forked from OSchip/llvm-project
87 lines
2.6 KiB
C++
87 lines
2.6 KiB
C++
//===-- PeepholeOptimizer.cpp - X86 Peephole Optimizer --------------------===//
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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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namespace {
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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 *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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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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MachineInstr *MI = *I;
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MachineInstr *Next = (I+1 != MBB.end()) ? *(I+1) : 0;
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unsigned Size = 0;
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switch (MI->getOpcode()) {
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case X86::MOVrr8:
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case X86::MOVrr16:
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case X86::MOVrr32: // 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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delete MI;
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return true;
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}
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return false;
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#if 0
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case X86::MOVir32: Size++;
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case X86::MOVir16: Size++;
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case X86::MOVir8:
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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::XORrr8,X86::XORrr16,X86::XORrr32};
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unsigned Reg = MI->getOperand(0).getReg();
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*I = BuildMI(Opcode[Size], 2, Reg).addReg(Reg).addReg(Reg);
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delete MI;
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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::BSWAPr32: // Change bswap EAX, bswap EAX into nothing
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if (Next->getOpcode() == X86::BSWAPr32 &&
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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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delete MI;
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delete Next;
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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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