C++ SSAUpdater::HasValueForBlock方法代码示例

/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
/// old header into the preheader.  If there were uses of the values produced by
/// these instruction that were outside of the loop, we have to insert PHI nodes
/// to merge the two values.  Do this now.
static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
                                            BasicBlock *OrigPreheader,
                                            ValueToValueMapTy &ValueMap) {
  // Remove PHI node entries that are no longer live.
  BasicBlock::iterator I, E = OrigHeader->end();
  for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
    PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreheader));

  // Now fix up users of the instructions in OrigHeader, inserting PHI nodes
  // as necessary.
  SSAUpdater SSA;
  for (I = OrigHeader->begin(); I != E; ++I) {
    Value *OrigHeaderVal = &*I;

    // If there are no uses of the value (e.g. because it returns void), there
    // is nothing to rewrite.
    if (OrigHeaderVal->use_empty())
      continue;

    Value *OrigPreHeaderVal = ValueMap.lookup(OrigHeaderVal);

    // The value now exits in two versions: the initial value in the preheader
    // and the loop "next" value in the original header.
    SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName());
    SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
    SSA.AddAvailableValue(OrigPreheader, OrigPreHeaderVal);

    // Visit each use of the OrigHeader instruction.
    for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
         UE = OrigHeaderVal->use_end(); UI != UE; ) {
      // Grab the use before incrementing the iterator.
      Use &U = *UI;

      // Increment the iterator before removing the use from the list.
      ++UI;

      // SSAUpdater can't handle a non-PHI use in the same block as an
      // earlier def. We can easily handle those cases manually.
      Instruction *UserInst = cast<Instruction>(U.getUser());
      if (!isa<PHINode>(UserInst)) {
        BasicBlock *UserBB = UserInst->getParent();

        // The original users in the OrigHeader are already using the
        // original definitions.
        if (UserBB == OrigHeader)
          continue;

        // Users in the OrigPreHeader need to use the value to which the
        // original definitions are mapped.
        if (UserBB == OrigPreheader) {
          U = OrigPreHeaderVal;
          continue;
        }
      }

      // Anything else can be handled by SSAUpdater.
      SSA.RewriteUse(U);
    }

    // Replace MetadataAsValue(ValueAsMetadata(OrigHeaderVal)) uses in debug
    // intrinsics.
    LLVMContext &C = OrigHeader->getContext();
    if (auto *VAM = ValueAsMetadata::getIfExists(OrigHeaderVal)) {
      if (auto *MAV = MetadataAsValue::getIfExists(C, VAM)) {
        for (auto UI = MAV->use_begin(), E = MAV->use_end(); UI != E; ) {
          // Grab the use before incrementing the iterator. Otherwise, altering
          // the Use will invalidate the iterator.
          Use &U = *UI++;
          DbgInfoIntrinsic *UserInst = dyn_cast<DbgInfoIntrinsic>(U.getUser());
          if (!UserInst) continue;

          // The original users in the OrigHeader are already using the original
          // definitions.
          BasicBlock *UserBB = UserInst->getParent();
          if (UserBB == OrigHeader)
            continue;

          // Users in the OrigPreHeader need to use the value to which the
          // original definitions are mapped and anything else can be handled by
          // the SSAUpdater. To avoid adding PHINodes, check if the value is
          // available in UserBB, if not substitute undef.
          Value *NewVal;
          if (UserBB == OrigPreheader)
            NewVal = OrigPreHeaderVal;
          else if (SSA.HasValueForBlock(UserBB))
            NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
          else
            NewVal = UndefValue::get(OrigHeaderVal->getType());
          U = MetadataAsValue::get(C, ValueAsMetadata::get(NewVal));
        }
      }
    }
  }
}

/// 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;
}

/// 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.
static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
                               const SmallVectorImpl<BasicBlock *> &ExitBlocks,
                               PredIteratorCache &PredCache, LoopInfo *LI) {
  SmallVector<Use *, 16> UsesToRewrite;

  // Tokens cannot be used in PHI nodes, so we skip over them.
  // We can run into tokens which are live out of a loop with catchswitch
  // instructions in Windows EH if the catchswitch has one catchpad which
  // is inside the loop and another which is not.
  if (Inst.getType()->isTokenTy())
    return false;

  BasicBlock *InstBB = Inst.getParent();

  for (Use &U : Inst.uses()) {
    Instruction *User = cast<Instruction>(U.getUser());
    BasicBlock *UserBB = User->getParent();
    if (PHINode *PN = dyn_cast<PHINode>(User))
      UserBB = PN->getIncomingBlock(U);

    if (InstBB != UserBB && !L.contains(UserBB))
      UsesToRewrite.push_back(&U);
  }

  // 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);

  SmallVector<PHINode *, 16> AddedPHIs;
  SmallVector<PHINode *, 8> PostProcessPHIs;

  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 (BasicBlock *ExitBB : ExitBlocks) {
    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(), PredCache.size(ExitBB),
                                  Inst.getName() + ".lcssa", &ExitBB->front());

    // Add inputs from inside the loop for this PHI.
    for (BasicBlock *Pred : PredCache.get(ExitBB)) {
      PN->addIncoming(&Inst, Pred);

      // 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 (!L.contains(Pred))
        UsesToRewrite.push_back(
            &PN->getOperandUse(PN->getOperandNumForIncomingValue(
                 PN->getNumIncomingValues() - 1)));
    }

    AddedPHIs.push_back(PN);

    // Remember that this phi makes the value alive in this block.
    SSAUpdate.AddAvailableValue(ExitBB, PN);

    // LoopSimplify might fail to simplify some loops (e.g. when indirect
    // branches are involved). In such situations, it might happen that an exit
    // for Loop L1 is the header of a disjoint Loop L2. Thus, when we create
    // PHIs in such an exit block, we are also inserting PHIs into L2's header.
    // This could break LCSSA form for L2 because these inserted PHIs can also
    // have uses outside of L2. Remember all PHIs in such situation as to
    // revisit than later on. FIXME: Remove this if indirectbr support into
    // LoopSimplify gets improved.
    if (auto *OtherLoop = LI->getLoopFor(ExitBB))
      if (!L.contains(OtherLoop))
        PostProcessPHIs.push_back(PN);
  }

  // Rewrite all uses outside the loop in terms of the new PHIs we just
  // inserted.
  for (Use *UseToRewrite : UsesToRewrite) {
    // 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.
//.........这里部分代码省略.........