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			516 lines
		
	
	
		
			19 KiB
		
	
	
	
		
			C++
		
	
	
	
	
	
			
		
		
	
	
			516 lines
		
	
	
		
			19 KiB
		
	
	
	
		
			C++
		
	
	
	
	
	
//===-- PeepholeOptimizer.cpp - X86 Peephole Optimizer --------------------===//
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// 
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//                     The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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// 
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//===----------------------------------------------------------------------===//
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//
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// This file contains a peephole optimizer for the X86.
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//
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//===----------------------------------------------------------------------===//
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#include "X86.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/Target/MRegisterInfo.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "Support/Statistic.h"
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#include "Support/STLExtras.h"
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using namespace llvm;
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namespace {
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  Statistic<> NumPHOpts("x86-peephole",
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                        "Number of peephole optimization performed");
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  Statistic<> NumPHMoves("x86-peephole", "Number of peephole moves folded");
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  struct PH : public MachineFunctionPass {
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    virtual bool runOnMachineFunction(MachineFunction &MF);
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    bool PeepholeOptimize(MachineBasicBlock &MBB,
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			  MachineBasicBlock::iterator &I);
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    virtual const char *getPassName() const { return "X86 Peephole Optimizer"; }
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  };
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}
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FunctionPass *llvm::createX86PeepholeOptimizerPass() { return new PH(); }
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bool PH::runOnMachineFunction(MachineFunction &MF) {
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  bool Changed = false;
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  for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI != E; ++BI)
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    for (MachineBasicBlock::iterator I = BI->begin(); I != BI->end(); )
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      if (PeepholeOptimize(*BI, I)) {
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	Changed = true;
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        ++NumPHOpts;
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      } else
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	++I;
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  return Changed;
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}
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bool PH::PeepholeOptimize(MachineBasicBlock &MBB,
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			  MachineBasicBlock::iterator &I) {
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  assert(I != MBB.end());
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  MachineBasicBlock::iterator NextI = next(I);
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  MachineInstr *MI = I;
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  MachineInstr *Next = (NextI != MBB.end()) ? &*NextI : (MachineInstr*)0;
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  unsigned Size = 0;
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  switch (MI->getOpcode()) {
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  case X86::MOV8rr:
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  case X86::MOV16rr:
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  case X86::MOV32rr:   // Destroy X = X copies...
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    if (MI->getOperand(0).getReg() == MI->getOperand(1).getReg()) {
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      I = MBB.erase(I);
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      return true;
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    }
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    return false;
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    // A large number of X86 instructions have forms which take an 8-bit
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    // immediate despite the fact that the operands are 16 or 32 bits.  Because
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    // this can save three bytes of code size (and icache space), we want to
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    // shrink them if possible.
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  case X86::IMUL16rri: case X86::IMUL32rri:
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    assert(MI->getNumOperands() == 3 && "These should all have 3 operands!");
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    if (MI->getOperand(2).isImmediate()) {
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      int Val = MI->getOperand(2).getImmedValue();
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      // If the value is the same when signed extended from 8 bits...
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      if (Val == (signed int)(signed char)Val) {
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        unsigned Opcode;
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        switch (MI->getOpcode()) {
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        default: assert(0 && "Unknown opcode value!");
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        case X86::IMUL16rri: Opcode = X86::IMUL16rri8; break;
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        case X86::IMUL32rri: Opcode = X86::IMUL32rri8; break;
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        }
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        unsigned R0 = MI->getOperand(0).getReg();
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        unsigned R1 = MI->getOperand(1).getReg();
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        I = MBB.insert(MBB.erase(I),
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                       BuildMI(Opcode, 2, R0).addReg(R1).addZImm((char)Val));
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        return true;
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      }
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    }
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    return false;
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#if 0
