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llvm-project/llvm/lib/CodeGen/RegAllocFast.cpp

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//===- RegAllocFast.cpp - A fast register allocator for debug code --------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
/// \file This register allocator allocates registers to a basic block at a
/// time, attempting to keep values in registers and reusing registers as
/// appropriate.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/IndexedMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SparseSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Metadata.h"
#include "llvm/InitializePasses.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <tuple>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "regalloc"
STATISTIC(NumStores, "Number of stores added");
STATISTIC(NumLoads , "Number of loads added");
STATISTIC(NumCoalesced, "Number of copies coalesced");
// FIXME: Remove this switch when all testcases are fixed!
static cl::opt<bool> IgnoreMissingDefs("rafast-ignore-missing-defs",
cl::Hidden);
static RegisterRegAlloc
fastRegAlloc("fast", "fast register allocator", createFastRegisterAllocator);
namespace {
class RegAllocFast : public MachineFunctionPass {
public:
static char ID;
RegAllocFast() : MachineFunctionPass(ID), StackSlotForVirtReg(-1) {}
private:
MachineFrameInfo *MFI;
MachineRegisterInfo *MRI;
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
RegisterClassInfo RegClassInfo;
/// Basic block currently being allocated.
MachineBasicBlock *MBB;
/// 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 = nullptr; ///< Last instr to use reg.
Register VirtReg; ///< Virtual register number.
MCPhysReg PhysReg = 0; ///< Currently held here.
bool LiveOut = false; ///< Register is possibly live out.
bool Reloaded = false; ///< Register was reloaded.
bool Error = false; ///< Could not allocate.
explicit LiveReg(Register VirtReg) : VirtReg(VirtReg) {}
unsigned getSparseSetIndex() const {
return Register::virtReg2Index(VirtReg);
}
};
using LiveRegMap = SparseSet<LiveReg>;
/// This map contains entries for each virtual register that is currently
/// available in a physical register.
LiveRegMap LiveVirtRegs;
/// Stores assigned virtual registers present in the bundle MI.
DenseMap<Register, MCPhysReg> BundleVirtRegsMap;
DenseMap<unsigned, SmallVector<MachineInstr *, 2>> LiveDbgValueMap;
/// List of DBG_VALUE that we encountered without the vreg being assigned
/// because they were placed after the last use of the vreg.
DenseMap<unsigned, SmallVector<MachineInstr *, 1>> DanglingDbgValues;
/// Has a bit set for every virtual register for which it was determined
/// that it is alive across blocks.
BitVector MayLiveAcrossBlocks;
/// State of a register unit.
enum RegUnitState {
/// A free register is not currently in use and can be allocated
/// immediately without checking aliases.
regFree,
/// A pre-assigned register has been assigned before register allocation
/// (e.g., setting up a call parameter).
regPreAssigned,
/// Used temporarily in reloadAtBegin() to mark register units that are
/// live-in to the basic block.
regLiveIn,
/// 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.
};
/// Maps each physical register to a RegUnitState enum or virtual register.
std::vector<unsigned> RegUnitStates;
SmallVector<MachineInstr *, 32> Coalesced;
using RegUnitSet = SparseSet<uint16_t, identity<uint16_t>>;
/// Set of register units that are used in the current instruction, and so
/// cannot be allocated.
RegUnitSet UsedInInstr;
RegUnitSet PhysRegUses;
SmallVector<uint16_t, 8> DefOperandIndexes;
void setPhysRegState(MCPhysReg PhysReg, unsigned NewState);
bool isPhysRegFree(MCPhysReg PhysReg) const;
/// Mark a physreg as used in this instruction.
void markRegUsedInInstr(MCPhysReg PhysReg) {
for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units)
UsedInInstr.insert(*Units);
}
/// Check if a physreg or any of its aliases are used in this instruction.
bool isRegUsedInInstr(MCPhysReg PhysReg, bool LookAtPhysRegUses) const {
for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units) {
if (UsedInInstr.count(*Units))
return true;
if (LookAtPhysRegUses && PhysRegUses.count(*Units))
return true;
}
return false;
}
/// Mark physical register as being used in a register use operand.
/// This is only used by the special livethrough handling code.
void markPhysRegUsedInInstr(MCPhysReg PhysReg) {
for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units)
PhysRegUses.insert(*Units);
}
/// Remove mark of physical register being used in the instruction.
void unmarkRegUsedInInstr(MCPhysReg PhysReg) {
for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units)
UsedInInstr.erase(*Units);
}
enum : unsigned {
spillClean = 50,
spillDirty = 100,
spillPrefBonus = 20,
spillImpossible = ~0u
};
public:
StringRef getPassName() const override { return "Fast Register Allocator"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::NoPHIs);
}
MachineFunctionProperties getSetProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::NoVRegs);
}
MachineFunctionProperties getClearedProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::IsSSA);
}
private:
bool runOnMachineFunction(MachineFunction &MF) override;
void allocateBasicBlock(MachineBasicBlock &MBB);
void addRegClassDefCounts(std::vector<unsigned> &RegClassDefCounts,
Register Reg) const;
void allocateInstruction(MachineInstr &MI);
void handleDebugValue(MachineInstr &MI);
void handleBundle(MachineInstr &MI);
bool usePhysReg(MachineInstr &MI, MCPhysReg PhysReg);
bool definePhysReg(MachineInstr &MI, MCPhysReg PhysReg);
bool displacePhysReg(MachineInstr &MI, MCPhysReg PhysReg);
void freePhysReg(MCPhysReg PhysReg);
unsigned calcSpillCost(MCPhysReg PhysReg) const;
LiveRegMap::iterator findLiveVirtReg(Register VirtReg) {
return LiveVirtRegs.find(Register::virtReg2Index(VirtReg));
}
LiveRegMap::const_iterator findLiveVirtReg(Register VirtReg) const {
return LiveVirtRegs.find(Register::virtReg2Index(VirtReg));
}
void assignVirtToPhysReg(MachineInstr &MI, LiveReg &, MCPhysReg PhysReg);
void allocVirtReg(MachineInstr &MI, LiveReg &LR, Register Hint,
bool LookAtPhysRegUses = false);
void allocVirtRegUndef(MachineOperand &MO);
void assignDanglingDebugValues(MachineInstr &Def, Register VirtReg,
MCPhysReg Reg);
void defineLiveThroughVirtReg(MachineInstr &MI, unsigned OpNum,
Register VirtReg);
void defineVirtReg(MachineInstr &MI, unsigned OpNum, Register VirtReg,
bool LookAtPhysRegUses = false);
void useVirtReg(MachineInstr &MI, unsigned OpNum, Register VirtReg);
MachineBasicBlock::iterator
getMBBBeginInsertionPoint(MachineBasicBlock &MBB,
SmallSet<Register, 2> &PrologLiveIns) const;
void reloadAtBegin(MachineBasicBlock &MBB);
void setPhysReg(MachineInstr &MI, MachineOperand &MO, MCPhysReg PhysReg);
Register traceCopies(Register VirtReg) const;
Register traceCopyChain(Register Reg) const;
int getStackSpaceFor(Register VirtReg);
void spill(MachineBasicBlock::iterator Before, Register VirtReg,
MCPhysReg AssignedReg, bool Kill, bool LiveOut);
void reload(MachineBasicBlock::iterator Before, Register VirtReg,
MCPhysReg PhysReg);
bool mayLiveOut(Register VirtReg);
bool mayLiveIn(Register VirtReg);
void dumpState() const;
};
} // end anonymous namespace
char RegAllocFast::ID = 0;
INITIALIZE_PASS(RegAllocFast, "regallocfast", "Fast Register Allocator", false,
false)
void RegAllocFast::setPhysRegState(MCPhysReg PhysReg, unsigned NewState) {
for (MCRegUnitIterator UI(PhysReg, TRI); UI.isValid(); ++UI)
RegUnitStates[*UI] = NewState;
}
bool RegAllocFast::isPhysRegFree(MCPhysReg PhysReg) const {
for (MCRegUnitIterator UI(PhysReg, TRI); UI.isValid(); ++UI) {
if (RegUnitStates[*UI] != regFree)
return false;
}
return true;
}
/// This allocates space for the specified virtual register to be held on the
/// stack.
