lib/Analysis/Delinearization.cpp

   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/IR/Constants.h"
  18 #include "llvm/Analysis/LoopInfo.h"
  19 #include "llvm/Analysis/Passes.h"
  20 #include "llvm/Analysis/ScalarEvolution.h"
  21 #include "llvm/Analysis/ScalarEvolutionExpressions.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/CommandLine.h"
  30 #include "llvm/Support/Debug.h"
  31 #include "llvm/Support/raw_ostream.h"
  32
  33 using namespace llvm;
  34
  35 #define DL_NAME "delinearize"
  36 #define DEBUG_TYPE DL_NAME
  37
  38 namespace {
  39
  40 class Delinearization : public FunctionPass {
  41   Delinearization(const Delinearization &); // do not implement
  42 protected:
  43   Function *F;
  44   LoopInfo *LI;
  45   ScalarEvolution *SE;
  46
  47 public:
  48   static char ID; // Pass identification, replacement for typeid
  49
  50   Delinearization() : FunctionPass(ID) {
  51     initializeDelinearizationPass(*PassRegistry::getPassRegistry());
  52   }
  53   bool runOnFunction(Function &F) override;
  54   void getAnalysisUsage(AnalysisUsage &AU) const override;
  55   void print(raw_ostream &O, const Module *M = nullptr) const override;
  56 };
  57
  58 } // end anonymous namespace
  59
  60 void Delinearization::getAnalysisUsage(AnalysisUsage &AU) const {
  61   AU.setPreservesAll();
  62   AU.addRequired<LoopInfo>();
  63   AU.addRequired<ScalarEvolution>();
  64 }
  65
  66 bool Delinearization::runOnFunction(Function &F) {
  67   this->F = &F;
  68   SE = &getAnalysis<ScalarEvolution>();
  69   LI = &getAnalysis<LoopInfo>();
  70   return false;
  71 }
  72
  73 static Value *getPointerOperand(Instruction &Inst) {
  74   if (LoadInst *Load = dyn_cast<LoadInst>(&Inst))
  75     return Load->getPointerOperand();
  76   else if (StoreInst *Store = dyn_cast<StoreInst>(&Inst))
  77     return Store->getPointerOperand();
  78   else if (GetElementPtrInst *Gep = dyn_cast<GetElementPtrInst>(&Inst))
  79     return Gep->getPointerOperand();
  80   return nullptr;
  81 }
  82
  83 void Delinearization::print(raw_ostream &O, const Module *) const {
  84   O << "Delinearization on function " << F->getName() << ":\n";
  85   for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
  86     Instruction *Inst = &(*I);
  87
  88     // Only analyze loads and stores.
  89     if (!isa<StoreInst>(Inst) && !isa<LoadInst>(Inst) &&
  90         !isa<GetElementPtrInst>(Inst))
  91       continue;
  92
  93     const BasicBlock *BB = Inst->getParent();
  94     // Delinearize the memory access as analyzed in all the surrounding loops.
  95     // Do not analyze memory accesses outside loops.
  96     for (Loop *L = LI->getLoopFor(BB); L != nullptr; L = L->getParentLoop()) {
  97       const SCEV *AccessFn = SE->getSCEVAtScope(getPointerOperand(*Inst), L);
  98
  99       const SCEVUnknown *BasePointer =
 100           dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFn));
 101       // Do not delinearize if we cannot find the base pointer.
 102       if (!BasePointer)
 103         break;
 104       AccessFn = SE->getMinusSCEV(AccessFn, BasePointer);
 105       const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(AccessFn);
 106
 107       // Do not try to delinearize memory accesses that are not AddRecs.
 108       if (!AR)
 109         break;
 110
 111
 112       O << "\n";
 113       O << "Inst:" << *Inst << "\n";
 114       O << "In Loop with Header: " << L->getHeader()->getName() << "\n";
 115       O << "AddRec: " << *AR << "\n";
 116
 117       SmallVector<const SCEV *, 3> Subscripts, Sizes;
 118       AR->delinearize(*SE, Subscripts, Sizes, SE->getElementSize(Inst));
 119       if (Subscripts.size() == 0 || Sizes.size() == 0 ||
 120           Subscripts.size() != Sizes.size()) {
 121         O << "failed to delinearize\n";
 122         continue;
 123       }
 124
 125       O << "Base offset: " << *BasePointer << "\n";
 126       O << "ArrayDecl[UnknownSize]";
 127       int Size = Subscripts.size();
 128       for (int i = 0; i < Size - 1; i++)
 129         O << "[" << *Sizes[i] << "]";
 130       O << " with elements of " << *Sizes[Size - 1] << " bytes.\n";
 131
 132       O << "ArrayRef";
 133       for (int i = 0; i < Size; i++)
 134         O << "[" << *Subscripts[i] << "]";
 135       O << "\n";
 136     }
 137   }
 138 }
 139
 140 char Delinearization::ID = 0;
 141 static const char delinearization_name[] = "Delinearization";
 142 INITIALIZE_PASS_BEGIN(Delinearization, DL_NAME, delinearization_name, true,
 143                       true)
 144 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
 145 INITIALIZE_PASS_END(Delinearization, DL_NAME, delinearization_name, true, true)
 146
 147 FunctionPass *llvm::createDelinearizationPass() { return new Delinearization; }