AliasAnalysis.h revision fc188b95b81332c12043173c7f517341c6ad27a9 
1//===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by the LLVM research group and is distributed under
6// the University of Illinois Open Source License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines the generic AliasAnalysis interface, which is used as the
11// common interface used by all clients of alias analysis information, and
12// implemented by all alias analysis implementations.  Mod/Ref information is
13// also captured by this interface.
14//
15// Implementations of this interface must implement the various virtual methods,
16// which automatically provides functionality for the entire suite of client
17// APIs.
18//
19// This API represents memory as a (Pointer, Size) pair.  The Pointer component
20// specifies the base memory address of the region, the Size specifies how large
21// of an area is being queried.  If Size is 0, two pointers only alias if they
22// are exactly equal.  If size is greater than zero, but small, the two pointers
23// alias if the areas pointed to overlap.  If the size is very large (ie, ~0U),
24// then the two pointers alias if they may be pointing to components of the same
25// memory object.  Pointers that point to two completely different objects in
26// memory never alias, regardless of the value of the Size component.
27//
28//===----------------------------------------------------------------------===//
29
30#ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H
31#define LLVM_ANALYSIS_ALIAS_ANALYSIS_H
32
33#include "llvm/Support/CallSite.h"
34#include "llvm/Pass.h"
35
36namespace llvm {
37
38class LoadInst;
39class StoreInst;
40class TargetData;
41class AnalysisUsage;
42class Pass;
43
44class AliasAnalysis {
45  const TargetData *TD;
46protected:
47  /// InitializeAliasAnalysis - Subclasses must call this method to initialize
48  /// the AliasAnalysis interface before any other methods are called.  This is
49  /// typically called by the run* methods of these subclasses.  This may be
50  /// called multiple times.
51  ///
52  void InitializeAliasAnalysis(Pass *P);
53
54  // getAnalysisUsage - All alias analysis implementations should invoke this
55  // directly (using AliasAnalysis::getAnalysisUsage(AU)) to make sure that
56  // TargetData is required by the pass.
57  virtual void getAnalysisUsage(AnalysisUsage &AU) const;
58
59public:
60  AliasAnalysis() : TD(0) {}
61  virtual ~AliasAnalysis();  // We want to be subclassed
62
63  /// getTargetData - Every alias analysis implementation depends on the size of
64  /// data items in the current Target.  This provides a uniform way to handle
65  /// it.
66  const TargetData &getTargetData() const { return *TD; }
67
68  //===--------------------------------------------------------------------===//
69  /// Alias Queries...
70  ///
71
72  /// Alias analysis result - Either we know for sure that it does not alias, we
73  /// know for sure it must alias, or we don't know anything: The two pointers
74  /// _might_ alias.  This enum is designed so you can do things like:
75  ///     if (AA.alias(P1, P2)) { ... }
76  /// to check to see if two pointers might alias.
77  ///
78  enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
79
80  /// alias - The main low level interface to the alias analysis implementation.
81  /// Returns a Result indicating whether the two pointers are aliased to each
82  /// other.  This is the interface that must be implemented by specific alias
83  /// analysis implementations.
84  ///
85  virtual AliasResult alias(const Value *V1, unsigned V1Size,
86                            const Value *V2, unsigned V2Size) {
87    return MayAlias;
88  }
89
90  /// getMustAliases - If there are any pointers known that must alias this
91  /// pointer, return them now.  This allows alias-set based alias analyses to
92  /// perform a form a value numbering (which is exposed by load-vn).  If an
93  /// alias analysis supports this, it should ADD any must aliased pointers to
94  /// the specified vector.
95  ///
96  virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) {}
97
98
99  //===--------------------------------------------------------------------===//
100  /// Simple mod/ref information...
101  ///
102
103  /// ModRefResult - Represent the result of a mod/ref query.  Mod and Ref are
104  /// bits which may be or'd together.
105  ///
106  enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
107
108  /// getModRefInfo - Return information about whether or not an instruction may
109  /// read or write memory specified by the pointer operand.  An instruction
110  /// that doesn't read or write memory may be trivially LICM'd for example.
111
112  /// getModRefInfo (for call sites) - Return whether information about whether
113  /// a particular call site modifies or reads the memory specified by the
114  /// pointer.
115  ///
116  virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
117    return ModRef;
118  }
119
120  /// getModRefInfo - Return information about whether two call sites may refer
121  /// to the same set of memory locations.  This function returns NoModRef if
122  /// the two calls refer to disjoint memory locations, Ref if they both read
123  /// some of the same memory, Mod if they both write to some of the same
124  /// memory, and ModRef if they read and write to the same memory.
125  ///
126  virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
127    return ModRef;
128  }
129
130  /// Convenience functions...
131  ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size);
132  ModRefResult getModRefInfo(StoreInst*S, Value *P, unsigned Size);
133  ModRefResult getModRefInfo(CallInst  *C, Value *P, unsigned Size) {
134    return getModRefInfo(CallSite(C), P, Size);
135  }
136  ModRefResult getModRefInfo(InvokeInst*I, Value *P, unsigned Size) {
137    return getModRefInfo(CallSite(I), P, Size);
138  }
139  ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) {
140    switch (I->getOpcode()) {
141    case Instruction::Load:   return getModRefInfo((LoadInst*)I, P, Size);
142    case Instruction::Store:  return getModRefInfo((StoreInst*)I, P, Size);
143    case Instruction::Call:   return getModRefInfo((CallInst*)I, P, Size);
144    case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size);
145    default:                  return NoModRef;
146    }
147  }
148
149  /// canBasicBlockModify - Return true if it is possible for execution of the
150  /// specified basic block to modify the value pointed to by Ptr.
151  ///
152  bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size);
153
154  /// canInstructionRangeModify - Return true if it is possible for the
155  /// execution of the specified instructions to modify the value pointed to by
156  /// Ptr.  The instructions to consider are all of the instructions in the
157  /// range of [I1,I2] INCLUSIVE.  I1 and I2 must be in the same basic block.
158  ///
159  bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
160                                 const Value *Ptr, unsigned Size);
161};
162
163// Because of the way .a files work, we must force the BasicAA implementation to
164// be pulled in if the AliasAnalysis header is included.  Otherwise we run
165// the risk of AliasAnalysis being used, but the default implementation not
166// being linked into the tool that uses it.
167//
168extern void BasicAAStub();
169static IncludeFile HDR_INCLUDE_BASICAA_CPP((void*)&BasicAAStub);
170
171} // End llvm namespace
172
173#endif
174