lib/CodeGen/InstrSelection/InstrSelection.cpp - fp2-dev/platform/external/llvm - Gitiles

 //===- InstrSelection.cpp - Machine Independent Inst Selection Driver -----===//
 //
 // Machine-independent driver file for instruction selection.  This file
 // constructs a forest of BURG instruction trees and then uses the
 // BURG-generated tree grammar (BURM) to find the optimal instruction sequences
 // for a given machine.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/CodeGen/InstrSelection.h"
 #include "llvm/CodeGen/InstrSelectionSupport.h"
 #include "llvm/CodeGen/InstrForest.h"
 #include "llvm/CodeGen/MachineCodeForInstruction.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/Target/TargetRegInfo.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Function.h"
 #include "llvm/iPHINode.h"
 #include "llvm/Pass.h"
 #include "Support/CommandLine.h"
 #include "Support/LeakDetector.h"
 using std::vector;

 std::vector<MachineInstr*>
 FixConstantOperandsForInstr(Instruction* vmInstr, MachineInstr* minstr,
                             TargetMachine& target);

 namespace {
   //===--------------------------------------------------------------------===//
   // SelectDebugLevel - Allow command line control over debugging.
   //
   enum SelectDebugLevel_t {
     Select_NoDebugInfo,
     Select_PrintMachineCode,
     Select_DebugInstTrees,
     Select_DebugBurgTrees,
   };

   // Enable Debug Options to be specified on the command line
   cl::opt<SelectDebugLevel_t>
   SelectDebugLevel("dselect", cl::Hidden,
                    cl::desc("enable instruction selection debug information"),
                    cl::values(
      clEnumValN(Select_NoDebugInfo,      "n", "disable debug output"),
      clEnumValN(Select_PrintMachineCode, "y", "print generated machine code"),
      clEnumValN(Select_DebugInstTrees,   "i",
                 "print debugging info for instruction selection"),
      clEnumValN(Select_DebugBurgTrees,   "b", "print burg trees"),
                               0));


   //===--------------------------------------------------------------------===//
   //  InstructionSelection Pass
   //
   // This is the actual pass object that drives the instruction selection
   // process.
   //
   class InstructionSelection : public FunctionPass {
     TargetMachine &Target;
     void InsertCodeForPhis(Function &F);
     void InsertPhiElimInstructions(BasicBlock *BB,
                                    const vector<MachineInstr*>& CpVec);
     void SelectInstructionsForTree(InstrTreeNode* treeRoot, int goalnt);
     void PostprocessMachineCodeForTree(InstructionNode* instrNode,
                                        int ruleForNode, short* nts);
   public:
     InstructionSelection(TargetMachine &T) : Target(T) {}

     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       AU.setPreservesCFG();
     }

     bool runOnFunction(Function &F);
     virtual const char *getPassName() const { return "Instruction Selection"; }
   };
 }

 TmpInstruction::TmpInstruction(MachineCodeForInstruction& mcfi,
                                Value *s1, Value *s2, const std::string &name)
   : Instruction(s1->getType(), Instruction::UserOp1, name)
 {
   mcfi.addTemp(this);

   Operands.push_back(Use(s1, this));  // s1 must be nonnull
   if (s2) {
     Operands.push_back(Use(s2, this));
   }

   // TmpInstructions should not be garbage checked.
   LeakDetector::removeGarbageObject(this);
 }

 // Constructor that requires the type of the temporary to be specified.
 // Both S1 and S2 may be NULL.(
 TmpInstruction::TmpInstruction(MachineCodeForInstruction& mcfi,
                                const Type *Ty, Value *s1, Value* s2,
                                const std::string &name)
   : Instruction(Ty, Instruction::UserOp1, name)
 {
   mcfi.addTemp(this);

   if (s1) { Operands.push_back(Use(s1, this)); }
   if (s2) { Operands.push_back(Use(s2, this)); }

