llvm-project/polly/lib/Analysis/TempScopInfo.cpp

//===---------- TempScopInfo.cpp  - Extract TempScops ---------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Collect information about the control flow regions detected by the Scop
// detection, such that this information can be translated info its polyhedral
// representation.
//
//===----------------------------------------------------------------------===//

#include "polly/TempScopInfo.h"
#include "polly/CodeGen/BlockGenerators.h"
#include "polly/LinkAllPasses.h"
#include "polly/ScopDetection.h"
#include "polly/Support/GICHelper.h"
#include "polly/Support/SCEVValidator.h"
#include "polly/Support/ScopHelper.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Analysis/RegionIterator.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"

using namespace llvm;
using namespace polly;

#define DEBUG_TYPE "polly-analyze-ir"

//===----------------------------------------------------------------------===//
/// Helper Classes

void IRAccess::print(raw_ostream &OS) const {
  if (isRead())
    OS << "Read ";
  else {
    if (isMayWrite())
      OS << "May";
    OS << "Write ";
  }
  OS << BaseAddress->getName() << '[' << *Offset << "]\n";
}

void Comparison::print(raw_ostream &OS) const {
  // Not yet implemented.
}

/// Helper function to print the condition
static void printBBCond(raw_ostream &OS, const BBCond &Cond) {
  assert(!Cond.empty() && "Unexpected empty condition!");
  Cond[0].print(OS);
  for (unsigned i = 1, e = Cond.size(); i != e; ++i) {
    OS << " && ";
    Cond[i].print(OS);
  }
}

inline raw_ostream &operator<<(raw_ostream &OS, const BBCond &Cond) {
  printBBCond(OS, Cond);
  return OS;
}

//===----------------------------------------------------------------------===//
// TempScop implementation
TempScop::~TempScop() {}

void TempScop::print(raw_ostream &OS, ScalarEvolution *SE, LoopInfo *LI) const {
  OS << "Scop: " << R.getNameStr() << "\n";

  printDetail(OS, SE, LI, &R, 0);
}

void TempScop::printDetail(raw_ostream &OS, ScalarEvolution *SE, LoopInfo *LI,
                           const Region *CurR, unsigned ind) const {
  // FIXME: Print other details rather than memory accesses.
  for (const auto &CurBlock : CurR->blocks()) {
    AccFuncMapType::const_iterator AccSetIt = AccFuncMap.find(CurBlock);

    // Ignore trivial blocks that do not contain any memory access.
    if (AccSetIt == AccFuncMap.end())
      continue;

    OS.indent(ind) << "BB: " << CurBlock->getName() << '\n';
    typedef AccFuncSetType::const_iterator access_iterator;
    const AccFuncSetType &AccFuncs = AccSetIt->second;

    for (access_iterator AI = AccFuncs.begin(), AE = AccFuncs.end(); AI != AE;
         ++AI)
      AI->first.print(OS.indent(ind + 2));
  }
}

void TempScopInfo::buildPHIAccesses(PHINode *PHI, Region &R,
                                    AccFuncSetType &Functions,
                                    Region *NonAffineSubRegion) {
  if (canSynthesize(PHI, LI, SE, &R))
    return;

  // PHI nodes are modeled as if they had been demoted prior to the SCoP
  // detection. Hence, the PHI is a load of a new memory location in which the
  // incoming value was written at the end of the incoming basic block.
  bool Written = false;
  for (unsigned u = 0; u < PHI->getNumIncomingValues(); u++) {
    Value *Op = PHI->getIncomingValue(u);
    BasicBlock *OpBB = PHI->getIncomingBlock(u);

    if (!R.contains(OpBB))
      continue;

    // Do not build scalar dependences inside a non-affine subregion.
    if (NonAffineSubRegion && NonAffineSubRegion->contains(OpBB))
      continue;

    Instruction *OpI = dyn_cast<Instruction>(Op);
    if (OpI) {
      BasicBlock *OpIBB = OpI->getParent();
      // As we pretend there is a use (or more precise a write) of OpI in OpBB
      // we have to insert a scalar dependence from the definition of OpI to
      // OpBB if the definition is not in OpBB.
      if (OpIBB != OpBB) {
        IRAccess ScalarRead(IRAccess::READ, OpI, ZeroOffset, 1, true);
        AccFuncMap[OpBB].push_back(std::make_pair(ScalarRead, PHI));
        IRAccess ScalarWrite(IRAccess::MUST_WRITE, OpI, ZeroOffset, 1, true);
        AccFuncMap[OpIBB].push_back(std::make_pair(ScalarWrite, OpI));
      }
    }

    // If the operand is a constant, global or argument we need an access
    // instruction and just choose the PHI.
    if (!OpI)
      OpI = PHI;

    Written = true;