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  case X86::IMUL16rmi: case X86::IMUL32rmi:
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    assert(MI->getNumOperands() == 6 && "These should all have 6 operands!");
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    if (MI->getOperand(5).isImmediate()) {
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      int Val = MI->getOperand(5).getImmedValue();
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      // If the value is the same when signed extended from 8 bits...
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      if (Val == (signed int)(signed char)Val) {
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        unsigned Opcode;
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        switch (MI->getOpcode()) {
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        default: assert(0 && "Unknown opcode value!");
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        case X86::IMUL16rmi: Opcode = X86::IMUL16rmi8; break;
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        case X86::IMUL32rmi: Opcode = X86::IMUL32rmi8; break;
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        }
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        unsigned R0 = MI->getOperand(0).getReg();
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        unsigned R1 = MI->getOperand(1).getReg();
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        unsigned Scale = MI->getOperand(2).getImmedValue();
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        unsigned R2 = MI->getOperand(3).getReg();
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        unsigned Offset = MI->getOperand(4).getImmedValue();
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        I = MBB.insert(MBB.erase(I),
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                       BuildMI(Opcode, 5, R0).addReg(R1).addZImm(Scale).
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                             addReg(R2).addSImm(Offset).addZImm((char)Val));
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        return true;
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      }
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    }
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    return false;
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#endif
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  case X86::ADD16ri:  case X86::ADD32ri:  case X86::ADC32ri:
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  case X86::SUB16ri:  case X86::SUB32ri:  case X86::SBB32ri:
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  case X86::AND16ri:  case X86::AND32ri:
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  case X86::OR16ri:   case X86::OR32ri:
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  case X86::XOR16ri:  case X86::XOR32ri:
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    assert(MI->getNumOperands() == 2 && "These should all have 2 operands!");
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    if (MI->getOperand(1).isImmediate()) {
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      int Val = MI->getOperand(1).getImmedValue();
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      // If the value is the same when signed extended from 8 bits...
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      if (Val == (signed int)(signed char)Val) {
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        unsigned Opcode;
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        switch (MI->getOpcode()) {
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        default: assert(0 && "Unknown opcode value!");
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        case X86::ADD16ri:  Opcode = X86::ADD16ri8; break;
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        case X86::ADD32ri:  Opcode = X86::ADD32ri8; break;
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        case X86::ADC32ri:  Opcode = X86::ADC32ri8; break;
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        case X86::SUB16ri:  Opcode = X86::SUB16ri8; break;
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        case X86::SUB32ri:  Opcode = X86::SUB32ri8; break;
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        case X86::SBB32ri:  Opcode = X86::SBB32ri8; break;
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        case X86::AND16ri:  Opcode = X86::AND16ri8; break;
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        case X86::AND32ri:  Opcode = X86::AND32ri8; break;
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        case X86::OR16ri:   Opcode = X86::OR16ri8; break;
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        case X86::OR32ri:   Opcode = X86::OR32ri8; break;
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        case X86::XOR16ri:  Opcode = X86::XOR16ri8; break;
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        case X86::XOR32ri:  Opcode = X86::XOR32ri8; break;
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        }
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        unsigned R0 = MI->getOperand(0).getReg();
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        I = MBB.insert(MBB.erase(I),
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                    BuildMI(Opcode, 1, R0, MachineOperand::UseAndDef)
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                      .addZImm((char)Val));
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        return true;
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      }
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    }
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    return false;
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  case X86::ADD16mi:  case X86::ADD32mi:  case X86::ADC32mi:
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  case X86::SUB16mi:  case X86::SUB32mi:  case X86::SBB32mi:
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  case X86::AND16mi:  case X86::AND32mi:
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  case X86::OR16mi:  case X86::OR32mi:
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  case X86::XOR16mi:  case X86::XOR32mi:
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    assert(MI->getNumOperands() == 5 && "These should all have 5 operands!");
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    if (MI->getOperand(4).isImmediate()) {
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      int Val = MI->getOperand(4).getImmedValue();
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      // If the value is the same when signed extended from 8 bits...
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      if (Val == (signed int)(signed char)Val) {
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        unsigned Opcode;
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        switch (MI->getOpcode()) {
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        default: assert(0 && "Unknown opcode value!");
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        case X86::ADD16mi:  Opcode = X86::ADD16mi8; break;
