//===-- PeepholeOptimizer.cpp - X86 Peephole Optimizer --------------------===// // // This file contains a peephole optimizer for the X86. // //===----------------------------------------------------------------------===// #include "X86.h" #include "llvm/CodeGen/MachineFunctionPass.h" #include "llvm/CodeGen/MachineInstrBuilder.h" namespace { struct PH : public MachineFunctionPass { virtual bool runOnMachineFunction(MachineFunction &MF); bool PeepholeOptimize(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I); virtual const char *getPassName() const { return "X86 Peephole Optimizer"; } }; } Pass *createX86PeepholeOptimizerPass() { return new PH(); } bool PH::runOnMachineFunction(MachineFunction &MF) { bool Changed = false; for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI != E; ++BI) for (MachineBasicBlock::iterator I = BI->begin(); I != BI->end(); ) if (PeepholeOptimize(*BI, I)) Changed = true; else ++I; return Changed; } bool PH::PeepholeOptimize(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I) { MachineInstr *MI = *I; MachineInstr *Next = (I+1 != MBB.end()) ? *(I+1) : 0; unsigned Size = 0; switch (MI->getOpcode()) { case X86::MOVrr8: case X86::MOVrr16: case X86::MOVrr32: // Destroy X = X copies... if (MI->getOperand(0).getReg() == MI->getOperand(1).getReg()) { I = MBB.erase(I); delete MI; return true; } return false; #if 0 case X86::MOVir32: Size++; case X86::MOVir16: Size++; case X86::MOVir8: // FIXME: We can only do this transformation if we know that flags are not // used here, because XOR clobbers the flags! if (MI->getOperand(1).isImmediate()) { // avoid mov EAX, <value> int Val = MI->getOperand(1).getImmedValue(); if (Val == 0) { // mov EAX, 0 -> xor EAX, EAX static const unsigned Opcode[] ={X86::XORrr8,X86::XORrr16,X86::XORrr32}; unsigned Reg = MI->getOperand(0).getReg(); *I = BuildMI(Opcode[Size], 2, Reg).addReg(Reg).addReg(Reg); delete MI; return true; } else if (Val == -1) { // mov EAX, -1 -> or EAX, -1 // TODO: 'or Reg, -1' has a smaller encoding than 'mov Reg, -1' } } return false; #endif case X86::BSWAPr32: // Change bswap EAX, bswap EAX into nothing if (Next->getOpcode() == X86::BSWAPr32 && MI->getOperand(0).getReg() == Next->getOperand(0).getReg()) { I = MBB.erase(MBB.erase(I)); delete MI; delete Next; return true; } return false; default: return false; } }