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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/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");
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.
unsigned VirtReg; ///< Virtual register number.
MCPhysReg PhysReg = 0; ///< Currently held here.
unsigned short LastOpNum = 0; ///< OpNum on LastUse.
bool Dirty = false; ///< Register needs spill.
explicit LiveReg(unsigned VirtReg) : VirtReg(VirtReg) {}
unsigned getSparseSetIndex() const {
return TargetRegisterInfo::virtReg2Index(VirtReg);
}
};
using LiveRegMap = SparseSet<LiveReg>;
/// This map contains entries for each virtual register that is currently
/// available in a physical register.
LiveRegMap LiveVirtRegs;
DenseMap<unsigned, SmallVector<MachineInstr *, 2>> LiveDbgValueMap;
/// State of a physical register.
enum RegState {
/// A disabled register is not available for allocation, but an alias may
/// be in use. A register can only be moved out of the disabled state if
/// all aliases are disabled.
regDisabled,
/// A free register is not currently in use and can be allocated
/// immediately without checking aliases.
regFree,
/// A reserved register has been assigned explicitly (e.g., setting up a
/// call parameter), and it remains reserved until it is used.
regReserved
/// A register state may also be a virtual register number, indication
/// that the physical register is currently allocated to a virtual
/// register. In that case, LiveVirtRegs contains the inverse mapping.
};
/// Maps each physical register to a RegState enum or a virtual register.
std::vector<unsigned> PhysRegState;
SmallVector<unsigned, 16> VirtDead;
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;
void setPhysRegState(MCPhysReg PhysReg, unsigned NewState);
/// 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) const {
for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units)
if (UsedInInstr.count(*Units))
return true;
return false;
}
enum : unsigned {
spillClean = 50,
spillDirty = 100,
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);
}
private:
bool runOnMachineFunction(MachineFunction &MF) override;
void allocateBasicBlock(MachineBasicBlock &MBB);
void allocateInstruction(MachineInstr &MI);
void handleDebugValue(MachineInstr &MI);
void handleThroughOperands(MachineInstr &MI,
SmallVectorImpl<unsigned> &VirtDead);
bool isLastUseOfLocalReg(const MachineOperand &MO) const;
void addKillFlag(const LiveReg &LRI);
void killVirtReg(LiveReg &LR);
void killVirtReg(unsigned VirtReg);
void spillVirtReg(MachineBasicBlock::iterator MI, LiveReg &LR);
void spillVirtReg(MachineBasicBlock::iterator MI, unsigned VirtReg);
void usePhysReg(MachineOperand &MO);
void definePhysReg(MachineBasicBlock::iterator MI, MCPhysReg PhysReg,
RegState NewState);
unsigned calcSpillCost(MCPhysReg PhysReg) const;
void assignVirtToPhysReg(LiveReg &, MCPhysReg PhysReg);
LiveRegMap::iterator findLiveVirtReg(unsigned VirtReg) {
return LiveVirtRegs.find(TargetRegisterInfo::virtReg2Index(VirtReg));
}
LiveRegMap::const_iterator findLiveVirtReg(unsigned VirtReg) const {
return LiveVirtRegs.find(TargetRegisterInfo::virtReg2Index(VirtReg));
}
void allocVirtReg(MachineInstr &MI, LiveReg &LR, unsigned Hint);
void allocVirtRegUndef(MachineOperand &MO);
MCPhysReg defineVirtReg(MachineInstr &MI, unsigned OpNum, unsigned VirtReg,
unsigned Hint);
LiveReg &reloadVirtReg(MachineInstr &MI, unsigned OpNum, unsigned VirtReg,
unsigned Hint);
void spillAll(MachineBasicBlock::iterator MI);
bool setPhysReg(MachineInstr &MI, MachineOperand &MO, MCPhysReg PhysReg);
int getStackSpaceFor(unsigned VirtReg);
void spill(MachineBasicBlock::iterator Before, unsigned VirtReg,
MCPhysReg AssignedReg, bool Kill);
void reload(MachineBasicBlock::iterator Before, unsigned VirtReg,
MCPhysReg PhysReg);
void dumpState();
};
} // end anonymous namespace
char RegAllocFast::ID = 0;
INITIALIZE_PASS(RegAllocFast, "regallocfast", "Fast Register Allocator", false,
false)
void RegAllocFast::setPhysRegState(MCPhysReg PhysReg, unsigned NewState) {
PhysRegState[PhysReg] = NewState;
}
/// This allocates space for the specified virtual register to be held on the
/// stack.
int RegAllocFast::getStackSpaceFor(unsigned 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);
unsigned Align = TRI->getSpillAlignment(RC);
int FrameIdx = MFI->CreateSpillStackObject(Size, Align);
// Assign the slot.
