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
32using namespace llvm;
33
34#define DL_NAME "delinearize"
35#define DEBUG_TYPE DL_NAME
36
37namespace {
38
39class Delinearization : public FunctionPass {
40  Delinearization(const Delinearization &); // do not implement
41protected:
42  Function *F;
43  LoopInfo *LI;
44  ScalarEvolution *SE;
45
46public:
47  static char ID; // Pass identification, replacement for typeid
48
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
59void Delinearization::getAnalysisUsage(AnalysisUsage &AU) const {
60  AU.setPreservesAll();
61  AU.addRequired<LoopInfoWrapperPass>();
62  AU.addRequired<ScalarEvolutionWrapperPass>();
63}
64
65bool Delinearization::runOnFunction(Function &F) {
66  this->F = &F;
67  SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
68  LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
69  return false;
70}
71
72static 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
82void 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
133char Delinearization::ID = 0;
134static const char delinearization_name[] = "Delinearization";
135INITIALIZE_PASS_BEGIN(Delinearization, DL_NAME, delinearization_name, true,
136                      true)
137INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
138INITIALIZE_PASS_END(Delinearization, DL_NAME, delinearization_name, true, true)
139
140FunctionPass *llvm::createDelinearizationPass() { return new Delinearization; }
141