int RegAllocFast::getStackSpaceFor(Register VirtReg) {
// Find the location Reg would belong...
int SS = StackSlotForVirtReg[VirtReg];
// Already has space allocated?
if (SS != -1)
return SS;
// Allocate a new stack object for this spill location...
const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
unsigned Size = TRI->getSpillSize(RC);
Align Alignment = TRI->getSpillAlign(RC);
int FrameIdx = MFI->CreateSpillStackObject(Size, Alignment);
// Assign the slot.
StackSlotForVirtReg[VirtReg] = FrameIdx;
return FrameIdx;
}
static bool dominates(MachineBasicBlock &MBB,
MachineBasicBlock::const_iterator A,
MachineBasicBlock::const_iterator B) {
auto MBBEnd = MBB.end();
if (B == MBBEnd)
return true;
MachineBasicBlock::const_iterator I = MBB.begin();
for (; &*I != A && &*I != B; ++I)
;
return &*I == A;
}
/// Returns false if \p VirtReg is known to not live out of the current block.
bool RegAllocFast::mayLiveOut(Register VirtReg) {
if (MayLiveAcrossBlocks.test(Register::virtReg2Index(VirtReg))) {
// Cannot be live-out if there are no successors.
return !MBB->succ_empty();
}
const MachineInstr *SelfLoopDef = nullptr;
// If this block loops back to itself, it is necessary to check whether the
// use comes after the def.
if (MBB->isSuccessor(MBB)) {
SelfLoopDef = MRI->getUniqueVRegDef(VirtReg);
if (!SelfLoopDef) {
MayLiveAcrossBlocks.set(Register::virtReg2Index(VirtReg));
return true;
}
}
// See if the first \p Limit uses of the register are all in the current
// block.
static const unsigned Limit = 8;
unsigned C = 0;
for (const MachineInstr &UseInst : MRI->use_nodbg_instructions(VirtReg)) {
if (UseInst.getParent() != MBB || ++C >= Limit) {
MayLiveAcrossBlocks.set(Register::virtReg2Index(VirtReg));
// Cannot be live-out if there are no successors.
return !MBB->succ_empty();
}
if (SelfLoopDef) {
// Try to handle some simple cases to avoid spilling and reloading every
// value inside a self looping block.
if (SelfLoopDef == &UseInst ||
!dominates(*MBB, SelfLoopDef->getIterator(), UseInst.getIterator())) {
MayLiveAcrossBlocks.set(Register::virtReg2Index(VirtReg));
return true;
}
}
}
return false;
}
/// Returns false if \p VirtReg is known to not be live into the current block.
bool RegAllocFast::mayLiveIn(Register VirtReg) {
if (MayLiveAcrossBlocks.test(Register::virtReg2Index(VirtReg)))
return !MBB->pred_empty();
// See if the first \p Limit def of the register are all in the current block.
static const unsigned Limit = 8;
unsigned C = 0;
for (const MachineInstr &DefInst : MRI->def_instructions(VirtReg)) {
if (DefInst.getParent() != MBB || ++C >= Limit) {
MayLiveAcrossBlocks.set(Register::virtReg2Index(VirtReg));
return !MBB->pred_empty();
}
}
return false;
}
/// Insert spill instruction for \p AssignedReg before \p Before. Update
/// DBG_VALUEs with \p VirtReg operands with the stack slot.
void RegAllocFast::spill(MachineBasicBlock::iterator Before, Register VirtReg,
MCPhysReg AssignedReg, bool Kill, bool LiveOut) {
LLVM_DEBUG(dbgs() << "Spilling " << printReg(VirtReg, TRI)
<< " in " << printReg(AssignedReg, TRI));
int FI = getStackSpaceFor(VirtReg);
LLVM_DEBUG(dbgs() << " to stack slot #" << FI << '\n');
const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
TII->storeRegToStackSlot(*MBB, Before, AssignedReg, Kill, FI, &RC, TRI);
++NumStores;
MachineBasicBlock::iterator FirstTerm = MBB->getFirstTerminator();
// When we spill a virtual register, we will have spill instructions behind
// every definition of it, meaning we can switch all the DBG_VALUEs over
// to just reference the stack slot.
SmallVectorImpl<MachineInstr *> &LRIDbgValues = LiveDbgValueMap[VirtReg];
for (MachineInstr *DBG : LRIDbgValues) {
MachineInstr *NewDV = buildDbgValueForSpill(*MBB, Before, *DBG, FI);
assert(NewDV->getParent() == MBB && "dangling parent pointer");
(void)NewDV;
LLVM_DEBUG(dbgs() << "Inserting debug info due to spill:\n" << *NewDV);
if (LiveOut) {
// We need to insert a DBG_VALUE at the end of the block if the spill slot
// is live out, but there is another use of the value after the
// spill. This will allow LiveDebugValues to see the correct live out
// value to propagate to the successors.