StackSlotForVirtReg[VirtReg] = FrameIdx;
return FrameIdx;
}
/// 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, unsigned VirtReg,
MCPhysReg AssignedReg, bool Kill) {
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;
// If this register is used by DBG_VALUE then insert new DBG_VALUE to
// identify spilled location as the place to find corresponding variable's
// value.
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);
}
// 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, unsigned 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;
}
/// Return true if MO is the only remaining reference to its virtual register,
/// and it is guaranteed to be a block-local register.
bool RegAllocFast::isLastUseOfLocalReg(const MachineOperand &MO) const {
// If the register has ever been spilled or reloaded, we conservatively assume
// it is a global register used in multiple blocks.
if (StackSlotForVirtReg[MO.getReg()] != -1)
return false;
// Check that the use/def chain has exactly one operand - MO.
MachineRegisterInfo::reg_nodbg_iterator I = MRI->reg_nodbg_begin(MO.getReg());
if (&*I != &MO)
return false;
return ++I == MRI->reg_nodbg_end();
}
/// Set kill flags on last use of a virtual register.
void RegAllocFast::addKillFlag(const LiveReg &LR) {
if (!LR.LastUse) return;
MachineOperand &MO = LR.LastUse->getOperand(LR.LastOpNum);
if (MO.isUse() && !LR.LastUse->isRegTiedToDefOperand(LR.LastOpNum)) {
if (MO.getReg() == LR.PhysReg)
MO.setIsKill();
// else, don't do anything we are problably redefining a
// subreg of this register and given we don't track which
// lanes are actually dead, we cannot insert a kill flag here.
// Otherwise we may end up in a situation like this:
// ... = (MO) physreg:sub1, implicit killed physreg
// ... <== Here we would allow later pass to reuse physreg:sub1
// which is potentially wrong.
// LR:sub0 = ...
// ... = LR.sub1 <== This is going to use physreg:sub1
}
}
/// Mark virtreg as no longer available.
void RegAllocFast::killVirtReg(LiveReg &LR) {
addKillFlag(LR);
assert(PhysRegState[LR.PhysReg] == LR.VirtReg &&
"Broken RegState mapping");
setPhysRegState(LR.PhysReg, regFree);
LR.PhysReg = 0;
}
/// Mark virtreg as no longer available.
void RegAllocFast::killVirtReg(unsigned VirtReg) {
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"killVirtReg needs a virtual register");
LiveRegMap::iterator LRI = findLiveVirtReg(VirtReg);
if (LRI != LiveVirtRegs.end() && LRI->PhysReg)
killVirtReg(*LRI);
}
/// This method spills the value specified by VirtReg into the corresponding
/// stack slot if needed.
void RegAllocFast::spillVirtReg(MachineBasicBlock::iterator MI,
unsigned VirtReg) {
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Spilling a physical register is illegal!");
LiveRegMap::iterator LRI = findLiveVirtReg(VirtReg);
assert(LRI != LiveVirtRegs.end() && LRI->PhysReg &&
"Spilling unmapped virtual register");
spillVirtReg(MI, *LRI);
}
/// Do the actual work of spilling.
void RegAllocFast::spillVirtReg(MachineBasicBlock::iterator MI, LiveReg &LR) {
assert(PhysRegState[LR.PhysReg] == LR.VirtReg && "Broken RegState mapping");
if (LR.Dirty) {
// If this physreg is used by the instruction, we want to kill it on the
// instruction, not on the spill.