    IRAccess ScalarAccess(IRAccess::MUST_WRITE, PHI, ZeroOffset, 1, true);
    AccFuncMap[OpBB].push_back(std::make_pair(ScalarAccess, OpI));
  }

  if (Written) {
    IRAccess ScalarAccess(IRAccess::READ, PHI, ZeroOffset, 1, true);
    Functions.push_back(std::make_pair(ScalarAccess, PHI));
  }
}

bool TempScopInfo::buildScalarDependences(Instruction *Inst, Region *R,
                                          Region *NonAffineSubRegion) {
  bool canSynthesizeInst = canSynthesize(Inst, LI, SE, R);
  if (isIgnoredIntrinsic(Inst))
    return false;

  bool AnyCrossStmtUse = false;
  BasicBlock *ParentBB = Inst->getParent();

  for (User *U : Inst->users()) {
    Instruction *UI = dyn_cast<Instruction>(U);

    // Ignore the strange user
    if (UI == 0)
      continue;

    BasicBlock *UseParent = UI->getParent();

    // Ignore the users in the same BB (statement)
    if (UseParent == ParentBB)
      continue;

    // Do not build scalar dependences inside a non-affine subregion.
    if (NonAffineSubRegion && NonAffineSubRegion->contains(UseParent))
      continue;

    // Check whether or not the use is in the SCoP.
    if (!R->contains(UseParent)) {
      AnyCrossStmtUse = true;
      continue;
    }

    // If the instruction can be synthesized and the user is in the region
    // we do not need to add scalar dependences.
    if (canSynthesizeInst)
      continue;

    // No need to translate these scalar dependences into polyhedral form,
    // because synthesizable scalars can be generated by the code generator.
    if (canSynthesize(UI, LI, SE, R))
      continue;

    // Skip PHI nodes in the region as they handle their operands on their own.
    if (isa<PHINode>(UI))
      continue;

    // Now U is used in another statement.
    AnyCrossStmtUse = true;

    // Do not build a read access that is not in the current SCoP
    // Use the def instruction as base address of the IRAccess, so that it will
    // become the name of the scalar access in the polyhedral form.
    IRAccess ScalarAccess(IRAccess::READ, Inst, ZeroOffset, 1, true);
    AccFuncMap[UseParent].push_back(std::make_pair(ScalarAccess, UI));
  }

  return AnyCrossStmtUse;
}

extern MapInsnToMemAcc InsnToMemAcc;

IRAccess
TempScopInfo::buildIRAccess(Instruction *Inst, Loop *L, Region *R,
                            const ScopDetection::BoxedLoopsSetTy *BoxedLoops) {
  unsigned Size;
  Type *SizeType;
  enum IRAccess::TypeKind Type;

  if (LoadInst *Load = dyn_cast<LoadInst>(Inst)) {
    SizeType = Load->getType();
    Size = TD->getTypeStoreSize(SizeType);
    Type = IRAccess::READ;
  } else {
    StoreInst *Store = cast<StoreInst>(Inst);
    SizeType = Store->getValueOperand()->getType();
    Size = TD->getTypeStoreSize(SizeType);
    Type = IRAccess::MUST_WRITE;
  }

  const SCEV *AccessFunction = SE->getSCEVAtScope(getPointerOperand(*Inst), L);
  const SCEVUnknown *BasePointer =
      dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFunction));

  assert(BasePointer && "Could not find base pointer");
  AccessFunction = SE->getMinusSCEV(AccessFunction, BasePointer);

  MemAcc *Acc = InsnToMemAcc[Inst];
  if (PollyDelinearize && Acc)
    return IRAccess(Type, BasePointer->getValue(), AccessFunction, Size, true,
                    Acc->DelinearizedSubscripts, Acc->Shape->DelinearizedSizes);

  // Check if the access depends on a loop contained in a non-affine subregion.
  bool isVariantInNonAffineLoop = false;
  if (BoxedLoops) {
    SetVector<const Loop *> Loops;
    findLoops(AccessFunction, Loops);
    for (const Loop *L : Loops)
      if (BoxedLoops->count(L))
        isVariantInNonAffineLoop = true;
  }

  bool IsAffine = !isVariantInNonAffineLoop &&
                  isAffineExpr(R, AccessFunction, *SE, BasePointer->getValue());

