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llvm/lib/CodeGen/RegAllocFast.cpp
Jakob Stoklund Olesen d9e5c764bf Freeze reserved registers before starting register allocation. 
The register allocators don't currently support adding reserved
registers while they are running.  Extend the MRI API to keep track of
the set of reserved registers when register allocation started.

Target hooks like hasFP() and needsStackRealignment() can look at this
set to avoid reserving more registers during register allocation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147577 91177308-0d34-0410-b5e6-96231b3b80d8
2012-01-05 00:26:49 +00:00

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//===-- RegAllocFast.cpp - A fast register allocator for debug code -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This register allocator allocates registers to a basic block at a time,
// attempting to keep values in registers and reusing registers as appropriate.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "RegisterClassInfo.h"
#include "llvm/BasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/IndexedMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
using namespace llvm;
STATISTIC(NumStores, "Number of stores added");
STATISTIC(NumLoads , "Number of loads added");
STATISTIC(NumCopies, "Number of copies coalesced");
static RegisterRegAlloc
fastRegAlloc("fast", "fast register allocator", createFastRegisterAllocator);
namespace {
class RAFast : public MachineFunctionPass {
public:
static char ID;
RAFast() : MachineFunctionPass(ID), StackSlotForVirtReg(-1),
isBulkSpilling(false) {
initializePHIEliminationPass(*PassRegistry::getPassRegistry());
initializeTwoAddressInstructionPassPass(*PassRegistry::getPassRegistry());
}
private:
const TargetMachine *TM;
MachineFunction *MF;
MachineRegisterInfo *MRI;
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
RegisterClassInfo RegClassInfo;
// Basic block currently being allocated.
MachineBasicBlock *MBB;
// StackSlotForVirtReg - Maps virtual regs to the frame index where these
// values are spilled.
IndexedMap<int, VirtReg2IndexFunctor> StackSlotForVirtReg;
// Everything we know about a live virtual register.
struct LiveReg {
MachineInstr *LastUse; // Last instr to use reg.
unsigned PhysReg; // Currently held here.
unsigned short LastOpNum; // OpNum on LastUse.
bool Dirty; // Register needs spill.
LiveReg(unsigned p=0) : LastUse(0), PhysReg(p), LastOpNum(0),
Dirty(false) {}
};
typedef DenseMap<unsigned, LiveReg> LiveRegMap;
typedef LiveRegMap::value_type LiveRegEntry;
// LiveVirtRegs - This map contains entries for each virtual register
// that is currently available in a physical register.
LiveRegMap LiveVirtRegs;
DenseMap<unsigned, SmallVector<MachineInstr *, 4> > LiveDbgValueMap;
// RegState - Track the state of a physical register.
enum RegState {
// A disabled register is not available for allocation, but an alias may
// be in use. A register can only be moved out of the disabled state if
// all aliases are disabled.
regDisabled,
// A free register is not currently in use and can be allocated
// immediately without checking aliases.
regFree,
// A reserved register has been assigned explicitly (e.g., setting up a
// call parameter), and it remains reserved until it is used.
regReserved
// A register state may also be a virtual register number, indication that
// the physical register is currently allocated to a virtual register. In
// that case, LiveVirtRegs contains the inverse mapping.
};
// PhysRegState - One of the RegState enums, or a virtreg.
std::vector<unsigned> PhysRegState;
// UsedInInstr - BitVector of physregs that are used in the current
// instruction, and so cannot be allocated.
BitVector UsedInInstr;
// SkippedInstrs - Descriptors of instructions whose clobber list was
// ignored because all registers were spilled. It is still necessary to
// mark all the clobbered registers as used by the function.
SmallPtrSet<const MCInstrDesc*, 4> SkippedInstrs;
// isBulkSpilling - This flag is set when LiveRegMap will be cleared
// completely after spilling all live registers. LiveRegMap entries should
// not be erased.
bool isBulkSpilling;
enum {
spillClean = 1,
spillDirty = 100,
spillImpossible = ~0u
};
public:
virtual const char *getPassName() const {
return "Fast Register Allocator";
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequiredID(PHIEliminationID);
AU.addRequiredID(TwoAddressInstructionPassID);
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
bool runOnMachineFunction(MachineFunction &Fn);
void AllocateBasicBlock();
void handleThroughOperands(MachineInstr *MI,
SmallVectorImpl<unsigned> &VirtDead);
int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC);
bool isLastUseOfLocalReg(MachineOperand&);
void addKillFlag(const LiveReg&);
void killVirtReg(LiveRegMap::iterator);
void killVirtReg(unsigned VirtReg);
void spillVirtReg(MachineBasicBlock::iterator MI, LiveRegMap::iterator);
void spillVirtReg(MachineBasicBlock::iterator MI, unsigned VirtReg);
void usePhysReg(MachineOperand&);
void definePhysReg(MachineInstr *MI, unsigned PhysReg, RegState NewState);
unsigned calcSpillCost(unsigned PhysReg) const;
void assignVirtToPhysReg(LiveRegEntry &LRE, unsigned PhysReg);
void allocVirtReg(MachineInstr *MI, LiveRegEntry &LRE, unsigned Hint);
LiveRegMap::iterator defineVirtReg(MachineInstr *MI, unsigned OpNum,
unsigned VirtReg, unsigned Hint);
LiveRegMap::iterator reloadVirtReg(MachineInstr *MI, unsigned OpNum,
unsigned VirtReg, unsigned Hint);
void spillAll(MachineInstr *MI);
bool setPhysReg(MachineInstr *MI, unsigned OpNum, unsigned PhysReg);
};
char RAFast::ID = 0;
}
/// getStackSpaceFor - This allocates space for the specified virtual register
/// to be held on the stack.
