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/SetVector.h"
20 #include "llvm/Analysis/AliasAnalysis.h"
21 #include "llvm/Analysis/AliasSetTracker.h"
22 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
23 #include "llvm/IR/ValueHandle.h"
24 #include "llvm/Support/raw_ostream.h"
31 class ScalarEvolution;
35 /// Optimization analysis message produced during vectorization. Messages inform
36 /// the user why vectorization did not occur.
37 class VectorizationReport {
42 VectorizationReport(Instruction *I = nullptr)
43 : Message("loop not vectorized: "), Instr(I) {}
45 template <typename A> VectorizationReport &operator<<(const A &Value) {
46 raw_string_ostream Out(Message);
51 Instruction *getInstr() { return Instr; }
53 std::string &str() { return Message; }
54 operator Twine() { return Message; }
56 /// \brief Emit an analysis note with the debug location from the instruction
57 /// in \p Message if available. Otherwise use the location of \p TheLoop.
58 static void emitAnalysis(VectorizationReport &Message,
59 const Function *TheFunction, const Loop *TheLoop);
62 /// \brief Drive the analysis of memory accesses in the loop
64 /// This class is responsible for analyzing the memory accesses of a loop. It
65 /// collects the accesses and then its main helper the AccessAnalysis class
66 /// finds and categorizes the dependences in buildDependenceSets.
68 /// For memory dependences that can be analyzed at compile time, it determines
69 /// whether the dependence is part of cycle inhibiting vectorization. This work
70 /// is delegated to the MemoryDepChecker class.
72 /// For memory dependences that cannot be determined at compile time, it
73 /// generates run-time checks to prove independence. This is done by
74 /// AccessAnalysis::canCheckPtrAtRT and the checks are maintained by the
75 /// RuntimePointerCheck class.
76 class LoopAccessInfo {
78 /// \brief Collection of parameters used from the vectorizer.
79 struct VectorizerParams {
80 /// \brief Maximum simd width.
81 unsigned MaxVectorWidth;
83 /// \brief VF as overridden by the user.
84 unsigned VectorizationFactor;
85 /// \brief Interleave factor as overridden by the user.
86 unsigned VectorizationInterleave;
88 /// \\brief When performing memory disambiguation checks at runtime do not
89 /// make more than this number of comparisons.
90 unsigned RuntimeMemoryCheckThreshold;
92 VectorizerParams(unsigned MaxVectorWidth, unsigned VectorizationFactor,
93 unsigned VectorizationInterleave,
94 unsigned RuntimeMemoryCheckThreshold)
95 : MaxVectorWidth(MaxVectorWidth),
96 VectorizationFactor(VectorizationFactor),
97 VectorizationInterleave(VectorizationInterleave),
98 RuntimeMemoryCheckThreshold(RuntimeMemoryCheckThreshold) {}
101 /// This struct holds information about the memory runtime legality check that
102 /// a group of pointers do not overlap.
103 struct RuntimePointerCheck {
104 RuntimePointerCheck() : Need(false) {}
106 /// Reset the state of the pointer runtime information.
113 DependencySetId.clear();
117 /// Insert a pointer and calculate the start and end SCEVs.
118 void insert(ScalarEvolution *SE, Loop *Lp, Value *Ptr, bool WritePtr,
119 unsigned DepSetId, unsigned ASId, ValueToValueMap &Strides);
121 /// \brief Decide whether we need to issue a run-time check for pointer at
122 /// index \p I and \p J to prove their independence.
123 bool needsChecking(unsigned I, unsigned J) const;
125 /// This flag indicates if we need to add the runtime check.
127 /// Holds the pointers that we need to check.
128 SmallVector<TrackingVH<Value>, 2> Pointers;
129 /// Holds the pointer value at the beginning of the loop.
130 SmallVector<const SCEV*, 2> Starts;
131 /// Holds the pointer value at the end of the loop.
132 SmallVector<const SCEV*, 2> Ends;
133 /// Holds the information if this pointer is used for writing to memory.
134 SmallVector<bool, 2> IsWritePtr;
135 /// Holds the id of the set of pointers that could be dependent because of a
136 /// shared underlying object.
137 SmallVector<unsigned, 2> DependencySetId;
138 /// Holds the id of the disjoint alias set to which this pointer belongs.
139 SmallVector<unsigned, 2> AliasSetId;
142 LoopAccessInfo(Function *F, Loop *L, ScalarEvolution *SE,
143 const DataLayout *DL, const TargetLibraryInfo *TLI,
144 AliasAnalysis *AA, DominatorTree *DT,
145 const VectorizerParams &VectParams)
146 : TheFunction(F), TheLoop(L), SE(SE), DL(DL), TLI(TLI), AA(AA), DT(DT),
147 NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1U),
148 VectParams(VectParams) {}
150 /// Return true we can analyze the memory accesses in the loop and there are
151 /// no memory dependence cycles. Replaces symbolic strides using Strides.
152 bool canVectorizeMemory(ValueToValueMap &Strides);
154 RuntimePointerCheck *getRuntimePointerCheck() { return &PtrRtCheck; }
156 /// Return true if the block BB needs to be predicated in order for the loop
157 /// to be vectorized.
158 static bool blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
161 /// Returns true if the value V is uniform within the loop.
162 bool isUniform(Value *V);
164 unsigned getMaxSafeDepDistBytes() const { return MaxSafeDepDistBytes; }
165 unsigned getNumStores() const { return NumStores; }
166 unsigned getNumLoads() const { return NumLoads;}
168 /// \brief Add code that checks at runtime if the accessed arrays overlap.
170 /// Returns a pair of instructions where the first element is the first
171 /// instruction generated in possibly a sequence of instructions and the
172 /// second value is the final comparator value or NULL if no check is needed.
173 std::pair<Instruction *, Instruction *> addRuntimeCheck(Instruction *Loc);
176 void emitAnalysis(VectorizationReport &Message);
178 /// We need to check that all of the pointers in this list are disjoint
180 RuntimePointerCheck PtrRtCheck;
181 Function *TheFunction;
184 const DataLayout *DL;
185 const TargetLibraryInfo *TLI;
192 unsigned MaxSafeDepDistBytes;
194 /// \brief Vectorizer parameters used by the analysis.
195 VectorizerParams VectParams;
198 Value *stripIntegerCast(Value *V);
200 ///\brief Return the SCEV corresponding to a pointer with the symbolic stride
201 ///replaced with constant one.
203 /// If \p OrigPtr is not null, use it to look up the stride value instead of \p
204 /// Ptr. \p PtrToStride provides the mapping between the pointer value and its
205 /// stride as collected by LoopVectorizationLegality::collectStridedAccess.
206 const SCEV *replaceSymbolicStrideSCEV(ScalarEvolution *SE,
207 ValueToValueMap &PtrToStride,
208 Value *Ptr, Value *OrigPtr = nullptr);
210 } // End llvm namespace