  SmallVector<const SCEV *, 4> Subscripts, Sizes;
  Subscripts.push_back(AccessFunction);
  Sizes.push_back(SE->getConstant(ZeroOffset->getType(), Size));

  if (!IsAffine && Type == IRAccess::MUST_WRITE)
    Type = IRAccess::MAY_WRITE;

  return IRAccess(Type, BasePointer->getValue(), AccessFunction, Size, IsAffine,
                  Subscripts, Sizes);
}

void TempScopInfo::buildAccessFunctions(Region &R, Region &SR) {

  if (SD->isNonAffineSubRegion(&SR, &R)) {
    for (BasicBlock *BB : SR.blocks())
      buildAccessFunctions(R, *BB, &SR);
    return;
  }

  for (auto I = SR.element_begin(), E = SR.element_end(); I != E; ++I)
    if (I->isSubRegion())
      buildAccessFunctions(R, *I->getNodeAs<Region>());
    else
      buildAccessFunctions(R, *I->getNodeAs<BasicBlock>());
}

void TempScopInfo::buildAccessFunctions(Region &R, BasicBlock &BB,
                                        Region *NonAffineSubRegion) {
  AccFuncSetType Functions;
  Loop *L = LI->getLoopFor(&BB);

  // The set of loops contained in non-affine subregions that are part of R.
  const ScopDetection::BoxedLoopsSetTy *BoxedLoops = SD->getBoxedLoops(&R);

  for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) {
    Instruction *Inst = I;
    if (isa<LoadInst>(Inst) || isa<StoreInst>(Inst))
      Functions.push_back(
          std::make_pair(buildIRAccess(Inst, L, &R, BoxedLoops), Inst));

    if (PHINode *PHI = dyn_cast<PHINode>(Inst))
      buildPHIAccesses(PHI, R, Functions, NonAffineSubRegion);

    if (!isa<StoreInst>(Inst) &&
        buildScalarDependences(Inst, &R, NonAffineSubRegion)) {
      // If the Instruction is used outside the statement, we need to build the
      // write access.
      IRAccess ScalarAccess(IRAccess::MUST_WRITE, Inst, ZeroOffset, 1, true);
      Functions.push_back(std::make_pair(ScalarAccess, Inst));
    }
  }

  if (Functions.empty())
    return;

  AccFuncSetType &Accs = AccFuncMap[&BB];
  Accs.insert(Accs.end(), Functions.begin(), Functions.end());
}

void TempScopInfo::buildAffineCondition(Value &V, bool inverted,
                                        Comparison **Comp) const {
  if (ConstantInt *C = dyn_cast<ConstantInt>(&V)) {
    // If this is always true condition, we will create 0 <= 1,
    // otherwise we will create 0 >= 1.
    const SCEV *LHS = SE->getConstant(C->getType(), 0);
    const SCEV *RHS = SE->getConstant(C->getType(), 1);

    if (C->isOne() == inverted)
      *Comp = new Comparison(LHS, RHS, ICmpInst::ICMP_SLE);
    else
      *Comp = new Comparison(LHS, RHS, ICmpInst::ICMP_SGE);

    return;
  }

  ICmpInst *ICmp = dyn_cast<ICmpInst>(&V);
  assert(ICmp && "Only ICmpInst of constant as condition supported!");

  Loop *L = LI->getLoopFor(ICmp->getParent());
  const SCEV *LHS = SE->getSCEVAtScope(ICmp->getOperand(0), L);
  const SCEV *RHS = SE->getSCEVAtScope(ICmp->getOperand(1), L);

  ICmpInst::Predicate Pred = ICmp->getPredicate();

  // Invert the predicate if needed.
  if (inverted)
    Pred = ICmpInst::getInversePredicate(Pred);

  switch (Pred) {
  case ICmpInst::ICMP_UGT:
  case ICmpInst::ICMP_UGE:
  case ICmpInst::ICMP_ULT:
  case ICmpInst::ICMP_ULE:
    // TODO: At the moment we need to see everything as signed. This is an
    //       correctness issue that needs to be solved.
    // AffLHS->setUnsigned();
    // AffRHS->setUnsigned();
    break;
  default:
    break;
  }

  *Comp = new Comparison(LHS, RHS, Pred);
}

void TempScopInfo::buildCondition(BasicBlock *BB, Region &R) {
  BasicBlock *RegionEntry = R.getEntry();
  BBCond Cond;

  DomTreeNode *BBNode = DT->getNode(BB), *EntryNode = DT->getNode(RegionEntry);
  assert(BBNode && EntryNode && "Get null node while building condition!");

  // Walk up the dominance tree until reaching the entry node. Collect all
  // branching blocks on the path to BB except if BB postdominates the block
  // containing the condition.
  SmallVector<BasicBlock *, 4> DominatorBrBlocks;
  while (BBNode != EntryNode) {
    BasicBlock *CurBB = BBNode->getBlock();
    BBNode = BBNode->getIDom();
    assert(BBNode && "BBNode should not reach the root node!");

    if (PDT->dominates(CurBB, BBNode->getBlock()))
      continue;

    BranchInst *Br = dyn_cast<BranchInst>(BBNode->getBlock()->getTerminator());
    assert(Br && "A Valid Scop should only contain branch instruction");

    if (Br->isUnconditional())
      continue;