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        case X86::ADD32mi:  Opcode = X86::ADD32mi8; break;
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        case X86::ADC32mi:  Opcode = X86::ADC32mi8; break;
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        case X86::SUB16mi:  Opcode = X86::SUB16mi8; break;
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        case X86::SUB32mi:  Opcode = X86::SUB32mi8; break;
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        case X86::SBB32mi:  Opcode = X86::SBB32mi8; break;
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        case X86::AND16mi:  Opcode = X86::AND16mi8; break;
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        case X86::AND32mi:  Opcode = X86::AND32mi8; break;
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        case X86::OR16mi:   Opcode = X86::OR16mi8; break;
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        case X86::OR32mi:   Opcode = X86::OR32mi8; break;
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        case X86::XOR16mi:  Opcode = X86::XOR16mi8; break;
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        case X86::XOR32mi:  Opcode = X86::XOR32mi8; break;
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        }
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        unsigned R0 = MI->getOperand(0).getReg();
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        unsigned Scale = MI->getOperand(1).getImmedValue();
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        unsigned R1 = MI->getOperand(2).getReg();
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        unsigned Offset = MI->getOperand(3).getImmedValue();
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        I = MBB.insert(MBB.erase(I),
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                       BuildMI(Opcode, 5).addReg(R0).addZImm(Scale).
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                             addReg(R1).addSImm(Offset).addZImm((char)Val));
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        return true;
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      }
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    }
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    return false;
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#if 0
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  case X86::MOV32ri: Size++;
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  case X86::MOV16ri: Size++;
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  case X86::MOV8ri:
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    // FIXME: We can only do this transformation if we know that flags are not
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    // used here, because XOR clobbers the flags!
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    if (MI->getOperand(1).isImmediate()) {         // avoid mov EAX, <value>
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      int Val = MI->getOperand(1).getImmedValue();
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      if (Val == 0) {                              // mov EAX, 0 -> xor EAX, EAX
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	static const unsigned Opcode[] ={X86::XOR8rr,X86::XOR16rr,X86::XOR32rr};
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	unsigned Reg = MI->getOperand(0).getReg();
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	I = MBB.insert(MBB.erase(I),
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                       BuildMI(Opcode[Size], 2, Reg).addReg(Reg).addReg(Reg));
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	return true;
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      } else if (Val == -1) {                     // mov EAX, -1 -> or EAX, -1
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	// TODO: 'or Reg, -1' has a smaller encoding than 'mov Reg, -1'
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      }
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    }
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    return false;
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#endif
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  case X86::BSWAP32r:        // Change bswap EAX, bswap EAX into nothing
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    if (Next->getOpcode() == X86::BSWAP32r &&
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	MI->getOperand(0).getReg() == Next->getOperand(0).getReg()) {
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      I = MBB.erase(MBB.erase(I));
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      return true;
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    }
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    return false;
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  default:
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    return false;
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  }
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}
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namespace {
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  class UseDefChains : public MachineFunctionPass {
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    std::vector<MachineInstr*> DefiningInst;
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  public:
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    // getDefinition - Return the machine instruction that defines the specified
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    // SSA virtual register.
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    MachineInstr *getDefinition(unsigned Reg) {
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      assert(MRegisterInfo::isVirtualRegister(Reg) &&
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             "use-def chains only exist for SSA registers!");
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      assert(Reg - MRegisterInfo::FirstVirtualRegister < DefiningInst.size() &&
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             "Unknown register number!");
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      assert(DefiningInst[Reg-MRegisterInfo::FirstVirtualRegister] &&
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             "Unknown register number!");
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      return DefiningInst[Reg-MRegisterInfo::FirstVirtualRegister];
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    }
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    // setDefinition - Update the use-def chains to indicate that MI defines
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    // register Reg.
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    void setDefinition(unsigned Reg, MachineInstr *MI) {
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      if (Reg-MRegisterInfo::FirstVirtualRegister >= DefiningInst.size())
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        DefiningInst.resize(Reg-MRegisterInfo::FirstVirtualRegister+1);
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      DefiningInst[Reg-MRegisterInfo::FirstVirtualRegister] = MI;