   // TmpInstructions should not be garbage checked.
   LeakDetector::removeGarbageObject(this);
 }


 bool InstructionSelection::runOnFunction(Function &F)
 {
   //
   // Build the instruction trees to be given as inputs to BURG.
   //
   InstrForest instrForest(&F);

   if (SelectDebugLevel >= Select_DebugInstTrees)
     {
       std::cerr << "\n\n*** Input to instruction selection for function "
 	        << F.getName() << "\n\n" << F
                 << "\n\n*** Instruction trees for function "
                 << F.getName() << "\n\n";
       instrForest.dump();
     }

   //
   // Invoke BURG instruction selection for each tree
   //
   for (InstrForest::const_root_iterator RI = instrForest.roots_begin();
        RI != instrForest.roots_end(); ++RI)
     {
       InstructionNode* basicNode = *RI;
       assert(basicNode->parent() == NULL && "A `root' node has a parent?");

       // Invoke BURM to label each tree node with a state
       burm_label(basicNode);

       if (SelectDebugLevel >= Select_DebugBurgTrees)
 	{
 	  printcover(basicNode, 1, 0);
 	  std::cerr << "\nCover cost == " << treecost(basicNode, 1, 0) <<"\n\n";
 	  printMatches(basicNode);
 	}

       // Then recursively walk the tree to select instructions
       SelectInstructionsForTree(basicNode, /*goalnt*/1);
     }

   //
   // Create the MachineBasicBlock records and add all of the MachineInstrs
   // defined in the MachineCodeForInstruction objects to also live in the
   // MachineBasicBlock objects.
   //
   MachineFunction &MF = MachineFunction::get(&F);
   for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
     MachineBasicBlock *MCBB = new MachineBasicBlock(BI);
     MF.getBasicBlockList().push_back(MCBB);

     for (BasicBlock::iterator II = BI->begin(); II != BI->end(); ++II) {
       MachineCodeForInstruction &mvec = MachineCodeForInstruction::get(II);
       MCBB->insert(MCBB->end(), mvec.begin(), mvec.end());
     }
   }

   // Insert phi elimination code
   InsertCodeForPhis(F);

   if (SelectDebugLevel >= Select_PrintMachineCode)
     {
       std::cerr << "\n*** Machine instructions after INSTRUCTION SELECTION\n";
       MachineFunction::get(&F).dump();
     }

   return true;
 }


 //-------------------------------------------------------------------------
 // This method inserts phi elimination code for all BBs in a method
 //-------------------------------------------------------------------------

 void
 InstructionSelection::InsertCodeForPhis(Function &F)
 {
   // for all basic blocks in function
   //
   MachineFunction &MF = MachineFunction::get(&F);
   for (MachineFunction::iterator BB = MF.begin(); BB != MF.end(); ++BB) {
     for (BasicBlock::const_iterator IIt = BB->getBasicBlock()->begin();
          const PHINode *PN = dyn_cast<PHINode>(IIt); ++IIt) {
       // FIXME: This is probably wrong...
       Value *PhiCpRes = new PHINode(PN->getType(), "PhiCp:");

       // The leak detector shouldn't track these nodes.  They are not garbage,
       // even though their parent field is never filled in.
       //
       LeakDetector::removeGarbageObject(PhiCpRes);

       // for each incoming value of the phi, insert phi elimination
       //
       for (unsigned i = 0; i < PN->getNumIncomingValues(); ++i) {
         // insert the copy instruction to the predecessor BB
         vector<MachineInstr*> mvec, CpVec;
         Target.getRegInfo().cpValue2Value(PN->getIncomingValue(i), PhiCpRes,
                                           mvec);
         for (vector<MachineInstr*>::iterator MI=mvec.begin();
              MI != mvec.end(); ++MI) {
           vector<MachineInstr*> CpVec2 =
             FixConstantOperandsForInstr(const_cast<PHINode*>(PN), *MI, Target);
           CpVec2.push_back(*MI);
           CpVec.insert(CpVec.end(), CpVec2.begin(), CpVec2.end());
         }