bool SpillKill = MachineBasicBlock::iterator(LR.LastUse) != MI;
LR.Dirty = false;
spill(MI, LR.VirtReg, LR.PhysReg, SpillKill);
if (SpillKill)
LR.LastUse = nullptr; // Don't kill register again
}
killVirtReg(LR);
}
/// Spill all dirty virtregs without killing them.
void RegAllocFast::spillAll(MachineBasicBlock::iterator MI) {
if (LiveVirtRegs.empty())
return;
// The LiveRegMap is keyed by an unsigned (the virtreg number), so the order
// of spilling here is deterministic, if arbitrary.
for (LiveReg &LR : LiveVirtRegs) {
if (!LR.PhysReg)
continue;
spillVirtReg(MI, LR);
}
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.
void RegAllocFast::usePhysReg(MachineOperand &MO) {
// Ignore undef uses.
if (MO.isUndef())
return;
unsigned PhysReg = MO.getReg();
assert(TargetRegisterInfo::isPhysicalRegister(PhysReg) &&
"Bad usePhysReg operand");
markRegUsedInInstr(PhysReg);
switch (PhysRegState[PhysReg]) {
case regDisabled:
break;
case regReserved:
PhysRegState[PhysReg] = regFree;
LLVM_FALLTHROUGH;
case regFree:
MO.setIsKill();
return;
default:
// The physreg was allocated to a virtual register. That means the value we
// wanted has been clobbered.
llvm_unreachable("Instruction uses an allocated register");
}
// Maybe a superregister is reserved?
for (MCRegAliasIterator AI(PhysReg, TRI, false); AI.isValid(); ++AI) {
MCPhysReg Alias = *AI;
switch (PhysRegState[Alias]) {
case regDisabled:
break;
case regReserved:
// Either PhysReg is a subregister of Alias and we mark the
// whole register as free, or PhysReg is the superregister of
// Alias and we mark all the aliases as disabled before freeing
// PhysReg.
// In the latter case, since PhysReg was disabled, this means that
// its value is defined only by physical sub-registers. This check
// is performed by the assert of the default case in this loop.
// Note: The value of the superregister may only be partial
// defined, that is why regDisabled is a valid state for aliases.
assert((TRI->isSuperRegister(PhysReg, Alias) ||
TRI->isSuperRegister(Alias, PhysReg)) &&
"Instruction is not using a subregister of a reserved register");
LLVM_FALLTHROUGH;
case regFree:
if (TRI->isSuperRegister(PhysReg, Alias)) {
// Leave the superregister in the working set.
setPhysRegState(Alias, regFree);
MO.getParent()->addRegisterKilled(Alias, TRI, true);
return;
}
// Some other alias was in the working set - clear it.
setPhysRegState(Alias, regDisabled);
break;
default:
llvm_unreachable("Instruction uses an alias of an allocated register");
}
}
// All aliases are disabled, bring register into working set.
setPhysRegState(PhysReg, regFree);
MO.setIsKill();
}
/// Mark PhysReg as reserved or free after spilling any virtregs. This is very
/// similar to defineVirtReg except the physreg is reserved instead of
/// allocated.
void RegAllocFast::definePhysReg(MachineBasicBlock::iterator MI,
MCPhysReg PhysReg, RegState NewState) {
markRegUsedInInstr(PhysReg);
switch (unsigned VirtReg = PhysRegState[PhysReg]) {
case regDisabled:
break;
default:
spillVirtReg(MI, VirtReg);
LLVM_FALLTHROUGH;
case regFree:
case regReserved:
setPhysRegState(PhysReg, NewState);
return;
}
// This is a disabled register, disable all aliases.
