lib/CodeGen/SelectionDAG/ScheduleDAG.cpp

//===---- ScheduleDAG.cpp - Implement the ScheduleDAG class ---------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by James M. Laskey and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This implements a simple two pass scheduler.  The first pass attempts to push
// backward any lengthy instructions and critical paths.  The second pass packs
// instructions into semi-optimal time slots.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "sched"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetInstrItineraries.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Support/Debug.h"
#include <iostream>
using namespace llvm;


/// CountResults - The results of target nodes have register or immediate
/// operands first, then an optional chain, and optional flag operands (which do
/// not go into the machine instrs.)
static unsigned CountResults(SDNode *Node) {
  unsigned N = Node->getNumValues();
  while (N && Node->getValueType(N - 1) == MVT::Flag)
    --N;
  if (N && Node->getValueType(N - 1) == MVT::Other)
    --N;    // Skip over chain result.
  return N;
}

/// CountOperands  The inputs to target nodes have any actual inputs first,
/// followed by an optional chain operand, then flag operands.  Compute the
/// number of actual operands that  will go into the machine instr.
static unsigned CountOperands(SDNode *Node) {
  unsigned N = Node->getNumOperands();
  while (N && Node->getOperand(N - 1).getValueType() == MVT::Flag)
    --N;
  if (N && Node->getOperand(N - 1).getValueType() == MVT::Other)
    --N; // Ignore chain if it exists.
  return N;
}

/// CreateVirtualRegisters - Add result register values for things that are
/// defined by this instruction.
unsigned ScheduleDAG::CreateVirtualRegisters(MachineInstr *MI,
                                             unsigned NumResults,
                                             const TargetInstrDescriptor &II) {
  // Create the result registers for this node and add the result regs to
  // the machine instruction.
  const TargetOperandInfo *OpInfo = II.OpInfo;
  unsigned ResultReg = RegMap->createVirtualRegister(OpInfo[0].RegClass);
  MI->addRegOperand(ResultReg, MachineOperand::Def);
  for (unsigned i = 1; i != NumResults; ++i) {
    assert(OpInfo[i].RegClass && "Isn't a register operand!");
    MI->addRegOperand(RegMap->createVirtualRegister(OpInfo[i].RegClass),
                      MachineOperand::Def);
  }
  return ResultReg;
}

/// EmitNode - Generate machine code for an node and needed dependencies.
///
void ScheduleDAG::EmitNode(NodeInfo *NI) {
  unsigned VRBase = 0;                 // First virtual register for node
  SDNode *Node = NI->Node;
  
  // If machine instruction
  if (Node->isTargetOpcode()) {
    unsigned Opc = Node->getTargetOpcode();
    const TargetInstrDescriptor &II = TII->get(Opc);

    unsigned NumResults = CountResults(Node);
    unsigned NodeOperands = CountOperands(Node);
    unsigned NumMIOperands = NodeOperands + NumResults;
#ifndef NDEBUG
    assert((unsigned(II.numOperands) == NumMIOperands || II.numOperands == -1)&&
           "#operands for dag node doesn't match .td file!"); 
#endif

    // Create the new machine instruction.
    MachineInstr *MI = new MachineInstr(Opc, NumMIOperands, true, true);
    
    // Add result register values for things that are defined by this
    // instruction.
    
    // If the node is only used by a CopyToReg and the dest reg is a vreg, use
    // the CopyToReg'd destination register instead of creating a new vreg.
    if (NumResults == 1) {
      for (SDNode::use_iterator UI = Node->use_begin(), E = Node->use_end();
           UI != E; ++UI) {
        SDNode *Use = *UI;
        if (Use->getOpcode() == ISD::CopyToReg && 
            Use->getOperand(2).Val == Node) {
          unsigned Reg = cast<RegisterSDNode>(Use->getOperand(1))->getReg();
          if (MRegisterInfo::isVirtualRegister(Reg)) {
            VRBase = Reg;
            MI->addRegOperand(Reg, MachineOperand::Def);
            break;
          }
        }
      }
    }
    
    // Otherwise, create new virtual registers.
    if (NumResults && VRBase == 0)
      VRBase = CreateVirtualRegisters(MI, NumResults, II);
    
    // Emit all of the actual operands of this instruction, adding them to the
    // instruction as appropriate.
    for (unsigned i = 0; i != NodeOperands; ++i) {
      if (Node->getOperand(i).isTargetOpcode()) {
        // Note that this case is redundant with the final else block, but we
        // include it because it is the most common and it makes the logic
        // simpler here.
        assert(Node->getOperand(i).getValueType() != MVT::Other &&
               Node->getOperand(i).getValueType() != MVT::Flag &&
               "Chain and flag operands should occur at end of operand list!");

        // Get/emit the operand.
        unsigned VReg = getVR(Node->getOperand(i));
        MI->addRegOperand(VReg, MachineOperand::Use);
        
