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