int RAFast::getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC) {
// Find the location Reg would belong...
int SS = StackSlotForVirtReg[VirtReg];
if (SS != -1)
return SS; // Already has space allocated?
// Allocate a new stack object for this spill location...
int FrameIdx = MF->getFrameInfo()->CreateSpillStackObject(RC->getSize(),
RC->getAlignment());
// Assign the slot.
StackSlotForVirtReg[VirtReg] = FrameIdx;
return FrameIdx;
}
/// isLastUseOfLocalReg - Return true if MO is the only remaining reference to
/// its virtual register, and it is guaranteed to be a block-local register.
///
bool RAFast::isLastUseOfLocalReg(MachineOperand &MO) {
// Check for non-debug uses or defs following MO.
// This is the most likely way to fail - fast path it.
MachineOperand *Next = &MO;
while ((Next = Next->getNextOperandForReg()))
if (!Next->isDebug())
return false;
// If the register has ever been spilled or reloaded, we conservatively assume
// it is a global register used in multiple blocks.
if (StackSlotForVirtReg[MO.getReg()] != -1)
return false;
// Check that the use/def chain has exactly one operand - MO.
return &MRI->reg_nodbg_begin(MO.getReg()).getOperand() == &MO;
}
/// addKillFlag - Set kill flags on last use of a virtual register.
void RAFast::addKillFlag(const LiveReg &LR) {
if (!LR.LastUse) return;
MachineOperand &MO = LR.LastUse->getOperand(LR.LastOpNum);
if (MO.isUse() && !LR.LastUse->isRegTiedToDefOperand(LR.LastOpNum)) {
if (MO.getReg() == LR.PhysReg)
MO.setIsKill();
else
LR.LastUse->addRegisterKilled(LR.PhysReg, TRI, true);
}
}
/// killVirtReg - Mark virtreg as no longer available.
void RAFast::killVirtReg(LiveRegMap::iterator LRI) {
addKillFlag(LRI->second);
const LiveReg &LR = LRI->second;
assert(PhysRegState[LR.PhysReg] == LRI->first && "Broken RegState mapping");
PhysRegState[LR.PhysReg] = regFree;
// Erase from LiveVirtRegs unless we're spilling in bulk.
if (!isBulkSpilling)
LiveVirtRegs.erase(LRI);
}
/// killVirtReg - Mark virtreg as no longer available.
void RAFast::killVirtReg(unsigned VirtReg) {
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"killVirtReg needs a virtual register");
LiveRegMap::iterator LRI = LiveVirtRegs.find(VirtReg);
if (LRI != LiveVirtRegs.end())
killVirtReg(LRI);
}
/// spillVirtReg - This method spills the value specified by VirtReg into the
/// corresponding stack slot if needed.
void RAFast::spillVirtReg(MachineBasicBlock::iterator MI, unsigned VirtReg) {
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Spilling a physical register is illegal!");
LiveRegMap::iterator LRI = LiveVirtRegs.find(VirtReg);
assert(LRI != LiveVirtRegs.end() && "Spilling unmapped virtual register");
spillVirtReg(MI, LRI);
}
/// spillVirtReg - Do the actual work of spilling.
void RAFast::spillVirtReg(MachineBasicBlock::iterator MI,
LiveRegMap::iterator LRI) {
LiveReg &LR = LRI->second;
assert(PhysRegState[LR.PhysReg] == LRI->first && "Broken RegState mapping");
if (LR.Dirty) {
// If this physreg is used by the instruction, we want to kill it on the
// instruction, not on the spill.
bool SpillKill = LR.LastUse != MI;
LR.Dirty = false;
DEBUG(dbgs() << "Spilling " << PrintReg(LRI->first, TRI)
<< " in " << PrintReg(LR.PhysReg, TRI));
const TargetRegisterClass *RC = MRI->getRegClass(LRI->first);
int FI = getStackSpaceFor(LRI->first, RC);
DEBUG(dbgs() << " to stack slot #" << FI << "\n");
TII->storeRegToStackSlot(*MBB, MI, LR.PhysReg, SpillKill, FI, RC, TRI);
++NumStores; // Update statistics
// If this register is used by DBG_VALUE then insert new DBG_VALUE to
// identify spilled location as the place to find corresponding variable's
// value.
