1 //===---- Delinearization.cpp - MultiDimensional Index Delinearization ----===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This implements an analysis pass that tries to delinearize all GEP
11 // instructions in all loops using the SCEV analysis functionality. This pass is
12 // only used for testing purposes: if your pass needs delinearization, please
13 // use the on-demand SCEVAddRecExpr::delinearize() function.
14 //
15 //===----------------------------------------------------------------------===//
16
17 #include "llvm/Analysis/LoopInfo.h"
18 #include "llvm/Analysis/Passes.h"
19 #include "llvm/Analysis/ScalarEvolution.h"
20 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
21 #include "llvm/IR/Constants.h"
22 #include "llvm/IR/DerivedTypes.h"
23 #include "llvm/IR/Function.h"
24 #include "llvm/IR/InstIterator.h"
25 #include "llvm/IR/Instructions.h"
26 #include "llvm/IR/LLVMContext.h"
27 #include "llvm/IR/Type.h"
28 #include "llvm/Pass.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Support/raw_ostream.h"
31
32 using namespace llvm;
33
34 #define DL_NAME "delinearize"
35 #define DEBUG_TYPE DL_NAME
36
37 namespace {
38
39 class Delinearization : public FunctionPass {
40 Delinearization(const Delinearization &); // do not implement
41 protected:
42 Function *F;
43 LoopInfo *LI;
44 ScalarEvolution *SE;
45
46 public:
47 static char ID; // Pass identification, replacement for typeid
48
Delinearization()49 Delinearization() : FunctionPass(ID) {
50 initializeDelinearizationPass(*PassRegistry::getPassRegistry());
51 }
52 bool runOnFunction(Function &F) override;
53 void getAnalysisUsage(AnalysisUsage &AU) const override;
54 void print(raw_ostream &O, const Module *M = nullptr) const override;
55 };
56
57 } // end anonymous namespace
58
getAnalysisUsage(AnalysisUsage & AU) const59 void Delinearization::getAnalysisUsage(AnalysisUsage &AU) const {
60 AU.setPreservesAll();
61 AU.addRequired<LoopInfoWrapperPass>();
62 AU.addRequired<ScalarEvolutionWrapperPass>();
63 }
64
runOnFunction(Function & F)65 bool Delinearization::runOnFunction(Function &F) {
66 this->F = &F;
67 SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
68 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
69 return false;
70 }
71
getPointerOperand(Instruction & Inst)72 static Value *getPointerOperand(Instruction &Inst) {
73 if (LoadInst *Load = dyn_cast<LoadInst>(&Inst))
74 return Load->getPointerOperand();
75 else if (StoreInst *Store = dyn_cast<StoreInst>(&Inst))
76 return Store->getPointerOperand();
77 else if (GetElementPtrInst *Gep = dyn_cast<GetElementPtrInst>(&Inst))
78 return Gep->getPointerOperand();
79 return nullptr;
80 }
81
print(raw_ostream & O,const Module *) const82 void Delinearization::print(raw_ostream &O, const Module *) const {
83 O << "Delinearization on function " << F->getName() << ":\n";
84 for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
85 Instruction *Inst = &(*I);
86
87 // Only analyze loads and stores.
88 if (!isa<StoreInst>(Inst) && !isa<LoadInst>(Inst) &&
89 !isa<GetElementPtrInst>(Inst))
90 continue;
91
92 const BasicBlock *BB = Inst->getParent();
93 // Delinearize the memory access as analyzed in all the surrounding loops.
94 // Do not analyze memory accesses outside loops.
95 for (Loop *L = LI->getLoopFor(BB); L != nullptr; L = L->getParentLoop()) {
96 const SCEV *AccessFn = SE->getSCEVAtScope(getPointerOperand(*Inst), L);
97
98 const SCEVUnknown *BasePointer =
99 dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFn));
100 // Do not delinearize if we cannot find the base pointer.
101 if (!BasePointer)
102 break;
103 AccessFn = SE->getMinusSCEV(AccessFn, BasePointer);
104
105 O << "\n";
106 O << "Inst:" << *Inst << "\n";
107 O << "In Loop with Header: " << L->getHeader()->getName() << "\n";
108 O << "AccessFunction: " << *AccessFn << "\n";
109
110 SmallVector<const SCEV *, 3> Subscripts, Sizes;
111 SE->delinearize(AccessFn, Subscripts, Sizes, SE->getElementSize(Inst));
112 if (Subscripts.size() == 0 || Sizes.size() == 0 ||
113 Subscripts.size() != Sizes.size()) {
114 O << "failed to delinearize\n";
115 continue;
116 }
117
118 O << "Base offset: " << *BasePointer << "\n";
119 O << "ArrayDecl[UnknownSize]";
120 int Size = Subscripts.size();
121 for (int i = 0; i < Size - 1; i++)
122 O << "[" << *Sizes[i] << "]";
123 O << " with elements of " << *Sizes[Size - 1] << " bytes.\n";
124
125 O << "ArrayRef";
126 for (int i = 0; i < Size; i++)
127 O << "[" << *Subscripts[i] << "]";
128 O << "\n";
129 }
130 }
131 }
132
133 char Delinearization::ID = 0;
134 static const char delinearization_name[] = "Delinearization";
INITIALIZE_PASS_BEGIN(Delinearization,DL_NAME,delinearization_name,true,true)135 INITIALIZE_PASS_BEGIN(Delinearization, DL_NAME, delinearization_name, true,
136 true)
137 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
138 INITIALIZE_PASS_END(Delinearization, DL_NAME, delinearization_name, true, true)
139
140 FunctionPass *llvm::createDelinearizationPass() { return new Delinearization; }
141