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,
63 /// \brief Drive the analysis of memory accesses in the loop
65 /// This class is responsible for analyzing the memory accesses of a loop. It
66 /// collects the accesses and then its main helper the AccessAnalysis class
67 /// finds and categorizes the dependences in buildDependenceSets.
69 /// For memory dependences that can be analyzed at compile time, it determines
70 /// whether the dependence is part of cycle inhibiting vectorization. This work
71 /// is delegated to the MemoryDepChecker class.
73 /// For memory dependences that cannot be determined at compile time, it
74 /// generates run-time checks to prove independence. This is done by
75 /// AccessAnalysis::canCheckPtrAtRT and the checks are maintained by the
76 /// RuntimePointerCheck class.
77 class LoopAccessInfo {
79 /// \brief Collection of parameters used from the vectorizer.
80 struct VectorizerParams {
81 /// \brief Maximum simd width.
82 unsigned MaxVectorWidth;
84 /// \brief VF as overridden by the user.
85 unsigned VectorizationFactor;
86 /// \brief Interleave factor as overridden by the user.
87 unsigned VectorizationInterleave;
89 /// \\brief When performing memory disambiguation checks at runtime do not
90 /// make more than this number of comparisons.
91 unsigned RuntimeMemoryCheckThreshold;
93 VectorizerParams(unsigned MaxVectorWidth,
94 unsigned VectorizationFactor,
95 unsigned VectorizationInterleave,
96 unsigned RuntimeMemoryCheckThreshold) :
97 MaxVectorWidth(MaxVectorWidth),
98 VectorizationFactor(VectorizationFactor),
99 VectorizationInterleave(VectorizationInterleave),
100 RuntimeMemoryCheckThreshold(RuntimeMemoryCheckThreshold) {}
103 /// This struct holds information about the memory runtime legality check that
104 /// a group of pointers do not overlap.
105 struct RuntimePointerCheck {
106 RuntimePointerCheck() : Need(false) {}
108 /// Reset the state of the pointer runtime information.
115 DependencySetId.clear();
119 /// Insert a pointer and calculate the start and end SCEVs.
120 void insert(ScalarEvolution *SE, Loop *Lp, Value *Ptr, bool WritePtr,
121 unsigned DepSetId, unsigned ASId, ValueToValueMap &Strides);
123 /// \brief Decide whether we need to issue a run-time check for pointer at
124 /// index \p I and \p J to prove their independence.
125 bool needsChecking(unsigned I, unsigned J) const;
127 /// This flag indicates if we need to add the runtime check.
129 /// Holds the pointers that we need to check.
130 SmallVector<TrackingVH<Value>, 2> Pointers;
131 /// Holds the pointer value at the beginning of the loop.
132 SmallVector<const SCEV*, 2> Starts;
133 /// Holds the pointer value at the end of the loop.
134 SmallVector<const SCEV*, 2> Ends;
135 /// Holds the information if this pointer is used for writing to memory.
136 SmallVector<bool, 2> IsWritePtr;
137 /// Holds the id of the set of pointers that could be dependent because of a
138 /// shared underlying object.
139 SmallVector<unsigned, 2> DependencySetId;
140 /// Holds the id of the disjoint alias set to which this pointer belongs.
141 SmallVector<unsigned, 2> AliasSetId;
144 LoopAccessInfo(Function *F, Loop *L, ScalarEvolution *SE,
145 const DataLayout *DL, const TargetLibraryInfo *TLI,
146 AliasAnalysis *AA, DominatorTree *DT,
147 const VectorizerParams &VectParams) :
148 TheFunction(F), TheLoop(L), SE(SE), DL(DL), TLI(TLI), AA(AA), DT(DT),
149 NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1U),
150 VectParams(VectParams) {}
152 /// Return true we can analyze the memory accesses in the loop and there are
153 /// no memory dependence cycles. Replaces symbolic strides using Strides.
154 bool canVectorizeMemory(ValueToValueMap &Strides);
156 RuntimePointerCheck *getRuntimePointerCheck() { return &PtrRtCheck; }
158 /// Return true if the block BB needs to be predicated in order for the loop
159 /// to be vectorized.
160 static bool blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
163 /// Returns true if the value V is uniform within the loop.
164 bool isUniform(Value *V);
166 unsigned getMaxSafeDepDistBytes() const { return MaxSafeDepDistBytes; }
167 unsigned getNumStores() const { return NumStores; }
168 unsigned getNumLoads() const { return NumLoads;}
170 /// \brief Add code that checks at runtime if the accessed arrays overlap.
172 /// Returns a pair of instructions where the first element is the first
173 /// instruction generated in possibly a sequence of instructions and the
174 /// second value is the final comparator value or NULL if no check is needed.
175 std::pair<Instruction *, Instruction *> addRuntimeCheck(Instruction *Loc);
178 void emitAnalysis(VectorizationReport &Message);
180 /// We need to check that all of the pointers in this list are disjoint
182 RuntimePointerCheck PtrRtCheck;
183 Function *TheFunction;
186 const DataLayout *DL;
187 const TargetLibraryInfo *TLI;
194 unsigned MaxSafeDepDistBytes;
196 /// \brief Vectorizer parameters used by the analysis.
197 VectorizerParams VectParams;
200 Value *stripIntegerCast(Value *V);
202 ///\brief Return the SCEV corresponding to a pointer with the symbolic stride
203 ///replaced with constant one.
205 /// If \p OrigPtr is not null, use it to look up the stride value instead of \p
206 /// Ptr. \p PtrToStride provides the mapping between the pointer value and its
207 /// stride as collected by LoopVectorizationLegality::collectStridedAccess.
208 const SCEV *replaceSymbolicStrideSCEV(ScalarEvolution *SE,
209 ValueToValueMap &PtrToStride,
210 Value *Ptr, Value *OrigPtr = nullptr);
212 } // End llvm namespace