SmallVector<MachineInstr *, 4> &LRIDbgValues = LiveDbgValueMap[LRI->first];
for (unsigned li = 0, le = LRIDbgValues.size(); li != le; ++li) {
MachineInstr *DBG = LRIDbgValues[li];
const MDNode *MDPtr =
DBG->getOperand(DBG->getNumOperands()-1).getMetadata();
int64_t Offset = 0;
if (DBG->getOperand(1).isImm())
Offset = DBG->getOperand(1).getImm();
DebugLoc DL;
if (MI == MBB->end()) {
// If MI is at basic block end then use last instruction's location.
MachineBasicBlock::iterator EI = MI;
DL = (--EI)->getDebugLoc();
}
else
DL = MI->getDebugLoc();
if (MachineInstr *NewDV =
TII->emitFrameIndexDebugValue(*MF, FI, Offset, MDPtr, DL)) {
MachineBasicBlock *MBB = DBG->getParent();
MBB->insert(MI, NewDV);
DEBUG(dbgs() << "Inserting debug info due to spill:" << "\n" << *NewDV);
}
}
// Now this register is spilled there is should not be any DBG_VALUE pointing
// to this register because they are all pointing to spilled value now.
LRIDbgValues.clear();
if (SpillKill)
LR.LastUse = 0; // Don't kill register again
}
killVirtReg(LRI);
}
/// spillAll - Spill all dirty virtregs without killing them.
void RAFast::spillAll(MachineInstr *MI) {
if (LiveVirtRegs.empty()) return;
isBulkSpilling = true;
// The LiveRegMap is keyed by an unsigned (the virtreg number), so the order
// of spilling here is deterministic, if arbitrary.
for (LiveRegMap::iterator i = LiveVirtRegs.begin(), e = LiveVirtRegs.end();
i != e; ++i)
spillVirtReg(MI, i);
LiveVirtRegs.clear();
isBulkSpilling = false;
}
/// usePhysReg - Handle the direct use of a physical register.
/// Check that the register is not used by a virtreg.
/// Kill the physreg, marking it free.
/// This may add implicit kills to MO->getParent() and invalidate MO.
void RAFast::usePhysReg(MachineOperand &MO) {
unsigned PhysReg = MO.getReg();
assert(TargetRegisterInfo::isPhysicalRegister(PhysReg) &&
"Bad usePhysReg operand");
switch (PhysRegState[PhysReg]) {
case regDisabled:
break;
case regReserved:
PhysRegState[PhysReg] = regFree;
// Fall through
case regFree:
UsedInInstr.set(PhysReg);
MO.setIsKill();
return;
default:
// The physreg was allocated to a virtual register. That means the value we
// wanted has been clobbered.
llvm_unreachable("Instruction uses an allocated register");
}
// Maybe a superregister is reserved?
for (const unsigned *AS = TRI->getAliasSet(PhysReg);
unsigned Alias = *AS; ++AS) {
switch (PhysRegState[Alias]) {
case regDisabled:
break;
case regReserved:
assert(TRI->isSuperRegister(PhysReg, Alias) &&
"Instruction is not using a subregister of a reserved register");
// Leave the superregister in the working set.
PhysRegState[Alias] = regFree;
UsedInInstr.set(Alias);
MO.getParent()->addRegisterKilled(Alias, TRI, true);
return;
case regFree:
if (TRI->isSuperRegister(PhysReg, Alias)) {
// Leave the superregister in the working set.
UsedInInstr.set(Alias);
MO.getParent()->addRegisterKilled(Alias, TRI, true);
return;
}
// Some other alias was in the working set - clear it.
PhysRegState[Alias] = regDisabled;
break;
default:
llvm_unreachable("Instruction uses an alias of an allocated register");
}
}
// All aliases are disabled, bring register into working set.
PhysRegState[PhysReg] = regFree;
UsedInInstr.set(PhysReg);
MO.setIsKill();
}
/// definePhysReg - Mark PhysReg as reserved or free after spilling any
/// virtregs. This is very similar to defineVirtReg except the physreg is
/// reserved instead of allocated.
void RAFast::definePhysReg(MachineInstr *MI, unsigned PhysReg,
RegState NewState) {
UsedInInstr.set(PhysReg);
switch (unsigned VirtReg = PhysRegState[PhysReg]) {
case regDisabled:
break;
default:
spillVirtReg(MI, VirtReg);
// Fall through.
case regFree:
case regReserved:
PhysRegState[PhysReg] = NewState;
return;
}
// This is a disabled register, disable all aliases.
PhysRegState[PhysReg] = NewState;
for (const unsigned *AS = TRI->getAliasSet(PhysReg);
unsigned Alias = *AS; ++AS) {
switch (unsigned VirtReg = PhysRegState[Alias]) {
case regDisabled:
break;
default:
spillVirtReg(MI, VirtReg);
// Fall through.
case regFree:
case regReserved:
PhysRegState[Alias] = regDisabled;
if (TRI->isSuperRegister(PhysReg, Alias))
return;
break;
}
}
}
// calcSpillCost - Return the cost of spilling clearing out PhysReg and
// aliases so it is free for allocation.
