utils/TableGen/DAGISelMatcherOpt.cpp - llvm-project/llvm - Git at Google

 //===- DAGISelMatcherOpt.cpp - Optimize a DAG Matcher ---------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the DAG Matcher optimizer.
 //
 //===----------------------------------------------------------------------===//

 #include "Basic/SDNodeProperties.h"
 #include "Common/CodeGenDAGPatterns.h"
 #include "Common/DAGISelMatcher.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;

 #define DEBUG_TYPE "isel-opt"

 /// ContractNodes - Turn multiple matcher node patterns like 'MoveChild+Record'
 /// into single compound nodes like RecordChild.
 static void ContractNodes(std::unique_ptr<Matcher> &MatcherPtr,
                           const CodeGenDAGPatterns &CGP) {
   // If we reached the end of the chain, we're done.
   Matcher *N = MatcherPtr.get();
   if (!N)
     return;

   // If we have a scope node, walk down all of the children.
   if (ScopeMatcher *Scope = dyn_cast<ScopeMatcher>(N)) {
     for (unsigned i = 0, e = Scope->getNumChildren(); i != e; ++i) {
       std::unique_ptr<Matcher> Child(Scope->takeChild(i));
       ContractNodes(Child, CGP);
       Scope->resetChild(i, Child.release());
     }
     return;
   }

   // If we found a movechild node with a node that comes in a 'foochild' form,
   // transform it.
   if (MoveChildMatcher *MC = dyn_cast<MoveChildMatcher>(N)) {
     Matcher *New = nullptr;
     if (RecordMatcher *RM = dyn_cast<RecordMatcher>(MC->getNext()))
       if (MC->getChildNo() < 8) // Only have RecordChild0...7
         New = new RecordChildMatcher(MC->getChildNo(), RM->getWhatFor(),
                                      RM->getResultNo());

     if (CheckTypeMatcher *CT = dyn_cast<CheckTypeMatcher>(MC->getNext()))
       if (MC->getChildNo() < 8 && // Only have CheckChildType0...7
           CT->getResNo() == 0)    // CheckChildType checks res #0
         New = new CheckChildTypeMatcher(MC->getChildNo(), CT->getType());

     if (CheckSameMatcher *CS = dyn_cast<CheckSameMatcher>(MC->getNext()))
       if (MC->getChildNo() < 4) // Only have CheckChildSame0...3
         New = new CheckChildSameMatcher(MC->getChildNo(), CS->getMatchNumber());

     if (CheckIntegerMatcher *CI = dyn_cast<CheckIntegerMatcher>(MC->getNext()))
       if (MC->getChildNo() < 5) // Only have CheckChildInteger0...4
         New = new CheckChildIntegerMatcher(MC->getChildNo(), CI->getValue());

     if (auto *CCC = dyn_cast<CheckCondCodeMatcher>(MC->getNext()))
       if (MC->getChildNo() == 2) // Only have CheckChild2CondCode
         New = new CheckChild2CondCodeMatcher(CCC->getCondCodeName());

     if (New) {
       // Insert the new node.
       New->setNext(MatcherPtr.release());
       MatcherPtr.reset(New);
       // Remove the old one.
       MC->setNext(MC->getNext()->takeNext());
       return ContractNodes(MatcherPtr, CGP);
     }
   }

   // Zap movechild -> moveparent.
   if (MoveChildMatcher *MC = dyn_cast<MoveChildMatcher>(N))
     if (MoveParentMatcher *MP = dyn_cast<MoveParentMatcher>(MC->getNext())) {
       MatcherPtr.reset(MP->takeNext());
       return ContractNodes(MatcherPtr, CGP);
     }

   // Turn EmitNode->CompleteMatch into MorphNodeTo if we can.
   if (EmitNodeMatcher *EN = dyn_cast<EmitNodeMatcher>(N))
     if (CompleteMatchMatcher *CM =
             dyn_cast<CompleteMatchMatcher>(EN->getNext())) {
       // We can only use MorphNodeTo if the result values match up.
       unsigned RootResultFirst = EN->getFirstResultSlot();
       bool ResultsMatch = true;
       for (unsigned i = 0, e = CM->getNumResults(); i != e; ++i)
         if (CM->getResult(i) != RootResultFirst + i)
           ResultsMatch = false;

       // If the selected node defines a subset of the glue/chain results, we
       // can't use MorphNodeTo.  For example, we can't use MorphNodeTo if the
       // matched pattern has a chain but the root node doesn't.
       const PatternToMatch &Pattern = CM->getPattern();

       if (!EN->hasChain() &&
           Pattern.getSrcPattern().NodeHasProperty(SDNPHasChain, CGP))
         ResultsMatch = false;

       // If the matched node has glue and the output root doesn't, we can't
       // use MorphNodeTo.
       //
       // NOTE: Strictly speaking, we don't have to check for glue here
       // because the code in the pattern generator doesn't handle it right.  We
       // do it anyway for thoroughness.
       if (!EN->hasOutGlue() &&
           Pattern.getSrcPattern().NodeHasProperty(SDNPOutGlue, CGP))
         ResultsMatch = false;

