegerType>(DL.getIntPtrType(I.getType()));
227  IsOffsetKnown = true;
228  Offset = APInt(IntPtrTy->getBitWidth(), 0);
229  PI.reset();
230 
231  // Enqueue the uses of this pointer.
232  enqueueUsers(I);
233 
234  // Visit all the uses off the worklist until it is empty.
235  while (!Worklist.empty()) {
236  UseToVisit ToVisit = Worklist.pop_back_val();
237  U = ToVisit.UseAndIsOffsetKnown.getPointer();
239  if (IsOffsetKnown)
240  Offset = std::move(ToVisit.Offset);
241 
242  Instruction *I = cast<Instruction>(U->getUser());
243  static_cast<DerivedT*>(this)->visit(I);
244  if (PI.isAborted())
245  break;
246  }
247  return PI;
248  }
249 
250 protected:
252  if (SI.getValueOperand() == U->get())
253  PI.setEscaped(&SI);
254  }
255 
257  enqueueUsers(BC);
258  }
259 
261  PI.setEscaped(&I);
262  }
263 
265  if (GEPI.use_empty())
266  return;
267 
268  // If we can't walk the GEP, clear the offset.
269  if (!adjustOffsetForGEP(GEPI)) {
270  IsOffsetKnown = false;
271  Offset = APInt();
272  }
273 
274  // Enqueue the users now that the offset has been adjusted.
275  enqueueUsers(GEPI);
276  }
277 
278  // No-op intrinsics which we know don't escape the pointer to to logic in
279  // some other function.
283  switch (II.getIntrinsicID()) {
284  default:
285  return Base::visitIntrinsicInst(II);
286 
287  case Intrinsic::lifetime_start:
288  case Intrinsic::lifetime_end:
289  return; // No-op intrinsics.
290  }
291  }
292 
293  // Generically, arguments to calls and invokes escape the pointer to some
294  // other function. Mark that.
297  Base::visitCallSite(CS);
298  }
299 };
300 
301 } // end namespace llvm
302 
303 #endif // LLVM_ANALYSIS_PTRUSEVISITOR_H
Value * getValueOperand()
Definition: Instructions.h:395
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:109
void setEscaped(Instruction *I=nullptr)
Mark the pointer as escaped.
void setInt(IntType IntVal)
Base class for instruction visitors.
Definition: InstVisitor.h:81
void visitCallSite(CallSite CS)
void visitMemIntrinsic(MemIntrinsic &I)
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
PointerTy getPointer() const
Use * U
The use currently being visited.
SmallPtrSet< Use *, 8 > VisitedUses
A set of visited uses to break cycles in unreachable code.
Implementation of non-dependent functionality for PtrUseVisitor.
Definition: PtrUseVisitor.h:56
This class provides information about the result of a visit.
Definition: PtrUseVisitor.h:63
Instruction * getAbortingInst() const
Get the instruction causing the visit to abort.
Definition: PtrUseVisitor.h:84
PtrUseVisitor(const DataLayout &DL)
This defines the Use class.
void visitBitCastInst(BitCastInst &BC)
void setPointer(PointerTy PtrVal)
bool IsOffsetKnown
True if we have a known constant offset for the use currently being visited.
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
bool isAborted() const
Did we abort the visit early?
Definition: PtrUseVisitor.h:76
InstrTy * getInstruction() const
Definition: CallSite.h:92
void visitStoreInst(StoreInst &SI)
PtrUseVisitorBase(const DataLayout &DL)
Note that the constructor is protected because this class must be a base class, we can&#39;t create insta...
This file implements a class to represent arbitrary precision integral constant values and operations...
This class represents a cast from a pointer to an integer.
A struct of the data needed to visit a particular use.
A base class for visitors over the uses of a pointer value.
SmallVector< UseToVisit, 8 > Worklist
The worklist of to-visit uses.
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:245
void setAborted(Instruction *I=nullptr)
Mark the visit as aborted.
Definition: PtrUseVisitor.h:93
IntType getInt() const
This class represents a no-op cast from one type to another.
An instruction for storing to memory.
Definition: Instructions.h:306
void visitDbgInfoIntrinsic(DbgInfoIntrinsic &I)
an instruction for type-safe pointer arithmetic to access elements of arrays and structs ...
Definition: Instructions.h:837
IntegerType * getIntPtrType(LLVMContext &C, unsigned AddressSpace=0) const
Returns an integer type with size at least as big as that of a pointer in the given address space...
Definition: DataLayout.cpp:702
void enqueueUsers(Instruction &I)
Enqueue the users of this instruction in the visit worklist.
bool isPointerTy() const
True if this is an instance of PointerType.
Definition: Type.h:221
Class to represent integer types.
Definition: DerivedTypes.h:40
PtrInfo PI
The info collected about the pointer being visited thus far.
Intrinsic::ID getIntrinsicID() const
Return the intrinsic ID of this intrinsic.
Definition: IntrinsicInst.h:51
bool adjustOffsetForGEP(GetElementPtrInst &GEPI)
Walk the operands of a GEP and adjust the offset as appropriate.
This is the common base class for memset/memcpy/memmove.
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:418
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:864
This is the common base class for debug info intrinsics.
Definition: IntrinsicInst.h:67
void setEscapedAndAborted(Instruction *I=nullptr)
Mark the pointer as escaped, and the visit as aborted.
void visitGetElementPtrInst(GetElementPtrInst &GEPI)
Class for arbitrary precision integers.
Definition: APInt.h:69
void visitIntrinsicInst(IntrinsicInst &II)
void visitPtrToIntInst(PtrToIntInst &I)
#define I(x, y, z)
Definition: MD5.cpp:58
Instruction * getEscapingInst() const
Get the instruction causing the pointer to escape.
Definition: PtrUseVisitor.h:89
void reset()
Reset the pointer info, clearing all state.
Definition: PtrUseVisitor.h:68
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
APInt Offset
The constant offset of the use if that is known.
PtrInfo visitPtr(Instruction &I)
Recursively visit the uses of the given pointer.
bool use_empty() const
Definition: Value.h:328
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:44
bool isEscaped() const
Is the pointer escaped at some point?
Definition: PtrUseVisitor.h:79