llvm/lib/CodeGen/InstrSelection/InstrForest.cpp

//===-- InstrForest.cpp - Build instruction forest for inst selection -----===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
//  The key goal is to group instructions into a single
//  tree if one or more of them might be potentially combined into a single
//  complex instruction in the target machine.
//  Since this grouping is completely machine-independent, we do it as
//  aggressive as possible to exploit any possible target instructions.
//  In particular, we group two instructions O and I if:
//      (1) Instruction O computes an operand used by instruction I,
//  and (2) O and I are part of the same basic block,
//  and (3) O has only a single use, viz., I.
// 
//===----------------------------------------------------------------------===//

#include "llvm/Constant.h"
#include "llvm/Function.h"
#include "llvm/iTerminators.h"
#include "llvm/iMemory.h"
#include "llvm/Type.h"
#include "llvm/CodeGen/InstrForest.h"
#include "llvm/CodeGen/MachineCodeForInstruction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "Support/STLExtras.h"
#include "Config/alloca.h"

namespace llvm {

//------------------------------------------------------------------------ 
// class InstrTreeNode
//------------------------------------------------------------------------ 

void
InstrTreeNode::dump(int dumpChildren, int indent) const {
  dumpNode(indent);
  
  if (dumpChildren) {
    if (LeftChild)
      LeftChild->dump(dumpChildren, indent+1);
    if (RightChild)
      RightChild->dump(dumpChildren, indent+1);
  }
}


InstructionNode::InstructionNode(Instruction* I)
  : InstrTreeNode(NTInstructionNode, I), codeIsFoldedIntoParent(false)
{
  opLabel = I->getOpcode();

  // Distinguish special cases of some instructions such as Ret and Br
  // 
  if (opLabel == Instruction::Ret && cast<ReturnInst>(I)->getReturnValue()) {
    opLabel = RetValueOp;              	 // ret(value) operation
  }
  else if (opLabel ==Instruction::Br && !cast<BranchInst>(I)->isUnconditional())
  {
    opLabel = BrCondOp;		// br(cond) operation
  } else if (opLabel >= Instruction::SetEQ && opLabel <= Instruction::SetGT) {
    opLabel = SetCCOp;		// common label for all SetCC ops
  } else if (opLabel == Instruction::Alloca && I->getNumOperands() > 0) {
    opLabel = AllocaN;		 // Alloca(ptr, N) operation
  } else if (opLabel == Instruction::GetElementPtr &&
             cast<GetElementPtrInst>(I)->hasIndices()) {
    opLabel = opLabel + 100;		 // getElem with index vector
  } else if (opLabel == Instruction::Xor &&
             BinaryOperator::isNot(I)) {
    opLabel = (I->getType() == Type::BoolTy)?  NotOp  // boolean Not operator
      : BNotOp; // bitwise Not operator
  } else if (opLabel == Instruction::And || opLabel == Instruction::Or ||
             opLabel == Instruction::Xor) {
    // Distinguish bitwise operators from logical operators!
    if (I->getType() != Type::BoolTy)
      opLabel = opLabel + 100;	 // bitwise operator
  } else if (opLabel == Instruction::Cast) {
    const Type *ITy = I->getType();
    switch(ITy->getPrimitiveID())
    {
    case Type::BoolTyID:    opLabel = ToBoolTy;    break;
    case Type::UByteTyID:   opLabel = ToUByteTy;   break;
    case Type::SByteTyID:   opLabel = ToSByteTy;   break;
    case Type::UShortTyID:  opLabel = ToUShortTy;  break;
    case Type::ShortTyID:   opLabel = ToShortTy;   break;
    case Type::UIntTyID:    opLabel = ToUIntTy;    break;
    case Type::IntTyID:     opLabel = ToIntTy;     break;
    case Type::ULongTyID:   opLabel = ToULongTy;   break;
    case Type::LongTyID:    opLabel = ToLongTy;    break;
    case Type::FloatTyID:   opLabel = ToFloatTy;   break;
    case Type::DoubleTyID:  opLabel = ToDoubleTy;  break;
    case Type::ArrayTyID:   opLabel = ToArrayTy;   break;
    case Type::PointerTyID: opLabel = ToPointerTy; break;
    default:
      // Just use `Cast' opcode otherwise. It's probably ignored.
      break;
    }
  }
}