// Returns 0 when PhysReg is free or disabled with all aliases disabled - it
// can be allocated directly.
// Returns spillImpossible when PhysReg or an alias can't be spilled.
unsigned RAFast::calcSpillCost(unsigned PhysReg) const {
if (UsedInInstr.test(PhysReg)) {
DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " is already used in instr.\n");
return spillImpossible;
}
switch (unsigned VirtReg = PhysRegState[PhysReg]) {
case regDisabled:
break;
case regFree:
return 0;
case regReserved:
DEBUG(dbgs() << PrintReg(VirtReg, TRI) << " corresponding "
<< PrintReg(PhysReg, TRI) << " is reserved already.\n");
return spillImpossible;
default:
return LiveVirtRegs.lookup(VirtReg).Dirty ? spillDirty : spillClean;
}
// This is a disabled register, add up cost of aliases.
DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " is disabled.\n");
unsigned Cost = 0;
for (const unsigned *AS = TRI->getAliasSet(PhysReg);
unsigned Alias = *AS; ++AS) {
if (UsedInInstr.test(Alias))
return spillImpossible;
switch (unsigned VirtReg = PhysRegState[Alias]) {
case regDisabled:
break;
case regFree:
++Cost;
break;
case regReserved:
return spillImpossible;
default:
Cost += LiveVirtRegs.lookup(VirtReg).Dirty ? spillDirty : spillClean;
break;
}
}
return Cost;
}
/// assignVirtToPhysReg - This method updates local state so that we know
/// that PhysReg is the proper container for VirtReg now. The physical
/// register must not be used for anything else when this is called.
///
void RAFast::assignVirtToPhysReg(LiveRegEntry &LRE, unsigned PhysReg) {
DEBUG(dbgs() << "Assigning " << PrintReg(LRE.first, TRI) << " to "
<< PrintReg(PhysReg, TRI) << "\n");
PhysRegState[PhysReg] = LRE.first;
assert(!LRE.second.PhysReg && "Already assigned a physreg");
LRE.second.PhysReg = PhysReg;
}
/// allocVirtReg - Allocate a physical register for VirtReg.
void RAFast::allocVirtReg(MachineInstr *MI, LiveRegEntry &LRE, unsigned Hint) {
const unsigned VirtReg = LRE.first;
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Can only allocate virtual registers");
const TargetRegisterClass *RC = MRI->getRegClass(VirtReg);
// Ignore invalid hints.
if (Hint && (!TargetRegisterInfo::isPhysicalRegister(Hint) ||
!RC->contains(Hint) || !RegClassInfo.isAllocatable(Hint)))
Hint = 0;
// Take hint when possible.
if (Hint) {
// Ignore the hint if we would have to spill a dirty register.
unsigned Cost = calcSpillCost(Hint);
if (Cost < spillDirty) {
if (Cost)
definePhysReg(MI, Hint, regFree);
return assignVirtToPhysReg(LRE, Hint);
}
}
ArrayRef<unsigned> AO = RegClassInfo.getOrder(RC);
// First try to find a completely free register.
for (ArrayRef<unsigned>::iterator I = AO.begin(), E = AO.end(); I != E; ++I) {
unsigned PhysReg = *I;
if (PhysRegState[PhysReg] == regFree && !UsedInInstr.test(PhysReg))
return assignVirtToPhysReg(LRE, PhysReg);
}
DEBUG(dbgs() << "Allocating " << PrintReg(VirtReg) << " from "
<< RC->getName() << "\n");
unsigned BestReg = 0, BestCost = spillImpossible;
for (ArrayRef<unsigned>::iterator I = AO.begin(), E = AO.end(); I != E; ++I) {
unsigned Cost = calcSpillCost(*I);
DEBUG(dbgs() << "\tRegister: " << PrintReg(*I, TRI) << "\n");
DEBUG(dbgs() << "\tCost: " << Cost << "\n");
DEBUG(dbgs() << "\tBestCost: " << BestCost << "\n");
// Cost is 0 when all aliases are already disabled.
if (Cost == 0)
return assignVirtToPhysReg(LRE, *I);
if (Cost < BestCost)
BestReg = *I, BestCost = Cost;
}
if (BestReg) {
definePhysReg(MI, BestReg, regFree);
return assignVirtToPhysReg(LRE, BestReg);
}
// Nothing we can do. Report an error and keep going with a bad allocation.
MI->emitError("ran out of registers during register allocation");
definePhysReg(MI, *AO.begin(), regFree);
assignVirtToPhysReg(LRE, *AO.begin());
}
/// defineVirtReg - Allocate a register for VirtReg and mark it as dirty.
