C++ PHINode::insertBefore方法代码示例

void BlockGenerator::createScalarFinalization(Region &R) {
  // The exit block of the __unoptimized__ region.
  BasicBlock *ExitBB = R.getExitingBlock();
  // The merge block __just after__ the region and the optimized region.
  BasicBlock *MergeBB = R.getExit();

  // The exit block of the __optimized__ region.
  BasicBlock *OptExitBB = *(pred_begin(MergeBB));
  if (OptExitBB == ExitBB)
    OptExitBB = *(++pred_begin(MergeBB));

  Builder.SetInsertPoint(OptExitBB->getTerminator());
  for (const auto &EscapeMapping : EscapeMap) {
    // Extract the escaping instruction and the escaping users as well as the
    // alloca the instruction was demoted to.
    Instruction *EscapeInst = EscapeMapping.getFirst();
    const auto &EscapeMappingValue = EscapeMapping.getSecond();
    const EscapeUserVectorTy &EscapeUsers = EscapeMappingValue.second;
    AllocaInst *ScalarAddr = EscapeMappingValue.first;

    // Reload the demoted instruction in the optimized version of the SCoP.
    Instruction *EscapeInstReload =
        Builder.CreateLoad(ScalarAddr, EscapeInst->getName() + ".final_reload");

    // Create the merge PHI that merges the optimized and unoptimized version.
    PHINode *MergePHI = PHINode::Create(EscapeInst->getType(), 2,
                                        EscapeInst->getName() + ".merge");
    MergePHI->insertBefore(MergeBB->getFirstInsertionPt());

    // Add the respective values to the merge PHI.
    MergePHI->addIncoming(EscapeInstReload, OptExitBB);
    MergePHI->addIncoming(EscapeInst, ExitBB);

    // The information of scalar evolution about the escaping instruction needs
    // to be revoked so the new merged instruction will be used.
    if (SE.isSCEVable(EscapeInst->getType()))
      SE.forgetValue(EscapeInst);

    // Replace all uses of the demoted instruction with the merge PHI.
    for (Instruction *EUser : EscapeUsers)
      EUser->replaceUsesOfWith(EscapeInst, MergePHI);
  }
}

//.........这里部分代码省略.........

  while (!Blocks.empty()) {
    BasicBlock *BB = Blocks.front();
    Blocks.pop_front();

    // First split the block and update dominance information.
    BasicBlock *BBCopy = splitBB(BB);
    BasicBlock *BBCopyIDom = repairDominance(BB, BBCopy);

    // In order to remap PHI nodes we store also basic block mappings.
    BlockMap[BB] = BBCopy;

    // Get the mapping for this block and initialize it with the mapping
    // available at its immediate dominator (in the new region).
    ValueMapT &RegionMap = RegionMaps[BBCopy];
    RegionMap = RegionMaps[BBCopyIDom];

    // Copy the block with the BlockGenerator.
    copyBB(Stmt, BB, BBCopy, RegionMap, GlobalMap, LTS);

    // In order to remap PHI nodes we store also basic block mappings.
    BlockMap[BB] = BBCopy;

    // Add values to incomplete PHI nodes waiting for this block to be copied.
    for (const PHINodePairTy &PHINodePair : IncompletePHINodeMap[BB])
      addOperandToPHI(Stmt, PHINodePair.first, PHINodePair.second, BB,
                      GlobalMap, LTS);
    IncompletePHINodeMap[BB].clear();

    // And continue with new successors inside the region.
    for (auto SI = succ_begin(BB), SE = succ_end(BB); SI != SE; SI++)
      if (R->contains(*SI) && SeenBlocks.insert(*SI).second)
        Blocks.push_back(*SI);
  }

  // Now create a new dedicated region exit block and add it to the region map.
  BasicBlock *ExitBBCopy =
      SplitBlock(Builder.GetInsertBlock(), Builder.GetInsertPoint(), &DT, &LI);
  ExitBBCopy->setName("polly.stmt." + R->getExit()->getName() + ".exit");
  BlockMap[R->getExit()] = ExitBBCopy;

  repairDominance(R->getExit(), ExitBBCopy);

  // As the block generator doesn't handle control flow we need to add the
  // region control flow by hand after all blocks have been copied.
  for (BasicBlock *BB : SeenBlocks) {

    BranchInst *BI = cast<BranchInst>(BB->getTerminator());

    BasicBlock *BBCopy = BlockMap[BB];
    Instruction *BICopy = BBCopy->getTerminator();

    ValueMapT &RegionMap = RegionMaps[BBCopy];
    RegionMap.insert(BlockMap.begin(), BlockMap.end());

