1 //===- llvm/Analysis/LoopAccessAnalysis.h -----------------------*- 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 interface for the loop memory dependence framework that
11 // was originally developed for the Loop Vectorizer.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_ANALYSIS_LOOPACCESSANALYSIS_H
16 #define LLVM_ANALYSIS_LOOPACCESSANALYSIS_H
18 #include "llvm/ADT/EquivalenceClasses.h"
19 #include "llvm/ADT/Optional.h"
20 #include "llvm/ADT/SetVector.h"
21 #include "llvm/Analysis/AliasAnalysis.h"
22 #include "llvm/Analysis/AliasSetTracker.h"
23 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
24 #include "llvm/IR/ValueHandle.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Support/raw_ostream.h"
33 class ScalarEvolution;
37 /// Optimization analysis message produced during vectorization. Messages inform
38 /// the user why vectorization did not occur.
39 class VectorizationReport {
44 VectorizationReport(Instruction *I = nullptr)
45 : Message("loop not vectorized: "), Instr(I) {}
47 template <typename A> VectorizationReport &operator<<(const A &Value) {
48 raw_string_ostream Out(Message);
53 Instruction *getInstr() { return Instr; }
55 std::string &str() { return Message; }
56 operator Twine() { return Message; }
58 /// \brief Emit an analysis note for \p PassName with the debug location from
59 /// the instruction in \p Message if available. Otherwise use the location of
61 static void emitAnalysis(VectorizationReport &Message,
62 const Function *TheFunction,
64 const char *PassName);
67 /// \brief Collection of parameters shared beetween the Loop Vectorizer and the
68 /// Loop Access Analysis.
69 struct VectorizerParams {
70 /// \brief Maximum SIMD width.
71 static const unsigned MaxVectorWidth;
73 /// \brief VF as overridden by the user.
74 static unsigned VectorizationFactor;
75 /// \brief Interleave factor as overridden by the user.
76 static unsigned VectorizationInterleave;
78 /// \\brief When performing memory disambiguation checks at runtime do not
79 /// make more than this number of comparisons.
80 static const unsigned RuntimeMemoryCheckThreshold;
83 /// \brief Drive the analysis of memory accesses in the loop
85 /// This class is responsible for analyzing the memory accesses of a loop. It
86 /// collects the accesses and then its main helper the AccessAnalysis class
87 /// finds and categorizes the dependences in buildDependenceSets.
89 /// For memory dependences that can be analyzed at compile time, it determines
90 /// whether the dependence is part of cycle inhibiting vectorization. This work
91 /// is delegated to the MemoryDepChecker class.
93 /// For memory dependences that cannot be determined at compile time, it
94 /// generates run-time checks to prove independence. This is done by
95 /// AccessAnalysis::canCheckPtrAtRT and the checks are maintained by the
96 /// RuntimePointerCheck class.
97 class LoopAccessInfo {
99 /// This struct holds information about the memory runtime legality check that
100 /// a group of pointers do not overlap.
101 struct RuntimePointerCheck {
102 RuntimePointerCheck() : Need(false) {}
104 /// Reset the state of the pointer runtime information.
111 DependencySetId.clear();
115 /// Insert a pointer and calculate the start and end SCEVs.
116 void insert(ScalarEvolution *SE, Loop *Lp, Value *Ptr, bool WritePtr,
117 unsigned DepSetId, unsigned ASId, ValueToValueMap &Strides);
119 /// This flag indicates if we need to add the runtime check.
121 /// Holds the pointers that we need to check.
122 SmallVector<TrackingVH<Value>, 2> Pointers;
123 /// Holds the pointer value at the beginning of the loop.
124 SmallVector<const SCEV*, 2> Starts;
125 /// Holds the pointer value at the end of the loop.
126 SmallVector<const SCEV*, 2> Ends;
127 /// Holds the information if this pointer is used for writing to memory.
128 SmallVector<bool, 2> IsWritePtr;
129 /// Holds the id of the set of pointers that could be dependent because of a
130 /// shared underlying object.
131 SmallVector<unsigned, 2> DependencySetId;
132 /// Holds the id of the disjoint alias set to which this pointer belongs.
