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llvm-mirror/lib/CodeGen/RegAllocFast.cpp
Quentin Colombet 98457980f5 [RAFast] Don't dereference MBB::end 
When RAFast sees liveins in on a basic block, it uses that information
to initialize the availability of the registers. The called
method uses an instruction as one of its argument and in the liveins
case, RAFast was dereferencing MBB::begin which can be MBB::end for
empty basic block.

Change the API of definePhysReg to use MachineBasicBlock::iterator
instead of MachineInstr so that we don't dereference an
invalid iterator while making the call.

rdar://problem/36952401

llvm-svn: 323710
2018-01-29 23:42:37 +00:00

1119 lines
40 KiB
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//===- RegAllocFast.cpp - A fast register allocator for debug code --------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \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(NumCopies, "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 v) : VirtReg(v) {}
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 *, 4>> LiveDbgValueMap;
/// Track the state of a physical register.
enum RegState {
/// A disabled register is not available for allocation, but an alias may
/// be in use. A register can only be moved out of the disabled state if
/// all aliases are disabled.
regDisabled,
/// A free register is not currently in use and can be allocated
/// immediately without checking aliases.
regFree,
/// A reserved register has been assigned explicitly (e.g., setting up a
/// call parameter), and it remains reserved until it is used.
regReserved
/// A register state may also be a virtual register number, indication
/// that the physical register is currently allocated to a virtual
/// register. In that case, LiveVirtRegs contains the inverse mapping.
};
/// One of the RegState enums, or a virtreg.
std::vector<unsigned> PhysRegState;
SmallVector<unsigned, 16> VirtDead;
SmallVector<MachineInstr *, 32> Coalesced;
/// Set of register units.
using UsedInInstrSet = SparseSet<unsigned>;
/// Set of register units that are used in the current instruction, and so
/// cannot be allocated.
UsedInInstrSet UsedInInstr;
/// 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;
}
/// This flag is set when LiveRegMap will be cleared completely after
/// spilling all live registers. LiveRegMap entries should not be erased.
bool isBulkSpilling = false;
enum : unsigned {
spillClean = 1,
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 &Fn) override;
void allocateBasicBlock(MachineBasicBlock &MBB);
void handleThroughOperands(MachineInstr &MI,
SmallVectorImpl<unsigned> &VirtDead);
int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass &RC);
bool isLastUseOfLocalReg(const MachineOperand &MO) const;
void addKillFlag(const LiveReg &LRI);
void killVirtReg(LiveRegMap::iterator LRI);
void killVirtReg(unsigned VirtReg);
void spillVirtReg(MachineBasicBlock::iterator MI, LiveRegMap::iterator);
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));
}
LiveRegMap::iterator assignVirtToPhysReg(unsigned VReg, MCPhysReg PhysReg);
LiveRegMap::iterator allocVirtReg(MachineInstr &MI, LiveRegMap::iterator,
unsigned Hint);
LiveRegMap::iterator defineVirtReg(MachineInstr &MI, unsigned OpNum,
unsigned VirtReg, unsigned Hint);
LiveRegMap::iterator reloadVirtReg(MachineInstr &MI, unsigned OpNum,
unsigned VirtReg, unsigned Hint);
void spillAll(MachineBasicBlock::iterator MI);
bool setPhysReg(MachineInstr &MI, unsigned OpNum, MCPhysReg PhysReg);
void dumpState();
};
} // end anonymous namespace
char RegAllocFast::ID = 0;
INITIALIZE_PASS(RegAllocFast, "regallocfast", "Fast Register Allocator", false,
false)
/// This allocates space for the specified virtual register to be held on the
/// stack.
int RegAllocFast::getStackSpaceFor(unsigned VirtReg,
const TargetRegisterClass &RC) {
// 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...
unsigned Size = TRI->getSpillSize(RC);
unsigned Align = TRI->getSpillAlignment(RC);
int FrameIdx = MFI->CreateSpillStackObject(Size, Align);
// Assign the slot.
