LowerSubregs.cpp

//===-- LowerSubregs.cpp - Subregister Lowering instruction pass ----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Christopher Lamb and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "lowersubregs"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Function.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Compiler.h"
using namespace llvm;

namespace {
  struct VISIBILITY_HIDDEN LowerSubregsInstructionPass
   : public MachineFunctionPass {
    static char ID; // Pass identification, replacement for typeid
    LowerSubregsInstructionPass() : MachineFunctionPass((intptr_t)&ID) {}
    
    const char *getPassName() const {
      return "Subregister lowering instruction pass";
    }

    /// runOnMachineFunction - pass entry point
    bool runOnMachineFunction(MachineFunction&);
  };

  char LowerSubregsInstructionPass::ID = 0;
}

FunctionPass *llvm::createLowerSubregsPass() { 
  return new LowerSubregsInstructionPass(); 
}

// Returns the Register Class of a physical register
static const TargetRegisterClass *getPhysicalRegisterRegClass(
        const MRegisterInfo &MRI,
        unsigned reg) {
  assert(MRegisterInfo::isPhysicalRegister(reg) &&
         "reg must be a physical register");
  // 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)->contains(reg))
      return *I;
  assert(false && "Couldn't find the register class");
  return 0;
}

static bool isSubRegOf(const MRegisterInfo &MRI,
                       unsigned SubReg,
                       unsigned SupReg) {
  const TargetRegisterDesc &RD = MRI[SubReg];
  for (const unsigned *reg = RD.SuperRegs; *reg != 0; ++reg)
    if (*reg == SupReg)
      return true;
      
  return false;
}


/// runOnMachineFunction - Reduce subregister inserts and extracts to register
/// copies.
///
bool LowerSubregsInstructionPass::runOnMachineFunction(MachineFunction &MF) {
  DOUT << "Machine Function\n";
  const TargetMachine &TM = MF.getTarget();
  const MRegisterInfo &MRI = *TM.getRegisterInfo();
  
  bool MadeChange = false;

  DOUT << "********** LOWERING SUBREG INSTRS **********\n";
  DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';

  for (MachineFunction::iterator mbbi = MF.begin(), mbbe = MF.end();
       mbbi != mbbe; ++mbbi) {
    for (MachineBasicBlock::iterator mi = mbbi->begin(), me = mbbi->end();
         mi != me; ++mi) {

      if (mi->getOpcode() == TargetInstrInfo::EXTRACT_SUBREG) {
        assert(mi->getOperand(0).isRegister() && mi->getOperand(0).isDef() &&
               mi->getOperand(1).isRegister() && mi->getOperand(1).isUse() &&
               mi->getOperand(2).isImm() && "Malformed extract_subreg");
      
        unsigned SuperReg = mi->getOperand(1).getReg();
        unsigned SubIdx = mi->getOperand(2).getImm();
        
        assert(MRegisterInfo::isPhysicalRegister(SuperReg) &&
               "Extract supperg source must be a physical register");
        unsigned SrcReg = MRI.getSubReg(SuperReg, SubIdx);
        unsigned DstReg = mi->getOperand(0).getReg();
        
        DOUT << "subreg: CONVERTING: " << *mi;
        
        if (SrcReg != DstReg) {
          const TargetRegisterClass *TRC = 0;
          if (MRegisterInfo::isPhysicalRegister(DstReg)) {
            TRC = getPhysicalRegisterRegClass(MRI, DstReg);
          } else {
            TRC = MF.getSSARegMap()->getRegClass(DstReg);
          }
          assert(TRC == getPhysicalRegisterRegClass(MRI, SrcReg) &&
                  "Extract subreg and Dst must be of same register class");
        
          MRI.copyRegToReg(*mbbi, mi, DstReg, SrcReg, TRC);
          MachineBasicBlock::iterator dmi = mi;
          DOUT << "subreg: " << *(--dmi);
        }
        
        DOUT << "\n";
        mbbi->erase(mi);
        MadeChange = true;
      
      } else if (mi->getOpcode() == TargetInstrInfo::INSERT_SUBREG) {
      
        unsigned DstReg = 0;
        unsigned SrcReg = 0;
        unsigned InsReg = 0;
        unsigned SubIdx = 0;
        