 #if 0
       // If the root result node defines more results than the source root node
       // *and* has a chain or glue input, then we can't match it because it
       // would end up replacing the extra result with the chain/glue.
       if ((EN->hasGlue() || EN->hasChain()) &&
           EN->getNumNonChainGlueVTs() > ... need to get no results reliably ...)
         ResultMatch = false;
 #endif

       if (ResultsMatch) {
         const SmallVectorImpl<MVT::SimpleValueType> &VTs = EN->getVTList();
         const SmallVectorImpl<unsigned> &Operands = EN->getOperandList();
         MatcherPtr.reset(new MorphNodeToMatcher(
             EN->getInstruction(), VTs, Operands, EN->hasChain(),
             EN->hasInGlue(), EN->hasOutGlue(), EN->hasMemRefs(),
             EN->getNumFixedArityOperands(), Pattern));
         return;
       }

       // FIXME2: Kill off all the SelectionDAG::SelectNodeTo and getMachineNode
       // variants.
     }

   ContractNodes(N->getNextPtr(), CGP);

   // If we have a CheckType/CheckChildType/Record node followed by a
   // CheckOpcode, invert the two nodes.  We prefer to do structural checks
   // before type checks, as this opens opportunities for factoring on targets
   // like X86 where many operations are valid on multiple types.
   if ((isa<CheckTypeMatcher>(N) || isa<CheckChildTypeMatcher>(N) ||
        isa<RecordMatcher>(N)) &&
       isa<CheckOpcodeMatcher>(N->getNext())) {
     // Unlink the two nodes from the list.
     Matcher *CheckType = MatcherPtr.release();
     Matcher *CheckOpcode = CheckType->takeNext();
     Matcher *Tail = CheckOpcode->takeNext();

     // Relink them.
     MatcherPtr.reset(CheckOpcode);
     CheckOpcode->setNext(CheckType);
     CheckType->setNext(Tail);
     return ContractNodes(MatcherPtr, CGP);
   }

   // If we have a MoveParent followed by a MoveChild, we convert it to
   // MoveSibling.
   if (auto *MP = dyn_cast<MoveParentMatcher>(N)) {
     if (auto *MC = dyn_cast<MoveChildMatcher>(MP->getNext())) {
       auto *MS = new MoveSiblingMatcher(MC->getChildNo());
       MS->setNext(MC->takeNext());
       MatcherPtr.reset(MS);
       return ContractNodes(MatcherPtr, CGP);
     }
     if (auto *RC = dyn_cast<RecordChildMatcher>(MP->getNext())) {
       if (auto *MC = dyn_cast<MoveChildMatcher>(RC->getNext())) {
         if (RC->getChildNo() == MC->getChildNo()) {
           auto *MS = new MoveSiblingMatcher(MC->getChildNo());
           auto *RM = new RecordMatcher(RC->getWhatFor(), RC->getResultNo());
           // Insert the new node.
           RM->setNext(MC->takeNext());
           MS->setNext(RM);
           MatcherPtr.reset(MS);
           return ContractNodes(MatcherPtr, CGP);
         }
       }
     }
   }
 }

 /// FindNodeWithKind - Scan a series of matchers looking for a matcher with a
 /// specified kind.  Return null if we didn't find one otherwise return the
 /// matcher.
 static Matcher *FindNodeWithKind(Matcher *M, Matcher::KindTy Kind) {
   for (; M; M = M->getNext())
     if (M->getKind() == Kind)
       return M;
   return nullptr;
 }

 /// FactorNodes - Turn matches like this:
 ///   Scope
 ///     OPC_CheckType i32
 ///       ABC
 ///     OPC_CheckType i32
 ///       XYZ
 /// into:
 ///   OPC_CheckType i32
 ///     Scope
 ///       ABC
 ///       XYZ
 ///
 static void FactorNodes(std::unique_ptr<Matcher> &InputMatcherPtr) {
   // Look for a push node. Iterates instead of recurses to reduce stack usage.
   ScopeMatcher *Scope = nullptr;
   std::unique_ptr<Matcher> *RebindableMatcherPtr = &InputMatcherPtr;
   while (!Scope) {
     // If we reached the end of the chain, we're done.
     Matcher *N = RebindableMatcherPtr->get();
     if (!N)
       return;

     // If this is not a push node, just scan for one.
     Scope = dyn_cast<ScopeMatcher>(N);
     if (!Scope)
       RebindableMatcherPtr = &(N->getNextPtr());
   }
   std::unique_ptr<Matcher> &MatcherPtr = *RebindableMatcherPtr;

   // Okay, pull together the children of the scope node into a vector so we can
   // inspect it more easily.
   SmallVector<Matcher *, 32> OptionsToMatch;

   for (unsigned i = 0, e = Scope->getNumChildren(); i != e; ++i) {
     // Factor the subexpression.
     std::unique_ptr<Matcher> Child(Scope->takeChild(i));
     FactorNodes(Child);

     // If the child is a ScopeMatcher we can just merge its contents.
     if (auto *SM = dyn_cast<ScopeMatcher>(Child.get())) {
       for (unsigned j = 0, e = SM->getNumChildren(); j != e; ++j)
         OptionsToMatch.push_back(SM->takeChild(j));
     } else {
       OptionsToMatch.push_back(Child.release());
     }
   }