StackSlotForVirtReg[VirtReg] = FrameIdx;
return FrameIdx;
}
/// 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(LiveRegMap::iterator LRI) {
addKillFlag(*LRI);
assert(PhysRegState[LRI->PhysReg] == LRI->VirtReg &&
"Broken RegState mapping");
PhysRegState[LRI->PhysReg] = regFree;
// Erase from LiveVirtRegs unless we're spilling in bulk.
if (!isBulkSpilling)
LiveVirtRegs.erase(LRI);
}
/// 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())
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() && "Spilling unmapped virtual register");
spillVirtReg(MI, LRI);
}
/// Do the actual work of spilling.
void RegAllocFast::spillVirtReg(MachineBasicBlock::iterator MI,
LiveRegMap::iterator LRI) {
LiveReg &LR = *LRI;
assert(PhysRegState[LR.PhysReg] == LRI->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;
DEBUG(dbgs() << "Spilling " << printReg(LRI->VirtReg, TRI)
<< " in " << printReg(LR.PhysReg, TRI));
const TargetRegisterClass &RC = *MRI->getRegClass(LRI->VirtReg);
int FI = getStackSpaceFor(LRI->VirtReg, RC);
DEBUG(dbgs() << " to stack slot #" << FI << "\n");
TII->storeRegToStackSlot(*MBB, MI, LR.PhysReg, SpillKill, FI, &RC, TRI);
++NumStores; // Update statistics
// If this register is used by DBG_VALUE then insert new DBG_VALUE to
// identify spilled location as the place to find corresponding variable's
// value.
SmallVectorImpl<MachineInstr *> &LRIDbgValues =
LiveDbgValueMap[LRI->VirtReg];
for (MachineInstr *DBG : LRIDbgValues) {
MachineInstr *NewDV = buildDbgValueForSpill(*MBB, MI, *DBG, FI);
assert(NewDV->getParent() == MBB && "dangling parent pointer");
(void)NewDV;
DEBUG(dbgs() << "Inserting debug info due to spill:" << "\n" << *NewDV);
}
// Now this register is spilled there is should not be any DBG_VALUE
// pointing to this register because they are all pointing to spilled value
// now.
LRIDbgValues.clear();
if (SpillKill)
LR.LastUse = nullptr; // Don't kill register again
}
killVirtReg(LRI);
}
/// Spill all dirty virtregs without killing them.
void RegAllocFast::spillAll(MachineBasicBlock::iterator MI) {
if (LiveVirtRegs.empty()) return;
isBulkSpilling = true;
// The LiveRegMap is keyed by an unsigned (the virtreg number), so the order
// of spilling here is deterministic, if arbitrary.
for (LiveRegMap::iterator I = LiveVirtRegs.begin(), E = LiveVirtRegs.end();
I != E; ++I)
spillVirtReg(MI, I);
LiveVirtRegs.clear();
isBulkSpilling = false;
}
/// 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.
PhysRegState[Alias] = regFree;
MO.getParent()->addRegisterKilled(Alias, TRI, true);
return;
}
// Some other alias was in the working set - clear it.
PhysRegState[Alias] = regDisabled;
break;
default:
llvm_unreachable("Instruction uses an alias of an allocated register");
}
}
// All aliases are disabled, bring register into working set.
PhysRegState[PhysReg] = regFree;
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:
PhysRegState[PhysReg] = NewState;
return;
}
// This is a disabled register, disable all aliases.