MachineInstr *ClonedDV = MBB->getParent()->CloneMachineInstr(NewDV);
MBB->insert(FirstTerm, ClonedDV);
LLVM_DEBUG(dbgs() << "Cloning debug info due to live out spill\n");
}
// Rewrite unassigned dbg_values to use the stack slot.
MachineOperand &MO = DBG->getOperand(0);
if (MO.isReg() && MO.getReg() == 0)
updateDbgValueForSpill(*DBG, FI);
}
// 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();
}
/// Insert reload instruction for \p PhysReg before \p Before.
void RegAllocFast::reload(MachineBasicBlock::iterator Before, Register VirtReg,
MCPhysReg PhysReg) {
LLVM_DEBUG(dbgs() << "Reloading " << printReg(VirtReg, TRI) << " into "
<< printReg(PhysReg, TRI) << '\n');
int FI = getStackSpaceFor(VirtReg);
const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
TII->loadRegFromStackSlot(*MBB, Before, PhysReg, FI, &RC, TRI);
++NumLoads;
}
/// Get basic block begin insertion point.
/// This is not just MBB.begin() because surprisingly we have EH_LABEL
/// instructions marking the begin of a basic block. This means we must insert
/// new instructions after such labels...
MachineBasicBlock::iterator
RegAllocFast::getMBBBeginInsertionPoint(
MachineBasicBlock &MBB, SmallSet<Register, 2> &PrologLiveIns) const {
MachineBasicBlock::iterator I = MBB.begin();
while (I != MBB.end()) {
if (I->isLabel()) {
++I;
continue;
}
// Most reloads should be inserted after prolog instructions.
if (!TII->isBasicBlockPrologue(*I))
break;
// However if a prolog instruction reads a register that needs to be
// reloaded, the reload should be inserted before the prolog.
for (MachineOperand &MO : I->operands()) {
if (MO.isReg())
PrologLiveIns.insert(MO.getReg());
}
++I;
}
return I;
}
/// Reload all currently assigned virtual registers.
void RegAllocFast::reloadAtBegin(MachineBasicBlock &MBB) {
if (LiveVirtRegs.empty())
return;
for (MachineBasicBlock::RegisterMaskPair P : MBB.liveins()) {
MCPhysReg Reg = P.PhysReg;
// Set state to live-in. This possibly overrides mappings to virtual
// registers but we don't care anymore at this point.
setPhysRegState(Reg, regLiveIn);
}
SmallSet<Register, 2> PrologLiveIns;
// The LiveRegMap is keyed by an unsigned (the virtreg number), so the order
// of spilling here is deterministic, if arbitrary.
MachineBasicBlock::iterator InsertBefore
= getMBBBeginInsertionPoint(MBB, PrologLiveIns);
for (const LiveReg &LR : LiveVirtRegs) {
MCPhysReg PhysReg = LR.PhysReg;
if (PhysReg == 0)
continue;
MCRegister FirstUnit = *MCRegUnitIterator(PhysReg, TRI);
if (RegUnitStates[FirstUnit] == regLiveIn)
continue;
assert((&MBB != &MBB.getParent()->front() || IgnoreMissingDefs) &&
"no reload in start block. Missing vreg def?");
if (PrologLiveIns.count(PhysReg)) {
// FIXME: Theoretically this should use an insert point skipping labels
// but I'm not sure how labels should interact with prolog instruction
// that need reloads.
reload(MBB.begin(), LR.VirtReg, PhysReg);
} else
reload(InsertBefore, LR.VirtReg, PhysReg);
}
LiveVirtRegs.clear();
}
/// 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.
bool RegAllocFast::usePhysReg(MachineInstr &MI, MCPhysReg Reg) {
assert(Register::isPhysicalRegister(Reg) && "expected physreg");
bool displacedAny = displacePhysReg(MI, Reg);
setPhysRegState(Reg, regPreAssigned);
markRegUsedInInstr(Reg);
return displacedAny;
}
bool RegAllocFast::definePhysReg(MachineInstr &MI, MCPhysReg Reg) {
bool displacedAny = displacePhysReg(MI, Reg);
setPhysRegState(Reg, regPreAssigned);
return displacedAny;
}
/// Mark PhysReg as reserved or free after spilling any virtregs. This is very
/// similar to defineVirtReg except the physreg is reserved instead of
/// allocated.
bool RegAllocFast::displacePhysReg(MachineInstr &MI, MCPhysReg PhysReg) {
bool displacedAny = false;
for (MCRegUnitIterator UI(PhysReg, TRI); UI.isValid(); ++UI) {
unsigned Unit = *UI;
switch (unsigned VirtReg = RegUnitStates[Unit]) {
default: {
LiveRegMap::iterator LRI = findLiveVirtReg(VirtReg);
assert(LRI != LiveVirtRegs.end() && "datastructures in sync");
MachineBasicBlock::iterator ReloadBefore =
std::next((MachineBasicBlock::iterator)MI.getIterator());
reload(ReloadBefore, VirtReg, LRI->PhysReg);
setPhysRegState(LRI->PhysReg, regFree);
LRI->PhysReg = 0;
LRI->Reloaded = true;
displacedAny = true;
break;
}
case regPreAssigned:
RegUnitStates[Unit] = regFree;
displacedAny = true;
break;
case regFree:
break;
}
}
return displacedAny;
}
void RegAllocFast::freePhysReg(MCPhysReg PhysReg) {
LLVM_DEBUG(dbgs() << "Freeing " << printReg(PhysReg, TRI) << ':');
MCRegister FirstUnit = *MCRegUnitIterator(PhysReg, TRI);
switch (unsigned VirtReg = RegUnitStates[FirstUnit]) {
case regFree:
LLVM_DEBUG(dbgs() << '\n');
return;
case regPreAssigned:
LLVM_DEBUG(dbgs() << '\n');
setPhysRegState(PhysReg, regFree);
return;
default: {
LiveRegMap::iterator LRI = findLiveVirtReg(VirtReg);
assert(LRI != LiveVirtRegs.end());
LLVM_DEBUG(dbgs() << ' ' << printReg(LRI->VirtReg, TRI) << '\n');
setPhysRegState(LRI->PhysReg, regFree);
LRI->PhysReg = 0;
}
return;
}
}
/// 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 RegAllocFast::calcSpillCost(MCPhysReg PhysReg) const {
for (MCRegUnitIterator UI(PhysReg, TRI); UI.isValid(); ++UI) {
switch (unsigned VirtReg = RegUnitStates[*UI]) {
case regFree:
break;
case regPreAssigned:
LLVM_DEBUG(dbgs() << "Cannot spill pre-assigned "
<< printReg(PhysReg, TRI) << '\n');
return spillImpossible;
default: {
bool SureSpill = StackSlotForVirtReg[VirtReg] != -1 ||
findLiveVirtReg(VirtReg)->LiveOut;
return SureSpill ? spillClean : spillDirty;
}
}
}
return 0;
}
void RegAllocFast::assignDanglingDebugValues(MachineInstr &Definition,
Register VirtReg, MCPhysReg Reg) {
auto UDBGValIter = DanglingDbgValues.find(VirtReg);
if (UDBGValIter == DanglingDbgValues.end())
return;
SmallVectorImpl<MachineInstr*> &Dangling = UDBGValIter->second;
for (MachineInstr *DbgValue : Dangling) {
assert(DbgValue->isDebugValue());
MachineOperand &MO = DbgValue->getOperand(0);
if (!MO.isReg())
continue;
// Test whether the physreg survives from the definition to the DBG_VALUE.
