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//===-- 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"; }
};
}
FunctionPass *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;
// A large number of X86 instructions have forms which take an 8-bit
// immediate despite the fact that the operands are 16 or 32 bits. Because
// this can save three bytes of code size (and icache space), we want to
// shrink them if possible.
case X86::ADDri16: case X86::ADDri32:
case X86::SUBri16: case X86::SUBri32:
case X86::IMULri16: case X86::IMULri32:
case X86::ANDri16: case X86::ANDri32:
case X86::ORri16: case X86::ORri32:
case X86::XORri16: case X86::XORri32:
assert(MI->getNumOperands() == 3 && "These should all have 3 operands!");
if (MI->getOperand(2).isImmediate()) {
int Val = MI->getOperand(2).getImmedValue();
// If the value is the same when signed extended from 8 bits...
if (Val == (signed int)(signed char)Val) {
unsigned Opcode;
switch (MI->getOpcode()) {
default: assert(0 && "Unknown opcode value!");
case X86::ADDri16: Opcode = X86::ADDri16b; break;
case X86::ADDri32: Opcode = X86::ADDri32b; break;
case X86::SUBri16: Opcode = X86::SUBri16b; break;
case X86::SUBri32: Opcode = X86::SUBri32b; break;
case X86::IMULri16: Opcode = X86::IMULri16b; break;
case X86::IMULri32: Opcode = X86::IMULri32b; break;
case X86::ANDri16: Opcode = X86::ANDri16b; break;
case X86::ANDri32: Opcode = X86::ANDri32b; break;
case X86::ORri16: Opcode = X86::ORri16b; break;
case X86::ORri32: Opcode = X86::ORri32b; break;
case X86::XORri16: Opcode = X86::XORri16b; break;
case X86::XORri32: Opcode = X86::XORri32b; break;
}
unsigned R0 = MI->getOperand(0).getReg();
unsigned R1 = MI->getOperand(1).getReg();
*I = BuildMI(Opcode, 2, R0).addReg(R1).addZImm((char)Val);
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;
}
}
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