RAFast::LiveRegMap::iterator
RAFast::defineVirtReg(MachineInstr *MI, unsigned OpNum,
unsigned VirtReg, unsigned Hint) {
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Not a virtual register");
LiveRegMap::iterator LRI;
bool New;
tie(LRI, New) = LiveVirtRegs.insert(std::make_pair(VirtReg, LiveReg()));
LiveReg &LR = LRI->second;
if (New) {
// If there is no hint, peek at the only use of this register.
if ((!Hint || !TargetRegisterInfo::isPhysicalRegister(Hint)) &&
MRI->hasOneNonDBGUse(VirtReg)) {
const MachineInstr &UseMI = *MRI->use_nodbg_begin(VirtReg);
// It's a copy, use the destination register as a hint.
if (UseMI.isCopyLike())
Hint = UseMI.getOperand(0).getReg();
}
allocVirtReg(MI, *LRI, Hint);
} else if (LR.LastUse) {
// Redefining a live register - kill at the last use, unless it is this
// instruction defining VirtReg multiple times.
if (LR.LastUse != MI || LR.LastUse->getOperand(LR.LastOpNum).isUse())
addKillFlag(LR);
}
assert(LR.PhysReg && "Register not assigned");
LR.LastUse = MI;
LR.LastOpNum = OpNum;
LR.Dirty = true;
UsedInInstr.set(LR.PhysReg);
return LRI;
}
/// reloadVirtReg - Make sure VirtReg is available in a physreg and return it.
RAFast::LiveRegMap::iterator
RAFast::reloadVirtReg(MachineInstr *MI, unsigned OpNum,
unsigned VirtReg, unsigned Hint) {
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Not a virtual register");
LiveRegMap::iterator LRI;
bool New;
tie(LRI, New) = LiveVirtRegs.insert(std::make_pair(VirtReg, LiveReg()));
LiveReg &LR = LRI->second;
MachineOperand &MO = MI->getOperand(OpNum);
if (New) {
allocVirtReg(MI, *LRI, Hint);
const TargetRegisterClass *RC = MRI->getRegClass(VirtReg);
int FrameIndex = getStackSpaceFor(VirtReg, RC);
DEBUG(dbgs() << "Reloading " << PrintReg(VirtReg, TRI) << " into "
<< PrintReg(LR.PhysReg, TRI) << "\n");
TII->loadRegFromStackSlot(*MBB, MI, LR.PhysReg, FrameIndex, RC, TRI);
++NumLoads;
} else if (LR.Dirty) {
if (isLastUseOfLocalReg(MO)) {
DEBUG(dbgs() << "Killing last use: " << MO << "\n");
if (MO.isUse())
MO.setIsKill();
else
MO.setIsDead();
} else if (MO.isKill()) {
DEBUG(dbgs() << "Clearing dubious kill: " << MO << "\n");
MO.setIsKill(false);
} else if (MO.isDead()) {
DEBUG(dbgs() << "Clearing dubious dead: " << MO << "\n");
MO.setIsDead(false);
}
} else if (MO.isKill()) {
// We must remove kill flags from uses of reloaded registers because the
// register would be killed immediately, and there might be a second use:
// %foo = OR %x<kill>, %x
// This would cause a second reload of %x into a different register.
DEBUG(dbgs() << "Clearing clean kill: " << MO << "\n");
MO.setIsKill(false);
} else if (MO.isDead()) {
DEBUG(dbgs() << "Clearing clean dead: " << MO << "\n");
MO.setIsDead(false);
}
assert(LR.PhysReg && "Register not assigned");
LR.LastUse = MI;
LR.LastOpNum = OpNum;
UsedInInstr.set(LR.PhysReg);
return LRI;
}
// setPhysReg - Change operand OpNum in MI the refer the PhysReg, considering
// subregs. This may invalidate any operand pointers.
// Return true if the operand kills its register.
bool RAFast::setPhysReg(MachineInstr *MI, unsigned OpNum, unsigned PhysReg) {
MachineOperand &MO = MI->getOperand(OpNum);
if (!MO.getSubReg()) {
MO.setReg(PhysReg);
return MO.isKill() || MO.isDead();
}
// Handle subregister index.
MO.setReg(PhysReg ? TRI->getSubReg(PhysReg, MO.getSubReg()) : 0);
MO.setSubReg(0);
// A kill flag implies killing the full register. Add corresponding super
// register kill.
if (MO.isKill()) {
MI->addRegisterKilled(PhysReg, TRI, true);
return true;
}
return MO.isDead();
}
// Handle special instruction operand like early clobbers and tied ops when
// there are additional physreg defines.
void RAFast::handleThroughOperands(MachineInstr *MI,
SmallVectorImpl<unsigned> &VirtDead) {
DEBUG(dbgs() << "Scanning for through registers:");
SmallSet<unsigned, 8> ThroughRegs;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
if (MO.isEarlyClobber() || MI->isRegTiedToDefOperand(i) ||
(MO.getSubReg() && MI->readsVirtualRegister(Reg))) {
if (ThroughRegs.insert(Reg))
DEBUG(dbgs() << ' ' << PrintReg(Reg));
}
}
// If any physreg defines collide with preallocated through registers,
// we must spill and reallocate.
