1 //===-- PeepholeOptimizer.cpp - X86 Peephole Optimizer --------------------===//
3 // This file contains a peephole optimizer for the X86.
5 //===----------------------------------------------------------------------===//
8 #include "llvm/CodeGen/MachineFunctionPass.h"
9 #include "llvm/CodeGen/MachineInstrBuilder.h"
12 struct PH : public MachineFunctionPass {
13 virtual bool runOnMachineFunction(MachineFunction &MF);
15 bool PeepholeOptimize(MachineBasicBlock &MBB,
16 MachineBasicBlock::iterator &I);
18 virtual const char *getPassName() const { return "X86 Peephole Optimizer"; }
22 FunctionPass *createX86PeepholeOptimizerPass() { return new PH(); }
24 bool PH::runOnMachineFunction(MachineFunction &MF) {
27 for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI != E; ++BI)
28 for (MachineBasicBlock::iterator I = BI->begin(); I != BI->end(); )
29 if (PeepholeOptimize(*BI, I))
38 bool PH::PeepholeOptimize(MachineBasicBlock &MBB,
39 MachineBasicBlock::iterator &I) {
40 MachineInstr *MI = *I;
41 MachineInstr *Next = (I+1 != MBB.end()) ? *(I+1) : 0;
43 switch (MI->getOpcode()) {
46 case X86::MOVrr32: // Destroy X = X copies...
47 if (MI->getOperand(0).getReg() == MI->getOperand(1).getReg()) {
55 case X86::MOVir32: Size++;
56 case X86::MOVir16: Size++;
58 // FIXME: We can only do this transformation if we know that flags are not
59 // used here, because XOR clobbers the flags!
60 if (MI->getOperand(1).isImmediate()) { // avoid mov EAX, <value>
61 int Val = MI->getOperand(1).getImmedValue();
62 if (Val == 0) { // mov EAX, 0 -> xor EAX, EAX
63 static const unsigned Opcode[] ={X86::XORrr8,X86::XORrr16,X86::XORrr32};
64 unsigned Reg = MI->getOperand(0).getReg();
65 *I = BuildMI(Opcode[Size], 2, Reg).addReg(Reg).addReg(Reg);
68 } else if (Val == -1) { // mov EAX, -1 -> or EAX, -1
69 // TODO: 'or Reg, -1' has a smaller encoding than 'mov Reg, -1'
74 case X86::BSWAPr32: // Change bswap EAX, bswap EAX into nothing
75 if (Next->getOpcode() == X86::BSWAPr32 &&
76 MI->getOperand(0).getReg() == Next->getOperand(0).getReg()) {
77 I = MBB.erase(MBB.erase(I));