   // Loop over options to match, merging neighboring patterns with identical
   // starting nodes into a shared matcher.
   auto E = OptionsToMatch.end();
   for (auto I = OptionsToMatch.begin(); I != E; ++I) {
     // If there are no other matchers left, there's nothing to merge with.
     auto J = std::next(I);
     if (J == E)
       break;

     // Remember where we started. We'll use this to move non-equal elements.
     auto K = J;

     // Find the set of matchers that start with this node.
     Matcher *Optn = *I;

     // See if the next option starts with the same matcher.  If the two
     // neighbors *do* start with the same matcher, we can factor the matcher out
     // of at least these two patterns.  See what the maximal set we can merge
     // together is.
     SmallVector<Matcher *, 8> EqualMatchers;
     EqualMatchers.push_back(Optn);

     // Factor all of the known-equal matchers after this one into the same
     // group.
     while (J != E && (*J)->isEqual(Optn))
       EqualMatchers.push_back(*J++);

     // If we found a non-equal matcher, see if it is contradictory with the
     // current node.  If so, we know that the ordering relation between the
     // current sets of nodes and this node don't matter.  Look past it to see if
     // we can merge anything else into this matching group.
     while (J != E) {
       Matcher *ScanMatcher = *J;

       // If we found an entry that matches out matcher, merge it into the set to
       // handle.
       if (Optn->isEqual(ScanMatcher)) {
         // It is equal after all, add the option to EqualMatchers.
         EqualMatchers.push_back(ScanMatcher);
         ++J;
         continue;
       }

       // If the option we're checking for contradicts the start of the list,
       // move it earlier in OptionsToMatch for the next iteration of the outer
       // loop. Then continue searching for equal or contradictory matchers.
       if (Optn->isContradictory(ScanMatcher)) {
         *K++ = *J++;
         continue;
       }

       // If we're scanning for a simple node, see if it occurs later in the
       // sequence.  If so, and if we can move it up, it might be contradictory
       // or the same as what we're looking for.  If so, reorder it.
       if (Optn->isSimplePredicateOrRecordNode()) {
         Matcher *M2 = FindNodeWithKind(ScanMatcher, Optn->getKind());
         if (M2 && M2 != ScanMatcher && M2->canMoveBefore(ScanMatcher) &&
             (M2->isEqual(Optn) || M2->isContradictory(Optn))) {
           Matcher *MatcherWithoutM2 = ScanMatcher->unlinkNode(M2);
           M2->setNext(MatcherWithoutM2);
           *J = M2;
           continue;
         }
       }

       // Otherwise, we don't know how to handle this entry, we have to bail.
       break;
     }

     if (J != E &&
         // Don't print if it's obvious nothing extract could be merged anyway.
         std::next(J) != E) {
       LLVM_DEBUG(errs() << "Couldn't merge this:\n"; Optn->print(errs(), 4);
                  errs() << "into this:\n"; (*J)->print(errs(), 4);
                  (*std::next(J))->printOne(errs());
                  if (std::next(J, 2) != E)(*std::next(J, 2))->printOne(errs());
                  errs() << "\n");
     }

     // If we removed any equal matchers, we may need to slide the rest of the
     // elements down for the next iteration of the outer loop.
     if (J != K) {
       while (J != E)
         *K++ = *J++;

       // Update end pointer for outer loop.
       E = K;
     }

     // If we only found one option starting with this matcher, no factoring is
     // possible. Put the Matcher back in OptionsToMatch.
     if (EqualMatchers.size() == 1) {
       *I = EqualMatchers[0];
       continue;
     }

     // Factor these checks by pulling the first node off each entry and
     // discarding it.  Take the first one off the first entry to reuse.
     Matcher *Shared = Optn;
     Optn = Optn->takeNext();
     EqualMatchers[0] = Optn;

     // Remove and delete the first node from the other matchers we're factoring.
     for (unsigned i = 1, e = EqualMatchers.size(); i != e; ++i) {
       Matcher *Tmp = EqualMatchers[i]->takeNext();
       delete EqualMatchers[i];
       EqualMatchers[i] = Tmp;
       assert(!Optn == !Tmp && "Expected all to be null if any are null");
     }

     if (EqualMatchers[0]) {
       Shared->setNext(new ScopeMatcher(std::move(EqualMatchers)));

       // Recursively factor the newly created node.
       FactorNodes(Shared->getNextPtr());
     }

     // Put the new Matcher where we started in OptionsToMatch.
     *I = Shared;
   }

   // Trim the array to match the updated end.
   if (E != OptionsToMatch.end())
     OptionsToMatch.erase(E, OptionsToMatch.end());

   // If we're down to a single pattern to match, then we don't need this scope
   // anymore.
   if (OptionsToMatch.size() == 1) {
     MatcherPtr.reset(OptionsToMatch[0]);
     return;
   }

   if (OptionsToMatch.empty()) {
     MatcherPtr.reset();
     return;
   }

   // If our factoring failed (didn't achieve anything) see if we can simplify in
   // other ways.

