ScopHelper.cpp

Go to the documentation of this file.

//===- ScopHelper.cpp - Some Helper Functions for Scop.  ------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Small functions that help with Scop and LLVM-IR.
//
//===----------------------------------------------------------------------===//
 
#include "polly/Support/ScopHelper.h"
#include "polly/Options.h"
#include "polly/ScopInfo.h"
#include "polly/Support/SCEVValidator.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
#include <optional>
 
using namespace llvm;
using namespace polly;
 
#define DEBUG_TYPE "polly-scop-helper"
 
static cl::list<std::string> DebugFunctions(
    "polly-debug-func",
    cl::desc("Allow calls to the specified functions in SCoPs even if their "
             "side-effects are unknown. This can be used to do debug output in "
             "Polly-transformed code."),
    cl::Hidden, cl::CommaSeparated, cl::cat(PollyCategory));
 
// Ensures that there is just one predecessor to the entry node from outside the
// region.
// The identity of the region entry node is preserved.
static void simplifyRegionEntry(Region *R, DominatorTree *DT, LoopInfo *LI,
                                RegionInfo *RI) {
  BasicBlock *EnteringBB = R->getEnteringBlock();
  BasicBlock *Entry = R->getEntry();
 
  // Before (one of):
  //
  //                       \    /            //
  //                      EnteringBB         //
  //                        |    \------>    //
  //   \   /                |                //
  //   Entry <--\         Entry <--\         //
  //   /   \    /         /   \    /         //
  //        ....               ....          //
 
  // Create single entry edge if the region has multiple entry edges.
  if (!EnteringBB) {
    SmallVector<BasicBlock *, 4> Preds;
    for (BasicBlock *P : predecessors(Entry))
      if (!R->contains(P))
        Preds.push_back(P);
 
    BasicBlock *NewEntering =
        SplitBlockPredecessors(Entry, Preds, ".region_entering", DT, LI);
 
    if (RI) {
      // The exit block of predecessing regions must be changed to NewEntering
      for (BasicBlock *ExitPred : predecessors(NewEntering)) {
        Region *RegionOfPred = RI->getRegionFor(ExitPred);
        if (RegionOfPred->getExit() != Entry)
          continue;
 
        while (!RegionOfPred->isTopLevelRegion() &&
               RegionOfPred->getExit() == Entry) {
          RegionOfPred->replaceExit(NewEntering);
          RegionOfPred = RegionOfPred->getParent();
        }
      }
 
      // Make all ancestors use EnteringBB as entry; there might be edges to it
      Region *AncestorR = R->getParent();
      RI->setRegionFor(NewEntering, AncestorR);
      while (!AncestorR->isTopLevelRegion() && AncestorR->getEntry() == Entry) {
        AncestorR->replaceEntry(NewEntering);
        AncestorR = AncestorR->getParent();
      }
    }
 
    EnteringBB = NewEntering;
  }
  assert(R->getEnteringBlock() == EnteringBB);
 
  // After:
  //
  //    \    /       //
  //  EnteringBB     //
  //      |          //
  //      |          //
  //    Entry <--\   //
  //    /   \    /   //
  //         ....    //
}
 
// Ensure that the region has a single block that branches to the exit node.
static void simplifyRegionExit(Region *R, DominatorTree *DT, LoopInfo *LI,
                               RegionInfo *RI) {
  BasicBlock *ExitBB = R->getExit();
  BasicBlock *ExitingBB = R->getExitingBlock();
 
  // Before:
  //
  //   (Region)   ______/  //
  //      \  |   /         //
  //       ExitBB          //
  //       /    \          //
 
  if (!ExitingBB) {
    SmallVector<BasicBlock *, 4> Preds;
    for (BasicBlock *P : predecessors(ExitBB))
      if (R->contains(P))
        Preds.push_back(P);
 
    //  Preds[0] Preds[1]      otherBB //
    //         \  |  ________/         //
    //          \ | /                  //
    //           BB                    //
    ExitingBB =
        SplitBlockPredecessors(ExitBB, Preds, ".region_exiting", DT, LI);
    // Preds[0] Preds[1]      otherBB  //
    //        \  /           /         //
    // BB.region_exiting    /          //
    //                  \  /           //
    //                   BB            //
 
    if (RI)
      RI->setRegionFor(ExitingBB, R);
 