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    }
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    // removeDefinition - Update the use-def chains to forget about Reg
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    // entirely.
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    void removeDefinition(unsigned Reg) {
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      assert(getDefinition(Reg));      // Check validity
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      DefiningInst[Reg-MRegisterInfo::FirstVirtualRegister] = 0;
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    }
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    virtual bool runOnMachineFunction(MachineFunction &MF) {
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      for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI!=E; ++BI)
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        for (MachineBasicBlock::iterator I = BI->begin(); I != BI->end(); ++I) {
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          for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
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            MachineOperand &MO = I->getOperand(i);
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            if (MO.isRegister() && MO.isDef() && !MO.isUse() &&
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                MRegisterInfo::isVirtualRegister(MO.getReg()))
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              setDefinition(MO.getReg(), I);
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          }
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        }
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      return false;
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    }
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    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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      AU.setPreservesAll();
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      MachineFunctionPass::getAnalysisUsage(AU);
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    }
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    virtual void releaseMemory() {
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      std::vector<MachineInstr*>().swap(DefiningInst);
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    }
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  };
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  RegisterAnalysis<UseDefChains> X("use-def-chains",
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                                "use-def chain construction for machine code");
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}
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namespace {
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  Statistic<> NumSSAPHOpts("x86-ssa-peephole",
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                           "Number of SSA peephole optimization performed");
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  /// SSAPH - This pass is an X86-specific, SSA-based, peephole optimizer.  This
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  /// pass is really a bad idea: a better instruction selector should completely
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  /// supersume it.  However, that will take some time to develop, and the
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  /// simple things this can do are important now.
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  class SSAPH : public MachineFunctionPass {
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    UseDefChains *UDC;
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  public:
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    virtual bool runOnMachineFunction(MachineFunction &MF);
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    bool PeepholeOptimize(MachineBasicBlock &MBB,
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			  MachineBasicBlock::iterator &I);
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    virtual const char *getPassName() const {
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      return "X86 SSA-based Peephole Optimizer";
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    }
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    /// Propagate - Set MI[DestOpNo] = Src[SrcOpNo], optionally change the
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    /// opcode of the instruction, then return true.
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    bool Propagate(MachineInstr *MI, unsigned DestOpNo,
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                   MachineInstr *Src, unsigned SrcOpNo, unsigned NewOpcode = 0){
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      MI->getOperand(DestOpNo) = Src->getOperand(SrcOpNo);
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      if (NewOpcode) MI->setOpcode(NewOpcode);
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      return true;
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    }
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    /// OptimizeAddress - If we can fold the addressing arithmetic for this
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    /// memory instruction into the instruction itself, do so and return true.
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    bool OptimizeAddress(MachineInstr *MI, unsigned OpNo);
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    /// getDefininingInst - If the specified operand is a read of an SSA
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    /// register, return the machine instruction defining it, otherwise, return
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    /// null.
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    MachineInstr *getDefiningInst(MachineOperand &MO) {
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      if (MO.isDef() || !MO.isRegister() ||
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          !MRegisterInfo::isVirtualRegister(MO.getReg())) return 0;
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      return UDC->getDefinition(MO.getReg());
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    }
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    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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      AU.addRequired<UseDefChains>();
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      AU.addPreserved<UseDefChains>();
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      MachineFunctionPass::getAnalysisUsage(AU);
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    }
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  };
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}
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FunctionPass *llvm::createX86SSAPeepholeOptimizerPass() { return new SSAPH(); }
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bool SSAPH::runOnMachineFunction(MachineFunction &MF) {
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  bool Changed = false;
