1 //===- llvm/Analysis/MemoryDependenceAnalysis.h - Memory Deps --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the MemoryDependenceAnalysis analysis pass.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_ANALYSIS_MEMORY_DEPENDENCE_H
15 #define LLVM_ANALYSIS_MEMORY_DEPENDENCE_H
17 #include "llvm/BasicBlock.h"
18 #include "llvm/Pass.h"
19 #include "llvm/ADT/DenseMap.h"
20 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/ADT/PointerIntPair.h"
31 /// MemDepResult - A memory dependence query can return one of three different
33 /// Normal : The query is dependent on a specific instruction.
34 /// NonLocal: The query does not depend on anything inside this block, but
35 /// we haven't scanned beyond the block to find out what.
36 /// None : The query does not depend on anything: we found the entry
37 /// block or the allocation site of the memory.
40 Invalid = 0, Normal, NonLocal, None
42 typedef PointerIntPair<Instruction*, 2, DepType> PairTy;
44 explicit MemDepResult(PairTy V) : Value(V) {}
46 MemDepResult() : Value(0, Invalid) {}
48 /// get methods: These are static ctor methods for creating various
49 /// MemDepResult kinds.
50 static MemDepResult get(Instruction *Inst) {
51 return MemDepResult(PairTy(Inst, Normal));
53 static MemDepResult getNonLocal() {
54 return MemDepResult(PairTy(0, NonLocal));
56 static MemDepResult getNone() {
57 return MemDepResult(PairTy(0, None));
60 /// isNormal - Return true if this MemDepResult represents a query that is
61 /// a normal instruction dependency.
62 bool isNormal() const { return Value.getInt() == Normal; }
64 /// isNonLocal - Return true if this MemDepResult represents an query that
65 /// is transparent to the start of the block, but where a non-local hasn't
67 bool isNonLocal() const { return Value.getInt() == NonLocal; }
69 /// isNone - Return true if this MemDepResult represents a query that
70 /// doesn't depend on any instruction.
71 bool isNone() const { return Value.getInt() == None; }
73 /// getInst() - If this is a normal dependency, return the instruction that
74 /// is depended on. Otherwise, return null.
75 Instruction *getInst() const { return isNormal() ? Value.getPointer() : 0; }
77 bool operator==(const MemDepResult &M) { return M.Value == Value; }
78 bool operator!=(const MemDepResult &M) { return M.Value != Value; }
81 /// MemoryDependenceAnalysis - This is an analysis that determines, for a
82 /// given memory operation, what preceding memory operations it depends on.
83 /// It builds on alias analysis information, and tries to provide a lazy,
84 /// caching interface to a common kind of alias information query.
86 /// The dependency information returned is somewhat unusual, but is pragmatic.
87 /// If queried about a store or call that might modify memory, the analysis
88 /// will return the instruction[s] that may either load from that memory or
89 /// store to it. If queried with a load or call that can never modify memory,
90 /// the analysis will return calls and stores that might modify the pointer,
91 /// but generally does not return loads unless a) they are volatile, or
92 /// b) they load from *must-aliased* pointers. Returning a dependence on
93 /// must-alias'd pointers instead of all pointers interacts well with the
94 /// internal caching mechanism.
96 class MemoryDependenceAnalysis : public FunctionPass {
97 /// DepType - This enum is used to indicate what flavor of dependence this
98 /// is. If the type is Normal, there is an associated instruction pointer.
100 /// Dirty - Entries with this marker occur in a LocalDeps map or
101 /// NonLocalDeps map when the instruction they previously referenced was
102 /// removed from MemDep. In either case, the entry may include an
103 /// instruction pointer. If so, the pointer is an instruction in the
104 /// block where scanning can start from, saving some work.
106 /// In a default-constructed DepResultTy object, the type will be Dirty
107 /// and the instruction pointer will be null.
111 /// Normal - This is a normal instruction dependence. The pointer member
112 /// of the DepResultTy pair holds the instruction.
115 /// None - This dependence type indicates that the query does not depend
116 /// on any instructions, either because it is not a memory instruction or
117 /// because it scanned to the definition of the memory (alloca/malloc)
121 /// NonLocal - This marker indicates that the query has no dependency in
122 /// the specified block. To find out more, the client should query other
123 /// predecessor blocks.