    // Change the exit of nested regions, but not the region itself,
    R->replaceExitRecursive(ExitingBB);
    R->replaceExit(ExitBB);
  }
  assert(ExitingBB == R->getExitingBlock());
 
  // After:
  //
  //     \   /                //
  //    ExitingBB     _____/  //
  //          \      /        //
  //           ExitBB         //
  //           /    \         //
}
 
void polly::simplifyRegion(Region *R, DominatorTree *DT, LoopInfo *LI,
                           RegionInfo *RI) {
  assert(R && !R->isTopLevelRegion());
  assert(!RI || RI == R->getRegionInfo());
  assert((!RI || DT) &&
         "RegionInfo requires DominatorTree to be updated as well");
 
  simplifyRegionEntry(R, DT, LI, RI);
  simplifyRegionExit(R, DT, LI, RI);
  assert(R->isSimple());
}
 
// Split the block into two successive blocks.
//
// Like llvm::SplitBlock, but also preserves RegionInfo
static BasicBlock *splitBlock(BasicBlock *Old, BasicBlock::iterator SplitPt,
                              DominatorTree *DT, llvm::LoopInfo *LI,
                              RegionInfo *RI) {
  assert(Old);
 
  // Before:
  //
  //  \   /  //
  //   Old   //
  //  /   \  //
 
  BasicBlock *NewBlock = llvm::SplitBlock(Old, SplitPt, DT, LI);
 
  if (RI) {
    Region *R = RI->getRegionFor(Old);
    RI->setRegionFor(NewBlock, R);
  }
 
  // After:
  //
  //   \   /    //
  //    Old     //
  //     |      //
  //  NewBlock  //
  //   /   \    //
 
  return NewBlock;
}
 
void polly::splitEntryBlockForAlloca(BasicBlock *EntryBlock, DominatorTree *DT,
                                     LoopInfo *LI, RegionInfo *RI) {
  // Find first non-alloca instruction. Every basic block has a non-alloca
  // instruction, as every well formed basic block has a terminator.
  BasicBlock::iterator I = EntryBlock->begin();
  while (isa<AllocaInst>(I))
    ++I;
 
  // splitBlock updates DT, LI and RI.
  splitBlock(EntryBlock, I, DT, LI, RI);
}
 
void polly::recordAssumption(polly::RecordedAssumptionsTy *RecordedAssumptions,
                             polly::AssumptionKind Kind, isl::set Set,
                             DebugLoc Loc, polly::AssumptionSign Sign,
                             BasicBlock *BB, bool RTC) {
  assert((Set.is_params() || BB) &&
         "Assumptions without a basic block must be parameter sets");
  if (RecordedAssumptions)
    RecordedAssumptions->push_back({Kind, Sign, Set, Loc, BB, RTC});
}
 
/// ScopExpander generates IR the the value of a SCEV that represents a value
/// from a SCoP.
///
/// IMPORTANT: There are two ScalarEvolutions at play here. First, the SE that
/// was used to analyze the original SCoP (not actually referenced anywhere
/// here, but passed as argument to make the distinction clear). Second, GenSE
/// which is the SE for the function that the code is emitted into. SE and GenSE
/// may be different when the generated code is to be emitted into an outlined
/// function, e.g. for a parallel loop. That is, each SCEV is to be used only by
/// the SE that "owns" it and ScopExpander handles the translation between them.
/// The SCEVVisitor methods are only to be called on SCEVs of the original SE.
/// Their job is to create a new SCEV for GenSE. The nested SCEVExpander is to
/// be used only with SCEVs belonging to GenSE. Currently SCEVs do not store a
/// reference to the ScalarEvolution they belong to, so a mixup does not
/// immediately cause a crash but certainly is a violation of its interface.
///
/// The SCEVExpander will __not__ generate any code for an existing SDiv/SRem
/// instruction but just use it, if it is referenced as a SCEVUnknown. We want
/// however to generate new code if the instruction is in the analyzed region
/// and we generate code outside/in front of that region. Hence, we generate the
/// code for the SDiv/SRem operands in front of the analyzed region and then
/// create a new SDiv/SRem operation there too.
struct ScopExpander final : SCEVVisitor<ScopExpander, const SCEV *> {
  friend struct SCEVVisitor<ScopExpander, const SCEV *>;
 