MCPhysReg SetToReg = Reg;
unsigned Limit = 20;
for (MachineBasicBlock::iterator I = std::next(Definition.getIterator()),
E = DbgValue->getIterator(); I != E; ++I) {
if (I->modifiesRegister(Reg, TRI) || --Limit == 0) {
LLVM_DEBUG(dbgs() << "Register did not survive for " << *DbgValue
<< '\n');
SetToReg = 0;
break;
}
}
MO.setReg(SetToReg);
if (SetToReg != 0)
MO.setIsRenamable();
}
Dangling.clear();
}
/// 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 RegAllocFast::assignVirtToPhysReg(MachineInstr &AtMI, LiveReg &LR,
MCPhysReg PhysReg) {
Register VirtReg = LR.VirtReg;
LLVM_DEBUG(dbgs() << "Assigning " << printReg(VirtReg, TRI) << " to "
<< printReg(PhysReg, TRI) << '\n');
assert(LR.PhysReg == 0 && "Already assigned a physreg");
assert(PhysReg != 0 && "Trying to assign no register");
LR.PhysReg = PhysReg;
setPhysRegState(PhysReg, VirtReg);
assignDanglingDebugValues(AtMI, VirtReg, PhysReg);
}
static bool isCoalescable(const MachineInstr &MI) {
return MI.isFullCopy();
}
Register RegAllocFast::traceCopyChain(Register Reg) const {
static const unsigned ChainLengthLimit = 3;
unsigned C = 0;
do {
if (Reg.isPhysical())
return Reg;
assert(Reg.isVirtual());
MachineInstr *VRegDef = MRI->getUniqueVRegDef(Reg);
if (!VRegDef || !isCoalescable(*VRegDef))
return 0;
Reg = VRegDef->getOperand(1).getReg();
} while (++C <= ChainLengthLimit);
return 0;
}
/// Check if any of \p VirtReg's definitions is a copy. If it is follow the
/// chain of copies to check whether we reach a physical register we can
/// coalesce with.
Register RegAllocFast::traceCopies(Register VirtReg) const {
static const unsigned DefLimit = 3;
unsigned C = 0;
for (const MachineInstr &MI : MRI->def_instructions(VirtReg)) {
if (isCoalescable(MI)) {
Register Reg = MI.getOperand(1).getReg();
Reg = traceCopyChain(Reg);
if (Reg.isValid())
return Reg;
}
if (++C >= DefLimit)
break;
}
return Register();
}
/// Allocates a physical register for VirtReg.
void RegAllocFast::allocVirtReg(MachineInstr &MI, LiveReg &LR,
Register Hint0, bool LookAtPhysRegUses) {
const Register VirtReg = LR.VirtReg;
assert(LR.PhysReg == 0);
const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
LLVM_DEBUG(dbgs() << "Search register for " << printReg(VirtReg)
<< " in class " << TRI->getRegClassName(&RC)
<< " with hint " << printReg(Hint0, TRI) << '\n');
// Take hint when possible.
if (Hint0.isPhysical() && MRI->isAllocatable(Hint0) && RC.contains(Hint0) &&
!isRegUsedInInstr(Hint0, LookAtPhysRegUses)) {
// Take hint if the register is currently free.
if (isPhysRegFree(Hint0)) {
LLVM_DEBUG(dbgs() << "\tPreferred Register 1: " << printReg(Hint0, TRI)
<< '\n');
assignVirtToPhysReg(MI, LR, Hint0);
return;
} else {
LLVM_DEBUG(dbgs() << "\tPreferred Register 0: " << printReg(Hint0, TRI)
<< " occupied\n");
}
} else {
Hint0 = Register();
}
// Try other hint.
Register Hint1 = traceCopies(VirtReg);
if (Hint1.isPhysical() && MRI->isAllocatable(Hint1) && RC.contains(Hint1) &&
!isRegUsedInInstr(Hint1, LookAtPhysRegUses)) {
// Take hint if the register is currently free.
if (isPhysRegFree(Hint1)) {
LLVM_DEBUG(dbgs() << "\tPreferred Register 0: " << printReg(Hint1, TRI)
<< '\n');
assignVirtToPhysReg(MI, LR, Hint1);
return;
} else {
LLVM_DEBUG(dbgs() << "\tPreferred Register 1: " << printReg(Hint1, TRI)
<< " occupied\n");
}
} else {
Hint1 = Register();
}
MCPhysReg BestReg = 0;
unsigned BestCost = spillImpossible;
ArrayRef<MCPhysReg> AllocationOrder = RegClassInfo.getOrder(&RC);
for (MCPhysReg PhysReg : AllocationOrder) {
LLVM_DEBUG(dbgs() << "\tRegister: " << printReg(PhysReg, TRI) << ' ');
if (isRegUsedInInstr(PhysReg, LookAtPhysRegUses)) {
LLVM_DEBUG(dbgs() << "already used in instr.\n");
continue;
}
unsigned Cost = calcSpillCost(PhysReg);
LLVM_DEBUG(dbgs() << "Cost: " << Cost << " BestCost: " << BestCost << '\n');
// Immediate take a register with cost 0.
if (Cost == 0) {
assignVirtToPhysReg(MI, LR, PhysReg);
return;
}
if (PhysReg == Hint0 || PhysReg == Hint1)
Cost -= spillPrefBonus;
if (Cost < BestCost) {
BestReg = PhysReg;
BestCost = Cost;
}
}
if (!BestReg) {
// Nothing we can do: Report an error and keep going with an invalid
// allocation.
