C++ PHINode::reserveOperandSpace方法代码示例

 /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
 /// Reserve space for the operands but do not fill them in yet.
 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
                              SSAUpdater *Updater) {
   PHINode *PHI = PHINode::Create(Updater->PrototypeValue->getType(),
                                  Updater->PrototypeValue->getName(),
                                  &BB->front());
   PHI->reserveOperandSpace(NumPreds);
   return PHI;
 }

/// ProcessInstruction - Given an instruction in the loop, check to see if it
/// has any uses that are outside the current loop.  If so, insert LCSSA PHI
/// nodes and rewrite the uses.
bool LCSSA::ProcessInstruction(Instruction *Inst,
                               const SmallVectorImpl<BasicBlock*> &ExitBlocks) {
  SmallVector<Use*, 16> UsesToRewrite;
  
  BasicBlock *InstBB = Inst->getParent();
  
  for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
       UI != E; ++UI) {
    User *U = *UI;
    BasicBlock *UserBB = cast<Instruction>(U)->getParent();
    if (PHINode *PN = dyn_cast<PHINode>(U))
      UserBB = PN->getIncomingBlock(UI);
    
    if (InstBB != UserBB && !inLoop(UserBB))
      UsesToRewrite.push_back(&UI.getUse());
  }

  // If there are no uses outside the loop, exit with no change.
  if (UsesToRewrite.empty()) return false;
  
  ++NumLCSSA; // We are applying the transformation

  // Invoke instructions are special in that their result value is not available
  // along their unwind edge. The code below tests to see whether DomBB dominates
  // the value, so adjust DomBB to the normal destination block, which is
  // effectively where the value is first usable.
  BasicBlock *DomBB = Inst->getParent();
  if (InvokeInst *Inv = dyn_cast<InvokeInst>(Inst))
    DomBB = Inv->getNormalDest();

  DomTreeNode *DomNode = DT->getNode(DomBB);

  SSAUpdater SSAUpdate;
  SSAUpdate.Initialize(Inst->getType(), Inst->getName());
  
  // Insert the LCSSA phi's into all of the exit blocks dominated by the
  // value, and add them to the Phi's map.
  for (SmallVectorImpl<BasicBlock*>::const_iterator BBI = ExitBlocks.begin(),
      BBE = ExitBlocks.end(); BBI != BBE; ++BBI) {
    BasicBlock *ExitBB = *BBI;
    if (!DT->dominates(DomNode, DT->getNode(ExitBB))) continue;
    
    // If we already inserted something for this BB, don't reprocess it.
    if (SSAUpdate.HasValueForBlock(ExitBB)) continue;
    
    PHINode *PN = PHINode::Create(Inst->getType(), Inst->getName()+".lcssa",
                                  ExitBB->begin());
    PN->reserveOperandSpace(PredCache.GetNumPreds(ExitBB));

    // Add inputs from inside the loop for this PHI.
    for (BasicBlock **PI = PredCache.GetPreds(ExitBB); *PI; ++PI) {
      PN->addIncoming(Inst, *PI);

      // If the exit block has a predecessor not within the loop, arrange for
      // the incoming value use corresponding to that predecessor to be
      // rewritten in terms of a different LCSSA PHI.
      if (!inLoop(*PI))
        UsesToRewrite.push_back(
          &PN->getOperandUse(
            PN->getOperandNumForIncomingValue(PN->getNumIncomingValues()-1)));
    }
    
    // Remember that this phi makes the value alive in this block.
    SSAUpdate.AddAvailableValue(ExitBB, PN);
  }
  
  // Rewrite all uses outside the loop in terms of the new PHIs we just
  // inserted.
  for (unsigned i = 0, e = UsesToRewrite.size(); i != e; ++i) {
    // If this use is in an exit block, rewrite to use the newly inserted PHI.
    // This is required for correctness because SSAUpdate doesn't handle uses in
    // the same block.  It assumes the PHI we inserted is at the end of the
    // block.
    Instruction *User = cast<Instruction>(UsesToRewrite[i]->getUser());
    BasicBlock *UserBB = User->getParent();
    if (PHINode *PN = dyn_cast<PHINode>(User))
      UserBB = PN->getIncomingBlock(*UsesToRewrite[i]);

    if (isa<PHINode>(UserBB->begin()) &&
        isExitBlock(UserBB, ExitBlocks)) {
      UsesToRewrite[i]->set(UserBB->begin());
      continue;
    }
    
    // Otherwise, do full PHI insertion.
    SSAUpdate.RewriteUse(*UsesToRewrite[i]);
  }
  
  return true;
}

//.........这里部分代码省略.........
    OtherBB = P;

  if (++PI == pred_end(DestBB))
    return false;
  