  explicit ScopExpander(const Region &R, ScalarEvolution &SE, Function *GenFn,
                        ScalarEvolution &GenSE, const char *Name,
                        ValueMapT *VMap, LoopToScevMapT *LoopMap,
                        BasicBlock *RTCBB)
      : Expander(GenSE, Name, /*PreserveLCSSA=*/false), Name(Name), R(R),
        VMap(VMap), LoopMap(LoopMap), RTCBB(RTCBB), GenSE(GenSE), GenFn(GenFn) {
  }
 
  Value *expandCodeFor(const SCEV *E, Type *Ty, BasicBlock::iterator IP) {
    assert(isInGenRegion(&*IP) &&
           "ScopExpander assumes to be applied to generated code region");
    const SCEV *GenE = visit(E);
    return Expander.expandCodeFor(GenE, Ty, IP);
  }
 
  const SCEV *visit(const SCEV *E) {
    // Cache the expansion results for intermediate SCEV expressions. A SCEV
    // expression can refer to an operand multiple times (e.g. "x*x), so
    // a naive visitor takes exponential time.
    if (SCEVCache.count(E))
      return SCEVCache[E];
    const SCEV *Result = SCEVVisitor::visit(E);
    SCEVCache[E] = Result;
    return Result;
  }
 
private:
  SCEVExpander Expander;
  const char *Name;
  const Region &R;
  ValueMapT *VMap;
  LoopToScevMapT *LoopMap;
  BasicBlock *RTCBB;
  DenseMap<const SCEV *, const SCEV *> SCEVCache;
 
  ScalarEvolution &GenSE;
  Function *GenFn;
 
  /// Is the instruction part of the original SCoP (in contrast to be located in
  /// the code-generated region)?
  bool isInOrigRegion(Instruction *Inst) {
    Function *Fn = R.getEntry()->getParent();
    bool isInOrigRegion = Inst->getFunction() == Fn && R.contains(Inst);
    assert((isInOrigRegion || GenFn == Inst->getFunction()) &&
           "Instruction expected to be either in the SCoP or the translated "
           "region");
    return isInOrigRegion;
  }
 
  bool isInGenRegion(Instruction *Inst) { return !isInOrigRegion(Inst); }
 
  const SCEV *visitGenericInst(const SCEVUnknown *E, Instruction *Inst,
                               BasicBlock::iterator IP) {
    if (!Inst || isInGenRegion(Inst))
      return E;
 
    assert(!Inst->mayThrow() && !Inst->mayReadOrWriteMemory() &&
           !isa<PHINode>(Inst));
 
    auto *InstClone = Inst->clone();
    for (auto &Op : Inst->operands()) {
      assert(GenSE.isSCEVable(Op->getType()));
      const SCEV *OpSCEV = GenSE.getSCEV(Op);
      auto *OpClone = expandCodeFor(OpSCEV, Op->getType(), IP);
      InstClone->replaceUsesOfWith(Op, OpClone);
    }
 
    InstClone->setName(Name + Inst->getName());
    InstClone->insertBefore(IP);
    return GenSE.getSCEV(InstClone);
  }
 
  const SCEV *visitUnknown(const SCEVUnknown *E) {
 
    // If a value mapping was given try if the underlying value is remapped.
    Value *NewVal = VMap ? VMap->lookup(E->getValue()) : nullptr;
    if (NewVal) {
      const SCEV *NewE = GenSE.getSCEV(NewVal);
 
      // While the mapped value might be different the SCEV representation might
      // not be. To this end we will check before we go into recursion here.
      // FIXME: SCEVVisitor must only visit SCEVs that belong to the original
      // SE. This calls it on SCEVs that belong GenSE.
      if (E != NewE)
        return visit(NewE);
    }
 