133 SmallVector<unsigned, 2> AliasSetId;
136 LoopAccessInfo(Loop *L, ScalarEvolution *SE, const DataLayout *DL,
137 const TargetLibraryInfo *TLI, AliasAnalysis *AA,
138 DominatorTree *DT, ValueToValueMap &Strides);
140 /// Return true we can analyze the memory accesses in the loop and there are
141 /// no memory dependence cycles.
142 bool canVectorizeMemory() { return CanVecMem; }
144 RuntimePointerCheck *getRuntimePointerCheck() { return &PtrRtCheck; }
146 /// Return true if the block BB needs to be predicated in order for the loop
147 /// to be vectorized.
148 static bool blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
151 /// Returns true if the value V is uniform within the loop.
152 bool isUniform(Value *V);
154 unsigned getMaxSafeDepDistBytes() const { return MaxSafeDepDistBytes; }
155 unsigned getNumStores() const { return NumStores; }
156 unsigned getNumLoads() const { return NumLoads;}
158 /// \brief Add code that checks at runtime if the accessed arrays overlap.
160 /// Returns a pair of instructions where the first element is the first
161 /// instruction generated in possibly a sequence of instructions and the
162 /// second value is the final comparator value or NULL if no check is needed.
163 std::pair<Instruction *, Instruction *> addRuntimeCheck(Instruction *Loc);
165 /// \brief The diagnostics report generated for the analysis. E.g. why we
166 /// couldn't analyze the loop.
167 Optional<VectorizationReport> &getReport() { return Report; }
169 /// \brief Used to ensure that if the analysis was run with speculating the
170 /// value of symbolic strides, the client queries it with the same assumption.
171 /// Only used in DEBUG build but we don't want NDEBUG-depedent ABI.
172 unsigned NumSymbolicStrides;
175 /// \brief Analyze the loop. Substitute symbolic strides using Strides.
176 void analyzeLoop(ValueToValueMap &Strides);
178 void emitAnalysis(VectorizationReport &Message);
180 /// We need to check that all of the pointers in this list are disjoint
182 RuntimePointerCheck PtrRtCheck;
185 const DataLayout *DL;
186 const TargetLibraryInfo *TLI;
193 unsigned MaxSafeDepDistBytes;
195 /// \brief Cache the result of analyzeLoop.
198 /// \brief The diagnostics report generated for the analysis. E.g. why we
199 /// couldn't analyze the loop.
200 Optional<VectorizationReport> Report;
203 Value *stripIntegerCast(Value *V);
205 ///\brief Return the SCEV corresponding to a pointer with the symbolic stride
206 ///replaced with constant one.
208 /// If \p OrigPtr is not null, use it to look up the stride value instead of \p
209 /// Ptr. \p PtrToStride provides the mapping between the pointer value and its
210 /// stride as collected by LoopVectorizationLegality::collectStridedAccess.
211 const SCEV *replaceSymbolicStrideSCEV(ScalarEvolution *SE,
212 ValueToValueMap &PtrToStride,
213 Value *Ptr, Value *OrigPtr = nullptr);
215 /// \brief This analysis provides dependence information for the memory accesses
218 /// It runs the analysis for a loop on demand. This can be initiated by
219 /// querying the loop access info via LAA::getInfo. getInfo return a
220 /// LoopAccessInfo object. See this class for the specifics of what information
222 class LoopAccessAnalysis : public FunctionPass {
226 LoopAccessAnalysis() : FunctionPass(ID) {
227 initializeLoopAccessAnalysisPass(*PassRegistry::getPassRegistry());
230 bool runOnFunction(Function &F) override;
232 void getAnalysisUsage(AnalysisUsage &AU) const override;
234 /// \brief Query the result of the loop access information for the loop \p L.
236 /// If the client speculates (and then issues run-time checks) for the values
237 /// of symbolic strides, \p Strides provides the mapping (see
238 /// replaceSymbolicStrideSCEV). If there is no cached result available run
240 LoopAccessInfo &getInfo(Loop *L, ValueToValueMap &Strides);
242 void releaseMemory() override {
243 // Invalidate the cache when the pass is freed.
244 LoopAccessInfoMap.clear();
248 /// \brief The cache.
249 DenseMap<Loop *, std::unique_ptr<LoopAccessInfo>> LoopAccessInfoMap;
251 // The used analysis passes.
253 const DataLayout *DL;
254 const TargetLibraryInfo *TLI;
258 } // End llvm namespace