  P = *PI;
  if (P != StoreBB) {
    if (OtherBB)
      return false;
    OtherBB = P;
  }
  if (++PI != pred_end(DestBB))
    return false;

  // Bail out if all the relevant blocks aren't distinct (this can happen,
  // for example, if SI is in an infinite loop)
  if (StoreBB == DestBB || OtherBB == DestBB)
    return false;

  // Verify that the other block ends in a branch and is not otherwise empty.
  BasicBlock::iterator BBI = OtherBB->getTerminator();
  BranchInst *OtherBr = dyn_cast<BranchInst>(BBI);
  if (!OtherBr || BBI == OtherBB->begin())
    return false;
  
  // If the other block ends in an unconditional branch, check for the 'if then
  // else' case.  there is an instruction before the branch.
  StoreInst *OtherStore = 0;
  if (OtherBr->isUnconditional()) {
    --BBI;
    // Skip over debugging info.
    while (isa<DbgInfoIntrinsic>(BBI) ||
           (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
      if (BBI==OtherBB->begin())
        return false;
      --BBI;
    }
    // If this isn't a store, isn't a store to the same location, or if the
    // alignments differ, bail out.
    OtherStore = dyn_cast<StoreInst>(BBI);
    if (!OtherStore || OtherStore->getOperand(1) != SI.getOperand(1) ||
        OtherStore->getAlignment() != SI.getAlignment())
      return false;
  } else {
    // Otherwise, the other block ended with a conditional branch. If one of the
    // destinations is StoreBB, then we have the if/then case.
    if (OtherBr->getSuccessor(0) != StoreBB && 
        OtherBr->getSuccessor(1) != StoreBB)
      return false;
    
    // Okay, we know that OtherBr now goes to Dest and StoreBB, so this is an
    // if/then triangle.  See if there is a store to the same ptr as SI that
    // lives in OtherBB.
    for (;; --BBI) {
      // Check to see if we find the matching store.
      if ((OtherStore = dyn_cast<StoreInst>(BBI))) {
        if (OtherStore->getOperand(1) != SI.getOperand(1) ||
            OtherStore->getAlignment() != SI.getAlignment())
          return false;
        break;
      }
      // If we find something that may be using or overwriting the stored
      // value, or if we run out of instructions, we can't do the xform.
      if (BBI->mayReadFromMemory() || BBI->mayWriteToMemory() ||
          BBI == OtherBB->begin())
        return false;
    }
    
    // In order to eliminate the store in OtherBr, we have to
    // make sure nothing reads or overwrites the stored value in
    // StoreBB.
    for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
      // FIXME: This should really be AA driven.
      if (I->mayReadFromMemory() || I->mayWriteToMemory())
        return false;
    }
  }
  
  // Insert a PHI node now if we need it.
  Value *MergedVal = OtherStore->getOperand(0);
  if (MergedVal != SI.getOperand(0)) {
    PHINode *PN = PHINode::Create(MergedVal->getType(), "storemerge");
    PN->reserveOperandSpace(2);
    PN->addIncoming(SI.getOperand(0), SI.getParent());
    PN->addIncoming(OtherStore->getOperand(0), OtherBB);
    MergedVal = InsertNewInstBefore(PN, DestBB->front());
  }
  
  // Advance to a place where it is safe to insert the new store and
  // insert it.
  BBI = DestBB->getFirstNonPHI();
  InsertNewInstBefore(new StoreInst(MergedVal, SI.getOperand(1),
                                    OtherStore->isVolatile(),
                                    SI.getAlignment()), *BBI);
  
  // Nuke the old stores.
  EraseInstFromFunction(SI);
  EraseInstFromFunction(*OtherStore);
  return true;
}

/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
/// is live in the middle of the specified block.
///
/// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
/// important case: if there is a definition of the rewritten value after the
/// 'use' in BB.  Consider code like this:
///
///      X1 = ...
///   SomeBB:
///      use(X)
///      X2 = ...
///      br Cond, SomeBB, OutBB
///
/// In this case, there are two values (X1 and X2) added to the AvailableVals
/// set by the client of the rewriter, and those values are both live out of
/// their respective blocks.  However, the use of X happens in the *middle* of
/// a block.  Because of this, we need to insert a new PHI node in SomeBB to
/// merge the appropriate values, and this value isn't live out of the block.
///
Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
  // If there is no definition of the renamed variable in this block, just use
  // GetValueAtEndOfBlock to do our work.
  if (!HasValueForBlock(BB))
    return GetValueAtEndOfBlock(BB);