DEBUG(dbgs() << "\nChecking for physdef collisions.\n");
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef()) continue;
unsigned Reg = MO.getReg();
if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
UsedInInstr.set(Reg);
if (ThroughRegs.count(PhysRegState[Reg]))
definePhysReg(MI, Reg, regFree);
for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
UsedInInstr.set(*AS);
if (ThroughRegs.count(PhysRegState[*AS]))
definePhysReg(MI, *AS, regFree);
}
}
SmallVector<unsigned, 8> PartialDefs;
DEBUG(dbgs() << "Allocating tied uses.\n");
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
if (MO.isUse()) {
unsigned DefIdx = 0;
if (!MI->isRegTiedToDefOperand(i, &DefIdx)) continue;
DEBUG(dbgs() << "Operand " << i << "("<< MO << ") is tied to operand "
<< DefIdx << ".\n");
LiveRegMap::iterator LRI = reloadVirtReg(MI, i, Reg, 0);
unsigned PhysReg = LRI->second.PhysReg;
setPhysReg(MI, i, PhysReg);
// Note: we don't update the def operand yet. That would cause the normal
// def-scan to attempt spilling.
} else if (MO.getSubReg() && MI->readsVirtualRegister(Reg)) {
DEBUG(dbgs() << "Partial redefine: " << MO << "\n");
// Reload the register, but don't assign to the operand just yet.
// That would confuse the later phys-def processing pass.
LiveRegMap::iterator LRI = reloadVirtReg(MI, i, Reg, 0);
PartialDefs.push_back(LRI->second.PhysReg);
}
}
DEBUG(dbgs() << "Allocating early clobbers.\n");
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
if (!MO.isEarlyClobber())
continue;
// Note: defineVirtReg may invalidate MO.
LiveRegMap::iterator LRI = defineVirtReg(MI, i, Reg, 0);
unsigned PhysReg = LRI->second.PhysReg;
if (setPhysReg(MI, i, PhysReg))
VirtDead.push_back(Reg);
}
// Restore UsedInInstr to a state usable for allocating normal virtual uses.
UsedInInstr.reset();
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || (MO.isDef() && !MO.isEarlyClobber())) continue;
unsigned Reg = MO.getReg();
if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
DEBUG(dbgs() << "\tSetting " << PrintReg(Reg, TRI)
<< " as used in instr\n");
UsedInInstr.set(Reg);
}
// Also mark PartialDefs as used to avoid reallocation.
for (unsigned i = 0, e = PartialDefs.size(); i != e; ++i)
UsedInInstr.set(PartialDefs[i]);
}
void RAFast::AllocateBasicBlock() {
DEBUG(dbgs() << "\nAllocating " << *MBB);
// FIXME: This should probably be added by instruction selection instead?
// If the last instruction in the block is a return, make sure to mark it as
// using all of the live-out values in the function. Things marked both call
// and return are tail calls; do not do this for them. The tail callee need
// not take the same registers as input that it produces as output, and there
// are dependencies for its input registers elsewhere.
if (!MBB->empty() && MBB->back().isReturn() &&
!MBB->back().isCall()) {
MachineInstr *Ret = &MBB->back();
for (MachineRegisterInfo::liveout_iterator
I = MF->getRegInfo().liveout_begin(),
E = MF->getRegInfo().liveout_end(); I != E; ++I) {
assert(TargetRegisterInfo::isPhysicalRegister(*I) &&
"Cannot have a live-out virtual register.");
// Add live-out registers as implicit uses.
Ret->addRegisterKilled(*I, TRI, true);
}
}
PhysRegState.assign(TRI->getNumRegs(), regDisabled);
assert(LiveVirtRegs.empty() && "Mapping not cleared form last block?");
MachineBasicBlock::iterator MII = MBB->begin();
// Add live-in registers as live.
for (MachineBasicBlock::livein_iterator I = MBB->livein_begin(),
E = MBB->livein_end(); I != E; ++I)
if (RegClassInfo.isAllocatable(*I))
definePhysReg(MII, *I, regReserved);
SmallVector<unsigned, 8> VirtDead;
SmallVector<MachineInstr*, 32> Coalesced;
// Otherwise, sequentially allocate each instruction in the MBB.
while (MII != MBB->end()) {
MachineInstr *MI = MII++;
const MCInstrDesc &MCID = MI->getDesc();
DEBUG({
dbgs() << "\n>> " << *MI << "Regs:";
for (unsigned Reg = 1, E = TRI->getNumRegs(); Reg != E; ++Reg) {
if (PhysRegState[Reg] == regDisabled) continue;
dbgs() << " " << TRI->getName(Reg);
switch(PhysRegState[Reg]) {
case regFree:
break;
case regReserved:
dbgs() << "*";
break;
default:
dbgs() << '=' << PrintReg(PhysRegState[Reg]);
if (LiveVirtRegs[PhysRegState[Reg]].Dirty)
dbgs() << "*";
assert(LiveVirtRegs[PhysRegState[Reg]].PhysReg == Reg &&
"Bad inverse map");
break;
}
}
dbgs() << '\n';
// Check that LiveVirtRegs is the inverse.