    Builder.SetInsertPoint(BBCopy);
    copyInstScalar(Stmt, BI, RegionMap, GlobalMap, LTS);
    BICopy->eraseFromParent();
  }

  // Add counting PHI nodes to all loops in the region that can be used as
  // replacement for SCEVs refering to the old loop.
  for (BasicBlock *BB : SeenBlocks) {
    Loop *L = LI.getLoopFor(BB);
    if (L == nullptr || L->getHeader() != BB)
      continue;

    BasicBlock *BBCopy = BlockMap[BB];
    Value *NullVal = Builder.getInt32(0);
    PHINode *LoopPHI =
        PHINode::Create(Builder.getInt32Ty(), 2, "polly.subregion.iv");
    Instruction *LoopPHIInc = BinaryOperator::CreateAdd(
        LoopPHI, Builder.getInt32(1), "polly.subregion.iv.inc");
    LoopPHI->insertBefore(BBCopy->begin());
    LoopPHIInc->insertBefore(BBCopy->getTerminator());

    for (auto *PredBB : make_range(pred_begin(BB), pred_end(BB))) {
      if (!R->contains(PredBB))
        continue;
      if (L->contains(PredBB))
        LoopPHI->addIncoming(LoopPHIInc, BlockMap[PredBB]);
      else
        LoopPHI->addIncoming(NullVal, BlockMap[PredBB]);
    }

    for (auto *PredBBCopy : make_range(pred_begin(BBCopy), pred_end(BBCopy)))
      if (LoopPHI->getBasicBlockIndex(PredBBCopy) < 0)
        LoopPHI->addIncoming(NullVal, PredBBCopy);

    LTS[L] = SE.getUnknown(LoopPHI);
  }

  // Add all mappings from the region to the global map so outside uses will use
  // the copied instructions.
  for (auto &BBMap : RegionMaps)
    GlobalMap.insert(BBMap.second.begin(), BBMap.second.end());

  // Reset the old insert point for the build.
  Builder.SetInsertPoint(ExitBBCopy->begin());
}

/// RewriteLoopExitValues - Check to see if this loop has a computable
/// loop-invariant execution count.  If so, this means that we can compute the
/// final value of any expressions that are recurrent in the loop, and
/// substitute the exit values from the loop into any instructions outside of
/// the loop that use the final values of the current expressions.
///
/// This is mostly redundant with the regular IndVarSimplify activities that
/// happen later, except that it's more powerful in some cases, because it's
/// able to brute-force evaluate arbitrary instructions as long as they have
/// constant operands at the beginning of the loop.
void IndVarSimplify::RewriteLoopExitValues(Loop *L,
                                           SCEVExpander &Rewriter) {
  // Verify the input to the pass in already in LCSSA form.
  assert(L->isLCSSAForm(*DT));

  SmallVector<BasicBlock*, 8> ExitBlocks;
  L->getUniqueExitBlocks(ExitBlocks);

  // Find all values that are computed inside the loop, but used outside of it.
  // Because of LCSSA, these values will only occur in LCSSA PHI Nodes.  Scan
  // the exit blocks of the loop to find them.
  for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
    BasicBlock *ExitBB = ExitBlocks[i];

    // If there are no PHI nodes in this exit block, then no values defined
    // inside the loop are used on this path, skip it.
    PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
    if (!PN) continue;

    unsigned NumPreds = PN->getNumIncomingValues();

    // Iterate over all of the PHI nodes.
    BasicBlock::iterator BBI = ExitBB->begin();
    while ((PN = dyn_cast<PHINode>(BBI++))) {
      if (PN->use_empty())
        continue; // dead use, don't replace it

      // SCEV only supports integer expressions for now.
      if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
        continue;

      // It's necessary to tell ScalarEvolution about this explicitly so that
      // it can walk the def-use list and forget all SCEVs, as it may not be
      // watching the PHI itself. Once the new exit value is in place, there
      // may not be a def-use connection between the loop and every instruction
      // which got a SCEVAddRecExpr for that loop.
      SE->forgetValue(PN);

      // Iterate over all of the values in all the PHI nodes.
      for (unsigned i = 0; i != NumPreds; ++i) {
        // If the value being merged in is not integer or is not defined
        // in the loop, skip it.
        Value *InVal = PN->getIncomingValue(i);
        if (!isa<Instruction>(InVal))
          continue;

        // If this pred is for a subloop, not L itself, skip it.
        if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
          continue; // The Block is in a subloop, skip it.