         InsertPhiElimInstructions(PN->getIncomingBlock(i), CpVec);
       }

       vector<MachineInstr*> mvec;
       Target.getRegInfo().cpValue2Value(PhiCpRes, const_cast<PHINode*>(PN),
                                         mvec);
       BB->insert(BB->begin(), mvec.begin(), mvec.end());
     }  // for each Phi Instr in BB
   } // for all BBs in function
 }

 //-------------------------------------------------------------------------
 // Thid method inserts a copy instruction to a predecessor BB as a result
 // of phi elimination.
 //-------------------------------------------------------------------------

 void
 InstructionSelection::InsertPhiElimInstructions(BasicBlock *BB,
                                             const vector<MachineInstr*>& CpVec)
 {
   Instruction *TermInst = (Instruction*)BB->getTerminator();
   MachineCodeForInstruction &MC4Term = MachineCodeForInstruction::get(TermInst);
   MachineInstr *FirstMIOfTerm = MC4Term.front();
   assert (FirstMIOfTerm && "No Machine Instrs for terminator");

   MachineFunction &MF = MachineFunction::get(BB->getParent());

   // FIXME: if PHI instructions existed in the machine code, this would be
   // unnecesary.
   MachineBasicBlock *MBB = 0;
   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
     if (I->getBasicBlock() == BB) {
       MBB = I;
       break;
     }

   // find the position of first machine instruction generated by the
   // terminator of this BB
   MachineBasicBlock::iterator MCIt =
     std::find(MBB->begin(), MBB->end(), FirstMIOfTerm);

   assert(MCIt != MBB->end() && "Start inst of terminator not found");

   // insert the copy instructions just before the first machine instruction
   // generated for the terminator
   MBB->insert(MCIt, CpVec.begin(), CpVec.end());
 }


 //---------------------------------------------------------------------------
 // Function SelectInstructionsForTree
 //
 // Recursively walk the tree to select instructions.
 // Do this top-down so that child instructions can exploit decisions
 // made at the child instructions.
 //
 // E.g., if br(setle(reg,const)) decides the constant is 0 and uses
 // a branch-on-integer-register instruction, then the setle node
 // can use that information to avoid generating the SUBcc instruction.
 //
 // Note that this cannot be done bottom-up because setle must do this
 // only if it is a child of the branch (otherwise, the result of setle
 // may be used by multiple instructions).
 //---------------------------------------------------------------------------

 void
 InstructionSelection::SelectInstructionsForTree(InstrTreeNode* treeRoot,
                                                 int goalnt)
 {
   // Get the rule that matches this node.
   //
   int ruleForNode = burm_rule(treeRoot->state, goalnt);

   if (ruleForNode == 0) {
     std::cerr << "Could not match instruction tree for instr selection\n";
     abort();
   }

   // Get this rule's non-terminals and the corresponding child nodes (if any)
   //
   short *nts = burm_nts[ruleForNode];

   // First, select instructions for the current node and rule.
   // (If this is a list node, not an instruction, then skip this step).
   // This function is specific to the target architecture.
   //
   if (treeRoot->opLabel != VRegListOp)
     {
       vector<MachineInstr*> minstrVec;

       InstructionNode* instrNode = (InstructionNode*)treeRoot;
       assert(instrNode->getNodeType() == InstrTreeNode::NTInstructionNode);

       GetInstructionsByRule(instrNode, ruleForNode, nts, Target, minstrVec);

       MachineCodeForInstruction &mvec =
         MachineCodeForInstruction::get(instrNode->getInstruction());
       mvec.insert(mvec.end(), minstrVec.begin(), minstrVec.end());
     }

   // Then, recursively compile the child nodes, if any.
   //
   if (nts[0])
     { // i.e., there is at least one kid
       InstrTreeNode* kids[2];
       int currentRule = ruleForNode;
       burm_kids(treeRoot, currentRule, kids);

       // First skip over any chain rules so that we don't visit
       // the current node again.
       //
       while (ThisIsAChainRule(currentRule))
 	{
 	  currentRule = burm_rule(treeRoot->state, nts[0]);
 	  nts = burm_nts[currentRule];
 	  burm_kids(treeRoot, currentRule, kids);
 	}

