lib/Analysis/Delinearization.cpp

   1 //===---- Delinearization.cpp - MultiDimensional Index Delinearization ----===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This implements an analysis pass that tries to delinearize all GEP
  10 // instructions in all loops using the SCEV analysis functionality. This pass is
  11 // only used for testing purposes: if your pass needs delinearization, please
  12 // use the on-demand SCEVAddRecExpr::delinearize() function.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "llvm/Analysis/LoopInfo.h"
  17 #include "llvm/Analysis/Passes.h"
  18 #include "llvm/Analysis/ScalarEvolution.h"
  19 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
  20 #include "llvm/IR/Constants.h"
  21 #include "llvm/IR/DerivedTypes.h"
  22 #include "llvm/IR/Function.h"
  23 #include "llvm/IR/InstIterator.h"
  24 #include "llvm/IR/Instructions.h"
  25 #include "llvm/IR/LLVMContext.h"
  26 #include "llvm/IR/Type.h"
  27 #include "llvm/Pass.h"
  28 #include "llvm/Support/Debug.h"
  29 #include "llvm/Support/raw_ostream.h"
  30
  31 using namespace llvm;
  32
  33 #define DL_NAME "delinearize"
  34 #define DEBUG_TYPE DL_NAME
  35
  36 namespace {
  37
  38 class Delinearization : public FunctionPass {
  39   Delinearization(const Delinearization &); // do not implement
  40 protected:
  41   Function *F;
  42   LoopInfo *LI;
  43   ScalarEvolution *SE;
  44
  45 public:
  46   static char ID; // Pass identification, replacement for typeid
  47
  48   Delinearization() : FunctionPass(ID) {
  49     initializeDelinearizationPass(*PassRegistry::getPassRegistry());
  50   }
  51   bool runOnFunction(Function &F) override;
  52   void getAnalysisUsage(AnalysisUsage &AU) const override;
  53   void print(raw_ostream &O, const Module *M = nullptr) const override;
  54 };
  55
  56 } // end anonymous namespace
  57
  58 void Delinearization::getAnalysisUsage(AnalysisUsage &AU) const {
  59   AU.setPreservesAll();
  60   AU.addRequired<LoopInfoWrapperPass>();
  61   AU.addRequired<ScalarEvolutionWrapperPass>();
  62 }
  63
  64 bool Delinearization::runOnFunction(Function &F) {
  65   this->F = &F;
  66   SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
  67   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
  68   return false;
  69 }
  70
  71 void Delinearization::print(raw_ostream &O, const Module *) const {
  72   O << "Delinearization on function " << F->getName() << ":\n";
  73   for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
  74     Instruction *Inst = &(*I);
  75
  76     // Only analyze loads and stores.
  77     if (!isa<StoreInst>(Inst) && !isa<LoadInst>(Inst) &&
  78         !isa<GetElementPtrInst>(Inst))
  79       continue;
  80
  81     const BasicBlock *BB = Inst->getParent();
  82     // Delinearize the memory access as analyzed in all the surrounding loops.
  83     // Do not analyze memory accesses outside loops.
  84     for (Loop *L = LI->getLoopFor(BB); L != nullptr; L = L->getParentLoop()) {
  85       const SCEV *AccessFn = SE->getSCEVAtScope(getPointerOperand(Inst), L);
  86
  87       const SCEVUnknown *BasePointer =
  88           dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFn));
  89       // Do not delinearize if we cannot find the base pointer.
  90       if (!BasePointer)
  91         break;
  92       AccessFn = SE->getMinusSCEV(AccessFn, BasePointer);
  93
  94       O << "\n";
  95       O << "Inst:" << *Inst << "\n";
  96       O << "In Loop with Header: " << L->getHeader()->getName() << "\n";
  97       O << "AccessFunction: " << *AccessFn << "\n";
  98
  99       SmallVector<const SCEV *, 3> Subscripts, Sizes;
 100       SE->delinearize(AccessFn, Subscripts, Sizes, SE->getElementSize(Inst));
 101       if (Subscripts.size() == 0 || Sizes.size() == 0 ||
 102           Subscripts.size() != Sizes.size()) {
 103         O << "failed to delinearize\n";
 104         continue;
 105       }
 106
 107       O << "Base offset: " << *BasePointer << "\n";
 108       O << "ArrayDecl[UnknownSize]";
 109       int Size = Subscripts.size();
 110       for (int i = 0; i < Size - 1; i++)
 111         O << "[" << *Sizes[i] << "]";
 112       O << " with elements of " << *Sizes[Size - 1] << " bytes.\n";
 113
 114       O << "ArrayRef";
 115       for (int i = 0; i < Size; i++)
 116         O << "[" << *Subscripts[i] << "]";
 117       O << "\n";
 118     }
 119   }
 120 }
 121
 122 char Delinearization::ID = 0;
 123 static const char delinearization_name[] = "Delinearization";
 124 INITIALIZE_PASS_BEGIN(Delinearization, DL_NAME, delinearization_name, true,
 125                       true)
 126 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
 127 INITIALIZE_PASS_END(Delinearization, DL_NAME, delinearization_name, true, true)
 128
 129 FunctionPass *llvm::createDelinearizationPass() { return new Delinearization; }