setPhysRegState(PhysReg, NewState);
for (MCRegAliasIterator AI(PhysReg, TRI, false); AI.isValid(); ++AI) {
MCPhysReg Alias = *AI;
switch (unsigned VirtReg = PhysRegState[Alias]) {
case regDisabled:
break;
default:
spillVirtReg(MI, VirtReg);
LLVM_FALLTHROUGH;
case regFree:
case regReserved:
setPhysRegState(Alias, regDisabled);
if (TRI->isSuperRegister(PhysReg, Alias))
return;
break;
}
}
}
/// 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 {
if (isRegUsedInInstr(PhysReg)) {
LLVM_DEBUG(dbgs() << printReg(PhysReg, TRI)
<< " is already used in instr.\n");
return spillImpossible;
}
switch (unsigned VirtReg = PhysRegState[PhysReg]) {
case regDisabled:
break;
case regFree:
return 0;
case regReserved:
LLVM_DEBUG(dbgs() << printReg(VirtReg, TRI) << " corresponding "
<< printReg(PhysReg, TRI) << " is reserved already.\n");
return spillImpossible;
default: {
LiveRegMap::const_iterator LRI = findLiveVirtReg(VirtReg);
assert(LRI != LiveVirtRegs.end() && LRI->PhysReg &&
"Missing VirtReg entry");
return LRI->Dirty ? spillDirty : spillClean;
}
}
// This is a disabled register, add up cost of aliases.
LLVM_DEBUG(dbgs() << printReg(PhysReg, TRI) << " is disabled.\n");
unsigned Cost = 0;
for (MCRegAliasIterator AI(PhysReg, TRI, false); AI.isValid(); ++AI) {
MCPhysReg Alias = *AI;
switch (unsigned VirtReg = PhysRegState[Alias]) {
case regDisabled:
break;
case regFree:
++Cost;
break;
case regReserved:
return spillImpossible;
default: {
LiveRegMap::const_iterator LRI = findLiveVirtReg(VirtReg);
assert(LRI != LiveVirtRegs.end() && LRI->PhysReg &&
"Missing VirtReg entry");
Cost += LRI->Dirty ? spillDirty : spillClean;
break;
}
}
}
return Cost;
}
/// 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(LiveReg &LR, MCPhysReg PhysReg) {
unsigned 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);
}
/// Allocates a physical register for VirtReg.
void RegAllocFast::allocVirtReg(MachineInstr &MI, LiveReg &LR, unsigned Hint) {
const unsigned VirtReg = LR.VirtReg;
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Can only allocate virtual registers");
const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
LLVM_DEBUG(dbgs() << "Search register for " << printReg(VirtReg)
<< " in class " << TRI->getRegClassName(&RC)
<< " with hint " << printReg(Hint, TRI) << '\n');
// Take hint when possible.
if (TargetRegisterInfo::isPhysicalRegister(Hint) &&
MRI->isAllocatable(Hint) && RC.contains(Hint)) {
// Ignore the hint if we would have to spill a dirty register.
unsigned Cost = calcSpillCost(Hint);
if (Cost < spillDirty) {
if (Cost)
definePhysReg(MI, Hint, regFree);
assignVirtToPhysReg(LR, Hint);
return;
}
}
MCPhysReg BestReg = 0;
unsigned BestCost = spillImpossible;
ArrayRef<MCPhysReg> AllocationOrder = RegClassInfo.getOrder(&RC);
for (MCPhysReg PhysReg : AllocationOrder) {
LLVM_DEBUG(dbgs() << "\tRegister: " << printReg(PhysReg, TRI) << ' ');
unsigned Cost = calcSpillCost(PhysReg);
LLVM_DEBUG(dbgs() << "Cost: " << Cost << " BestCost: " << BestCost << '\n');
// Immediate take a register with cost 0.
if (Cost == 0) {
assignVirtToPhysReg(LR, PhysReg);
return;
}
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");
definePhysReg(MI, *AllocationOrder.begin(), regFree);
assignVirtToPhysReg(LR, *AllocationOrder.begin());
return;
}
definePhysReg(MI, BestReg, regFree);
assignVirtToPhysReg(LR, BestReg);
}
void RegAllocFast::allocVirtRegUndef(MachineOperand &MO) {
assert(MO.isUndef() && "expected undef use");
unsigned VirtReg = MO.getReg();
assert(TargetRegisterInfo::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);
}
/// Allocates a register for VirtReg and mark it as dirty.