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  bool LocalChanged;
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  UDC = &getAnalysis<UseDefChains>();
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  do {
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    LocalChanged = false;
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    for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI != E; ++BI)
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      for (MachineBasicBlock::iterator I = BI->begin(); I != BI->end(); )
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        if (PeepholeOptimize(*BI, I)) {
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          LocalChanged = true;
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          ++NumSSAPHOpts;
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        } else
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          ++I;
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    Changed |= LocalChanged;
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  } while (LocalChanged);
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  return Changed;
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}
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static bool isValidScaleAmount(unsigned Scale) {
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  return Scale == 1 || Scale == 2 || Scale == 4 || Scale == 8;
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}
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/// OptimizeAddress - If we can fold the addressing arithmetic for this
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/// memory instruction into the instruction itself, do so and return true.
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bool SSAPH::OptimizeAddress(MachineInstr *MI, unsigned OpNo) {
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  MachineOperand &BaseRegOp      = MI->getOperand(OpNo+0);
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  MachineOperand &ScaleOp        = MI->getOperand(OpNo+1);
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  MachineOperand &IndexRegOp     = MI->getOperand(OpNo+2);
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  MachineOperand &DisplacementOp = MI->getOperand(OpNo+3);
 | 
						|
 | 
						|
  unsigned BaseReg  = BaseRegOp.hasAllocatedReg() ? BaseRegOp.getReg() : 0;
 | 
						|
  unsigned Scale    = ScaleOp.getImmedValue();
 | 
						|
  unsigned IndexReg = IndexRegOp.hasAllocatedReg() ? IndexRegOp.getReg() : 0;
 | 
						|
 | 
						|
  bool Changed = false;
 | 
						|
 | 
						|
  // If the base register is unset, and the index register is set with a scale
 | 
						|
  // of 1, move it to be the base register.
 | 
						|
  if (BaseRegOp.hasAllocatedReg() && BaseReg == 0 &&
 | 
						|
      Scale == 1 && IndexReg != 0) {
 | 
						|
    BaseRegOp.setReg(IndexReg);
 | 
						|
    IndexRegOp.setReg(0);
 | 
						|
    return true;
 | 
						|
  }
 | 
						|
 | 
						|
  // Attempt to fold instructions used by the base register into the instruction
 | 
						|
  if (MachineInstr *DefInst = getDefiningInst(BaseRegOp)) {
 | 
						|
    switch (DefInst->getOpcode()) {
 | 
						|
    case X86::MOV32ri:
 | 
						|
      // If there is no displacement set for this instruction set one now.
 | 
						|
      // FIXME: If we can fold two immediates together, we should do so!
 | 
						|
      if (DisplacementOp.isImmediate() && !DisplacementOp.getImmedValue()) {
 | 
						|
        if (DefInst->getOperand(1).isImmediate()) {
 | 
						|
          BaseRegOp.setReg(0);
 | 
						|
          return Propagate(MI, OpNo+3, DefInst, 1);
 | 
						|
        }
 | 
						|
      }
 | 
						|
      break;
 | 
						|
 | 
						|
    case X86::ADD32rr:
 | 
						|
      // If the source is a register-register add, and we do not yet have an
 | 
						|
      // index register, fold the add into the memory address.
 | 
						|
      if (IndexReg == 0) {
 | 
						|
        BaseRegOp = DefInst->getOperand(1);
 | 
						|
        IndexRegOp = DefInst->getOperand(2);
 | 
						|
        ScaleOp.setImmedValue(1);
 | 
						|
        return true;
 | 
						|
      }
 | 
						|
      break;
 | 
						|
 | 
						|
    case X86::SHL32ri:
 | 
						|
      // If this shift could be folded into the index portion of the address if
 | 
						|
      // it were the index register, move it to the index register operand now,
 | 
						|
      // so it will be folded in below.
 | 
						|
      if ((Scale == 1 || (IndexReg == 0 && IndexRegOp.hasAllocatedReg())) &&
 | 
						|
          DefInst->getOperand(2).getImmedValue() < 4) {
 | 
						|
        std::swap(BaseRegOp, IndexRegOp);
 | 
						|
        ScaleOp.setImmedValue(1); Scale = 1;
 | 
						|
        std::swap(IndexReg, BaseReg);
 | 
						|
        Changed = true;
 | 
						|
        break;
 | 
						|
      }
 | 
						|
    }
 | 
						|
  }
 | 
						|
 | 
						|
  // Attempt to fold instructions used by the index into the instruction
 | 
						|
  if (MachineInstr *DefInst = getDefiningInst(IndexRegOp)) {
 | 
						|
    switch (DefInst->getOpcode()) {
 | 
						|
    case X86::SHL32ri: {
 | 
						|
      // Figure out what the resulting scale would be if we folded this shift.
 | 
						|
      unsigned ResScale = Scale * (1 << DefInst->getOperand(2).getImmedValue());
 | 
						|
      if (isValidScaleAmount(ResScale)) {
 | 
						|
        IndexRegOp = DefInst->getOperand(1);
 | 
						|
        ScaleOp.setImmedValue(ResScale);
 | 
						|
        return true;
 | 
						|
      }
 | 
						|
      break;
 | 
						|
    }
 | 
						|
    }
 | 
						|
  }
 | 
						|
 | 
						|
  return Changed;
 | 
						|
}
 | 
						|
 | 
						|
bool SSAPH::PeepholeOptimize(MachineBasicBlock &MBB,
 | 
						|
                             MachineBasicBlock::iterator &I) {
 | 
						|
    MachineBasicBlock::iterator NextI = next(I);
 | 
						|
 | 
						|
  MachineInstr *MI = I;
 | 
						|
  MachineInstr *Next = (NextI != MBB.end()) ? &*NextI : (MachineInstr*)0;
 | 
						|
 | 
						|
  bool Changed = false;
 | 
						|
 | 
						|
  const TargetInstrInfo &TII = MBB.getParent()->getTarget().getInstrInfo();
 | 
						|
 | 
						|
  // Scan the operands of this instruction.  If any operands are
 | 
						|
  // register-register copies, replace the operand with the source.
 | 
						|
  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
 | 
						|
    // Is this an SSA register use?
 | 
						|
    if (MachineInstr *DefInst = getDefiningInst(MI->getOperand(i))) {
 | 
						|
      // If the operand is a vreg-vreg copy, it is always safe to replace the
 | 
						|
      // source value with the input operand.
 | 
						|
      unsigned Source, Dest;
 | 
						|
      if (TII.isMoveInstr(*DefInst, Source, Dest)) {
 | 
						|
        // Don't propagate physical registers into any instructions.
 | 
						|
        if (DefInst->getOperand(1).isRegister() &&
 | 
						|
            MRegisterInfo::isVirtualRegister(Source)) {
 | 
						|
          MI->getOperand(i).setReg(Source);
 | 
						|
          Changed = true;
 | 
						|
          ++NumPHMoves;
 | 
						|
        }
 | 
						|
      }
 | 
						|
    }
 | 
						|
  
