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//===-- LowerSubregs.cpp - Subregister Lowering instruction pass ----------===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This file defines a MachineFunction pass which runs after register
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// allocation that turns subreg insert/extract instructions into register
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// copies, as needed. This ensures correct codegen even if the coalescer
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// isn't able to remove all subreg instructions.
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "lowersubregs"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/Function.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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struct LowerSubregsInstructionPass : public MachineFunctionPass {
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const TargetRegisterInfo *TRI;
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const TargetInstrInfo *TII;
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static char ID; // Pass identification, replacement for typeid
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LowerSubregsInstructionPass() : MachineFunctionPass(ID) {}
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const char *getPassName() const {
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return "Subregister lowering instruction pass";
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addPreservedID(MachineLoopInfoID);
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AU.addPreservedID(MachineDominatorsID);
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MachineFunctionPass::getAnalysisUsage(AU);
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/// runOnMachineFunction - pass entry point
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bool runOnMachineFunction(MachineFunction&);
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bool LowerSubregToReg(MachineInstr *MI);
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bool LowerCopy(MachineInstr *MI);
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void TransferDeadFlag(MachineInstr *MI, unsigned DstReg,
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const TargetRegisterInfo *TRI);
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void TransferImplicitDefs(MachineInstr *MI);
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char LowerSubregsInstructionPass::ID = 0;
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FunctionPass *llvm::createLowerSubregsPass() {
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return new LowerSubregsInstructionPass();
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/// TransferDeadFlag - MI is a pseudo-instruction with DstReg dead,
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/// and the lowered replacement instructions immediately precede it.
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/// Mark the replacement instructions with the dead flag.
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LowerSubregsInstructionPass::TransferDeadFlag(MachineInstr *MI,
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const TargetRegisterInfo *TRI) {
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for (MachineBasicBlock::iterator MII =
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prior(MachineBasicBlock::iterator(MI)); ; --MII) {
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if (MII->addRegisterDead(DstReg, TRI))
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assert(MII != MI->getParent()->begin() &&
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"copyPhysReg output doesn't reference destination register!");
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/// TransferImplicitDefs - MI is a pseudo-instruction, and the lowered
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/// replacement instructions immediately precede it. Copy any implicit-def
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/// operands from MI to the replacement instruction.
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LowerSubregsInstructionPass::TransferImplicitDefs(MachineInstr *MI) {
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MachineBasicBlock::iterator CopyMI = MI;
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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MachineOperand &MO = MI->getOperand(i);
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if (!MO.isReg() || !MO.isImplicit() || MO.isUse())
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CopyMI->addOperand(MachineOperand::CreateReg(MO.getReg(), true, true));
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bool LowerSubregsInstructionPass::LowerSubregToReg(MachineInstr *MI) {
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MachineBasicBlock *MBB = MI->getParent();
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assert((MI->getOperand(0).isReg() && MI->getOperand(0).isDef()) &&
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MI->getOperand(1).isImm() &&
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(MI->getOperand(2).isReg() && MI->getOperand(2).isUse()) &&
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MI->getOperand(3).isImm() && "Invalid subreg_to_reg");
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unsigned DstReg = MI->getOperand(0).getReg();
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unsigned InsReg = MI->getOperand(2).getReg();
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assert(!MI->getOperand(2).getSubReg() && "SubIdx on physreg?");
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unsigned SubIdx = MI->getOperand(3).getImm();
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assert(SubIdx != 0 && "Invalid index for insert_subreg");
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unsigned DstSubReg = TRI->getSubReg(DstReg, SubIdx);
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assert(TargetRegisterInfo::isPhysicalRegister(DstReg) &&
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"Insert destination must be in a physical register");
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assert(TargetRegisterInfo::isPhysicalRegister(InsReg) &&
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"Inserted value must be in a physical register");
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DEBUG(dbgs() << "subreg: CONVERTING: " << *MI);
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if (DstSubReg == InsReg) {
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// No need to insert an identify copy instruction.
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// Watch out for case like this:
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// %RAX<def> = SUBREG_TO_REG 0, %EAX<kill>, 3
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// We must leave %RAX live.
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if (DstReg != InsReg) {
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MI->setDesc(TII->get(TargetOpcode::KILL));
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MI->RemoveOperand(3); // SubIdx
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MI->RemoveOperand(1); // Imm
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DEBUG(dbgs() << "subreg: replace by: " << *MI);
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DEBUG(dbgs() << "subreg: eliminated!");
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TII->copyPhysReg(*MBB, MI, MI->getDebugLoc(), DstSubReg, InsReg,
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MI->getOperand(2).isKill());
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// Transfer the kill/dead flags, if needed.
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if (MI->getOperand(0).isDead())
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TransferDeadFlag(MI, DstSubReg, TRI);
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MachineBasicBlock::iterator dMI = MI;
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dbgs() << "subreg: " << *(--dMI);
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DEBUG(dbgs() << '\n');
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bool LowerSubregsInstructionPass::LowerCopy(MachineInstr *MI) {
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MachineOperand &DstMO = MI->getOperand(0);
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MachineOperand &SrcMO = MI->getOperand(1);
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if (SrcMO.getReg() == DstMO.getReg()) {
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DEBUG(dbgs() << "identity copy: " << *MI);
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// No need to insert an identity copy instruction, but replace with a KILL
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// if liveness is changed.
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if (DstMO.isDead() || SrcMO.isUndef() || MI->getNumOperands() > 2) {
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// We must make sure the super-register gets killed. Replace the
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// instruction with KILL.
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MI->setDesc(TII->get(TargetOpcode::KILL));
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DEBUG(dbgs() << "replaced by: " << *MI);
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// Vanilla identity copy.
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MI->eraseFromParent();
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DEBUG(dbgs() << "real copy: " << *MI);
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TII->copyPhysReg(*MI->getParent(), MI, MI->getDebugLoc(),
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DstMO.getReg(), SrcMO.getReg(), SrcMO.isKill());
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TransferDeadFlag(MI, DstMO.getReg(), TRI);
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if (MI->getNumOperands() > 2)
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TransferImplicitDefs(MI);
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MachineBasicBlock::iterator dMI = MI;
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dbgs() << "replaced by: " << *(--dMI);
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MI->eraseFromParent();
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/// runOnMachineFunction - Reduce subregister inserts and extracts to register
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bool LowerSubregsInstructionPass::runOnMachineFunction(MachineFunction &MF) {
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DEBUG(dbgs() << "Machine Function\n"
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<< "********** LOWERING SUBREG INSTRS **********\n"
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<< "********** Function: "
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<< MF.getFunction()->getName() << '\n');
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TRI = MF.getTarget().getRegisterInfo();
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TII = MF.getTarget().getInstrInfo();
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bool MadeChange = false;
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for (MachineFunction::iterator mbbi = MF.begin(), mbbe = MF.end();
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mbbi != mbbe; ++mbbi) {
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for (MachineBasicBlock::iterator mi = mbbi->begin(), me = mbbi->end();
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MachineBasicBlock::iterator nmi = llvm::next(mi);
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MachineInstr *MI = mi;
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assert(!MI->isInsertSubreg() && "INSERT_SUBREG should no longer appear");
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assert(MI->getOpcode() != TargetOpcode::EXTRACT_SUBREG &&
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"EXTRACT_SUBREG should no longer appear");
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if (MI->isSubregToReg()) {
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MadeChange |= LowerSubregToReg(MI);
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} else if (MI->isCopy()) {
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MadeChange |= LowerCopy(MI);