PhysRegState[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:
PhysRegState[Alias] = regDisabled;
if (TRI->isSuperRegister(PhysReg, Alias))
return;
break;
}
}
}
/// \brief 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)) {
DEBUG(dbgs() << printReg(PhysReg, TRI) << " is already used in instr.\n");
return spillImpossible;
}
switch (unsigned VirtReg = PhysRegState[PhysReg]) {
case regDisabled:
break;
case regFree:
return 0;
case regReserved:
DEBUG(dbgs() << printReg(VirtReg, TRI) << " corresponding "
<< printReg(PhysReg, TRI) << " is reserved already.\n");
return spillImpossible;
default: {
LiveRegMap::const_iterator I = findLiveVirtReg(VirtReg);
assert(I != LiveVirtRegs.end() && "Missing VirtReg entry");
return I->Dirty ? spillDirty : spillClean;
}
}
// This is a disabled register, add up cost of aliases.
DEBUG(dbgs() << printReg(PhysReg, TRI) << " is disabled.\n");
unsigned Cost = 0;
for (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 I = findLiveVirtReg(VirtReg);
assert(I != LiveVirtRegs.end() && "Missing VirtReg entry");
Cost += I->Dirty ? spillDirty : spillClean;
break;
}
}
}
return Cost;
}
/// \brief 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) {
DEBUG(dbgs() << "Assigning " << printReg(LR.VirtReg, TRI) << " to "
<< printReg(PhysReg, TRI) << "\n");
PhysRegState[PhysReg] = LR.VirtReg;
assert(!LR.PhysReg && "Already assigned a physreg");
LR.PhysReg = PhysReg;
}
RegAllocFast::LiveRegMap::iterator
RegAllocFast::assignVirtToPhysReg(unsigned VirtReg, MCPhysReg PhysReg) {
LiveRegMap::iterator LRI = findLiveVirtReg(VirtReg);
assert(LRI != LiveVirtRegs.end() && "VirtReg disappeared");
assignVirtToPhysReg(*LRI, PhysReg);
return LRI;
}
/// Allocates a physical register for VirtReg.
RegAllocFast::LiveRegMap::iterator RegAllocFast::allocVirtReg(MachineInstr &MI,
LiveRegMap::iterator LRI, unsigned Hint) {
const unsigned VirtReg = LRI->VirtReg;
assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
"Can only allocate virtual registers");
// Take hint when possible.
const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
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);
// definePhysReg may kill virtual registers and modify LiveVirtRegs.
// That invalidates LRI, so run a new lookup for VirtReg.
return assignVirtToPhysReg(VirtReg, Hint);
}
}
// First try to find a completely free register.
ArrayRef<MCPhysReg> AO = RegClassInfo.getOrder(&RC);
for (MCPhysReg PhysReg : AO) {
if (PhysRegState[PhysReg] == regFree && !isRegUsedInInstr(PhysReg)) {
assignVirtToPhysReg(*LRI, PhysReg);
return LRI;
}
}
DEBUG(dbgs() << "Allocating " << printReg(VirtReg) << " from "
<< TRI->getRegClassName(&RC) << "\n");
unsigned BestReg = 0;
unsigned BestCost = spillImpossible;
for (MCPhysReg PhysReg : AO) {
unsigned Cost = calcSpillCost(PhysReg);
DEBUG(dbgs() << "\tRegister: " << printReg(PhysReg, TRI) << "\n");
DEBUG(dbgs() << "\tCost: " << Cost << "\n");
DEBUG(dbgs() << "\tBestCost: " << BestCost << "\n");
// Cost is 0 when all aliases are already disabled.
if (Cost == 0) {
assignVirtToPhysReg(*LRI, PhysReg);
return LRI;
}
if (Cost < BestCost)
BestReg = PhysReg, BestCost = Cost;
}
if (BestReg) {
definePhysReg(MI, BestReg, regFree);
// definePhysReg may kill virtual registers and modify LiveVirtRegs.
// That invalidates LRI, so run a new lookup for VirtReg.
return assignVirtToPhysReg(VirtReg, BestReg);
}
// Nothing we can do. Report an error and keep going with a bad 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, *AO.begin(), regFree);
return assignVirtToPhysReg(VirtReg, *AO.begin());
}
/// Allocates a register for VirtReg and mark it as dirty.