   // Check to see if all of the leading entries are now opcode checks.  If so,
   // we can convert this Scope to be a OpcodeSwitch instead.
   bool AllOpcodeChecks = true, AllTypeChecks = true;
   for (unsigned i = 0, e = OptionsToMatch.size(); i != e; ++i) {
     // Check to see if this breaks a series of CheckOpcodeMatchers.
     if (AllOpcodeChecks && !isa<CheckOpcodeMatcher>(OptionsToMatch[i])) {
 #if 0
       if (i > 3) {
         errs() << "FAILING OPC #" << i << "\n";
         OptionsToMatch[i]->dump();
       }
 #endif
       AllOpcodeChecks = false;
     }

     // Check to see if this breaks a series of CheckTypeMatcher's.
     if (AllTypeChecks) {
       CheckTypeMatcher *CTM = cast_or_null<CheckTypeMatcher>(
           FindNodeWithKind(OptionsToMatch[i], Matcher::CheckType));
       if (!CTM ||
           // iPTR checks could alias any other case without us knowing, don't
           // bother with them.
           CTM->getType() == MVT::iPTR ||
           // SwitchType only works for result #0.
           CTM->getResNo() != 0 ||
           // If the CheckType isn't at the start of the list, see if we can move
           // it there.
           !CTM->canMoveBefore(OptionsToMatch[i])) {
 #if 0
         if (i > 3 && AllTypeChecks) {
           errs() << "FAILING TYPE #" << i << "\n";
           OptionsToMatch[i]->dump();
         }
 #endif
         AllTypeChecks = false;
       }
     }
   }

   // If all the options are CheckOpcode's, we can form the SwitchOpcode, woot.
   if (AllOpcodeChecks) {
     StringSet<> Opcodes;
     SmallVector<std::pair<const SDNodeInfo *, Matcher *>, 8> Cases;
     for (unsigned i = 0, e = OptionsToMatch.size(); i != e; ++i) {
       CheckOpcodeMatcher *COM = cast<CheckOpcodeMatcher>(OptionsToMatch[i]);
       assert(Opcodes.insert(COM->getOpcode().getEnumName()).second &&
              "Duplicate opcodes not factored?");
       Cases.push_back(std::pair(&COM->getOpcode(), COM->takeNext()));
       delete COM;
     }

     MatcherPtr.reset(new SwitchOpcodeMatcher(std::move(Cases)));
     return;
   }

   // If all the options are CheckType's, we can form the SwitchType, woot.
   if (AllTypeChecks) {
     DenseMap<unsigned, unsigned> TypeEntry;
     SmallVector<std::pair<MVT::SimpleValueType, Matcher *>, 8> Cases;
     for (unsigned i = 0, e = OptionsToMatch.size(); i != e; ++i) {
       Matcher *M = FindNodeWithKind(OptionsToMatch[i], Matcher::CheckType);
       assert(M && isa<CheckTypeMatcher>(M) && "Unknown Matcher type");

       auto *CTM = cast<CheckTypeMatcher>(M);
       Matcher *MatcherWithoutCTM = OptionsToMatch[i]->unlinkNode(CTM);
       MVT::SimpleValueType CTMTy = CTM->getType();
       delete CTM;

       unsigned &Entry = TypeEntry[CTMTy];
       if (Entry != 0) {
         // If we have unfactored duplicate types, then we should factor them.
         Matcher *PrevMatcher = Cases[Entry - 1].second;
         if (ScopeMatcher *SM = dyn_cast<ScopeMatcher>(PrevMatcher)) {
           SM->setNumChildren(SM->getNumChildren() + 1);
           SM->resetChild(SM->getNumChildren() - 1, MatcherWithoutCTM);
           continue;
         }

         SmallVector<Matcher *, 2> Entries = {PrevMatcher, MatcherWithoutCTM};
         Cases[Entry - 1].second = new ScopeMatcher(std::move(Entries));
         continue;
       }

       Entry = Cases.size() + 1;
       Cases.push_back(std::pair(CTMTy, MatcherWithoutCTM));
     }

     // Make sure we recursively factor any scopes we may have created.
     for (auto &M : Cases) {
       if (ScopeMatcher *SM = dyn_cast<ScopeMatcher>(M.second)) {
         std::unique_ptr<Matcher> Scope(SM);
         FactorNodes(Scope);
         M.second = Scope.release();
         assert(M.second && "null matcher");
       }
     }

     if (Cases.size() != 1) {
       MatcherPtr.reset(new SwitchTypeMatcher(std::move(Cases)));
     } else {
       // If we factored and ended up with one case, create it now.
       MatcherPtr.reset(new CheckTypeMatcher(Cases[0].first, 0));
       MatcherPtr->setNext(Cases[0].second);
     }
     return;
   }

   // Reassemble the Scope node with the adjusted children.
   Scope->setNumChildren(OptionsToMatch.size());
   for (unsigned i = 0, e = OptionsToMatch.size(); i != e; ++i)
     Scope->resetChild(i, OptionsToMatch[i]);
 }

 void llvm::OptimizeMatcher(std::unique_ptr<Matcher> &MatcherPtr,
                            const CodeGenDAGPatterns &CGP) {
   ContractNodes(MatcherPtr, CGP);
   FactorNodes(MatcherPtr);
 }
	//===- DAGISelMatcherOpt.cpp - Optimize a DAG Matcher ---------------------===//
	//
	// 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
	//
	//===----------------------------------------------------------------------===//
	//
	// This file implements the DAG Matcher optimizer.
	//
	//===----------------------------------------------------------------------===//