void
InstructionNode::dumpNode(int indent) const {
  for (int i=0; i < indent; i++)
    std::cerr << "    ";
  std::cerr << getInstruction()->getOpcodeName()
            << " [label " << getOpLabel() << "]" << "\n";
}

void
VRegListNode::dumpNode(int indent) const {
  for (int i=0; i < indent; i++)
    std::cerr << "    ";
  
  std::cerr << "List" << "\n";
}


void
VRegNode::dumpNode(int indent) const {
  for (int i=0; i < indent; i++)
    std::cerr << "    ";
  
  std::cerr << "VReg " << getValue() << "\t(type "
            << (int) getValue()->getValueType() << ")" << "\n";
}

void
ConstantNode::dumpNode(int indent) const {
  for (int i=0; i < indent; i++)
    std::cerr << "    ";
  
  std::cerr << "Constant " << getValue() << "\t(type "
            << (int) getValue()->getValueType() << ")" << "\n";
}

void LabelNode::dumpNode(int indent) const {
  for (int i=0; i < indent; i++)
    std::cerr << "    ";
  
  std::cerr << "Label " << getValue() << "\n";
}

//------------------------------------------------------------------------
// class InstrForest
// 
// A forest of instruction trees, usually for a single method.
//------------------------------------------------------------------------ 

InstrForest::InstrForest(Function *F) {
  for (Function::iterator BB = F->begin(), FE = F->end(); BB != FE; ++BB) {
    for(BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
      buildTreeForInstruction(I);
  }
}

InstrForest::~InstrForest() {
  for_each(treeRoots.begin(), treeRoots.end(), deleter<InstructionNode>);
}

void InstrForest::dump() const {
  for (const_root_iterator I = roots_begin(); I != roots_end(); ++I)
    (*I)->dump(/*dumpChildren*/ 1, /*indent*/ 0);
}

inline void InstrForest::eraseRoot(InstructionNode* node) {
  for (RootSet::reverse_iterator RI=treeRoots.rbegin(), RE=treeRoots.rend();
       RI != RE; ++RI)
    if (*RI == node)
      treeRoots.erase(RI.base()-1);
}

inline void InstrForest::noteTreeNodeForInstr(Instruction *instr,
                                              InstructionNode *treeNode) {
  (*this)[instr] = treeNode;
  treeRoots.push_back(treeNode);	// mark node as root of a new tree
}


inline void InstrForest::setLeftChild(InstrTreeNode *parent,
                                      InstrTreeNode *child) {
  parent->LeftChild = child;
  child->Parent = parent;
  if (InstructionNode* instrNode = dyn_cast<InstructionNode>(child))
    eraseRoot(instrNode); // no longer a tree root
}

inline void InstrForest::setRightChild(InstrTreeNode *parent,
                                       InstrTreeNode *child) {
  parent->RightChild = child;
  child->Parent = parent;
  if (InstructionNode* instrNode = dyn_cast<InstructionNode>(child))
    eraseRoot(instrNode); // no longer a tree root
}


InstructionNode* InstrForest::buildTreeForInstruction(Instruction *instr) {
  InstructionNode *treeNode = getTreeNodeForInstr(instr);
  if (treeNode) {
    // treeNode has already been constructed for this instruction
    assert(treeNode->getInstruction() == instr);
    return treeNode;
  }
  
  // Otherwise, create a new tree node for this instruction.
  // 
  treeNode = new InstructionNode(instr);
  noteTreeNodeForInstr(instr, treeNode);
  
  if (instr->getOpcode() == Instruction::Call) {
    // Operands of call instruction
    return treeNode;
  }
  