MCPhysReg RegAllocFast::defineVirtReg(MachineInstr &MI, unsigned OpNum,
unsigned VirtReg, unsigned Hint) {
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Not a virtual register");
LiveRegMap::iterator LRI;
bool New;
std::tie(LRI, New) = LiveVirtRegs.insert(LiveReg(VirtReg));
if (!LRI->PhysReg) {
// If there is no hint, peek at the only use of this register.
if ((!Hint || !TargetRegisterInfo::isPhysicalRegister(Hint)) &&
MRI->hasOneNonDBGUse(VirtReg)) {
const MachineInstr &UseMI = *MRI->use_instr_nodbg_begin(VirtReg);
// It's a copy, use the destination register as a hint.
if (UseMI.isCopyLike())
Hint = UseMI.getOperand(0).getReg();
}
allocVirtReg(MI, *LRI, Hint);
} else if (LRI->LastUse) {
// Redefining a live register - kill at the last use, unless it is this
// instruction defining VirtReg multiple times.
if (LRI->LastUse != &MI || LRI->LastUse->getOperand(LRI->LastOpNum).isUse())
addKillFlag(*LRI);
}
assert(LRI->PhysReg && "Register not assigned");
LRI->LastUse = &MI;
LRI->LastOpNum = OpNum;
LRI->Dirty = true;
markRegUsedInInstr(LRI->PhysReg);
return LRI->PhysReg;
}
/// Make sure VirtReg is available in a physreg and return it.
RegAllocFast::LiveReg &RegAllocFast::reloadVirtReg(MachineInstr &MI,
unsigned OpNum,
unsigned VirtReg,
unsigned Hint) {
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Not a virtual register");
LiveRegMap::iterator LRI;
bool New;
std::tie(LRI, New) = LiveVirtRegs.insert(LiveReg(VirtReg));
MachineOperand &MO = MI.getOperand(OpNum);
if (!LRI->PhysReg) {
allocVirtReg(MI, *LRI, Hint);
reload(MI, VirtReg, LRI->PhysReg);
} else if (LRI->Dirty) {
if (isLastUseOfLocalReg(MO)) {
LLVM_DEBUG(dbgs() << "Killing last use: " << MO << '\n');
if (MO.isUse())
MO.setIsKill();
else
MO.setIsDead();
} else if (MO.isKill()) {
LLVM_DEBUG(dbgs() << "Clearing dubious kill: " << MO << '\n');
MO.setIsKill(false);
} else if (MO.isDead()) {
LLVM_DEBUG(dbgs() << "Clearing dubious dead: " << MO << '\n');
MO.setIsDead(false);
}
} else if (MO.isKill()) {
// We must remove kill flags from uses of reloaded registers because the
// register would be killed immediately, and there might be a second use:
// %foo = OR killed %x, %x
// This would cause a second reload of %x into a different register.
LLVM_DEBUG(dbgs() << "Clearing clean kill: " << MO << '\n');
MO.setIsKill(false);
} else if (MO.isDead()) {
LLVM_DEBUG(dbgs() << "Clearing clean dead: " << MO << '\n');
MO.setIsDead(false);
}
assert(LRI->PhysReg && "Register not assigned");
LRI->LastUse = &MI;
LRI->LastOpNum = OpNum;
markRegUsedInInstr(LRI->PhysReg);
return *LRI;
}
/// 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.
bool RegAllocFast::setPhysReg(MachineInstr &MI, MachineOperand &MO,
MCPhysReg PhysReg) {
bool Dead = MO.isDead();
if (!MO.getSubReg()) {
MO.setReg(PhysReg);
MO.setIsRenamable(true);
return MO.isKill() || Dead;
}
// Handle subregister index.
MO.setReg(PhysReg ? TRI->getSubReg(PhysReg, MO.getSubReg()) : 0);
MO.setIsRenamable(true);
MO.setSubReg(0);
// A kill flag implies killing the full register. Add corresponding super
// register kill.
if (MO.isKill()) {
MI.addRegisterKilled(PhysReg, TRI, true);
return true;
}
// A <def,read-undef> of a sub-register requires an implicit def of the full
// register.
if (MO.isDef() && MO.isUndef())
MI.addRegisterDefined(PhysReg, TRI);
return Dead;
}
// Handles special instruction operand like early clobbers and tied ops when
// there are additional physreg defines.
void RegAllocFast::handleThroughOperands(MachineInstr &MI,
SmallVectorImpl<unsigned> &VirtDead) {
LLVM_DEBUG(dbgs() << "Scanning for through registers:");
SmallSet<unsigned, 8> ThroughRegs;
for (const MachineOperand &MO : MI.operands()) {
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
if (MO.isEarlyClobber() || (MO.isUse() && MO.isTied()) ||
(MO.getSubReg() && MI.readsVirtualRegister(Reg))) {
if (ThroughRegs.insert(Reg).second)
LLVM_DEBUG(dbgs() << ' ' << printReg(Reg));
}
}
// If any physreg defines collide with preallocated through registers,
// we must spill and reallocate.