	#include "Basic/SDNodeProperties.h"
	#include "Common/CodeGenDAGPatterns.h"
	#include "Common/DAGISelMatcher.h"
	#include "llvm/ADT/StringSet.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/Support/raw_ostream.h"
	using namespace llvm;

	#define DEBUG_TYPE "isel-opt"

	/// ContractNodes - Turn multiple matcher node patterns like 'MoveChild+Record'
	/// into single compound nodes like RecordChild.
	static void ContractNodes(std::unique_ptr<Matcher> &MatcherPtr,
	const CodeGenDAGPatterns &CGP) {
	// If we reached the end of the chain, we're done.
	Matcher *N = MatcherPtr.get();
	if (!N)
	return;

	// If we have a scope node, walk down all of the children.
	if (ScopeMatcher *Scope = dyn_cast<ScopeMatcher>(N)) {
	for (unsigned i = 0, e = Scope->getNumChildren(); i != e; ++i) {
	std::unique_ptr<Matcher> Child(Scope->takeChild(i));
	ContractNodes(Child, CGP);
	Scope->resetChild(i, Child.release());
	}
	return;
	}

	// If we found a movechild node with a node that comes in a 'foochild' form,
	// transform it.
	if (MoveChildMatcher *MC = dyn_cast<MoveChildMatcher>(N)) {
	Matcher *New = nullptr;
	if (RecordMatcher *RM = dyn_cast<RecordMatcher>(MC->getNext()))
	if (MC->getChildNo() < 8) // Only have RecordChild0...7
	New = new RecordChildMatcher(MC->getChildNo(), RM->getWhatFor(),
	RM->getResultNo());

	if (CheckTypeMatcher *CT = dyn_cast<CheckTypeMatcher>(MC->getNext()))
	if (MC->getChildNo() < 8 && // Only have CheckChildType0...7
	CT->getResNo() == 0) // CheckChildType checks res #0
	New = new CheckChildTypeMatcher(MC->getChildNo(), CT->getType());

	if (CheckSameMatcher *CS = dyn_cast<CheckSameMatcher>(MC->getNext()))
	if (MC->getChildNo() < 4) // Only have CheckChildSame0...3
	New = new CheckChildSameMatcher(MC->getChildNo(), CS->getMatchNumber());

	if (CheckIntegerMatcher *CI = dyn_cast<CheckIntegerMatcher>(MC->getNext()))
	if (MC->getChildNo() < 5) // Only have CheckChildInteger0...4
	New = new CheckChildIntegerMatcher(MC->getChildNo(), CI->getValue());

	if (auto *CCC = dyn_cast<CheckCondCodeMatcher>(MC->getNext()))
	if (MC->getChildNo() == 2) // Only have CheckChild2CondCode
	New = new CheckChild2CondCodeMatcher(CCC->getCondCodeName());

	if (New) {
	// Insert the new node.
	New->setNext(MatcherPtr.release());
	MatcherPtr.reset(New);
	// Remove the old one.
	MC->setNext(MC->getNext()->takeNext());
	return ContractNodes(MatcherPtr, CGP);
	}
	}

	// Zap movechild -> moveparent.
	if (MoveChildMatcher *MC = dyn_cast<MoveChildMatcher>(N))
	if (MoveParentMatcher *MP = dyn_cast<MoveParentMatcher>(MC->getNext())) {
	MatcherPtr.reset(MP->takeNext());
	return ContractNodes(MatcherPtr, CGP);
	}

	// Turn EmitNode->CompleteMatch into MorphNodeTo if we can.
	if (EmitNodeMatcher *EN = dyn_cast<EmitNodeMatcher>(N))
	if (CompleteMatchMatcher *CM =
	dyn_cast<CompleteMatchMatcher>(EN->getNext())) {
	// We can only use MorphNodeTo if the result values match up.
	unsigned RootResultFirst = EN->getFirstResultSlot();
	bool ResultsMatch = true;
	for (unsigned i = 0, e = CM->getNumResults(); i != e; ++i)
	if (CM->getResult(i) != RootResultFirst + i)
	ResultsMatch = false;

	// If the selected node defines a subset of the glue/chain results, we
	// can't use MorphNodeTo. For example, we can't use MorphNodeTo if the
	// matched pattern has a chain but the root node doesn't.
	const PatternToMatch &Pattern = CM->getPattern();

	if (!EN->hasChain() &&
	Pattern.getSrcPattern().NodeHasProperty(SDNPHasChain, CGP))
	ResultsMatch = false;

	// If the matched node has glue and the output root doesn't, we can't
	// use MorphNodeTo.
	//
	// NOTE: Strictly speaking, we don't have to check for glue here
	// because the code in the pattern generator doesn't handle it right. We
	// do it anyway for thoroughness.
	if (!EN->hasOutGlue() &&
	Pattern.getSrcPattern().NodeHasProperty(SDNPOutGlue, CGP))
	ResultsMatch = false;