  // Otherwise, we have the hard case.  Get the live-in values for each
  // predecessor.
  SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
  Value *SingularValue = 0;

  // We can get our predecessor info by walking the pred_iterator list, but it
  // is relatively slow.  If we already have PHI nodes in this block, walk one
  // of them to get the predecessor list instead.
  if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
    for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
      BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
      Value *PredVal = GetValueAtEndOfBlock(PredBB);
      PredValues.push_back(std::make_pair(PredBB, PredVal));

      // Compute SingularValue.
      if (i == 0)
        SingularValue = PredVal;
      else if (PredVal != SingularValue)
        SingularValue = 0;
    }
  } else {
    bool isFirstPred = true;
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
      BasicBlock *PredBB = *PI;
      Value *PredVal = GetValueAtEndOfBlock(PredBB);
      PredValues.push_back(std::make_pair(PredBB, PredVal));

      // Compute SingularValue.
      if (isFirstPred) {
        SingularValue = PredVal;
        isFirstPred = false;
      } else if (PredVal != SingularValue)
        SingularValue = 0;
    }
  }

  // If there are no predecessors, just return undef.
  if (PredValues.empty())
    return UndefValue::get(PrototypeValue->getType());

  // Otherwise, if all the merged values are the same, just use it.
  if (SingularValue != 0)
    return SingularValue;

  // Otherwise, we do need a PHI: check to see if we already have one available
  // in this block that produces the right value.
  if (isa<PHINode>(BB->begin())) {
    DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
                                               PredValues.end());
    PHINode *SomePHI;
    for (BasicBlock::iterator It = BB->begin();
         (SomePHI = dyn_cast<PHINode>(It)); ++It) {
      if (IsEquivalentPHI(SomePHI, ValueMapping))
        return SomePHI;
    }
  }

  // Ok, we have no way out, insert a new one now.
  PHINode *InsertedPHI = PHINode::Create(PrototypeValue->getType(),
                                         PrototypeValue->getName(),
                                         &BB->front());
  InsertedPHI->reserveOperandSpace(PredValues.size());

  // Fill in all the predecessors of the PHI.
  for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
    InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);

  // See if the PHI node can be merged to a single value.  This can happen in
  // loop cases when we get a PHI of itself and one other value.
  if (Value *ConstVal = InsertedPHI->hasConstantValue()) {
    InsertedPHI->eraseFromParent();
    return ConstVal;
  }

  // If the client wants to know about all new instructions, tell it.
//.........这里部分代码省略.........

/// InsertUniqueBackedgeBlock - This method is called when the specified loop
/// has more than one backedge in it.  If this occurs, revector all of these
/// backedges to target a new basic block and have that block branch to the loop
/// header.  This ensures that loops have exactly one backedge.
///
BasicBlock *
LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
  assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");

  // Get information about the loop
  BasicBlock *Header = L->getHeader();
  Function *F = Header->getParent();

  // Unique backedge insertion currently depends on having a preheader.
  if (!Preheader)
    return 0;

  // Figure out which basic blocks contain back-edges to the loop header.
  std::vector<BasicBlock*> BackedgeBlocks;
  for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I){
    BasicBlock *P = *I;

    // Indirectbr edges cannot be split, so we must fail if we find one.
    if (isa<IndirectBrInst>(P->getTerminator()))
      return 0;

    if (P != Preheader) BackedgeBlocks.push_back(P);
  }

  // Create and insert the new backedge block...
  BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
                                           Header->getName()+".backedge", F);
  BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);

  DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block "
               << BEBlock->getName() << "\n");

  // Move the new backedge block to right after the last backedge block.
  Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
  F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);

  // Now that the block has been inserted into the function, create PHI nodes in
  // the backedge block which correspond to any PHI nodes in the header block.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *PN = cast<PHINode>(I);
    PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".be",
                                     BETerminator);
    NewPN->reserveOperandSpace(BackedgeBlocks.size());
    if (AA) AA->copyValue(PN, NewPN);

    // Loop over the PHI node, moving all entries except the one for the
    // preheader over to the new PHI node.
    unsigned PreheaderIdx = ~0U;
    bool HasUniqueIncomingValue = true;
    Value *UniqueValue = 0;
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
      BasicBlock *IBB = PN->getIncomingBlock(i);
      Value *IV = PN->getIncomingValue(i);
      if (IBB == Preheader) {
        PreheaderIdx = i;
      } else {
        NewPN->addIncoming(IV, IBB);
        if (HasUniqueIncomingValue) {
          if (UniqueValue == 0)
            UniqueValue = IV;
          else if (UniqueValue != IV)
            HasUniqueIncomingValue = false;
        }
      }
    }

