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llvm-mirror/lib/CodeGen/RegAllocFast.cpp
Tim Northover d6d3226a57 MachineBasicBlock: add liveout iterator aware of which liveins are defined by the runtime. 
Using this in RegAlloc fast reduces register pressure, and in some cases allows
x86 code to compile that wouldn't before.
2021-05-19 11:00:24 +01:00

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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<MachineOperand *, 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;
// Register masks attached to the current instruction.
SmallVector<const uint32_t *> RegMasks;
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 physreg is clobbered by instruction's regmask(s).
bool isClobberedByRegMasks(MCPhysReg PhysReg) const {
return llvm::any_of(RegMasks, [PhysReg](const uint32_t *Mask) {
return MachineOperand::clobbersPhysReg(Mask, PhysReg);
});
}
/// Check if a physreg or any of its aliases are used in this instruction.
bool isRegUsedInInstr(MCPhysReg PhysReg, bool LookAtPhysRegUses) const {
if (LookAtPhysRegUses && isClobberedByRegMasks(PhysReg))
return true;
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<MachineOperand *> &LRIDbgOperands = LiveDbgValueMap[VirtReg];
SmallDenseMap<MachineInstr *, SmallVector<const MachineOperand *>>
SpilledOperandsMap;
for (MachineOperand *MO : LRIDbgOperands)
SpilledOperandsMap[MO->getParent()].push_back(MO);
for (auto MISpilledOperands : SpilledOperandsMap) {
MachineInstr &DBG = *MISpilledOperands.first;
MachineInstr *NewDV = buildDbgValueForSpill(
*MBB, Before, *MISpilledOperands.first, FI, MISpilledOperands.second);
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.
// TODO We can potentially do this for list debug values as well if we know
// how the dbg_values are getting unassigned.
if (DBG.isNonListDebugValue()) {
MachineOperand &MO = DBG.getDebugOperand(0);
if (MO.isReg() && MO.getReg() == 0) {
updateDbgValueForSpill(DBG, FI, 0);
}
}
}
// 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.
LRIDbgOperands.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());
if (!DbgValue->hasDebugOperandForReg(VirtReg))
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;
}
}
for (MachineOperand &MO : DbgValue->getDebugOperandsForReg(VirtReg)) {
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();
RegMasks.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;
RegMasks.push_back(MO.getRegMask());
}
}
// 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;
}
assert((!MO.isTied() || !isClobberedByRegMasks(MO.getReg())) &&
"tied def assigned to clobbered register");
// 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) {
assert(!RegMasks.empty() && "expected RegMask");
// MRI bookkeeping.
for (const auto *RM : RegMasks)
MRI->addPhysRegsUsedFromRegMask(RM);
// Displace clobbered registers.
for (const LiveReg &LR : LiveVirtRegs) {
MCPhysReg PhysReg = LR.PhysReg;
if (PhysReg != 0 && isClobberedByRegMasks(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) {
// Ignore DBG_VALUEs that aren't based on virtual registers. These are
// mostly constants and frame indices.
for (Register Reg : MI.getUsedDebugRegs()) {
if (!Register::isVirtualRegister(Reg))
continue;
// 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, Reg);
LLVM_DEBUG(dbgs() << "Rewrite DBG_VALUE for spilled memory: " << MI);
continue;
}
// See if this virtual register has already been allocated to a physical
// register or spilled to a stack slot.
LiveRegMap::iterator LRI = findLiveVirtReg(Reg);
SmallVector<MachineOperand *> DbgOps;
for (MachineOperand &Op : MI.getDebugOperandsForReg(Reg))
DbgOps.push_back(&Op);
if (LRI != LiveVirtRegs.end() && LRI->PhysReg) {
// Update every use of Reg within MI.
for (auto &RegMO : DbgOps)
setPhysReg(MI, *RegMO, 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].append(DbgOps.begin(), DbgOps.end());
}
}
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 (auto &LiveReg : MBB.liveouts())
setPhysRegState(LiveReg.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");
// Nothing to do if the vreg was spilled in the meantime.
if (!DbgValue->hasDebugOperandForReg(UDBGPair.first))
continue;
LLVM_DEBUG(dbgs() << "Register did not survive for " << *DbgValue
<< '\n');
DbgValue->setDebugValueUndef();
}
}
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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