    Instruction *Inst = dyn_cast<Instruction>(E->getValue());
    BasicBlock::iterator IP;
    if (Inst && isInGenRegion(Inst))
      IP = Inst->getIterator();
    else if (R.getEntry()->getParent() != GenFn) {
      // RTCBB is in the original function, but we are generating for a
      // subfunction so we cannot emit to RTCBB. Usually, we land here only
      // because E->getValue() is not an instruction but a global or constant
      // which do not need to emit anything.
      IP = GenFn->getEntryBlock().getTerminator()->getIterator();
    } else if (Inst && RTCBB->getParent() == Inst->getFunction())
      IP = RTCBB->getTerminator()->getIterator();
    else
      IP = RTCBB->getParent()->getEntryBlock().getTerminator()->getIterator();
 
    if (!Inst || (Inst->getOpcode() != Instruction::SRem &&
                  Inst->getOpcode() != Instruction::SDiv))
      return visitGenericInst(E, Inst, IP);
 
    const SCEV *LHSScev = GenSE.getSCEV(Inst->getOperand(0));
    const SCEV *RHSScev = GenSE.getSCEV(Inst->getOperand(1));
 
    if (!GenSE.isKnownNonZero(RHSScev))
      RHSScev = GenSE.getUMaxExpr(RHSScev, GenSE.getConstant(E->getType(), 1));
 
    Value *LHS = expandCodeFor(LHSScev, E->getType(), IP);
    Value *RHS = expandCodeFor(RHSScev, E->getType(), IP);
 
    Inst = BinaryOperator::Create((Instruction::BinaryOps)Inst->getOpcode(),
                                  LHS, RHS, Inst->getName() + Name, IP);
    return GenSE.getSCEV(Inst);
  }
 
  /// The following functions will just traverse the SCEV and rebuild it using
  /// GenSE and the new operands returned by the traversal.
  ///
  ///{
  const SCEV *visitConstant(const SCEVConstant *E) { return E; }
  const SCEV *visitVScale(const SCEVVScale *E) { return E; }
  const SCEV *visitPtrToAddrExpr(const SCEVPtrToAddrExpr *E) {
    return GenSE.getPtrToAddrExpr(visit(E->getOperand()));
  }
  const SCEV *visitPtrToIntExpr(const SCEVPtrToIntExpr *E) {
    return GenSE.getPtrToIntExpr(visit(E->getOperand()), E->getType());
  }
  const SCEV *visitTruncateExpr(const SCEVTruncateExpr *E) {
    return GenSE.getTruncateExpr(visit(E->getOperand()), E->getType());
  }
  const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *E) {
    return GenSE.getZeroExtendExpr(visit(E->getOperand()), E->getType());
  }
  const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *E) {
    return GenSE.getSignExtendExpr(visit(E->getOperand()), E->getType());
  }
  const SCEV *visitUDivExpr(const SCEVUDivExpr *E) {
    auto *RHSScev = visit(E->getRHS());
    if (!GenSE.isKnownNonZero(RHSScev))
      RHSScev = GenSE.getUMaxExpr(RHSScev, GenSE.getConstant(E->getType(), 1));
    return GenSE.getUDivExpr(visit(E->getLHS()), RHSScev);
  }
  const SCEV *visitAddExpr(const SCEVAddExpr *E) {
    SmallVector<const SCEV *, 4> NewOps;
    for (const SCEV *Op : E->operands())
      NewOps.push_back(visit(Op));
    return GenSE.getAddExpr(NewOps);
  }
  const SCEV *visitMulExpr(const SCEVMulExpr *E) {
    SmallVector<const SCEV *, 4> NewOps;
    for (const SCEV *Op : E->operands())
      NewOps.push_back(visit(Op));
    return GenSE.getMulExpr(NewOps);
  }
  const SCEV *visitUMaxExpr(const SCEVUMaxExpr *E) {
    SmallVector<const SCEV *, 4> NewOps;
    for (const SCEV *Op : E->operands())
      NewOps.push_back(visit(Op));
    return GenSE.getUMaxExpr(NewOps);
  }
  const SCEV *visitSMaxExpr(const SCEVSMaxExpr *E) {
    SmallVector<const SCEV *, 4> NewOps;
    for (const SCEV *Op : E->operands())
      NewOps.push_back(visit(Op));
    return GenSE.getSMaxExpr(NewOps);
  }
  const SCEV *visitUMinExpr(const SCEVUMinExpr *E) {
    SmallVector<const SCEV *, 4> NewOps;
    for (const SCEV *Op : E->operands())
      NewOps.push_back(visit(Op));
    return GenSE.getUMinExpr(NewOps);
  }
  const SCEV *visitSMinExpr(const SCEVSMinExpr *E) {
    SmallVector<const SCEV *, 4> NewOps;
    for (const SCEV *Op : E->operands())
      NewOps.push_back(visit(Op));
    return GenSE.getSMinExpr(NewOps);
  }
  const SCEV *visitSequentialUMinExpr(const SCEVSequentialUMinExpr *E) {
    SmallVector<const SCEV *, 4> NewOps;
    for (const SCEV *Op : E->operands())
      NewOps.push_back(visit(Op));
    return GenSE.getUMinExpr(NewOps, /*Sequential=*/true);
  }
  const SCEV *visitAddRecExpr(const SCEVAddRecExpr *E) {
    SmallVector<const SCEV *, 4> NewOps;
    for (const SCEV *Op : E->operands())
      NewOps.push_back(visit(Op));
 
