llvm/lib/CodeGen/LowerSubregs.cpp
2010-08-06 18:33:48 +00:00

244 lines
8.6 KiB
C++

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