LLVM_DEBUG(dbgs() << "\nChecking for physdef collisions.\n");
for (const MachineOperand &MO : MI.operands()) {
if (!MO.isReg() || !MO.isDef()) continue;
unsigned Reg = MO.getReg();
if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
markRegUsedInInstr(Reg);
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
if (ThroughRegs.count(PhysRegState[*AI]))
definePhysReg(MI, *AI, regFree);
}
}
SmallVector<unsigned, 8> PartialDefs;
LLVM_DEBUG(dbgs() << "Allocating tied uses.\n");
for (unsigned I = 0, E = MI.getNumOperands(); I != E; ++I) {
MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
if (MO.isUse()) {
if (!MO.isTied()) continue;
LLVM_DEBUG(dbgs() << "Operand " << I << "(" << MO
<< ") is tied to operand " << MI.findTiedOperandIdx(I)
<< ".\n");
LiveReg &LR = reloadVirtReg(MI, I, Reg, 0);
MCPhysReg PhysReg = LR.PhysReg;
setPhysReg(MI, MO, PhysReg);
// Note: we don't update the def operand yet. That would cause the normal
// def-scan to attempt spilling.
} else if (MO.getSubReg() && MI.readsVirtualRegister(Reg)) {
LLVM_DEBUG(dbgs() << "Partial redefine: " << MO << '\n');
// Reload the register, but don't assign to the operand just yet.
// That would confuse the later phys-def processing pass.
LiveReg &LR = reloadVirtReg(MI, I, Reg, 0);
PartialDefs.push_back(LR.PhysReg);
}
}
LLVM_DEBUG(dbgs() << "Allocating early clobbers.\n");
for (unsigned I = 0, E = MI.getNumOperands(); I != E; ++I) {
const MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
if (!MO.isEarlyClobber())
continue;
// Note: defineVirtReg may invalidate MO.
MCPhysReg PhysReg = defineVirtReg(MI, I, Reg, 0);
if (setPhysReg(MI, MI.getOperand(I), PhysReg))
VirtDead.push_back(Reg);
}
// Restore UsedInInstr to a state usable for allocating normal virtual uses.
UsedInInstr.clear();
for (const MachineOperand &MO : MI.operands()) {
if (!MO.isReg() || (MO.isDef() && !MO.isEarlyClobber())) continue;
unsigned Reg = MO.getReg();
if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
LLVM_DEBUG(dbgs() << "\tSetting " << printReg(Reg, TRI)
<< " as used in instr\n");
markRegUsedInInstr(Reg);
}
// Also mark PartialDefs as used to avoid reallocation.
for (unsigned PartialDef : PartialDefs)
markRegUsedInInstr(PartialDef);
}
#ifndef NDEBUG
void RegAllocFast::dumpState() {
for (unsigned Reg = 1, E = TRI->getNumRegs(); Reg != E; ++Reg) {
if (PhysRegState[Reg] == regDisabled) continue;
dbgs() << " " << printReg(Reg, TRI);
switch(PhysRegState[Reg]) {
case regFree:
break;
case regReserved:
dbgs() << "*";
break;
default: {
dbgs() << '=' << printReg(PhysRegState[Reg]);
LiveRegMap::iterator LRI = findLiveVirtReg(PhysRegState[Reg]);
assert(LRI != LiveVirtRegs.end() && LRI->PhysReg &&
"Missing VirtReg entry");
if (LRI->Dirty)
dbgs() << "*";
assert(LRI->PhysReg == Reg && "Bad inverse map");
break;
}
}
}
dbgs() << '\n';
// Check that LiveVirtRegs is the inverse.