    const Loop *L = E->getLoop();
    const SCEV *GenLRepl = LoopMap ? LoopMap->lookup(L) : nullptr;
    if (!GenLRepl)
      return GenSE.getAddRecExpr(NewOps, L, E->getNoWrapFlags());
 
    // evaluateAtIteration replaces the SCEVAddrExpr with a direct calculation.
    const SCEV *Evaluated =
        SCEVAddRecExpr::evaluateAtIteration(NewOps, GenLRepl, GenSE);
 
    // FIXME: This emits a SCEV for GenSE (since GenLRepl will refer to the
    // induction variable of a generated loop), so we should not use SCEVVisitor
    // with it. However, it still contains references to the SCoP region.
    return visit(Evaluated);
  }
  ///}
};
 
Value *polly::expandCodeFor(Scop &S, llvm::ScalarEvolution &SE,
                            llvm::Function *GenFn, ScalarEvolution &GenSE,
                            const DataLayout &DL, const char *Name,
                            const SCEV *E, Type *Ty, BasicBlock::iterator IP,
                            ValueMapT *VMap, LoopToScevMapT *LoopMap,
                            BasicBlock *RTCBB) {
  ScopExpander Expander(S.getRegion(), SE, GenFn, GenSE, Name, VMap, LoopMap,
                        RTCBB);
  return Expander.expandCodeFor(E, Ty, IP);
}
 
Value *polly::getConditionFromTerminator(Instruction *TI) {
  if (BranchInst *BR = dyn_cast<BranchInst>(TI)) {
    if (BR->isUnconditional())
      return ConstantInt::getTrue(Type::getInt1Ty(TI->getContext()));
 
    return BR->getCondition();
  }
 
  if (SwitchInst *SI = dyn_cast<SwitchInst>(TI))
    return SI->getCondition();
 
  return nullptr;
}
 
Loop *polly::getLoopSurroundingScop(Scop &S, LoopInfo &LI) {
  // Start with the smallest loop containing the entry and expand that
  // loop until it contains all blocks in the region. If there is a loop
  // containing all blocks in the region check if it is itself contained
  // and if so take the parent loop as it will be the smallest containing
  // the region but not contained by it.
  Loop *L = LI.getLoopFor(S.getEntry());
  while (L) {
    bool AllContained = true;
    for (auto *BB : S.blocks())
      AllContained &= L->contains(BB);
    if (AllContained)
      break;
    L = L->getParentLoop();
  }
 
  return L ? (S.contains(L) ? L->getParentLoop() : L) : nullptr;
}
 
unsigned polly::getNumBlocksInLoop(Loop *L) {
  unsigned NumBlocks = L->getNumBlocks();
  SmallVector<BasicBlock *, 4> ExitBlocks;
  L->getExitBlocks(ExitBlocks);
 
  for (auto ExitBlock : ExitBlocks) {
    if (isa<UnreachableInst>(ExitBlock->getTerminator()))
      NumBlocks++;
  }
  return NumBlocks;
}
 
unsigned polly::getNumBlocksInRegionNode(RegionNode *RN) {
  if (!RN->isSubRegion())
    return 1;
 
  Region *R = RN->getNodeAs<Region>();
  return std::distance(R->block_begin(), R->block_end());
}
 