        // Check that InVal is defined in the loop.
        Instruction *Inst = cast<Instruction>(InVal);
        if (!L->contains(Inst))
          continue;

        // Okay, this instruction has a user outside of the current loop
        // and varies predictably *inside* the loop.  Evaluate the value it
        // contains when the loop exits, if possible.
        const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
        if (!ExitValue->isLoopInvariant(L))
          continue;

        Changed = true;
        ++NumReplaced;

        Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);

        DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
                     << "  LoopVal = " << *Inst << "\n");

        PN->setIncomingValue(i, ExitVal);

        // If this instruction is dead now, delete it.
        RecursivelyDeleteTriviallyDeadInstructions(Inst);

        if (NumPreds == 1) {
          // Completely replace a single-pred PHI. This is safe, because the
          // NewVal won't be variant in the loop, so we don't need an LCSSA phi
          // node anymore.
          PN->replaceAllUsesWith(ExitVal);
          RecursivelyDeleteTriviallyDeadInstructions(PN);
        }
      }
      if (NumPreds != 1) {
        // Clone the PHI and delete the original one. This lets IVUsers and
        // any other maps purge the original user from their records.
        PHINode *NewPN = cast<PHINode>(PN->clone());
        NewPN->takeName(PN);
        NewPN->insertBefore(PN);
        PN->replaceAllUsesWith(NewPN);
//.........这里部分代码省略.........

bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
  IU = &getAnalysis<IVUsers>();
  LI = &getAnalysis<LoopInfo>();
  SE = &getAnalysis<ScalarEvolution>();
  DT = &getAnalysis<DominatorTree>();
  Changed = false;

  // If there are any floating-point recurrences, attempt to
  // transform them to use integer recurrences.
  RewriteNonIntegerIVs(L);

  BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null
  const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);

  // Create a rewriter object which we'll use to transform the code with.
  SCEVExpander Rewriter(*SE);

  // Check to see if this loop has a computable loop-invariant execution count.
  // If so, this means that we can compute the final value of any expressions
  // that are recurrent in the loop, and substitute the exit values from the
  // loop into any instructions outside of the loop that use the final values of
  // the current expressions.
  //
  if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
    RewriteLoopExitValues(L, Rewriter);

  // Compute the type of the largest recurrence expression, and decide whether
  // a canonical induction variable should be inserted.
  const Type *LargestType = 0;
  bool NeedCannIV = false;
  if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
    LargestType = BackedgeTakenCount->getType();
    LargestType = SE->getEffectiveSCEVType(LargestType);
    // If we have a known trip count and a single exit block, we'll be
    // rewriting the loop exit test condition below, which requires a
    // canonical induction variable.
    if (ExitingBlock)
      NeedCannIV = true;
  }
  for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
    const Type *Ty =
      SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType());
    if (!LargestType ||
        SE->getTypeSizeInBits(Ty) >
          SE->getTypeSizeInBits(LargestType))
      LargestType = Ty;
    NeedCannIV = true;
  }

  // Now that we know the largest of the induction variable expressions
  // in this loop, insert a canonical induction variable of the largest size.
  Value *IndVar = 0;
  if (NeedCannIV) {
    // Check to see if the loop already has any canonical-looking induction
    // variables. If any are present and wider than the planned canonical
    // induction variable, temporarily remove them, so that the Rewriter
    // doesn't attempt to reuse them.
    SmallVector<PHINode *, 2> OldCannIVs;
    while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) {
      if (SE->getTypeSizeInBits(OldCannIV->getType()) >
          SE->getTypeSizeInBits(LargestType))
        OldCannIV->removeFromParent();
      else
        break;
      OldCannIVs.push_back(OldCannIV);
    }

    IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType);

    ++NumInserted;
    Changed = true;
    DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n');

    // Now that the official induction variable is established, reinsert
    // any old canonical-looking variables after it so that the IR remains
    // consistent. They will be deleted as part of the dead-PHI deletion at
    // the end of the pass.
    while (!OldCannIVs.empty()) {
      PHINode *OldCannIV = OldCannIVs.pop_back_val();
      OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI());
    }
  }

  // If we have a trip count expression, rewrite the loop's exit condition
  // using it.  We can currently only handle loops with a single exit.
  ICmpInst *NewICmp = 0;
  if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) &&
      !BackedgeTakenCount->isZero() &&
      ExitingBlock) {
    assert(NeedCannIV &&
           "LinearFunctionTestReplace requires a canonical induction variable");
    // Can't rewrite non-branch yet.
    if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()))
      NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
                                          ExitingBlock, BI, Rewriter);
  }

  // Rewrite IV-derived expressions. Clears the rewriter cache.
  RewriteIVExpressions(L, Rewriter);

//.........这里部分代码省略.........