126 typedef PointerIntPair<Instruction*, 2, DepType> DepResultTy;
128 // A map from instructions to their dependency.
129 typedef DenseMap<Instruction*, DepResultTy> LocalDepMapType;
130 LocalDepMapType LocalDeps;
132 typedef DenseMap<BasicBlock*, DepResultTy> NonLocalDepInfo;
134 /// PerInstNLInfo - This is the instruction we keep for each cached access
135 /// that we have for an instruction. The pointer is an owning pointer and
136 /// the bool indicates whether we have any dirty bits in the set.
137 typedef PointerIntPair<NonLocalDepInfo*, 1, bool> PerInstNLInfo;
139 // A map from instructions to their non-local dependencies.
140 typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType;
142 NonLocalDepMapType NonLocalDeps;
144 // A reverse mapping from dependencies to the dependees. This is
145 // used when removing instructions to keep the cache coherent.
146 typedef DenseMap<Instruction*,
147 SmallPtrSet<Instruction*, 4> > ReverseDepMapType;
148 ReverseDepMapType ReverseLocalDeps;
150 // A reverse mapping form dependencies to the non-local dependees.
151 ReverseDepMapType ReverseNonLocalDeps;
153 /// Current AA implementation, just a cache.
157 MemoryDependenceAnalysis() : FunctionPass(&ID) {}
160 /// Pass Implementation stuff. This doesn't do any analysis eagerly.
161 bool runOnFunction(Function &);
163 /// Clean up memory in between runs
164 void releaseMemory() {
166 for (NonLocalDepMapType::iterator I = NonLocalDeps.begin(),
167 E = NonLocalDeps.end(); I != E; ++I)
168 delete I->second.getPointer();
169 NonLocalDeps.clear();
170 ReverseLocalDeps.clear();
171 ReverseNonLocalDeps.clear();
174 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering
175 /// and Alias Analysis.
177 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
179 /// getDependency - Return the instruction on which a memory operation
180 /// depends. See the class comment for more details.
181 MemDepResult getDependency(Instruction *QueryInst);
183 /// getDependencyFrom - Return the instruction on which the memory operation
184 /// 'QueryInst' depends. This starts scanning from the instruction before
185 /// the position indicated by ScanIt.
187 /// Note that this method does no caching at all. You should use
188 /// getDependency where possible.
189 MemDepResult getDependencyFrom(Instruction *QueryInst,
190 BasicBlock::iterator ScanIt, BasicBlock *BB){
191 return ConvToResult(getDependencyFromInternal(QueryInst, ScanIt, BB));
195 /// getNonLocalDependency - Perform a full dependency query for the
196 /// specified instruction, returning the set of blocks that the value is
197 /// potentially live across. The returned set of results will include a
198 /// "NonLocal" result for all blocks where the value is live across.
200 /// This method assumes the instruction returns a "nonlocal" dependency
201 /// within its own block.
202 void getNonLocalDependency(Instruction *QueryInst,
203 SmallVectorImpl<std::pair<BasicBlock*,
204 MemDepResult> > &Result);
206 /// removeInstruction - Remove an instruction from the dependence analysis,
207 /// updating the dependence of instructions that previously depended on it.
208 void removeInstruction(Instruction *InstToRemove);
211 MemDepResult ConvToResult(DepResultTy R) {
212 if (R.getInt() == Normal)
213 return MemDepResult::get(R.getPointer());
214 if (R.getInt() == NonLocal)
215 return MemDepResult::getNonLocal();
216 assert(R.getInt() == None && "Unknown MemDepResult!");
217 return MemDepResult::getNone();
220 /// verifyRemoved - Verify that the specified instruction does not occur
221 /// in our internal data structures.
222 void verifyRemoved(Instruction *Inst) const;
224 /// getDependencyFromInternal - Return the instruction on which the memory
225 /// operation 'QueryInst' depends. This starts scanning from the
226 /// instruction before the position indicated by ScanIt.
227 DepResultTy getDependencyFromInternal(Instruction *QueryInst,
228 BasicBlock::iterator ScanIt, BasicBlock *BB);
229 DepResultTy getCallSiteDependency(CallSite C, BasicBlock::iterator ScanIt,
233 } // End llvm namespace