    DominatorBrBlocks.push_back(BBNode->getBlock());
  }

  RegionInfo *RI = R.getRegionInfo();
  // Iterate in reverse order over the dominating blocks.  Until a non-affine
  // branch was encountered add all conditions collected. If a non-affine branch
  // was encountered, stop as we overapproximate from here on anyway.
  for (auto BIt = DominatorBrBlocks.rbegin(), BEnd = DominatorBrBlocks.rend();
       BIt != BEnd; BIt++) {

    BasicBlock *BBNode = *BIt;
    BranchInst *Br = dyn_cast<BranchInst>(BBNode->getTerminator());
    assert(Br && "A Valid Scop should only contain branch instruction");
    assert(Br->isConditional() && "Assumed a conditional branch");

    if (SD->isNonAffineSubRegion(RI->getRegionFor(BBNode), &R))
      break;

    BasicBlock *TrueBB = Br->getSuccessor(0), *FalseBB = Br->getSuccessor(1);

    // Is BB on the ELSE side of the branch?
    bool inverted = DT->dominates(FalseBB, BB);

    // If both TrueBB and FalseBB dominate BB, one of them must be the target of
    // a back-edge, i.e. a loop header.
    if (inverted && DT->dominates(TrueBB, BB)) {
      assert(
          (DT->dominates(TrueBB, FalseBB) || DT->dominates(FalseBB, TrueBB)) &&
          "One of the successors should be the loop header and dominate the"
          "other!");

      // It is not an invert if the FalseBB is the header.
      if (DT->dominates(FalseBB, TrueBB))
        inverted = false;
    }

    Comparison *Cmp;
    buildAffineCondition(*(Br->getCondition()), inverted, &Cmp);
    Cond.push_back(*Cmp);
  }

  if (!Cond.empty())
    BBConds[BB] = Cond;
}

TempScop *TempScopInfo::buildTempScop(Region &R) {
  TempScop *TScop = new TempScop(R, BBConds, AccFuncMap);

  buildAccessFunctions(R, R);

  for (const auto &BB : R.blocks())
    buildCondition(BB, R);

  return TScop;
}

TempScop *TempScopInfo::getTempScop(const Region *R) const {
  TempScopMapType::const_iterator at = TempScops.find(R);
  return at == TempScops.end() ? 0 : at->second;
}

void TempScopInfo::print(raw_ostream &OS, const Module *) const {
  for (TempScopMapType::const_iterator I = TempScops.begin(),
                                       E = TempScops.end();
       I != E; ++I)
    I->second->print(OS, SE, LI);
}

bool TempScopInfo::runOnFunction(Function &F) {
  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
  PDT = &getAnalysis<PostDominatorTree>();
  SE = &getAnalysis<ScalarEvolution>();
  LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
  SD = &getAnalysis<ScopDetection>();
  AA = &getAnalysis<AliasAnalysis>();
  TD = &F.getParent()->getDataLayout();
  ZeroOffset = SE->getConstant(TD->getIntPtrType(F.getContext()), 0);

  for (ScopDetection::iterator I = SD->begin(), E = SD->end(); I != E; ++I) {
    if (!SD->isMaxRegionInScop(**I))
      continue;
    Region *R = const_cast<Region *>(*I);
    TempScops.insert(std::make_pair(R, buildTempScop(*R)));
  }

  return false;
}

void TempScopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.addRequiredTransitive<DominatorTreeWrapperPass>();
  AU.addRequiredTransitive<PostDominatorTree>();
  AU.addRequiredTransitive<LoopInfoWrapperPass>();
  AU.addRequiredTransitive<ScalarEvolution>();
  AU.addRequiredTransitive<ScopDetection>();
  AU.addRequiredID(IndependentBlocksID);
  AU.addRequired<AliasAnalysis>();
  AU.setPreservesAll();
}

TempScopInfo::~TempScopInfo() { clear(); }

void TempScopInfo::clear() {
  BBConds.clear();
  AccFuncMap.clear();
  DeleteContainerSeconds(TempScops);
  TempScops.clear();
}

//===----------------------------------------------------------------------===//
// TempScop information extraction pass implement
char TempScopInfo::ID = 0;

Pass *polly::createTempScopInfoPass() { return new TempScopInfo(); }

INITIALIZE_PASS_BEGIN(TempScopInfo, "polly-analyze-ir",
                      "Polly - Analyse the LLVM-IR in the detected regions",
                      false, false);
INITIALIZE_AG_DEPENDENCY(AliasAnalysis);
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass);
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass);
INITIALIZE_PASS_DEPENDENCY(PostDominatorTree);
INITIALIZE_PASS_DEPENDENCY(RegionInfoPass);
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution);
INITIALIZE_PASS_END(TempScopInfo, "polly-analyze-ir",
                    "Polly - Analyse the LLVM-IR in the detected regions",
                    false, false)