	#if 0
	// If the root result node defines more results than the source root node
	// and has a chain or glue input, then we can't match it because it
	// would end up replacing the extra result with the chain/glue.
	if ((EN->hasGlue() \|\| EN->hasChain()) &&
	EN->getNumNonChainGlueVTs() > ... need to get no results reliably ...)
	ResultMatch = false;
	#endif

	if (ResultsMatch) {
	const SmallVectorImpl<MVT::SimpleValueType> &VTs = EN->getVTList();
	const SmallVectorImpl<unsigned> &Operands = EN->getOperandList();
	MatcherPtr.reset(new MorphNodeToMatcher(
	EN->getInstruction(), VTs, Operands, EN->hasChain(),
	EN->hasInGlue(), EN->hasOutGlue(), EN->hasMemRefs(),
	EN->getNumFixedArityOperands(), Pattern));
	return;
	}

	// FIXME2: Kill off all the SelectionDAG::SelectNodeTo and getMachineNode
	// variants.
	}

	ContractNodes(N->getNextPtr(), CGP);

	// If we have a CheckType/CheckChildType/Record node followed by a
	// CheckOpcode, invert the two nodes. We prefer to do structural checks
	// before type checks, as this opens opportunities for factoring on targets
	// like X86 where many operations are valid on multiple types.
	if ((isa<CheckTypeMatcher>(N) \|\| isa<CheckChildTypeMatcher>(N) \|\|
	isa<RecordMatcher>(N)) &&
	isa<CheckOpcodeMatcher>(N->getNext())) {
	// Unlink the two nodes from the list.
	Matcher *CheckType = MatcherPtr.release();
	Matcher *CheckOpcode = CheckType->takeNext();
	Matcher *Tail = CheckOpcode->takeNext();

	// Relink them.
	MatcherPtr.reset(CheckOpcode);
	CheckOpcode->setNext(CheckType);
	CheckType->setNext(Tail);
	return ContractNodes(MatcherPtr, CGP);
	}

	// If we have a MoveParent followed by a MoveChild, we convert it to
	// MoveSibling.
	if (auto *MP = dyn_cast<MoveParentMatcher>(N)) {
	if (auto *MC = dyn_cast<MoveChildMatcher>(MP->getNext())) {
	auto *MS = new MoveSiblingMatcher(MC->getChildNo());
	MS->setNext(MC->takeNext());
	MatcherPtr.reset(MS);
	return ContractNodes(MatcherPtr, CGP);
	}
	if (auto *RC = dyn_cast<RecordChildMatcher>(MP->getNext())) {
	if (auto *MC = dyn_cast<MoveChildMatcher>(RC->getNext())) {
	if (RC->getChildNo() == MC->getChildNo()) {
	auto *MS = new MoveSiblingMatcher(MC->getChildNo());
	auto *RM = new RecordMatcher(RC->getWhatFor(), RC->getResultNo());
	// Insert the new node.
	RM->setNext(MC->takeNext());
	MS->setNext(RM);
	MatcherPtr.reset(MS);
	return ContractNodes(MatcherPtr, CGP);
	}
	}
	}
	}
	}

	/// FindNodeWithKind - Scan a series of matchers looking for a matcher with a
	/// specified kind. Return null if we didn't find one otherwise return the
	/// matcher.
	static Matcher FindNodeWithKind(Matcher M, Matcher::KindTy Kind) {
	for (; M; M = M->getNext())
	if (M->getKind() == Kind)
	return M;
	return nullptr;
	}

	/// FactorNodes - Turn matches like this:
	/// Scope
	/// OPC_CheckType i32
	/// ABC
	/// OPC_CheckType i32
	/// XYZ
	/// into:
	/// OPC_CheckType i32
	/// Scope
	/// ABC
	/// XYZ
	///
	static void FactorNodes(std::unique_ptr<Matcher> &InputMatcherPtr) {
	// Look for a push node. Iterates instead of recurses to reduce stack usage.
	ScopeMatcher *Scope = nullptr;
	std::unique_ptr<Matcher> *RebindableMatcherPtr = &InputMatcherPtr;
	while (!Scope) {
	// If we reached the end of the chain, we're done.
	Matcher *N = RebindableMatcherPtr->get();
	if (!N)
	return;

	// If this is not a push node, just scan for one.
	Scope = dyn_cast<ScopeMatcher>(N);
	if (!Scope)
	RebindableMatcherPtr = &(N->getNextPtr());
	}
	std::unique_ptr<Matcher> &MatcherPtr = *RebindableMatcherPtr;

	// Okay, pull together the children of the scope node into a vector so we can
	// inspect it more easily.
	SmallVector<Matcher *, 32> OptionsToMatch;

	for (unsigned i = 0, e = Scope->getNumChildren(); i != e; ++i) {
	// Factor the subexpression.
	std::unique_ptr<Matcher> Child(Scope->takeChild(i));
	FactorNodes(Child);

	// If the child is a ScopeMatcher we can just merge its contents.
	if (auto *SM = dyn_cast<ScopeMatcher>(Child.get())) {
	for (unsigned j = 0, e = SM->getNumChildren(); j != e; ++j)
	OptionsToMatch.push_back(SM->takeChild(j));
	} else {
	OptionsToMatch.push_back(Child.release());
	}
	}