Loop *polly::getRegionNodeLoop(RegionNode *RN, LoopInfo &LI) {
  if (!RN->isSubRegion()) {
    BasicBlock *BB = RN->getNodeAs<BasicBlock>();
    Loop *L = LI.getLoopFor(BB);
 
    // Unreachable statements are not considered to belong to a LLVM loop, as
    // they are not part of an actual loop in the control flow graph.
    // Nevertheless, we handle certain unreachable statements that are common
    // when modeling run-time bounds checks as being part of the loop to be
    // able to model them and to later eliminate the run-time bounds checks.
    //
    // Specifically, for basic blocks that terminate in an unreachable and
    // where the immediate predecessor is part of a loop, we assume these
    // basic blocks belong to the loop the predecessor belongs to. This
    // allows us to model the following code.
    //
    // for (i = 0; i < N; i++) {
    //   if (i > 1024)
    //     abort();            <- this abort might be translated to an
    //                            unreachable
    //
    //   A[i] = ...
    // }
    if (!L && isa<UnreachableInst>(BB->getTerminator()) && BB->getPrevNode())
      L = LI.getLoopFor(BB->getPrevNode());
    return L;
  }
 
  Region *NonAffineSubRegion = RN->getNodeAs<Region>();
  Loop *L = LI.getLoopFor(NonAffineSubRegion->getEntry());
  while (L && NonAffineSubRegion->contains(L))
    L = L->getParentLoop();
  return L;
}
 
static bool hasVariantIndex(GetElementPtrInst *Gep, Loop *L, Region &R,
                            ScalarEvolution &SE) {
  for (const Use &Val : llvm::drop_begin(Gep->operands(), 1)) {
    const SCEV *PtrSCEV = SE.getSCEVAtScope(Val, L);
    Loop *OuterLoop = R.outermostLoopInRegion(L);
    if (!SE.isLoopInvariant(PtrSCEV, OuterLoop))
      return true;
  }
  return false;
}
 
bool polly::isHoistableLoad(LoadInst *LInst, Region &R, LoopInfo &LI,
                            ScalarEvolution &SE, const DominatorTree &DT,
                            const InvariantLoadsSetTy &KnownInvariantLoads) {
  Loop *L = LI.getLoopFor(LInst->getParent());
  auto *Ptr = LInst->getPointerOperand();
 
  // A LoadInst is hoistable if the address it is loading from is also
  // invariant; in this case: another invariant load (whether that address
  // is also not written to has to be checked separately)
  // TODO: This only checks for a LoadInst->GetElementPtrInst->LoadInst
  // pattern generated by the Chapel frontend, but generally this applies
  // for any chain of instruction that does not also depend on any
  // induction variable
  if (auto *GepInst = dyn_cast<GetElementPtrInst>(Ptr)) {
    if (!hasVariantIndex(GepInst, L, R, SE)) {
      if (auto *DecidingLoad =
              dyn_cast<LoadInst>(GepInst->getPointerOperand())) {
        if (KnownInvariantLoads.count(DecidingLoad))
          return true;
      }
    }
  }
 
  const SCEV *PtrSCEV = SE.getSCEVAtScope(Ptr, L);
  while (L && R.contains(L)) {
    if (!SE.isLoopInvariant(PtrSCEV, L))
      return false;
    L = L->getParentLoop();
  }
 
  if (!Ptr->hasUseList())
    return true;
 
  for (auto *User : Ptr->users()) {
    auto *UserI = dyn_cast<Instruction>(User);
    if (!UserI || UserI->getFunction() != LInst->getFunction() ||
        !R.contains(UserI))
      continue;
    if (!UserI->mayWriteToMemory())
      continue;
 
    auto &BB = *UserI->getParent();
    if (DT.dominates(&BB, LInst->getParent()))
      return false;
 
    bool DominatesAllPredecessors = true;
    if (R.isTopLevelRegion()) {
      for (BasicBlock &I : *R.getEntry()->getParent())
        if (isa<ReturnInst>(I.getTerminator()) && !DT.dominates(&BB, &I))
          DominatesAllPredecessors = false;
    } else {
      for (auto Pred : predecessors(R.getExit()))
        if (R.contains(Pred) && !DT.dominates(&BB, Pred))
          DominatesAllPredecessors = false;
    }
 
    if (!DominatesAllPredecessors)
      continue;
 