       // Now we have the first non-chain rule so we have found
       // the actual child nodes.  Recursively compile them.
       //
       for (unsigned i = 0; nts[i]; i++)
 	{
 	  assert(i < 2);
 	  InstrTreeNode::InstrTreeNodeType nodeType = kids[i]->getNodeType();
 	  if (nodeType == InstrTreeNode::NTVRegListNode ||
 	      nodeType == InstrTreeNode::NTInstructionNode)
             SelectInstructionsForTree(kids[i], nts[i]);
 	}
     }

   // Finally, do any postprocessing on this node after its children
   // have been translated
   //
   if (treeRoot->opLabel != VRegListOp)
     PostprocessMachineCodeForTree((InstructionNode*)treeRoot, ruleForNode, nts);
 }

 //---------------------------------------------------------------------------
 // Function PostprocessMachineCodeForTree
 //
 // Apply any final cleanups to machine code for the root of a subtree
 // after selection for all its children has been completed.
 //
 void
 InstructionSelection::PostprocessMachineCodeForTree(InstructionNode* instrNode,
                                                     int ruleForNode,
                                                     short* nts)
 {
   // Fix up any constant operands in the machine instructions to either
   // use an immediate field or to load the constant into a register
   // Walk backwards and use direct indexes to allow insertion before current
   //
   Instruction* vmInstr = instrNode->getInstruction();
   MachineCodeForInstruction &mvec = MachineCodeForInstruction::get(vmInstr);
   for (unsigned i = mvec.size(); i != 0; --i)
     {
       vector<MachineInstr*> loadConstVec =
         FixConstantOperandsForInstr(vmInstr, mvec[i-1], Target);

       mvec.insert(mvec.begin()+i-1, loadConstVec.begin(), loadConstVec.end());
     }
 }


 //===----------------------------------------------------------------------===//
 // createInstructionSelectionPass - Public entrypoint for instruction selection
 // and this file as a whole...
 //
 FunctionPass *createInstructionSelectionPass(TargetMachine &T) {
   return new InstructionSelection(T);
 }
	//===- InstrSelection.cpp - Machine Independent Inst Selection Driver -----===//
	//
	// Machine-independent driver file for instruction selection. This file
	// constructs a forest of BURG instruction trees and then uses the
	// BURG-generated tree grammar (BURM) to find the optimal instruction sequences
	// for a given machine.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/CodeGen/InstrSelection.h"
	#include "llvm/CodeGen/InstrSelectionSupport.h"
	#include "llvm/CodeGen/InstrForest.h"
	#include "llvm/CodeGen/MachineCodeForInstruction.h"
	#include "llvm/CodeGen/MachineFunction.h"
	#include "llvm/Target/TargetRegInfo.h"
	#include "llvm/Target/TargetMachine.h"
	#include "llvm/Function.h"
	#include "llvm/iPHINode.h"
	#include "llvm/Pass.h"
	#include "Support/CommandLine.h"
	#include "Support/LeakDetector.h"
	using std::vector;

	std::vector<MachineInstr*>
	FixConstantOperandsForInstr(Instruction* vmInstr, MachineInstr* minstr,
	TargetMachine& target);

	namespace {
	//===--------------------------------------------------------------------===//
	// SelectDebugLevel - Allow command line control over debugging.
	//
	enum SelectDebugLevel_t {
	Select_NoDebugInfo,
	Select_PrintMachineCode,
	Select_DebugInstTrees,
	Select_DebugBurgTrees,
	};

	// Enable Debug Options to be specified on the command line
	cl::opt<SelectDebugLevel_t>
	SelectDebugLevel("dselect", cl::Hidden,
	cl::desc("enable instruction selection debug information"),
	cl::values(
	clEnumValN(Select_NoDebugInfo, "n", "disable debug output"),
	clEnumValN(Select_PrintMachineCode, "y", "print generated machine code"),
	clEnumValN(Select_DebugInstTrees, "i",
	"print debugging info for instruction selection"),
	clEnumValN(Select_DebugBurgTrees, "b", "print burg trees"),
	0));