for (LiveRegMap::iterator i = LiveVirtRegs.begin(),
e = LiveVirtRegs.end(); i != e; ++i) {
if (!i->PhysReg)
continue;
assert(TargetRegisterInfo::isVirtualRegister(i->VirtReg) &&
"Bad map key");
assert(TargetRegisterInfo::isPhysicalRegister(i->PhysReg) &&
"Bad map value");
assert(PhysRegState[i->PhysReg] == i->VirtReg && "Bad inverse map");
}
}
#endif
void RegAllocFast::allocateInstruction(MachineInstr &MI) {
const MCInstrDesc &MCID = MI.getDesc();
// If this is a copy, we may be able to coalesce.
unsigned CopySrcReg = 0;
unsigned CopyDstReg = 0;
unsigned CopySrcSub = 0;
unsigned CopyDstSub = 0;
if (MI.isCopy()) {
CopyDstReg = MI.getOperand(0).getReg();
CopySrcReg = MI.getOperand(1).getReg();
CopyDstSub = MI.getOperand(0).getSubReg();
CopySrcSub = MI.getOperand(1).getSubReg();
}
// Track registers used by instruction.
UsedInInstr.clear();
// First scan.
// Mark physreg uses and early clobbers as used.
// Find the end of the virtreg operands
unsigned VirtOpEnd = 0;
bool hasTiedOps = false;
bool hasEarlyClobbers = false;
bool hasPartialRedefs = false;
bool hasPhysDefs = false;
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
// Make sure MRI knows about registers clobbered by regmasks.
if (MO.isRegMask()) {
MRI->addPhysRegsUsedFromRegMask(MO.getRegMask());
continue;
}
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!Reg) continue;
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
VirtOpEnd = i+1;
if (MO.isUse()) {
hasTiedOps = hasTiedOps ||
MCID.getOperandConstraint(i, MCOI::TIED_TO) != -1;
} else {
if (MO.isEarlyClobber())
hasEarlyClobbers = true;
if (MO.getSubReg() && MI.readsVirtualRegister(Reg))
hasPartialRedefs = true;
}
continue;
}
if (!MRI->isAllocatable(Reg)) continue;
if (MO.isUse()) {
usePhysReg(MO);
} else if (MO.isEarlyClobber()) {
definePhysReg(MI, Reg,
(MO.isImplicit() || MO.isDead()) ? regFree : regReserved);
hasEarlyClobbers = true;
} else
hasPhysDefs = true;
}
// The instruction may have virtual register operands that must be allocated
// the same register at use-time and def-time: early clobbers and tied
// operands. If there are also physical defs, these registers must avoid
// both physical defs and uses, making them more constrained than normal
// operands.
// Similarly, if there are multiple defs and tied operands, we must make
// sure the same register is allocated to uses and defs.
// We didn't detect inline asm tied operands above, so just make this extra
// pass for all inline asm.
if (MI.isInlineAsm() || hasEarlyClobbers || hasPartialRedefs ||
(hasTiedOps && (hasPhysDefs || MCID.getNumDefs() > 1))) {
handleThroughOperands(MI, VirtDead);
// Don't attempt coalescing when we have funny stuff going on.
CopyDstReg = 0;
// Pretend we have early clobbers so the use operands get marked below.
// This is not necessary for the common case of a single tied use.
hasEarlyClobbers = true;
}
// Second scan.
// Allocate virtreg uses.
bool HasUndefUse = false;
for (unsigned I = 0; I != VirtOpEnd; ++I) {
MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
if (MO.isUse()) {
if (MO.isUndef()) {
HasUndefUse = true;
// There is no need to allocate a register for an undef use.
continue;
}
LiveReg &LR = reloadVirtReg(MI, I, Reg, CopyDstReg);
MCPhysReg PhysReg = LR.PhysReg;
CopySrcReg = (CopySrcReg == Reg || CopySrcReg == PhysReg) ? PhysReg : 0;
if (setPhysReg(MI, MO, PhysReg))
killVirtReg(LR);
}
}
// 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;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
assert(MO.isUndef() && "Should only have undef virtreg uses left");
allocVirtRegUndef(MO);
}
}
// Track registers defined by instruction - early clobbers and tied uses at
// this point.