    return false;
  }
 
  return true;
}
 
bool polly::isIgnoredIntrinsic(const Value *V) {
  if (auto *IT = dyn_cast<IntrinsicInst>(V)) {
    switch (IT->getIntrinsicID()) {
    // Lifetime markers are supported/ignored.
    case llvm::Intrinsic::lifetime_start:
    case llvm::Intrinsic::lifetime_end:
    // Invariant markers are supported/ignored.
    case llvm::Intrinsic::invariant_start:
    case llvm::Intrinsic::invariant_end:
    // Some misc annotations are supported/ignored.
    case llvm::Intrinsic::var_annotation:
    case llvm::Intrinsic::ptr_annotation:
    case llvm::Intrinsic::annotation:
    case llvm::Intrinsic::donothing:
    case llvm::Intrinsic::assume:
    // Some debug info intrinsics are supported/ignored.
    case llvm::Intrinsic::dbg_value:
    case llvm::Intrinsic::dbg_declare:
      return true;
    default:
      break;
    }
  }
  return false;
}
 
bool polly::canSynthesize(const Value *V, const Scop &S, ScalarEvolution *SE,
                          Loop *Scope) {
  if (!V || !SE->isSCEVable(V->getType()))
    return false;
 
  const InvariantLoadsSetTy &ILS = S.getRequiredInvariantLoads();
  if (const SCEV *Scev = SE->getSCEVAtScope(const_cast<Value *>(V), Scope))
    if (!isa<SCEVCouldNotCompute>(Scev))
      if (!hasScalarDepsInsideRegion(Scev, &S.getRegion(), Scope, false, ILS))
        return true;
 
  return false;
}
 
llvm::BasicBlock *polly::getUseBlock(const llvm::Use &U) {
  Instruction *UI = dyn_cast<Instruction>(U.getUser());
  if (!UI)
    return nullptr;
 
  if (PHINode *PHI = dyn_cast<PHINode>(UI))
    return PHI->getIncomingBlock(U);
 
  return UI->getParent();
}
 
llvm::Loop *polly::getFirstNonBoxedLoopFor(llvm::Loop *L, llvm::LoopInfo &LI,
                                           const BoxedLoopsSetTy &BoxedLoops) {
  while (BoxedLoops.count(L))
    L = L->getParentLoop();
  return L;
}
 
llvm::Loop *polly::getFirstNonBoxedLoopFor(llvm::BasicBlock *BB,
                                           llvm::LoopInfo &LI,
                                           const BoxedLoopsSetTy &BoxedLoops) {
  Loop *L = LI.getLoopFor(BB);
  return getFirstNonBoxedLoopFor(L, LI, BoxedLoops);
}
 
bool polly::isDebugCall(Instruction *Inst) {
  auto *CI = dyn_cast<CallInst>(Inst);
  if (!CI)
    return false;
 
  Function *CF = CI->getCalledFunction();
  if (!CF)
    return false;
 
  return std::find(DebugFunctions.begin(), DebugFunctions.end(),
                   CF->getName()) != DebugFunctions.end();
}
 
static bool hasDebugCall(BasicBlock *BB) {
  for (Instruction &Inst : *BB) {
    if (isDebugCall(&Inst))
      return true;
  }
  return false;
}
 
bool polly::hasDebugCall(ScopStmt *Stmt) {
  // Quick skip if no debug functions have been defined.
  if (DebugFunctions.empty())
    return false;
 
  if (!Stmt)
    return false;
 
  for (Instruction *Inst : Stmt->getInstructions())
    if (isDebugCall(Inst))
      return true;
 
  if (Stmt->isRegionStmt()) {
    for (BasicBlock *RBB : Stmt->getRegion()->blocks())
      if (RBB != Stmt->getEntryBlock() && ::hasDebugCall(RBB))
        return true;
  }
 
  return false;
}
 
/// Find a property in a LoopID.
static MDNode *findNamedMetadataNode(MDNode *LoopMD, StringRef Name) {
  if (!LoopMD)
    return nullptr;
  for (const MDOperand &X : drop_begin(LoopMD->operands(), 1)) {
    auto *OpNode = dyn_cast<MDNode>(X.get());
    if (!OpNode)
      continue;
 