 | 
						|
  
 | 
						|
  // Perform instruction specific optimizations.
 | 
						|
  switch (MI->getOpcode()) {
 | 
						|
 | 
						|
    // Register to memory stores.  Format: <base,scale,indexreg,immdisp>, srcreg
 | 
						|
  case X86::MOV32mr: case X86::MOV16mr: case X86::MOV8mr:
 | 
						|
  case X86::MOV32mi: case X86::MOV16mi: case X86::MOV8mi:
 | 
						|
    // Check to see if we can fold the source instruction into this one...
 | 
						|
    if (MachineInstr *SrcInst = getDefiningInst(MI->getOperand(4))) {
 | 
						|
      switch (SrcInst->getOpcode()) {
 | 
						|
        // Fold the immediate value into the store, if possible.
 | 
						|
      case X86::MOV8ri:  return Propagate(MI, 4, SrcInst, 1, X86::MOV8mi);
 | 
						|
      case X86::MOV16ri: return Propagate(MI, 4, SrcInst, 1, X86::MOV16mi);
 | 
						|
      case X86::MOV32ri: return Propagate(MI, 4, SrcInst, 1, X86::MOV32mi);
 | 
						|
      default: break;
 | 
						|
      }
 | 
						|
    }
 | 
						|
 | 
						|
    // If we can optimize the addressing expression, do so now.
 | 
						|
    if (OptimizeAddress(MI, 0))
 | 
						|
      return true;
 | 
						|
    break;
 | 
						|
 | 
						|
  case X86::MOV32rm:
 | 
						|
  case X86::MOV16rm:
 | 
						|
  case X86::MOV8rm:
 | 
						|
    // If we can optimize the addressing expression, do so now.
 | 
						|
    if (OptimizeAddress(MI, 1))
 | 
						|
      return true;
 | 
						|
    break;
 | 
						|
 | 
						|
  default: break;
 | 
						|
  }
 | 
						|
 | 
						|
  return Changed;
 | 
						|
}
 |