RegAllocFast::LiveRegMap::iterator 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 (New) {
// If there is no hint, peek at the only use of this register.
if ((!Hint || !TargetRegisterInfo::isPhysicalRegister(Hint)) &&
MRI->hasOneNonDBGUse(VirtReg)) {
const MachineInstr &UseMI = *MRI->use_instr_nodbg_begin(VirtReg);
// It's a copy, use the destination register as a hint.
if (UseMI.isCopyLike())
Hint = UseMI.getOperand(0).getReg();
}
LRI = 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;
}
/// Make sure VirtReg is available in a physreg and return it.
RegAllocFast::LiveRegMap::iterator 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 (New) {
LRI = allocVirtReg(MI, LRI, Hint);
const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
int FrameIndex = getStackSpaceFor(VirtReg, RC);
DEBUG(dbgs() << "Reloading " << printReg(VirtReg, TRI) << " into "
<< printReg(LRI->PhysReg, TRI) << "\n");
TII->loadRegFromStackSlot(*MBB, MI, LRI->PhysReg, FrameIndex, &RC, TRI);
++NumLoads;
} else if (LRI->Dirty) {
if (isLastUseOfLocalReg(MO)) {
DEBUG(dbgs() << "Killing last use: " << MO << "\n");
if (MO.isUse())
MO.setIsKill();
else
MO.setIsDead();
} else if (MO.isKill()) {
DEBUG(dbgs() << "Clearing dubious kill: " << MO << "\n");
MO.setIsKill(false);
} else if (MO.isDead()) {
DEBUG(dbgs() << "Clearing dubious dead: " << MO << "\n");
MO.setIsDead(false);
}
} else if (MO.isKill()) {
// We must remove kill flags from uses of reloaded registers because the
// register would be killed immediately, and there might be a second use:
// %foo = OR killed %x, %x
// This would cause a second reload of %x into a different register.
DEBUG(dbgs() << "Clearing clean kill: " << MO << "\n");
MO.setIsKill(false);
} else if (MO.isDead()) {
DEBUG(dbgs() << "Clearing clean dead: " << MO << "\n");
MO.setIsDead(false);
}
assert(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, unsigned OpNum,
MCPhysReg PhysReg) {
MachineOperand &MO = MI.getOperand(OpNum);
bool Dead = MO.isDead();
if (!MO.getSubReg()) {
MO.setReg(PhysReg);
MO.setIsRenamableIfNoExtraRegAllocReq();
return MO.isKill() || Dead;
}
// Handle subregister index.
MO.setReg(PhysReg ? TRI->getSubReg(PhysReg, MO.getSubReg()) : 0);
MO.setIsRenamableIfNoExtraRegAllocReq();
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) {
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)
DEBUG(dbgs() << ' ' << printReg(Reg));
}
}
// If any physreg defines collide with preallocated through registers,
// we must spill and reallocate.
DEBUG(dbgs() << "\nChecking for physdef collisions.\n");
for (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;
DEBUG(dbgs() << "Allocating tied uses.\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.isUse()) {
if (!MO.isTied()) continue;
DEBUG(dbgs() << "Operand " << I << "("<< MO << ") is tied to operand "
<< MI.findTiedOperandIdx(I) << ".\n");
LiveRegMap::iterator LRI = reloadVirtReg(MI, I, Reg, 0);
MCPhysReg PhysReg = LRI->PhysReg;
setPhysReg(MI, I, PhysReg);
// Note: we don't update the def operand yet. That would cause the normal
// def-scan to attempt spilling.
} else if (MO.getSubReg() && MI.readsVirtualRegister(Reg)) {
DEBUG(dbgs() << "Partial redefine: " << MO << "\n");
// Reload the register, but don't assign to the operand just yet.
// That would confuse the later phys-def processing pass.