for (LiveRegMap::iterator i = LiveVirtRegs.begin(),
e = LiveVirtRegs.end(); i != e; ++i) {
assert(TargetRegisterInfo::isVirtualRegister(i->first) &&
"Bad map key");
assert(TargetRegisterInfo::isPhysicalRegister(i->second.PhysReg) &&
"Bad map value");
assert(PhysRegState[i->second.PhysReg] == i->first &&
"Bad inverse map");
}
});
// Debug values are not allowed to change codegen in any way.
if (MI->isDebugValue()) {
bool ScanDbgValue = true;
while (ScanDbgValue) {
ScanDbgValue = false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
LiveRegMap::iterator LRI = LiveVirtRegs.find(Reg);
if (LRI != LiveVirtRegs.end())
setPhysReg(MI, i, LRI->second.PhysReg);
else {
int SS = StackSlotForVirtReg[Reg];
if (SS == -1) {
// We can't allocate a physreg for a DebugValue, sorry!
DEBUG(dbgs() << "Unable to allocate vreg used by DBG_VALUE");
MO.setReg(0);
}
else {
// Modify DBG_VALUE now that the value is in a spill slot.
int64_t Offset = MI->getOperand(1).getImm();
const MDNode *MDPtr =
MI->getOperand(MI->getNumOperands()-1).getMetadata();
DebugLoc DL = MI->getDebugLoc();
if (MachineInstr *NewDV =
TII->emitFrameIndexDebugValue(*MF, SS, Offset, MDPtr, DL)) {
DEBUG(dbgs() << "Modifying debug info due to spill:" <<
"\t" << *MI);
MachineBasicBlock *MBB = MI->getParent();
MBB->insert(MBB->erase(MI), NewDV);
// Scan NewDV operands from the beginning.
MI = NewDV;
ScanDbgValue = true;
break;
} else {
// We can't allocate a physreg for a DebugValue; sorry!
DEBUG(dbgs() << "Unable to allocate vreg used by DBG_VALUE");
MO.setReg(0);
}
}
}
LiveDbgValueMap[Reg].push_back(MI);
}
}
// Next instruction.
continue;
}
// If this is a copy, we may be able to coalesce.
unsigned CopySrc = 0, CopyDst = 0, CopySrcSub = 0, CopyDstSub = 0;
if (MI->isCopy()) {
CopyDst = MI->getOperand(0).getReg();
CopySrc = MI->getOperand(1).getReg();
CopyDstSub = MI->getOperand(0).getSubReg();
CopySrcSub = MI->getOperand(1).getSubReg();
}
// Track registers used by instruction.
UsedInInstr.reset();
// First scan.
// Mark physreg uses and early clobbers as used.
// Find the end of the virtreg operands
unsigned VirtOpEnd = 0;
bool hasTiedOps = false;
bool hasEarlyClobbers = false;
bool hasPartialRedefs = false;
bool hasPhysDefs = false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!Reg) continue;
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
VirtOpEnd = i+1;
if (MO.isUse()) {
hasTiedOps = hasTiedOps ||
MCID.getOperandConstraint(i, MCOI::TIED_TO) != -1;
} else {
if (MO.isEarlyClobber())
hasEarlyClobbers = true;
if (MO.getSubReg() && MI->readsVirtualRegister(Reg))
hasPartialRedefs = true;
}
continue;
}
if (!RegClassInfo.isAllocatable(Reg)) continue;
if (MO.isUse()) {
usePhysReg(MO);
} else if (MO.isEarlyClobber()) {
definePhysReg(MI, Reg, (MO.isImplicit() || MO.isDead()) ?
regFree : regReserved);
hasEarlyClobbers = true;
} else
hasPhysDefs = true;
}
// The instruction may have virtual register operands that must be allocated
// the same register at use-time and def-time: early clobbers and tied
// operands. If there are also physical defs, these registers must avoid
// both physical defs and uses, making them more constrained than normal
// operands.
// Similarly, if there are multiple defs and tied operands, we must make
// sure the same register is allocated to uses and defs.
// We didn't detect inline asm tied operands above, so just make this extra
// pass for all inline asm.
if (MI->isInlineAsm() || hasEarlyClobbers || hasPartialRedefs ||
(hasTiedOps && (hasPhysDefs || MCID.getNumDefs() > 1))) {
handleThroughOperands(MI, VirtDead);
// Don't attempt coalescing when we have funny stuff going on.
CopyDst = 0;
// Pretend we have early clobbers so the use operands get marked below.
// This is not necessary for the common case of a single tied use.
hasEarlyClobbers = true;
}
// Second scan.