if (MI.isInlineAsm())
MI.emitError("inline assembly requires more registers than available");
else
MI.emitError("ran out of registers during register allocation");
LR.Error = true;
LR.PhysReg = 0;
return;
}
displacePhysReg(MI, BestReg);
assignVirtToPhysReg(MI, LR, BestReg);
}
void RegAllocFast::allocVirtRegUndef(MachineOperand &MO) {
assert(MO.isUndef() && "expected undef use");
Register VirtReg = MO.getReg();
assert(Register::isVirtualRegister(VirtReg) && "Expected virtreg");
LiveRegMap::const_iterator LRI = findLiveVirtReg(VirtReg);
MCPhysReg PhysReg;
if (LRI != LiveVirtRegs.end() && LRI->PhysReg) {
PhysReg = LRI->PhysReg;
} else {
const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
ArrayRef<MCPhysReg> AllocationOrder = RegClassInfo.getOrder(&RC);
assert(!AllocationOrder.empty() && "Allocation order must not be empty");
PhysReg = AllocationOrder[0];
}
unsigned SubRegIdx = MO.getSubReg();
if (SubRegIdx != 0) {
PhysReg = TRI->getSubReg(PhysReg, SubRegIdx);
MO.setSubReg(0);
}
MO.setReg(PhysReg);
MO.setIsRenamable(true);
}
/// Variation of defineVirtReg() with special handling for livethrough regs
/// (tied or earlyclobber) that may interfere with preassigned uses.
void RegAllocFast::defineLiveThroughVirtReg(MachineInstr &MI, unsigned OpNum,
Register VirtReg) {
LiveRegMap::iterator LRI = findLiveVirtReg(VirtReg);
if (LRI != LiveVirtRegs.end()) {
MCPhysReg PrevReg = LRI->PhysReg;
if (PrevReg != 0 && isRegUsedInInstr(PrevReg, true)) {
LLVM_DEBUG(dbgs() << "Need new assignment for " << printReg(PrevReg, TRI)
<< " (tied/earlyclobber resolution)\n");
freePhysReg(PrevReg);
LRI->PhysReg = 0;
allocVirtReg(MI, *LRI, 0, true);
MachineBasicBlock::iterator InsertBefore =
std::next((MachineBasicBlock::iterator)MI.getIterator());
LLVM_DEBUG(dbgs() << "Copy " << printReg(LRI->PhysReg, TRI) << " to "
<< printReg(PrevReg, TRI) << '\n');
BuildMI(*MBB, InsertBefore, MI.getDebugLoc(),
TII->get(TargetOpcode::COPY), PrevReg)
.addReg(LRI->PhysReg, llvm::RegState::Kill);
}
MachineOperand &MO = MI.getOperand(OpNum);
if (MO.getSubReg() && !MO.isUndef()) {
LRI->LastUse = &MI;
}
}
return defineVirtReg(MI, OpNum, VirtReg, true);
}
/// Allocates a register for VirtReg definition. Typically the register is
/// already assigned from a use of the virtreg, however we still need to
/// perform an allocation if:
/// - It is a dead definition without any uses.
/// - The value is live out and all uses are in different basic blocks.
void RegAllocFast::defineVirtReg(MachineInstr &MI, unsigned OpNum,
Register VirtReg, bool LookAtPhysRegUses) {
assert(VirtReg.isVirtual() && "Not a virtual register");
MachineOperand &MO = MI.getOperand(OpNum);
LiveRegMap::iterator LRI;
bool New;
std::tie(LRI, New) = LiveVirtRegs.insert(LiveReg(VirtReg));
if (New) {
if (!MO.isDead()) {
if (mayLiveOut(VirtReg)) {
LRI->LiveOut = true;
} else {
// It is a dead def without the dead flag; add the flag now.
MO.setIsDead(true);
}
}
}
if (LRI->PhysReg == 0)
allocVirtReg(MI, *LRI, 0, LookAtPhysRegUses);
else {
assert(!isRegUsedInInstr(LRI->PhysReg, LookAtPhysRegUses) &&
"TODO: preassign mismatch");
LLVM_DEBUG(dbgs() << "In def of " << printReg(VirtReg, TRI)
<< " use existing assignment to "
<< printReg(LRI->PhysReg, TRI) << '\n');
}
MCPhysReg PhysReg = LRI->PhysReg;
assert(PhysReg != 0 && "Register not assigned");
if (LRI->Reloaded || LRI->LiveOut) {
if (!MI.isImplicitDef()) {
MachineBasicBlock::iterator SpillBefore =
std::next((MachineBasicBlock::iterator)MI.getIterator());
LLVM_DEBUG(dbgs() << "Spill Reason: LO: " << LRI->LiveOut << " RL: "
<< LRI->Reloaded << '\n');
bool Kill = LRI->LastUse == nullptr;
spill(SpillBefore, VirtReg, PhysReg, Kill, LRI->LiveOut);
LRI->LastUse = nullptr;
}
LRI->LiveOut = false;
LRI->Reloaded = false;
}
if (MI.getOpcode() == TargetOpcode::BUNDLE) {
BundleVirtRegsMap[VirtReg] = PhysReg;
}
markRegUsedInInstr(PhysReg);
setPhysReg(MI, MO, PhysReg);
}
/// Allocates a register for a VirtReg use.
void RegAllocFast::useVirtReg(MachineInstr &MI, unsigned OpNum,
Register VirtReg) {
assert(VirtReg.isVirtual() && "Not a virtual register");
MachineOperand &MO = MI.getOperand(OpNum);
LiveRegMap::iterator LRI;
bool New;
std::tie(LRI, New) = LiveVirtRegs.insert(LiveReg(VirtReg));
if (New) {
MachineOperand &MO = MI.getOperand(OpNum);
if (!MO.isKill()) {
if (mayLiveOut(VirtReg)) {
LRI->LiveOut = true;
} else {
// It is a last (killing) use without the kill flag; add the flag now.
MO.setIsKill(true);
}
}
} else {
assert((!MO.isKill() || LRI->LastUse == &MI) && "Invalid kill flag");
}
// If necessary allocate a register.
if (LRI->PhysReg == 0) {
assert(!MO.isTied() && "tied op should be allocated");
Register Hint;
if (MI.isCopy() && MI.getOperand(1).getSubReg() == 0) {
Hint = MI.getOperand(0).getReg();
assert(Hint.isPhysical() &&
"Copy destination should already be assigned");
}
allocVirtReg(MI, *LRI, Hint, false);
if (LRI->Error) {
const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
ArrayRef<MCPhysReg> AllocationOrder = RegClassInfo.getOrder(&RC);
setPhysReg(MI, MO, *AllocationOrder.begin());
return;
}
}
LRI->LastUse = &MI;
if (MI.getOpcode() == TargetOpcode::BUNDLE) {
BundleVirtRegsMap[VirtReg] = LRI->PhysReg;
}
markRegUsedInInstr(LRI->PhysReg);
setPhysReg(MI, MO, LRI->PhysReg);
}
/// Changes operand OpNum in MI the refer the PhysReg, considering subregs. This
/// may invalidate any operand pointers. Return true if the operand kills its
/// register.
void RegAllocFast::setPhysReg(MachineInstr &MI, MachineOperand &MO,
MCPhysReg PhysReg) {
if (!MO.getSubReg()) {
MO.setReg(PhysReg);
MO.setIsRenamable(true);
return;
}
// Handle subregister index.