	//===--------------------------------------------------------------------===//
	// InstructionSelection Pass
	//
	// This is the actual pass object that drives the instruction selection
	// process.
	//
	class InstructionSelection : public FunctionPass {
	TargetMachine &Target;
	void InsertCodeForPhis(Function &F);
	void InsertPhiElimInstructions(BasicBlock *BB,
	const vector<MachineInstr*>& CpVec);
	void SelectInstructionsForTree(InstrTreeNode* treeRoot, int goalnt);
	void PostprocessMachineCodeForTree(InstructionNode* instrNode,
	int ruleForNode, short* nts);
	public:
	InstructionSelection(TargetMachine &T) : Target(T) {}

	virtual void getAnalysisUsage(AnalysisUsage &AU) const {
	AU.setPreservesCFG();
	}

	bool runOnFunction(Function &F);
	virtual const char *getPassName() const { return "Instruction Selection"; }
	};
	}

	TmpInstruction::TmpInstruction(MachineCodeForInstruction& mcfi,
	Value s1, Value s2, const std::string &name)
	: Instruction(s1->getType(), Instruction::UserOp1, name)
	{
	mcfi.addTemp(this);

	Operands.push_back(Use(s1, this)); // s1 must be nonnull
	if (s2) {
	Operands.push_back(Use(s2, this));
	}

	// TmpInstructions should not be garbage checked.
	LeakDetector::removeGarbageObject(this);
	}

	// Constructor that requires the type of the temporary to be specified.
	// Both S1 and S2 may be NULL.(
	TmpInstruction::TmpInstruction(MachineCodeForInstruction& mcfi,
	const Type Ty, Value s1, Value* s2,
	const std::string &name)
	: Instruction(Ty, Instruction::UserOp1, name)
	{
	mcfi.addTemp(this);

	if (s1) { Operands.push_back(Use(s1, this)); }
	if (s2) { Operands.push_back(Use(s2, this)); }

	// TmpInstructions should not be garbage checked.
	LeakDetector::removeGarbageObject(this);
	}


	bool InstructionSelection::runOnFunction(Function &F)
	{
	//
	// Build the instruction trees to be given as inputs to BURG.
	//
	InstrForest instrForest(&F);

	if (SelectDebugLevel >= Select_DebugInstTrees)
	{
	std::cerr << "\n\n*** Input to instruction selection for function "
	<< F.getName() << "\n\n" << F
	<< "\n\n*** Instruction trees for function "
	<< F.getName() << "\n\n";
	instrForest.dump();
	}

	//
	// Invoke BURG instruction selection for each tree
	//
	for (InstrForest::const_root_iterator RI = instrForest.roots_begin();
	RI != instrForest.roots_end(); ++RI)
	{
	InstructionNode* basicNode = *RI;
	assert(basicNode->parent() == NULL && "A `root' node has a parent?");

	// Invoke BURM to label each tree node with a state
	burm_label(basicNode);

	if (SelectDebugLevel >= Select_DebugBurgTrees)
	{
	printcover(basicNode, 1, 0);
	std::cerr << "\nCover cost == " << treecost(basicNode, 1, 0) <<"\n\n";
	printMatches(basicNode);
	}

	// Then recursively walk the tree to select instructions
	SelectInstructionsForTree(basicNode, /goalnt/1);
	}

	//
	// Create the MachineBasicBlock records and add all of the MachineInstrs
	// defined in the MachineCodeForInstruction objects to also live in the
	// MachineBasicBlock objects.
	//
	MachineFunction &MF = MachineFunction::get(&F);
	for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
	MachineBasicBlock *MCBB = new MachineBasicBlock(BI);
	MF.getBasicBlockList().push_back(MCBB);

	for (BasicBlock::iterator II = BI->begin(); II != BI->end(); ++II) {
	MachineCodeForInstruction &mvec = MachineCodeForInstruction::get(II);
	MCBB->insert(MCBB->end(), mvec.begin(), mvec.end());
	}
	}

