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//===-- ExpandPostRAPseudos.cpp - Pseudo instruction expansion 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 pass that expands COPY and SUBREG_TO_REG pseudo
// instructions after register allocation.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
#define DEBUG_TYPE "postrapseudos"
namespace {
struct ExpandPostRA : public MachineFunctionPass {
private:
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
public:
static char ID; // Pass identification, replacement for typeid
ExpandPostRA() : MachineFunctionPass(ID) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addPreservedID(MachineLoopInfoID);
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
/// runOnMachineFunction - pass entry point
bool runOnMachineFunction(MachineFunction&) override;
private:
bool LowerSubregToReg(MachineInstr *MI);
bool LowerCopy(MachineInstr *MI);
void TransferImplicitDefs(MachineInstr *MI);
};
} // end anonymous namespace
char ExpandPostRA::ID = 0;
char &llvm::ExpandPostRAPseudosID = ExpandPostRA::ID;
INITIALIZE_PASS(ExpandPostRA, "postrapseudos",
"Post-RA pseudo instruction expansion pass", false, false)
/// 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
ExpandPostRA::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 ExpandPostRA::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 (MI->allDefsAreDead()) {
MI->setDesc(TII->get(TargetOpcode::KILL));
DEBUG(dbgs() << "subreg: replaced by: " << *MI);
return true;
}
if (DstSubReg == InsReg) {
// No need to insert an identity 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());
// Implicitly define DstReg for subsequent uses.
MachineBasicBlock::iterator CopyMI = MI;
--CopyMI;
CopyMI->addRegisterDefined(DstReg);
DEBUG(dbgs() << "subreg: " << *CopyMI);
}
DEBUG(dbgs() << '\n');
MBB->erase(MI);
return true;
}
bool ExpandPostRA::LowerCopy(MachineInstr *MI) {
if (MI->allDefsAreDead()) {
DEBUG(dbgs() << "dead copy: " << *MI);
MI->setDesc(TII->get(TargetOpcode::KILL));
DEBUG(dbgs() << "replaced by: " << *MI);
return true;
}
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 (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 (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 ExpandPostRA::runOnMachineFunction(MachineFunction &MF) {
DEBUG(dbgs() << "Machine Function\n"
<< "********** EXPANDING POST-RA PSEUDO INSTRS **********\n"
<< "********** Function: " << MF.getName() << '\n');
TRI = MF.getSubtarget().getRegisterInfo();
TII = MF.getSubtarget().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;) {
MachineInstr *MI = mi;
// Advance iterator here because MI may be erased.
++mi;
// Only expand pseudos.
if (!MI->isPseudo())
continue;
// Give targets a chance to expand even standard pseudos.
if (TII->expandPostRAPseudo(MI)) {
MadeChange = true;
continue;
}
// Expand standard pseudos.
switch (MI->getOpcode()) {
case TargetOpcode::SUBREG_TO_REG:
MadeChange |= LowerSubregToReg(MI);
break;
case TargetOpcode::COPY:
MadeChange |= LowerCopy(MI);
break;
case TargetOpcode::DBG_VALUE:
continue;
case TargetOpcode::INSERT_SUBREG:
case TargetOpcode::EXTRACT_SUBREG:
llvm_unreachable("Sub-register pseudos should have been eliminated.");
}
}
}
return MadeChange;
}
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