MO.setReg(PhysReg ? TRI->getSubReg(PhysReg, MO.getSubReg()) : MCRegister());
MO.setIsRenamable(true);
// Note: We leave the subreg number around a little longer in case of defs.
// This is so that the register freeing logic in allocateInstruction can still
// recognize this as subregister defs. The code there will clear the number.
if (!MO.isDef())
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;
}
// A <def,read-undef> of a sub-register requires an implicit def of the full
// register.
if (MO.isDef() && MO.isUndef()) {
if (MO.isDead())
MI.addRegisterDead(PhysReg, TRI, true);
else
MI.addRegisterDefined(PhysReg, TRI);
}
}
#ifndef NDEBUG
void RegAllocFast::dumpState() const {
for (unsigned Unit = 1, UnitE = TRI->getNumRegUnits(); Unit != UnitE;
++Unit) {
switch (unsigned VirtReg = RegUnitStates[Unit]) {
case regFree:
break;
case regPreAssigned:
dbgs() << " " << printRegUnit(Unit, TRI) << "[P]";
break;
case regLiveIn:
llvm_unreachable("Should not have regLiveIn in map");
default: {
dbgs() << ' ' << printRegUnit(Unit, TRI) << '=' << printReg(VirtReg);
LiveRegMap::const_iterator I = findLiveVirtReg(VirtReg);
assert(I != LiveVirtRegs.end() && "have LiveVirtRegs entry");
if (I->LiveOut || I->Reloaded) {
dbgs() << '[';
if (I->LiveOut) dbgs() << 'O';
if (I->Reloaded) dbgs() << 'R';
dbgs() << ']';
}
assert(TRI->hasRegUnit(I->PhysReg, Unit) && "inverse mapping present");
break;
}
}
}
dbgs() << '\n';
// Check that LiveVirtRegs is the inverse.
for (const LiveReg &LR : LiveVirtRegs) {
Register VirtReg = LR.VirtReg;
assert(VirtReg.isVirtual() && "Bad map key");
MCPhysReg PhysReg = LR.PhysReg;
if (PhysReg != 0) {
assert(Register::isPhysicalRegister(PhysReg) &&
"mapped to physreg");
for (MCRegUnitIterator UI(PhysReg, TRI); UI.isValid(); ++UI) {
assert(RegUnitStates[*UI] == VirtReg && "inverse map valid");
}
}
}
}
#endif
/// Count number of defs consumed from each register class by \p Reg
void RegAllocFast::addRegClassDefCounts(std::vector<unsigned> &RegClassDefCounts,
Register Reg) const {
assert(RegClassDefCounts.size() == TRI->getNumRegClasses());
if (Reg.isVirtual()) {
const TargetRegisterClass *OpRC = MRI->getRegClass(Reg);
for (unsigned RCIdx = 0, RCIdxEnd = TRI->getNumRegClasses();
RCIdx != RCIdxEnd; ++RCIdx) {
const TargetRegisterClass *IdxRC = TRI->getRegClass(RCIdx);
// FIXME: Consider aliasing sub/super registers.
if (OpRC->hasSubClassEq(IdxRC))
++RegClassDefCounts[RCIdx];
}
return;
}
for (unsigned RCIdx = 0, RCIdxEnd = TRI->getNumRegClasses();
RCIdx != RCIdxEnd; ++RCIdx) {
const TargetRegisterClass *IdxRC = TRI->getRegClass(RCIdx);
for (MCRegAliasIterator Alias(Reg, TRI, true); Alias.isValid(); ++Alias) {
if (IdxRC->contains(*Alias)) {
++RegClassDefCounts[RCIdx];
break;
}
}
}
}
void RegAllocFast::allocateInstruction(MachineInstr &MI) {
// The basic algorithm here is:
// 1. Mark registers of def operands as free
// 2. Allocate registers to use operands and place reload instructions for
// registers displaced by the allocation.
//
// However we need to handle some corner cases:
// - pre-assigned defs and uses need to be handled before the other def/use
// operands are processed to avoid the allocation heuristics clashing with
// the pre-assignment.
// - The "free def operands" step has to come last instead of first for tied
// operands and early-clobbers.
UsedInInstr.clear();
BundleVirtRegsMap.clear();
// Scan for special cases; Apply pre-assigned register defs to state.
bool HasPhysRegUse = false;
bool HasRegMask = false;
bool HasVRegDef = false;
bool HasDef = false;
bool HasEarlyClobber = false;
bool NeedToAssignLiveThroughs = false;
for (MachineOperand &MO : MI.operands()) {
if (MO.isReg()) {
Register Reg = MO.getReg();
if (Reg.isVirtual()) {
if (MO.isDef()) {
HasDef = true;
HasVRegDef = true;
if (MO.isEarlyClobber()) {
HasEarlyClobber = true;
NeedToAssignLiveThroughs = true;
}
if (MO.isTied() || (MO.getSubReg() != 0 && !MO.isUndef()))
NeedToAssignLiveThroughs = true;
}
} else if (Reg.isPhysical()) {
if (!MRI->isReserved(Reg)) {
if (MO.isDef()) {
HasDef = true;
bool displacedAny = definePhysReg(MI, Reg);
if (MO.isEarlyClobber())
HasEarlyClobber = true;
if (!displacedAny)
MO.setIsDead(true);
}
if (MO.readsReg())
HasPhysRegUse = true;
}
}
} else if (MO.isRegMask()) {
HasRegMask = true;
}
}
// Allocate virtreg defs.
if (HasDef) {
if (HasVRegDef) {
// Special handling for early clobbers, tied operands or subregister defs:
// Compared to "normal" defs these:
// - Must not use a register that is pre-assigned for a use operand.