    // Delete all of the incoming values from the old PN except the preheader's
    assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
    if (PreheaderIdx != 0) {
      PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
      PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
    }
    // Nuke all entries except the zero'th.
    for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
      PN->removeIncomingValue(e-i, false);

    // Finally, add the newly constructed PHI node as the entry for the BEBlock.
    PN->addIncoming(NewPN, BEBlock);

    // As an optimization, if all incoming values in the new PhiNode (which is a
    // subset of the incoming values of the old PHI node) have the same value,
    // eliminate the PHI Node.
    if (HasUniqueIncomingValue) {
      NewPN->replaceAllUsesWith(UniqueValue);
      if (AA) AA->deleteValue(NewPN);
      BEBlock->getInstList().erase(NewPN);
    }
  }

  // Now that all of the PHI nodes have been inserted and adjusted, modify the
  // backedge blocks to just to the BEBlock instead of the header.
  for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
    TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
    for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
      if (TI->getSuccessor(Op) == Header)
//.........这里部分代码省略.........

    bool ModuloSchedulerDriverPass::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
      
        subscripts subs(IncomingLoop);

        if (!loop_is_ms_able(IncomingLoop) ) return false; 

        // The header before the parallelized loop will be placed here
        BasicBlock* preheader = IncomingLoop->getLoopPreheader();
        assert(preheader && "Unable to get a hold of the preheader");

        // Balance all BasicBlocks in this loop
        for (Loop::block_iterator it=IncomingLoop->block_begin(); it!=IncomingLoop->block_end();++it) {
            duplicateValuesWithMultipleUses(*it,subs.getInductionVar());
        }

        // For each BB in loop
        for (Loop::block_iterator it=IncomingLoop->block_begin(); it!=IncomingLoop->block_end();++it) {
            instructionPriority  ip(*it);
            (*it)->setName("PipelinedLoop");
            
            // ++++++++ Preheader part +++++++++
            // Make a copy of the body for each instruction. Place a pointer to the 
            // parallel cloned instruction in the map below. Later on we will replace it 
            // with a PHINode.
            DenseMap<const Value *, Value *>  InstToPreheader;

            // For each Instruction in body of the loop, clone, store, etc.
            for (BasicBlock::iterator ib = (*it)->begin(), eb = (*it)->end(); ib!=eb; ++ib) {
                // If this is NOT a phi node
                if (!dyn_cast<PHINode>(ib)) {
                    // Get the priority of the instruction
                    unsigned int p = ip.getPriority(ib);
                    // This is the header version of each variable that goes into a PHI node.
                    // The other edge needs to come from the 'prev' iteration
                    // We subtract -1 because this is one iteration before 
                    // Store the result into the map of the cloned
                    InstToPreheader[ib] = copyLoopBodyToHeader(ib, subs.getInductionVar(), preheader, p-1);
                }
            }

            // ++++++++ Loop body part +++++++++
            // For each of the cloned increment the indexs if needed and place the PHINode.
            for (BasicBlock::iterator ib = (*it)->begin(), eb = (*it)->end(); ib!=eb; ++ib) {
                // If this is NOT a phi node
                if (!dyn_cast<PHINode>(ib)) {
                    unsigned int p = ip.getPriority(ib);

                    // If this variable is not dependent on i (not i:=i+1)
                    // then we need to replace each i to i+5 ...
                    // We also do not need to create a PHI node, etc.
                    if (!subs.isUsedByInductionVariable(ib)) {
                        
                        incrementInductionVarIfUsed(ib,subs.getInductionVar(),p);

                        // Create the new PHI Node to replace the node
                        if (!dyn_cast<StoreInst>(ib) && !ib->isTerminator()) {
                            std::string newname = "glue" + (*it)->getName();

                            //PHINode* np = PHINode::Create(ib->getType(), "glue", *it);
                            PHINode* np = PHINode::Create(ib->getType(), newname, *it);
                            ib->replaceAllUsesWith(np);
                            np->reserveOperandSpace(2);
                            np->addIncoming(InstToPreheader[ib], preheader);
                            np->addIncoming(ib, *it);
                            np->moveBefore((*it)->begin());
                        }

                    }// end of if this is not an IV node (i:=i+1) 
                }
            }
        }

        eliminateDuplicatedLoads(preheader);
        for (Loop::block_iterator it=IncomingLoop->block_begin(); it!=IncomingLoop->block_end();++it) {
            eliminateDuplicatedLoads(*it);
            for (BasicBlock::iterator in = (*it)->begin(); in != (*it)->end(); ++in) {
                foldAddInstructions(in);
            }
        }
        return true;
    }