//.........这里部分代码省略.........
  bool IsMustTailCall = CS.isMustTailCall();

  PHINode *CallPN = nullptr;

  // `musttail` calls must be followed by optional `bitcast`, and `ret`. The
  // split blocks will be terminated right after that so there're no users for
  // this phi in a `TailBB`.
  if (!IsMustTailCall && Instr->getNumUses())
    CallPN = PHINode::Create(Instr->getType(), Preds.size(), "phi.call");

  DEBUG(dbgs() << "split call-site : " << *Instr << " into \n");

  assert(Preds.size() == 2 && "The ValueToValueMaps array has size 2.");
  // ValueToValueMapTy is neither copy nor moveable, so we use a simple array
  // here.
  ValueToValueMapTy ValueToValueMaps[2];
  for (unsigned i = 0; i < Preds.size(); i++) {
    BasicBlock *PredBB = Preds[i].first;
    BasicBlock *SplitBlock = DuplicateInstructionsInSplitBetween(
        TailBB, PredBB, &*std::next(Instr->getIterator()), ValueToValueMaps[i]);
    assert(SplitBlock && "Unexpected new basic block split.");

    Instruction *NewCI =
        &*std::prev(SplitBlock->getTerminator()->getIterator());
    CallSite NewCS(NewCI);
    addConditions(NewCS, Preds[i].second);

    // Handle PHIs used as arguments in the call-site.
    for (PHINode &PN : TailBB->phis()) {
      unsigned ArgNo = 0;
      for (auto &CI : CS.args()) {
        if (&*CI == &PN) {
          NewCS.setArgument(ArgNo, PN.getIncomingValueForBlock(SplitBlock));
        }
        ++ArgNo;
      }
    }
    DEBUG(dbgs() << "    " << *NewCI << " in " << SplitBlock->getName()
                 << "\n");
    if (CallPN)
      CallPN->addIncoming(NewCI, SplitBlock);

    // Clone and place bitcast and return instructions before `TI`
    if (IsMustTailCall)
      copyMustTailReturn(SplitBlock, Instr, NewCI);
  }

  NumCallSiteSplit++;

  // FIXME: remove TI in `copyMustTailReturn`
  if (IsMustTailCall) {
    // Remove superfluous `br` terminators from the end of the Split blocks
    // NOTE: Removing terminator removes the SplitBlock from the TailBB's
    // predecessors. Therefore we must get complete list of Splits before
    // attempting removal.
    SmallVector<BasicBlock *, 2> Splits(predecessors((TailBB)));
    assert(Splits.size() == 2 && "Expected exactly 2 splits!");
    for (unsigned i = 0; i < Splits.size(); i++)
      Splits[i]->getTerminator()->eraseFromParent();

    // Erase the tail block once done with musttail patching
    TailBB->eraseFromParent();
    return;
  }

  auto *OriginalBegin = &*TailBB->begin();
  // Replace users of the original call with a PHI mering call-sites split.
  if (CallPN) {
    CallPN->insertBefore(OriginalBegin);
    Instr->replaceAllUsesWith(CallPN);
  }

  // Remove instructions moved to split blocks from TailBB, from the duplicated
  // call instruction to the beginning of the basic block. If an instruction
  // has any uses, add a new PHI node to combine the values coming from the
  // split blocks. The new PHI nodes are placed before the first original
  // instruction, so we do not end up deleting them. By using reverse-order, we
  // do not introduce unnecessary PHI nodes for def-use chains from the call
  // instruction to the beginning of the block.
  auto I = Instr->getReverseIterator();
  while (I != TailBB->rend()) {
    Instruction *CurrentI = &*I++;
    if (!CurrentI->use_empty()) {
      // If an existing PHI has users after the call, there is no need to create
      // a new one.
      if (isa<PHINode>(CurrentI))
        continue;
      PHINode *NewPN = PHINode::Create(CurrentI->getType(), Preds.size());
      for (auto &Mapping : ValueToValueMaps)
        NewPN->addIncoming(Mapping[CurrentI],
                           cast<Instruction>(Mapping[CurrentI])->getParent());
      NewPN->insertBefore(&*TailBB->begin());
      CurrentI->replaceAllUsesWith(NewPN);
    }
    CurrentI->eraseFromParent();
    // We are done once we handled the first original instruction in TailBB.
    if (CurrentI == OriginalBegin)
      break;
  }
}