UsedInInstr.clear();
if (hasEarlyClobbers) {
for (const MachineOperand &MO : MI.operands()) {
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
// Look for physreg defs and tied uses.
if (!MO.isDef() && !MO.isTied()) continue;
markRegUsedInInstr(Reg);
}
}
unsigned DefOpEnd = MI.getNumOperands();
if (MI.isCall()) {
// Spill all virtregs before a call. This serves one purpose: If an
// exception is thrown, the landing pad is going to expect to find
// registers in their spill slots.
// Note: although this is appealing to just consider all definitions
// as call-clobbered, this is not correct because some of those
// definitions may be used later on and we do not want to reuse
// those for virtual registers in between.
LLVM_DEBUG(dbgs() << " Spilling remaining registers before call.\n");
spillAll(MI);
}
// Third scan.
// Allocate defs and collect dead defs.
for (unsigned I = 0; I != DefOpEnd; ++I) {
const MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg() || !MO.isDef() || !MO.getReg() || MO.isEarlyClobber())
continue;
unsigned Reg = MO.getReg();
if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
if (!MRI->isAllocatable(Reg)) continue;
definePhysReg(MI, Reg, MO.isDead() ? regFree : regReserved);
continue;
}
MCPhysReg PhysReg = defineVirtReg(MI, I, Reg, CopySrcReg);
if (setPhysReg(MI, MI.getOperand(I), PhysReg)) {
VirtDead.push_back(Reg);
CopyDstReg = 0; // cancel coalescing;
} else
CopyDstReg = (CopyDstReg == Reg || CopyDstReg == PhysReg) ? PhysReg : 0;
}
// Kill dead defs after the scan to ensure that multiple defs of the same
// register are allocated identically. We didn't need to do this for uses
// because we are crerating our own kill flags, and they are always at the
// last use.
for (unsigned VirtReg : VirtDead)
killVirtReg(VirtReg);
VirtDead.clear();
LLVM_DEBUG(dbgs() << "<< " << MI);
if (CopyDstReg && CopyDstReg == CopySrcReg && CopyDstSub == CopySrcSub) {
LLVM_DEBUG(dbgs() << "Mark identity copy for removal\n");
Coalesced.push_back(&MI);
}
}
void RegAllocFast::handleDebugValue(MachineInstr &MI) {
MachineOperand &MO = MI.getOperand(0);
// Ignore DBG_VALUEs that aren't based on virtual registers. These are
// mostly constants and frame indices.
if (!MO.isReg())
return;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
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 {
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() << "Modifying debug info due to spill:" << "\t" << MI);
return;
}
// We can't allocate a physreg for a DebugValue, sorry!
LLVM_DEBUG(dbgs() << "Unable to allocate vreg used by DBG_VALUE");
MO.setReg(0);
}
// 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::allocateBasicBlock(MachineBasicBlock &MBB) {
this->MBB = &MBB;
LLVM_DEBUG(dbgs() << "\nAllocating " << MBB);
PhysRegState.assign(TRI->getNumRegs(), regDisabled);
assert(LiveVirtRegs.empty() && "Mapping not cleared from last block?");
MachineBasicBlock::iterator MII = MBB.begin();
// Add live-in registers as live.
for (const MachineBasicBlock::RegisterMaskPair LI : MBB.liveins())
if (MRI->isAllocatable(LI.PhysReg))
definePhysReg(MII, LI.PhysReg, regReserved);
VirtDead.clear();
Coalesced.clear();
// Otherwise, sequentially allocate each instruction in the MBB.
for (MachineInstr &MI : 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);
}
// Spill all physical registers holding virtual registers now.
LLVM_DEBUG(dbgs() << "Spilling live registers at end of block.\n");
spillAll(MBB.getFirstTerminator());
// Erase all the coalesced copies. We are delaying it until now because
// LiveVirtRegs might refer to the instrs.
for (MachineInstr *MI : Coalesced)
MBB.erase(MI);
NumCoalesced += Coalesced.size();
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);
UsedInInstr.clear();
UsedInInstr.setUniverse(TRI->getNumRegUnits());
// 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);
// 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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