	// Insert phi elimination code
	InsertCodeForPhis(F);

	if (SelectDebugLevel >= Select_PrintMachineCode)
	{
	std::cerr << "\n*** Machine instructions after INSTRUCTION SELECTION\n";
	MachineFunction::get(&F).dump();
	}

	return true;
	}


	//-------------------------------------------------------------------------
	// This method inserts phi elimination code for all BBs in a method
	//-------------------------------------------------------------------------

	void
	InstructionSelection::InsertCodeForPhis(Function &F)
	{
	// for all basic blocks in function
	//
	MachineFunction &MF = MachineFunction::get(&F);
	for (MachineFunction::iterator BB = MF.begin(); BB != MF.end(); ++BB) {
	for (BasicBlock::const_iterator IIt = BB->getBasicBlock()->begin();
	const PHINode *PN = dyn_cast<PHINode>(IIt); ++IIt) {
	// FIXME: This is probably wrong...
	Value *PhiCpRes = new PHINode(PN->getType(), "PhiCp:");

	// The leak detector shouldn't track these nodes. They are not garbage,
	// even though their parent field is never filled in.
	//
	LeakDetector::removeGarbageObject(PhiCpRes);

	// for each incoming value of the phi, insert phi elimination
	//
	for (unsigned i = 0; i < PN->getNumIncomingValues(); ++i) {
	// insert the copy instruction to the predecessor BB
	vector<MachineInstr*> mvec, CpVec;
	Target.getRegInfo().cpValue2Value(PN->getIncomingValue(i), PhiCpRes,
	mvec);
	for (vector<MachineInstr*>::iterator MI=mvec.begin();
	MI != mvec.end(); ++MI) {
	vector<MachineInstr*> CpVec2 =
	FixConstantOperandsForInstr(const_cast<PHINode>(PN), MI, Target);
	CpVec2.push_back(*MI);
	CpVec.insert(CpVec.end(), CpVec2.begin(), CpVec2.end());
	}

	InsertPhiElimInstructions(PN->getIncomingBlock(i), CpVec);
	}

	vector<MachineInstr*> mvec;
	Target.getRegInfo().cpValue2Value(PhiCpRes, const_cast<PHINode*>(PN),
	mvec);
	BB->insert(BB->begin(), mvec.begin(), mvec.end());
	} // for each Phi Instr in BB
	} // for all BBs in function
	}

	//-------------------------------------------------------------------------
	// Thid method inserts a copy instruction to a predecessor BB as a result
	// of phi elimination.
	//-------------------------------------------------------------------------

	void
	InstructionSelection::InsertPhiElimInstructions(BasicBlock *BB,
	const vector<MachineInstr*>& CpVec)
	{
	Instruction TermInst = (Instruction)BB->getTerminator();
	MachineCodeForInstruction &MC4Term = MachineCodeForInstruction::get(TermInst);
	MachineInstr *FirstMIOfTerm = MC4Term.front();
	assert (FirstMIOfTerm && "No Machine Instrs for terminator");

	MachineFunction &MF = MachineFunction::get(BB->getParent());

	// FIXME: if PHI instructions existed in the machine code, this would be
	// unnecesary.
	MachineBasicBlock *MBB = 0;
	for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
	if (I->getBasicBlock() == BB) {
	MBB = I;
	break;
	}

	// find the position of first machine instruction generated by the
	// terminator of this BB
	MachineBasicBlock::iterator MCIt =
	std::find(MBB->begin(), MBB->end(), FirstMIOfTerm);

	assert(MCIt != MBB->end() && "Start inst of terminator not found");

	// insert the copy instructions just before the first machine instruction
	// generated for the terminator
	MBB->insert(MCIt, CpVec.begin(), CpVec.end());
	}