	// Loop over options to match, merging neighboring patterns with identical
	// starting nodes into a shared matcher.
	auto E = OptionsToMatch.end();
	for (auto I = OptionsToMatch.begin(); I != E; ++I) {
	// If there are no other matchers left, there's nothing to merge with.
	auto J = std::next(I);
	if (J == E)
	break;

	// Remember where we started. We'll use this to move non-equal elements.
	auto K = J;

	// Find the set of matchers that start with this node.
	Matcher Optn = I;

	// See if the next option starts with the same matcher. If the two
	// neighbors do start with the same matcher, we can factor the matcher out
	// of at least these two patterns. See what the maximal set we can merge
	// together is.
	SmallVector<Matcher *, 8> EqualMatchers;
	EqualMatchers.push_back(Optn);

	// Factor all of the known-equal matchers after this one into the same
	// group.
	while (J != E && (*J)->isEqual(Optn))
	EqualMatchers.push_back(*J++);

	// If we found a non-equal matcher, see if it is contradictory with the
	// current node. If so, we know that the ordering relation between the
	// current sets of nodes and this node don't matter. Look past it to see if
	// we can merge anything else into this matching group.
	while (J != E) {
	Matcher ScanMatcher = J;

	// If we found an entry that matches out matcher, merge it into the set to
	// handle.
	if (Optn->isEqual(ScanMatcher)) {
	// It is equal after all, add the option to EqualMatchers.
	EqualMatchers.push_back(ScanMatcher);
	++J;
	continue;
	}

	// If the option we're checking for contradicts the start of the list,
	// move it earlier in OptionsToMatch for the next iteration of the outer
	// loop. Then continue searching for equal or contradictory matchers.
	if (Optn->isContradictory(ScanMatcher)) {
	K++ = J++;
	continue;
	}

	// If we're scanning for a simple node, see if it occurs later in the
	// sequence. If so, and if we can move it up, it might be contradictory
	// or the same as what we're looking for. If so, reorder it.
	if (Optn->isSimplePredicateOrRecordNode()) {
	Matcher *M2 = FindNodeWithKind(ScanMatcher, Optn->getKind());
	if (M2 && M2 != ScanMatcher && M2->canMoveBefore(ScanMatcher) &&
	(M2->isEqual(Optn) \|\| M2->isContradictory(Optn))) {
	Matcher *MatcherWithoutM2 = ScanMatcher->unlinkNode(M2);
	M2->setNext(MatcherWithoutM2);
	*J = M2;
	continue;
	}
	}

	// Otherwise, we don't know how to handle this entry, we have to bail.
	break;
	}

	if (J != E &&
	// Don't print if it's obvious nothing extract could be merged anyway.
	std::next(J) != E) {
	LLVM_DEBUG(errs() << "Couldn't merge this:\n"; Optn->print(errs(), 4);
	errs() << "into this:\n"; (*J)->print(errs(), 4);
	(*std::next(J))->printOne(errs());
	if (std::next(J, 2) != E)(*std::next(J, 2))->printOne(errs());
	errs() << "\n");
	}

	// If we removed any equal matchers, we may need to slide the rest of the
	// elements down for the next iteration of the outer loop.
	if (J != K) {
	while (J != E)
	K++ = J++;

	// Update end pointer for outer loop.
	E = K;
	}

	// If we only found one option starting with this matcher, no factoring is
	// possible. Put the Matcher back in OptionsToMatch.
	if (EqualMatchers.size() == 1) {
	*I = EqualMatchers[0];
	continue;
	}

	// Factor these checks by pulling the first node off each entry and
	// discarding it. Take the first one off the first entry to reuse.
	Matcher *Shared = Optn;
	Optn = Optn->takeNext();
	EqualMatchers[0] = Optn;

	// Remove and delete the first node from the other matchers we're factoring.
	for (unsigned i = 1, e = EqualMatchers.size(); i != e; ++i) {
	Matcher *Tmp = EqualMatchers[i]->takeNext();
	delete EqualMatchers[i];
	EqualMatchers[i] = Tmp;
	assert(!Optn == !Tmp && "Expected all to be null if any are null");
	}

	if (EqualMatchers[0]) {
	Shared->setNext(new ScopeMatcher(std::move(EqualMatchers)));

	// Recursively factor the newly created node.
	FactorNodes(Shared->getNextPtr());
	}

	// Put the new Matcher where we started in OptionsToMatch.
	*I = Shared;
	}

	// Trim the array to match the updated end.
	if (E != OptionsToMatch.end())
	OptionsToMatch.erase(E, OptionsToMatch.end());

	// If we're down to a single pattern to match, then we don't need this scope
	// anymore.
	if (OptionsToMatch.size() == 1) {
	MatcherPtr.reset(OptionsToMatch[0]);
	return;
	}

	if (OptionsToMatch.empty()) {
	MatcherPtr.reset();
	return;
	}

	// If our factoring failed (didn't achieve anything) see if we can simplify in
	// other ways.