  // If the instruction has more than 2 instruction operands,
  // then we need to create artificial list nodes to hold them.
  // (Note that we only count operands that get tree nodes, and not
  // others such as branch labels for a branch or switch instruction.)
  //
  // To do this efficiently, we'll walk all operands, build treeNodes
  // for all appropriate operands and save them in an array.  We then
  // insert children at the end, creating list nodes where needed.
  // As a performance optimization, allocate a child array only
  // if a fixed array is too small.
  // 
  int numChildren = 0;
  InstrTreeNode** childArray = new InstrTreeNode*[instr->getNumOperands()];
  
  //
  // Walk the operands of the instruction
  // 
  for (Instruction::op_iterator O = instr->op_begin(); O!=instr->op_end(); ++O)
    {
      Value* operand = *O;
      
      // Check if the operand is a data value, not an branch label, type,
      // method or module.  If the operand is an address type (i.e., label
      // or method) that is used in an non-branching operation, e.g., `add'.
      // that should be considered a data value.
    
      // Check latter condition here just to simplify the next IF.
      bool includeAddressOperand =
	(isa<BasicBlock>(operand) || isa<Function>(operand))
	&& !instr->isTerminator();
    
      if (includeAddressOperand || isa<Instruction>(operand) ||
	  isa<Constant>(operand) || isa<Argument>(operand) ||
	  isa<GlobalVariable>(operand))
      {
        // This operand is a data value
	
        // An instruction that computes the incoming value is added as a
        // child of the current instruction if:
        //   the value has only a single use
        //   AND both instructions are in the same basic block.
        //   AND the current instruction is not a PHI (because the incoming
        //		value is conceptually in a predecessor block,
        //		even though it may be in the same static block)
        // 
        // (Note that if the value has only a single use (viz., `instr'),
        //  the def of the value can be safely moved just before instr
        //  and therefore it is safe to combine these two instructions.)
        // 
        // In all other cases, the virtual register holding the value
        // is used directly, i.e., made a child of the instruction node.
        // 
        InstrTreeNode* opTreeNode;
        if (isa<Instruction>(operand) && operand->hasOneUse() &&
            cast<Instruction>(operand)->getParent() == instr->getParent() &&
            instr->getOpcode() != Instruction::PHI &&
            instr->getOpcode() != Instruction::Call)
        {
          // Recursively create a treeNode for it.
          opTreeNode = buildTreeForInstruction((Instruction*)operand);
        } else if (Constant *CPV = dyn_cast<Constant>(operand)) {
          // Create a leaf node for a constant
          opTreeNode = new ConstantNode(CPV);
        } else {
          // Create a leaf node for the virtual register
          opTreeNode = new VRegNode(operand);
        }

        childArray[numChildren++] = opTreeNode;
      }
    }
  
  //-------------------------------------------------------------------- 
  // Add any selected operands as children in the tree.
  // Certain instructions can have more than 2 in some instances (viz.,
  // a CALL or a memory access -- LOAD, STORE, and GetElemPtr -- to an
  // array or struct). Make the operands of every such instruction into
  // a right-leaning binary tree with the operand nodes at the leaves
  // and VRegList nodes as internal nodes.
  //-------------------------------------------------------------------- 
  
  InstrTreeNode *parent = treeNode;
  
  if (numChildren > 2) {
    unsigned instrOpcode = treeNode->getInstruction()->getOpcode();
    assert(instrOpcode == Instruction::PHI ||
           instrOpcode == Instruction::Call ||
           instrOpcode == Instruction::Load ||
           instrOpcode == Instruction::Store ||
           instrOpcode == Instruction::GetElementPtr);
  }
  
  // Insert the first child as a direct child
  if (numChildren >= 1)
    setLeftChild(parent, childArray[0]);

  int n;
  
  // Create a list node for children 2 .. N-1, if any
  for (n = numChildren-1; n >= 2; n--) {
    // We have more than two children
    InstrTreeNode *listNode = new VRegListNode();
    setRightChild(parent, listNode);
    setLeftChild(listNode, childArray[numChildren - n]);
    parent = listNode;
  }
  
  // Now insert the last remaining child (if any).
  if (numChildren >= 2) {
    assert(n == 1);
    setRightChild(parent, childArray[numChildren - 1]);
  }

  delete [] childArray;
  return treeNode;
}

} // End llvm namespace