        // Verify that it is right.
        assert(MRegisterInfo::isVirtualRegister(VReg) && "Not a vreg?");
        assert(II.OpInfo[i+NumResults].RegClass &&
               "Don't have operand info for this instruction!");
        assert(RegMap->getRegClass(VReg) == II.OpInfo[i+NumResults].RegClass &&
               "Register class of operand and regclass of use don't agree!");
      } else if (ConstantSDNode *C =
                 dyn_cast<ConstantSDNode>(Node->getOperand(i))) {
        MI->addZeroExtImm64Operand(C->getValue());
      } else if (RegisterSDNode*R =
                 dyn_cast<RegisterSDNode>(Node->getOperand(i))) {
        MI->addRegOperand(R->getReg(), MachineOperand::Use);
      } else if (GlobalAddressSDNode *TGA =
                       dyn_cast<GlobalAddressSDNode>(Node->getOperand(i))) {
        MI->addGlobalAddressOperand(TGA->getGlobal(), false, TGA->getOffset());
      } else if (BasicBlockSDNode *BB =
                       dyn_cast<BasicBlockSDNode>(Node->getOperand(i))) {
        MI->addMachineBasicBlockOperand(BB->getBasicBlock());
      } else if (FrameIndexSDNode *FI =
                       dyn_cast<FrameIndexSDNode>(Node->getOperand(i))) {
        MI->addFrameIndexOperand(FI->getIndex());
      } else if (ConstantPoolSDNode *CP = 
                    dyn_cast<ConstantPoolSDNode>(Node->getOperand(i))) {
        unsigned Idx = ConstPool->getConstantPoolIndex(CP->get());
        MI->addConstantPoolIndexOperand(Idx);
      } else if (ExternalSymbolSDNode *ES = 
                 dyn_cast<ExternalSymbolSDNode>(Node->getOperand(i))) {
        MI->addExternalSymbolOperand(ES->getSymbol(), false);
      } else {
        assert(Node->getOperand(i).getValueType() != MVT::Other &&
               Node->getOperand(i).getValueType() != MVT::Flag &&
               "Chain and flag operands should occur at end of operand list!");
        unsigned VReg = getVR(Node->getOperand(i));
        MI->addRegOperand(VReg, MachineOperand::Use);
        
        // Verify that it is right.
        assert(MRegisterInfo::isVirtualRegister(VReg) && "Not a vreg?");
        assert(II.OpInfo[i+NumResults].RegClass &&
               "Don't have operand info for this instruction!");
        assert(RegMap->getRegClass(VReg) == II.OpInfo[i+NumResults].RegClass &&
               "Register class of operand and regclass of use don't agree!");
      }
    }
    
    // Now that we have emitted all operands, emit this instruction itself.
    if ((II.Flags & M_USES_CUSTOM_DAG_SCHED_INSERTION) == 0) {
      BB->insert(BB->end(), MI);
    } else {
      // Insert this instruction into the end of the basic block, potentially
      // taking some custom action.
      BB = DAG.getTargetLoweringInfo().InsertAtEndOfBasicBlock(MI, BB);
    }
  } else {
    switch (Node->getOpcode()) {
    default:
      Node->dump(); 
      assert(0 && "This target-independent node should have been selected!");
    case ISD::EntryToken: // fall thru
    case ISD::TokenFactor:
      break;
    case ISD::CopyToReg: {
      unsigned InReg = getVR(Node->getOperand(2));
      unsigned DestReg = cast<RegisterSDNode>(Node->getOperand(1))->getReg();
      if (InReg != DestReg)   // Coallesced away the copy?
        MRI->copyRegToReg(*BB, BB->end(), DestReg, InReg,
                          RegMap->getRegClass(InReg));
      break;
    }
    case ISD::CopyFromReg: {
      unsigned SrcReg = cast<RegisterSDNode>(Node->getOperand(1))->getReg();
      if (MRegisterInfo::isVirtualRegister(SrcReg)) {
        VRBase = SrcReg;  // Just use the input register directly!
        break;
      }

      // If the node is only used by a CopyToReg and the dest reg is a vreg, use
      // the CopyToReg'd destination register instead of creating a new vreg.
      for (SDNode::use_iterator UI = Node->use_begin(), E = Node->use_end();
           UI != E; ++UI) {
        SDNode *Use = *UI;
        if (Use->getOpcode() == ISD::CopyToReg && 
            Use->getOperand(2).Val == Node) {
          unsigned DestReg = cast<RegisterSDNode>(Use->getOperand(1))->getReg();
          if (MRegisterInfo::isVirtualRegister(DestReg)) {
            VRBase = DestReg;
            break;
          }
        }
      }

      // Figure out the register class to create for the destreg.
      const TargetRegisterClass *TRC = 0;
      if (VRBase) {
        TRC = RegMap->getRegClass(VRBase);
      } else {

        // Pick the register class of the right type that contains this physreg.
        for (MRegisterInfo::regclass_iterator I = MRI->regclass_begin(),
             E = MRI->regclass_end(); I != E; ++I)
          if ((*I)->hasType(Node->getValueType(0)) &&
              (*I)->contains(SrcReg)) {
            TRC = *I;
            break;
          }
        assert(TRC && "Couldn't find register class for reg copy!");
      
        // Create the reg, emit the copy.
        VRBase = RegMap->createVirtualRegister(TRC);
      }
      MRI->copyRegToReg(*BB, BB->end(), VRBase, SrcReg, TRC);
      break;
    }
    }
  }

  assert(NI->VRBase == 0 && "Node emitted out of order - early");
  NI->VRBase = VRBase;
}

void ScheduleDAG::dump(const char *tag) const {
  std::cerr << tag; dump();
}

void ScheduleDAG::dump() const {
  print(std::cerr);
}

/// Run - perform scheduling.
///
MachineBasicBlock *ScheduleDAG::Run() {
  TII = TM.getInstrInfo();
  MRI = TM.getRegisterInfo();
  RegMap = BB->getParent()->getSSARegMap();
  ConstPool = BB->getParent()->getConstantPool();
  Schedule();
  return BB;
}