    auto *OpName = dyn_cast<MDString>(OpNode->getOperand(0));
    if (!OpName)
      continue;
    if (OpName->getString() == Name)
      return OpNode;
  }
  return nullptr;
}
 
static std::optional<const MDOperand *> findNamedMetadataArg(MDNode *LoopID,
                                                             StringRef Name) {
  MDNode *MD = findNamedMetadataNode(LoopID, Name);
  if (!MD)
    return std::nullopt;
  switch (MD->getNumOperands()) {
  case 1:
    return nullptr;
  case 2:
    return &MD->getOperand(1);
  default:
    llvm_unreachable("loop metadata has 0 or 1 operand");
  }
}
 
std::optional<Metadata *> polly::findMetadataOperand(MDNode *LoopMD,
                                                     StringRef Name) {
  MDNode *MD = findNamedMetadataNode(LoopMD, Name);
  if (!MD)
    return std::nullopt;
  switch (MD->getNumOperands()) {
  case 1:
    return nullptr;
  case 2:
    return MD->getOperand(1).get();
  default:
    llvm_unreachable("loop metadata must have 0 or 1 operands");
  }
}
 
static std::optional<bool> getOptionalBoolLoopAttribute(MDNode *LoopID,
                                                        StringRef Name) {
  MDNode *MD = findNamedMetadataNode(LoopID, Name);
  if (!MD)
    return std::nullopt;
  switch (MD->getNumOperands()) {
  case 1:
    return true;
  case 2:
    if (ConstantInt *IntMD =
            mdconst::extract_or_null<ConstantInt>(MD->getOperand(1).get()))
      return IntMD->getZExtValue();
    return true;
  }
  llvm_unreachable("unexpected number of options");
}
 
bool polly::getBooleanLoopAttribute(MDNode *LoopID, StringRef Name) {
  return getOptionalBoolLoopAttribute(LoopID, Name).value_or(false);
}
 
std::optional<int> polly::getOptionalIntLoopAttribute(MDNode *LoopID,
                                                      StringRef Name) {
  const MDOperand *AttrMD =
      findNamedMetadataArg(LoopID, Name).value_or(nullptr);
  if (!AttrMD)
    return std::nullopt;
 
  ConstantInt *IntMD = mdconst::extract_or_null<ConstantInt>(AttrMD->get());
  if (!IntMD)
    return std::nullopt;
 
  return IntMD->getSExtValue();
}
 
bool polly::hasDisableAllTransformsHint(Loop *L) {
  return llvm::hasDisableAllTransformsHint(L);
}
 
bool polly::hasDisableAllTransformsHint(llvm::MDNode *LoopID) {
  return getBooleanLoopAttribute(LoopID, "llvm.loop.disable_nonforced");
}
 
isl::id polly::getIslLoopAttr(isl::ctx Ctx, BandAttr *Attr) {
  assert(Attr && "Must be a valid BandAttr");
 
  // The name "Loop" signals that this id contains a pointer to a BandAttr.
  // The ScheduleOptimizer also uses the string "Inter iteration alias-free" in
  // markers, but it's user pointer is an llvm::Value.
  isl::id Result = isl::id::alloc(Ctx, "Loop with Metadata", Attr);
  Result = isl::manage(isl_id_set_free_user(Result.release(), [](void *Ptr) {
    BandAttr *Attr = reinterpret_cast<BandAttr *>(Ptr);
    delete Attr;
  }));
  return Result;
}
 
isl::id polly::createIslLoopAttr(isl::ctx Ctx, Loop *L) {
  if (!L)
    return {};
 
  // A loop without metadata does not need to be annotated.
  MDNode *LoopID = L->getLoopID();
  if (!LoopID)
    return {};
 
  BandAttr *Attr = new BandAttr();
  Attr->OriginalLoop = L;
  Attr->Metadata = L->getLoopID();
 
  return getIslLoopAttr(Ctx, Attr);
}
 
bool polly::isLoopAttr(const isl::id &Id) {
  if (Id.is_null())
    return false;
 
  return Id.get_name() == "Loop with Metadata";
}
 
BandAttr *polly::getLoopAttr(const isl::id &Id) {
  if (!isLoopAttr(Id))
    return nullptr;
 
  return reinterpret_cast<BandAttr *>(Id.get_user());
}