// - In order to solve tricky inline assembly constraints we change the
// heuristic to figure out a good operand order before doing
// assignments.
if (NeedToAssignLiveThroughs) {
DefOperandIndexes.clear();
PhysRegUses.clear();
// Track number of defs which may consume a register from the class.
std::vector<unsigned> RegClassDefCounts(TRI->getNumRegClasses(), 0);
assert(RegClassDefCounts[0] == 0);
LLVM_DEBUG(dbgs() << "Need to assign livethroughs\n");
for (unsigned I = 0, E = MI.getNumOperands(); I < E; ++I) {
const MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg())
continue;
Register Reg = MO.getReg();
if (MO.readsReg()) {
if (Reg.isPhysical()) {
LLVM_DEBUG(dbgs() << "mark extra used: " << printReg(Reg, TRI)
<< '\n');
markPhysRegUsedInInstr(Reg);
}
}
if (MO.isDef()) {
if (Reg.isVirtual())
DefOperandIndexes.push_back(I);
addRegClassDefCounts(RegClassDefCounts, Reg);
}
}
llvm::sort(DefOperandIndexes, [&](uint16_t I0, uint16_t I1) {
const MachineOperand &MO0 = MI.getOperand(I0);
const MachineOperand &MO1 = MI.getOperand(I1);
Register Reg0 = MO0.getReg();
Register Reg1 = MO1.getReg();
const TargetRegisterClass &RC0 = *MRI->getRegClass(Reg0);
const TargetRegisterClass &RC1 = *MRI->getRegClass(Reg1);
// Identify regclass that are easy to use up completely just in this
// instruction.
unsigned ClassSize0 = RegClassInfo.getOrder(&RC0).size();
unsigned ClassSize1 = RegClassInfo.getOrder(&RC1).size();
bool SmallClass0 = ClassSize0 < RegClassDefCounts[RC0.getID()];
bool SmallClass1 = ClassSize1 < RegClassDefCounts[RC1.getID()];
if (SmallClass0 > SmallClass1)
return true;
if (SmallClass0 < SmallClass1)
return false;
// Allocate early clobbers and livethrough operands first.
bool Livethrough0 = MO0.isEarlyClobber() || MO0.isTied() ||
(MO0.getSubReg() == 0 && !MO0.isUndef());
bool Livethrough1 = MO1.isEarlyClobber() || MO1.isTied() ||
(MO1.getSubReg() == 0 && !MO1.isUndef());
if (Livethrough0 > Livethrough1)
return true;
if (Livethrough0 < Livethrough1)
return false;
// Tie-break rule: operand index.
return I0 < I1;
});
for (uint16_t OpIdx : DefOperandIndexes) {
MachineOperand &MO = MI.getOperand(OpIdx);
LLVM_DEBUG(dbgs() << "Allocating " << MO << '\n');
unsigned Reg = MO.getReg();
if (MO.isEarlyClobber() || MO.isTied() ||
(MO.getSubReg() && !MO.isUndef())) {
defineLiveThroughVirtReg(MI, OpIdx, Reg);
} else {
defineVirtReg(MI, OpIdx, Reg);
}
}
} else {
// Assign virtual register defs.
for (unsigned I = 0, E = MI.getNumOperands(); I < E; ++I) {
MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg() || !MO.isDef())
continue;
Register Reg = MO.getReg();
if (Reg.isVirtual())
defineVirtReg(MI, I, Reg);
}
}
}
// Free registers occupied by defs.
// Iterate operands in reverse order, so we see the implicit super register
// defs first (we added them earlier in case of <def,read-undef>).
for (unsigned I = MI.getNumOperands(); I-- > 0;) {
MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg() || !MO.isDef())
continue;
// subreg defs don't free the full register. We left the subreg number
// around as a marker in setPhysReg() to recognize this case here.
if (MO.getSubReg() != 0) {
MO.setSubReg(0);
continue;
}
// Do not free tied operands and early clobbers.
if (MO.isTied() || MO.isEarlyClobber())
continue;
Register Reg = MO.getReg();
if (!Reg)
continue;
assert(Reg.isPhysical());
if (MRI->isReserved(Reg))
continue;
freePhysReg(Reg);
unmarkRegUsedInInstr(Reg);
}
}
// Displace clobbered registers.
if (HasRegMask) {
for (const MachineOperand &MO : MI.operands()) {
if (MO.isRegMask()) {
// MRI bookkeeping.
MRI->addPhysRegsUsedFromRegMask(MO.getRegMask());
// Displace clobbered registers.
const uint32_t *Mask = MO.getRegMask();
for (LiveRegMap::iterator LRI = LiveVirtRegs.begin(),
LRIE = LiveVirtRegs.end(); LRI != LRIE; ++LRI) {
MCPhysReg PhysReg = LRI->PhysReg;
if (PhysReg != 0 && MachineOperand::clobbersPhysReg(Mask, PhysReg))
displacePhysReg(MI, PhysReg);
}
}
}
}
// Apply pre-assigned register uses to state.
if (HasPhysRegUse) {
for (MachineOperand &MO : MI.operands()) {
if (!MO.isReg() || !MO.readsReg())
continue;
Register Reg = MO.getReg();
if (!Reg.isPhysical())
continue;
if (MRI->isReserved(Reg))
continue;
bool displacedAny = usePhysReg(MI, Reg);
if (!displacedAny && !MRI->isReserved(Reg))
MO.setIsKill(true);
}
}
// Allocate virtreg uses and insert reloads as necessary.
bool HasUndefUse = false;
for (unsigned I = 0; I < MI.getNumOperands(); ++I) {
MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg() || !MO.isUse())
continue;
Register Reg = MO.getReg();
if (!Reg.isVirtual())
continue;
if (MO.isUndef()) {
HasUndefUse = true;
continue;
}
// Populate MayLiveAcrossBlocks in case the use block is allocated before
// the def block (removing the vreg uses).
mayLiveIn(Reg);
assert(!MO.isInternalRead() && "Bundles not supported");
assert(MO.readsReg() && "reading use");
useVirtReg(MI, I, Reg);
}
// Allocate undef operands. This is a separate step because in a situation
// like ` = OP undef %X, %X` both operands need the same register assign
// so we should perform the normal assignment first.
if (HasUndefUse) {
for (MachineOperand &MO : MI.uses()) {
if (!MO.isReg() || !MO.isUse())
continue;
Register Reg = MO.getReg();
if (!Reg.isVirtual())
continue;
assert(MO.isUndef() && "Should only have undef virtreg uses left");
allocVirtRegUndef(MO);
}
}
// Free early clobbers.
if (HasEarlyClobber) {
for (unsigned I = MI.getNumOperands(); I-- > 0; ) {
MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg() || !MO.isDef() || !MO.isEarlyClobber())
continue;
// subreg defs don't free the full register. We left the subreg number
// around as a marker in setPhysReg() to recognize this case here.
if (MO.getSubReg() != 0) {
MO.setSubReg(0);
continue;
}
Register Reg = MO.getReg();
if (!Reg)
continue;
assert(Reg.isPhysical() && "should have register assigned");
// We sometimes get odd situations like:
// early-clobber %x0 = INSTRUCTION %x0
// which is semantically questionable as the early-clobber should
// apply before the use. But in practice we consider the use to
// happen before the early clobber now. Don't free the early clobber
// register in this case.