// Allocate virtreg uses.
for (unsigned i = 0; i != VirtOpEnd; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
if (MO.isUse()) {
LiveRegMap::iterator LRI = reloadVirtReg(MI, i, Reg, CopyDst);
unsigned PhysReg = LRI->second.PhysReg;
CopySrc = (CopySrc == Reg || CopySrc == PhysReg) ? PhysReg : 0;
if (setPhysReg(MI, i, PhysReg))
killVirtReg(LRI);
}
}
MRI->addPhysRegsUsed(UsedInInstr);
// Track registers defined by instruction - early clobbers and tied uses at
// this point.
UsedInInstr.reset();
if (hasEarlyClobbers) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
// Look for physreg defs and tied uses.
if (!MO.isDef() && !MI->isRegTiedToDefOperand(i)) continue;
UsedInInstr.set(Reg);
for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
UsedInInstr.set(*AS);
}
}
unsigned DefOpEnd = MI->getNumOperands();
if (MI->isCall()) {
// Spill all virtregs before a call. This serves two purposes: 1. If an
// exception is thrown, the landing pad is going to expect to find
// registers in their spill slots, and 2. we don't have to wade through
// all the <imp-def> operands on the call instruction.
DefOpEnd = VirtOpEnd;
DEBUG(dbgs() << " Spilling remaining registers before call.\n");
spillAll(MI);
// The imp-defs are skipped below, but we still need to mark those
// registers as used by the function.
SkippedInstrs.insert(&MCID);
}
// Third scan.
// Allocate defs and collect dead defs.
for (unsigned i = 0; i != DefOpEnd; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef() || !MO.getReg() || MO.isEarlyClobber())
continue;
unsigned Reg = MO.getReg();
if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
if (!RegClassInfo.isAllocatable(Reg)) continue;
definePhysReg(MI, Reg, (MO.isImplicit() || MO.isDead()) ?
regFree : regReserved);
continue;
}
LiveRegMap::iterator LRI = defineVirtReg(MI, i, Reg, CopySrc);
unsigned PhysReg = LRI->second.PhysReg;
if (setPhysReg(MI, i, PhysReg)) {
VirtDead.push_back(Reg);
CopyDst = 0; // cancel coalescing;
} else
CopyDst = (CopyDst == Reg || CopyDst == PhysReg) ? PhysReg : 0;
}
// Kill dead defs after the scan to ensure that multiple defs of the same
// register are allocated identically. We didn't need to do this for uses
// because we are crerating our own kill flags, and they are always at the
// last use.
for (unsigned i = 0, e = VirtDead.size(); i != e; ++i)
killVirtReg(VirtDead[i]);
VirtDead.clear();
MRI->addPhysRegsUsed(UsedInInstr);
if (CopyDst && CopyDst == CopySrc && CopyDstSub == CopySrcSub) {
DEBUG(dbgs() << "-- coalescing: " << *MI);
Coalesced.push_back(MI);
} else {
DEBUG(dbgs() << "<< " << *MI);
}
}
// Spill all physical registers holding virtual registers now.
DEBUG(dbgs() << "Spilling live registers at end of block.\n");
spillAll(MBB->getFirstTerminator());
// Erase all the coalesced copies. We are delaying it until now because
// LiveVirtRegs might refer to the instrs.
for (unsigned i = 0, e = Coalesced.size(); i != e; ++i)
MBB->erase(Coalesced[i]);
NumCopies += Coalesced.size();
DEBUG(MBB->dump());
}
/// runOnMachineFunction - Register allocate the whole function
///
bool RAFast::runOnMachineFunction(MachineFunction &Fn) {
DEBUG(dbgs() << "********** FAST REGISTER ALLOCATION **********\n"
<< "********** Function: "
<< ((Value*)Fn.getFunction())->getName() << '\n');
MF = &Fn;
MRI = &MF->getRegInfo();
TM = &Fn.getTarget();
TRI = TM->getRegisterInfo();
TII = TM->getInstrInfo();
MRI->freezeReservedRegs(Fn);
RegClassInfo.runOnMachineFunction(Fn);
UsedInInstr.resize(TRI->getNumRegs());
// initialize the virtual->physical register map to have a 'null'
// mapping for all virtual registers
StackSlotForVirtReg.resize(MRI->getNumVirtRegs());
// Loop over all of the basic blocks, eliminating virtual register references
for (MachineFunction::iterator MBBi = Fn.begin(), MBBe = Fn.end();
MBBi != MBBe; ++MBBi) {
MBB = &*MBBi;
AllocateBasicBlock();
}
// Make sure the set of used physregs is closed under subreg operations.
MRI->closePhysRegsUsed(*TRI);
// Add the clobber lists for all the instructions we skipped earlier.
for (SmallPtrSet<const MCInstrDesc*, 4>::const_iterator
I = SkippedInstrs.begin(), E = SkippedInstrs.end(); I != E; ++I)
if (const unsigned *Defs = (*I)->getImplicitDefs())
while (*Defs)
MRI->setPhysRegUsed(*Defs++);
SkippedInstrs.clear();
StackSlotForVirtReg.clear();
LiveDbgValueMap.clear();
return true;
}
FunctionPass *llvm::createFastRegisterAllocator() {
return new RAFast();
}
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