	// Check to see if all of the leading entries are now opcode checks. If so,
	// we can convert this Scope to be a OpcodeSwitch instead.
	bool AllOpcodeChecks = true, AllTypeChecks = true;
	for (unsigned i = 0, e = OptionsToMatch.size(); i != e; ++i) {
	// Check to see if this breaks a series of CheckOpcodeMatchers.
	if (AllOpcodeChecks && !isa<CheckOpcodeMatcher>(OptionsToMatch[i])) {
	#if 0
	if (i > 3) {
	errs() << "FAILING OPC #" << i << "\n";
	OptionsToMatch[i]->dump();
	}
	#endif
	AllOpcodeChecks = false;
	}

	// Check to see if this breaks a series of CheckTypeMatcher's.
	if (AllTypeChecks) {
	CheckTypeMatcher *CTM = cast_or_null<CheckTypeMatcher>(
	FindNodeWithKind(OptionsToMatch[i], Matcher::CheckType));
	if (!CTM \|\|
	// iPTR checks could alias any other case without us knowing, don't
	// bother with them.
	CTM->getType() == MVT::iPTR \|\|
	// SwitchType only works for result #0.
	CTM->getResNo() != 0 \|\|
	// If the CheckType isn't at the start of the list, see if we can move
	// it there.
	!CTM->canMoveBefore(OptionsToMatch[i])) {
	#if 0
	if (i > 3 && AllTypeChecks) {
	errs() << "FAILING TYPE #" << i << "\n";
	OptionsToMatch[i]->dump();
	}
	#endif
	AllTypeChecks = false;
	}
	}
	}

	// If all the options are CheckOpcode's, we can form the SwitchOpcode, woot.
	if (AllOpcodeChecks) {
	StringSet<> Opcodes;
	SmallVector<std::pair<const SDNodeInfo , Matcher >, 8> Cases;
	for (unsigned i = 0, e = OptionsToMatch.size(); i != e; ++i) {
	CheckOpcodeMatcher *COM = cast<CheckOpcodeMatcher>(OptionsToMatch[i]);
	assert(Opcodes.insert(COM->getOpcode().getEnumName()).second &&
	"Duplicate opcodes not factored?");
	Cases.push_back(std::pair(&COM->getOpcode(), COM->takeNext()));
	delete COM;
	}

	MatcherPtr.reset(new SwitchOpcodeMatcher(std::move(Cases)));
	return;
	}

	// If all the options are CheckType's, we can form the SwitchType, woot.
	if (AllTypeChecks) {
	DenseMap<unsigned, unsigned> TypeEntry;
	SmallVector<std::pair<MVT::SimpleValueType, Matcher *>, 8> Cases;
	for (unsigned i = 0, e = OptionsToMatch.size(); i != e; ++i) {
	Matcher *M = FindNodeWithKind(OptionsToMatch[i], Matcher::CheckType);
	assert(M && isa<CheckTypeMatcher>(M) && "Unknown Matcher type");

	auto *CTM = cast<CheckTypeMatcher>(M);
	Matcher *MatcherWithoutCTM = OptionsToMatch[i]->unlinkNode(CTM);
	MVT::SimpleValueType CTMTy = CTM->getType();
	delete CTM;

	unsigned &Entry = TypeEntry[CTMTy];
	if (Entry != 0) {
	// If we have unfactored duplicate types, then we should factor them.
	Matcher *PrevMatcher = Cases[Entry - 1].second;
	if (ScopeMatcher *SM = dyn_cast<ScopeMatcher>(PrevMatcher)) {
	SM->setNumChildren(SM->getNumChildren() + 1);
	SM->resetChild(SM->getNumChildren() - 1, MatcherWithoutCTM);
	continue;
	}

	SmallVector<Matcher *, 2> Entries = {PrevMatcher, MatcherWithoutCTM};
	Cases[Entry - 1].second = new ScopeMatcher(std::move(Entries));
	continue;
	}

	Entry = Cases.size() + 1;
	Cases.push_back(std::pair(CTMTy, MatcherWithoutCTM));
	}

	// Make sure we recursively factor any scopes we may have created.
	for (auto &M : Cases) {
	if (ScopeMatcher *SM = dyn_cast<ScopeMatcher>(M.second)) {
	std::unique_ptr<Matcher> Scope(SM);
	FactorNodes(Scope);
	M.second = Scope.release();
	assert(M.second && "null matcher");
	}
	}

	if (Cases.size() != 1) {
	MatcherPtr.reset(new SwitchTypeMatcher(std::move(Cases)));
	} else {
	// If we factored and ended up with one case, create it now.
	MatcherPtr.reset(new CheckTypeMatcher(Cases[0].first, 0));
	MatcherPtr->setNext(Cases[0].second);
	}
	return;
	}

	// Reassemble the Scope node with the adjusted children.
	Scope->setNumChildren(OptionsToMatch.size());
	for (unsigned i = 0, e = OptionsToMatch.size(); i != e; ++i)
	Scope->resetChild(i, OptionsToMatch[i]);
	}

	void llvm::OptimizeMatcher(std::unique_ptr<Matcher> &MatcherPtr,
	const CodeGenDAGPatterns &CGP) {
	ContractNodes(MatcherPtr, CGP);
	FactorNodes(MatcherPtr);
	}