LiveRegMap::iterator LRI = reloadVirtReg(MI, I, Reg, 0);
PartialDefs.push_back(LRI->PhysReg);
}
}
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.
LiveRegMap::iterator LRI = defineVirtReg(MI, I, Reg, 0);
MCPhysReg PhysReg = LRI->PhysReg;
if (setPhysReg(MI, 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;
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 I = findLiveVirtReg(PhysRegState[Reg]);
assert(I != LiveVirtRegs.end() && "Missing VirtReg entry");
if (I->Dirty)
dbgs() << "*";
assert(I->PhysReg == Reg && "Bad inverse map");
break;
}
}
}
dbgs() << '\n';
// Check that LiveVirtRegs is the inverse.
for (LiveRegMap::iterator i = LiveVirtRegs.begin(),
e = LiveVirtRegs.end(); i != e; ++i) {
assert(TargetRegisterInfo::isVirtualRegister(i->VirtReg) &&
"Bad map key");
assert(TargetRegisterInfo::isPhysicalRegister(i->PhysReg) &&
"Bad map value");
assert(PhysRegState[i->PhysReg] == i->VirtReg && "Bad inverse map");
}
}
#endif
void RegAllocFast::allocateBasicBlock(MachineBasicBlock &MBB) {
this->MBB = &MBB;
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) {
const MCInstrDesc &MCID = MI.getDesc();
DEBUG(
dbgs() << "\n>> " << MI << "Regs:";
dumpState()
);
// Debug values are not allowed to change codegen in any way.
if (MI.isDebugValue()) {
MachineInstr *DebugMI = &MI;
MachineOperand &MO = DebugMI->getOperand(0);
// Ignore DBG_VALUEs that aren't based on virtual registers. These are
// mostly constants and frame indices.
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
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);
if (LRI != LiveVirtRegs.end())
setPhysReg(*DebugMI, 0, LRI->PhysReg);
else {
int SS = StackSlotForVirtReg[Reg];
if (SS != -1) {
// Modify DBG_VALUE now that the value is in a spill slot.
updateDbgValueForSpill(*DebugMI, SS);
DEBUG(dbgs() << "Modifying debug info due to spill:"
<< "\t" << *DebugMI);
continue;
}
// We can't allocate a physreg for a DebugValue, sorry!
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(DebugMI);
continue;
}
// 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.
for (unsigned I = 0; I != VirtOpEnd; ++I) {
const MachineOperand &MO = MI.getOperand(I);
if (!MO.isReg()) continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
if (MO.isUse()) {
LiveRegMap::iterator LRI = reloadVirtReg(MI, I, Reg, CopyDstReg);
MCPhysReg PhysReg = LRI->PhysReg;
CopySrcReg = (CopySrcReg == Reg || CopySrcReg == PhysReg) ? PhysReg : 0;
if (setPhysReg(MI, I, PhysReg))
killVirtReg(LRI);
}
}
// 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.
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;
}
LiveRegMap::iterator LRI = defineVirtReg(MI, I, Reg, CopySrcReg);
MCPhysReg PhysReg = LRI->PhysReg;
if (setPhysReg(MI, 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();
if (CopyDstReg && CopyDstReg == CopySrcReg && CopyDstSub == CopySrcSub) {
DEBUG(dbgs() << "-- coalescing: " << MI);
Coalesced.push_back(&MI);
} else {
DEBUG(dbgs() << "<< " << MI);
}
}
// Spill all physical registers holding virtual registers now.
DEBUG(dbgs() << "Spilling live registers at end of block.\n");
spillAll(MBB.getFirstTerminator());
// Erase all the coalesced copies. We are delaying it until now because
// LiveVirtRegs might refer to the instrs.
for (MachineInstr *MI : Coalesced)
MBB.erase(MI);
NumCopies += Coalesced.size();
DEBUG(MBB.dump());
}
/// Allocates registers for a function.
bool RegAllocFast::runOnMachineFunction(MachineFunction &MF) {
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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