if (MI.readsRegister(Reg, TRI))
continue;
freePhysReg(Reg);
}
}
LLVM_DEBUG(dbgs() << "<< " << MI);
if (MI.isCopy() && MI.getOperand(0).getReg() == MI.getOperand(1).getReg() &&
MI.getNumOperands() == 2) {
LLVM_DEBUG(dbgs() << "Mark identity copy for removal\n");
Coalesced.push_back(&MI);
}
}
void RegAllocFast::handleDebugValue(MachineInstr &MI) {
MachineOperand &MO = MI.getDebugOperand(0);
// Ignore DBG_VALUEs that aren't based on virtual registers. These are
// mostly constants and frame indices.
if (!MO.isReg())
return;
Register Reg = MO.getReg();
if (!Register::isVirtualRegister(Reg))
return;
// Already spilled to a stackslot?
int SS = StackSlotForVirtReg[Reg];
if (SS != -1) {
// Modify DBG_VALUE now that the value is in a spill slot.
updateDbgValueForSpill(MI, SS);
LLVM_DEBUG(dbgs() << "Rewrite DBG_VALUE for spilled memory: " << MI);
return;
}
// See if this virtual register has already been allocated to a physical
// register or spilled to a stack slot.
LiveRegMap::iterator LRI = findLiveVirtReg(Reg);
if (LRI != LiveVirtRegs.end() && LRI->PhysReg) {
setPhysReg(MI, MO, LRI->PhysReg);
} else {
DanglingDbgValues[Reg].push_back(&MI);
}
// If Reg hasn't been spilled, put this DBG_VALUE in LiveDbgValueMap so
// that future spills of Reg will have DBG_VALUEs.
LiveDbgValueMap[Reg].push_back(&MI);
}
void RegAllocFast::handleBundle(MachineInstr &MI) {
MachineBasicBlock::instr_iterator BundledMI = MI.getIterator();
++BundledMI;
while (BundledMI->isBundledWithPred()) {
for (unsigned I = 0; I < BundledMI->getNumOperands(); ++I) {
MachineOperand &MO = BundledMI->getOperand(I);
if (!MO.isReg())
continue;
Register Reg = MO.getReg();
if (!Reg.isVirtual())
continue;
DenseMap<Register, MCPhysReg>::iterator DI;
DI = BundleVirtRegsMap.find(Reg);
assert(DI != BundleVirtRegsMap.end() && "Unassigned virtual register");
setPhysReg(MI, MO, DI->second);
}
++BundledMI;
}
}
void RegAllocFast::allocateBasicBlock(MachineBasicBlock &MBB) {
this->MBB = &MBB;
LLVM_DEBUG(dbgs() << "\nAllocating " << MBB);
RegUnitStates.assign(TRI->getNumRegUnits(), regFree);
assert(LiveVirtRegs.empty() && "Mapping not cleared from last block?");
for (MachineBasicBlock *Succ : MBB.successors()) {
for (const MachineBasicBlock::RegisterMaskPair &LI : Succ->liveins())
setPhysRegState(LI.PhysReg, regPreAssigned);
}
Coalesced.clear();
// Traverse block in reverse order allocating instructions one by one.
for (MachineInstr &MI : reverse(MBB)) {
LLVM_DEBUG(
dbgs() << "\n>> " << MI << "Regs:";
dumpState()
);
// Special handling for debug values. Note that they are not allowed to
// affect codegen of the other instructions in any way.
if (MI.isDebugValue()) {
handleDebugValue(MI);
continue;
}
allocateInstruction(MI);
// Once BUNDLE header is assigned registers, same assignments need to be
// done for bundled MIs.
if (MI.getOpcode() == TargetOpcode::BUNDLE) {
handleBundle(MI);
}
}
LLVM_DEBUG(
dbgs() << "Begin Regs:";
dumpState()
);
// Spill all physical registers holding virtual registers now.
LLVM_DEBUG(dbgs() << "Loading live registers at begin of block.\n");
reloadAtBegin(MBB);
// Erase all the coalesced copies. We are delaying it until now because
// LiveVirtRegs might refer to the instrs.
for (MachineInstr *MI : Coalesced)
MBB.erase(MI);
NumCoalesced += Coalesced.size();
for (auto &UDBGPair : DanglingDbgValues) {
for (MachineInstr *DbgValue : UDBGPair.second) {
assert(DbgValue->isDebugValue() && "expected DBG_VALUE");
MachineOperand &MO = DbgValue->getOperand(0);
// Nothing to do if the vreg was spilled in the meantime.
if (!MO.isReg())
continue;
LLVM_DEBUG(dbgs() << "Register did not survive for " << *DbgValue
<< '\n');
MO.setReg(0);
}
}
DanglingDbgValues.clear();
LLVM_DEBUG(MBB.dump());
}
bool RegAllocFast::runOnMachineFunction(MachineFunction &MF) {
LLVM_DEBUG(dbgs() << "********** FAST REGISTER ALLOCATION **********\n"
<< "********** Function: " << MF.getName() << '\n');
MRI = &MF.getRegInfo();
const TargetSubtargetInfo &STI = MF.getSubtarget();
TRI = STI.getRegisterInfo();
TII = STI.getInstrInfo();
MFI = &MF.getFrameInfo();
MRI->freezeReservedRegs(MF);
RegClassInfo.runOnMachineFunction(MF);
unsigned NumRegUnits = TRI->getNumRegUnits();
UsedInInstr.clear();
UsedInInstr.setUniverse(NumRegUnits);
PhysRegUses.clear();
PhysRegUses.setUniverse(NumRegUnits);
// initialize the virtual->physical register map to have a 'null'
// mapping for all virtual registers
unsigned NumVirtRegs = MRI->getNumVirtRegs();
StackSlotForVirtReg.resize(NumVirtRegs);
LiveVirtRegs.setUniverse(NumVirtRegs);
MayLiveAcrossBlocks.clear();
MayLiveAcrossBlocks.resize(NumVirtRegs);
// Loop over all of the basic blocks, eliminating virtual register references
for (MachineBasicBlock &MBB : MF)
allocateBasicBlock(MBB);
// All machine operands and other references to virtual registers have been
// replaced. Remove the virtual registers.
MRI->clearVirtRegs();
StackSlotForVirtReg.clear();
LiveDbgValueMap.clear();
return true;
}
FunctionPass *llvm::createFastRegisterAllocator() {
return new RegAllocFast();
}
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