        // If only have 3 operands, then the source superreg is undef
        // and we can supress the copy from the undef value
        if (mi->getNumOperands() == 3) {
          assert((mi->getOperand(0).isRegister() && mi->getOperand(0).isDef()) &&
                 (mi->getOperand(1).isRegister() && mi->getOperand(1).isUse()) &&
                  mi->getOperand(2).isImm() && "Invalid extract_subreg");
          DstReg = mi->getOperand(0).getReg();
          SrcReg = DstReg;
          InsReg = mi->getOperand(1).getReg();
          SubIdx = mi->getOperand(2).getImm();
        } else if (mi->getNumOperands() == 4) {
          assert((mi->getOperand(0).isRegister() && mi->getOperand(0).isDef()) &&
                 (mi->getOperand(1).isRegister() && mi->getOperand(1).isUse()) &&
                 (mi->getOperand(2).isRegister() && mi->getOperand(2).isUse()) &&
                  mi->getOperand(3).isImm() && "Invalid extract_subreg");
          DstReg = mi->getOperand(0).getReg();
          SrcReg = mi->getOperand(1).getReg();
          InsReg = mi->getOperand(2).getReg();
          SubIdx = mi->getOperand(3).getImm();     
        } else 
          assert(0 && "Malformed extract_subreg");
      
        assert(SubIdx != 0 && "Invalid index for extract_subreg");
        unsigned DstSubReg = MRI.getSubReg(DstReg, SubIdx);
        
        assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
               "Insert superreg source must be in a physical register");
        assert(MRegisterInfo::isPhysicalRegister(DstReg) &&
               "Insert destination must be in a physical register");
        assert(MRegisterInfo::isPhysicalRegister(InsReg) &&
               "Inserted value must be in a physical register");
        
        DOUT << "subreg: CONVERTING: " << *mi;
               
        // If the inserted register is already allocated into a subregister
        // of the destination, we copy the subreg into the source
        // However, this is only safe if the insert instruction is the kill
        // of the source register
        bool revCopyOrder = isSubRegOf(MRI, InsReg, DstReg);    
        if (revCopyOrder) {
          if (mi->getOperand(1).isKill()) {
            DstSubReg = MRI.getSubReg(SrcReg, SubIdx);
            // Insert sub-register copy
            const TargetRegisterClass *TRC1 = 0;
            if (MRegisterInfo::isPhysicalRegister(InsReg)) {
              TRC1 = getPhysicalRegisterRegClass(MRI, InsReg);
            } else {
              TRC1 = MF.getSSARegMap()->getRegClass(InsReg);
            }
            
            MRI.copyRegToReg(*mbbi, mi, DstSubReg, InsReg, TRC1);
            MachineBasicBlock::iterator dmi = mi;
            DOUT << "subreg: " << *(--dmi);
          } else {
            assert(0 && "Don't know how to convert this insert");
          }
        }
        
        if (SrcReg != DstReg) {
          // Insert super-register copy
          const TargetRegisterClass *TRC0 = 0;
          if (MRegisterInfo::isPhysicalRegister(DstReg)) {
            TRC0 = getPhysicalRegisterRegClass(MRI, DstReg);
          } else {
            TRC0 = MF.getSSARegMap()->getRegClass(DstReg);
          }
          assert(TRC0 == getPhysicalRegisterRegClass(MRI, SrcReg) &&
                  "Insert superreg and Dst must be of same register class");
        
          MRI.copyRegToReg(*mbbi, mi, DstReg, SrcReg, TRC0);
          MachineBasicBlock::iterator dmi = mi;
          DOUT << "subreg: " << *(--dmi);
        }
        
        if (!revCopyOrder && InsReg != DstSubReg) {
          // Insert sub-register copy
          const TargetRegisterClass *TRC1 = 0;
          if (MRegisterInfo::isPhysicalRegister(InsReg)) {
            TRC1 = getPhysicalRegisterRegClass(MRI, InsReg);
          } else {
            TRC1 = MF.getSSARegMap()->getRegClass(InsReg);
          }
          
          MRI.copyRegToReg(*mbbi, mi, DstSubReg, InsReg, TRC1);
          MachineBasicBlock::iterator dmi = mi;
          DOUT << "subreg: " << *(--dmi);
        }
        
        DOUT << "\n";
        mbbi->erase(mi);
        MadeChange = true;
      }
    }
  }

  return MadeChange;
}