	//---------------------------------------------------------------------------
	// Function SelectInstructionsForTree
	//
	// Recursively walk the tree to select instructions.
	// Do this top-down so that child instructions can exploit decisions
	// made at the child instructions.
	//
	// E.g., if br(setle(reg,const)) decides the constant is 0 and uses
	// a branch-on-integer-register instruction, then the setle node
	// can use that information to avoid generating the SUBcc instruction.
	//
	// Note that this cannot be done bottom-up because setle must do this
	// only if it is a child of the branch (otherwise, the result of setle
	// may be used by multiple instructions).
	//---------------------------------------------------------------------------

	void
	InstructionSelection::SelectInstructionsForTree(InstrTreeNode* treeRoot,
	int goalnt)
	{
	// Get the rule that matches this node.
	//
	int ruleForNode = burm_rule(treeRoot->state, goalnt);

	if (ruleForNode == 0) {
	std::cerr << "Could not match instruction tree for instr selection\n";
	abort();
	}

	// Get this rule's non-terminals and the corresponding child nodes (if any)
	//
	short *nts = burm_nts[ruleForNode];

	// First, select instructions for the current node and rule.
	// (If this is a list node, not an instruction, then skip this step).
	// This function is specific to the target architecture.
	//
	if (treeRoot->opLabel != VRegListOp)
	{
	vector<MachineInstr*> minstrVec;

	InstructionNode* instrNode = (InstructionNode*)treeRoot;
	assert(instrNode->getNodeType() == InstrTreeNode::NTInstructionNode);

	GetInstructionsByRule(instrNode, ruleForNode, nts, Target, minstrVec);

	MachineCodeForInstruction &mvec =
	MachineCodeForInstruction::get(instrNode->getInstruction());
	mvec.insert(mvec.end(), minstrVec.begin(), minstrVec.end());
	}

	// Then, recursively compile the child nodes, if any.
	//
	if (nts[0])
	{ // i.e., there is at least one kid
	InstrTreeNode* kids[2];
	int currentRule = ruleForNode;
	burm_kids(treeRoot, currentRule, kids);

	// First skip over any chain rules so that we don't visit
	// the current node again.
	//
	while (ThisIsAChainRule(currentRule))
	{
	currentRule = burm_rule(treeRoot->state, nts[0]);
	nts = burm_nts[currentRule];
	burm_kids(treeRoot, currentRule, kids);
	}

	// Now we have the first non-chain rule so we have found
	// the actual child nodes. Recursively compile them.
	//
	for (unsigned i = 0; nts[i]; i++)
	{
	assert(i < 2);
	InstrTreeNode::InstrTreeNodeType nodeType = kids[i]->getNodeType();
	if (nodeType == InstrTreeNode::NTVRegListNode \|\|
	nodeType == InstrTreeNode::NTInstructionNode)
	SelectInstructionsForTree(kids[i], nts[i]);
	}
	}

	// Finally, do any postprocessing on this node after its children
	// have been translated
	//
	if (treeRoot->opLabel != VRegListOp)
	PostprocessMachineCodeForTree((InstructionNode*)treeRoot, ruleForNode, nts);
	}

	//---------------------------------------------------------------------------
	// Function PostprocessMachineCodeForTree
	//
	// Apply any final cleanups to machine code for the root of a subtree
	// after selection for all its children has been completed.
	//
	void
	InstructionSelection::PostprocessMachineCodeForTree(InstructionNode* instrNode,
	int ruleForNode,
	short* nts)
	{
	// Fix up any constant operands in the machine instructions to either
	// use an immediate field or to load the constant into a register
	// Walk backwards and use direct indexes to allow insertion before current
	//
	Instruction* vmInstr = instrNode->getInstruction();
	MachineCodeForInstruction &mvec = MachineCodeForInstruction::get(vmInstr);
	for (unsigned i = mvec.size(); i != 0; --i)
	{
	vector<MachineInstr*> loadConstVec =
	FixConstantOperandsForInstr(vmInstr, mvec[i-1], Target);

	mvec.insert(mvec.begin()+i-1, loadConstVec.begin(), loadConstVec.end());
	}
	}



	//===----------------------------------------------------------------------===//
	// createInstructionSelectionPass - Public entrypoint for instruction selection
	// and this file as a whole...
	//
	FunctionPass *createInstructionSelectionPass(TargetMachine &T) {
	return new InstructionSelection(T);
	}