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llvm/lib/CodeGen/RegAllocLinearScan.cpp
Jeffrey Yasskin 8e68c38735 Change all self assignments X=X to (void)X, so that we can turn on a 
new gcc warning that complains on self-assignments and
self-initializations.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122458 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-23 00:58:24 +00:00

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//===-- RegAllocLinearScan.cpp - Linear Scan register allocator -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a linear scan register allocator.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "LiveDebugVariables.h"
#include "VirtRegMap.h"
#include "VirtRegRewriter.h"
#include "Spiller.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Function.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/CodeGen/RegisterCoalescer.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/ADT/EquivalenceClasses.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <set>
#include <queue>
#include <memory>
#include <cmath>
using namespace llvm;
STATISTIC(NumIters , "Number of iterations performed");
STATISTIC(NumBacktracks, "Number of times we had to backtrack");
STATISTIC(NumCoalesce, "Number of copies coalesced");
STATISTIC(NumDowngrade, "Number of registers downgraded");
static cl::opt<bool>
NewHeuristic("new-spilling-heuristic",
cl::desc("Use new spilling heuristic"),
cl::init(false), cl::Hidden);
static cl::opt<bool>
PreSplitIntervals("pre-alloc-split",
cl::desc("Pre-register allocation live interval splitting"),
cl::init(false), cl::Hidden);
static cl::opt<bool>
TrivCoalesceEnds("trivial-coalesce-ends",
cl::desc("Attempt trivial coalescing of interval ends"),
cl::init(false), cl::Hidden);
static RegisterRegAlloc
linearscanRegAlloc("linearscan", "linear scan register allocator",
createLinearScanRegisterAllocator);
namespace {
// When we allocate a register, add it to a fixed-size queue of
// registers to skip in subsequent allocations. This trades a small
// amount of register pressure and increased spills for flexibility in
// the post-pass scheduler.
//
// Note that in a the number of registers used for reloading spills
// will be one greater than the value of this option.
//
// One big limitation of this is that it doesn't differentiate between
// different register classes. So on x86-64, if there is xmm register
// pressure, it can caused fewer GPRs to be held in the queue.
static cl::opt<unsigned>
NumRecentlyUsedRegs("linearscan-skip-count",
cl::desc("Number of registers for linearscan to remember"
"to skip."),
cl::init(0),
cl::Hidden);
struct RALinScan : public MachineFunctionPass {
static char ID;
RALinScan() : MachineFunctionPass(ID) {
initializeLiveDebugVariablesPass(*PassRegistry::getPassRegistry());
initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
initializeRegisterCoalescerAnalysisGroup(
*PassRegistry::getPassRegistry());
initializeCalculateSpillWeightsPass(*PassRegistry::getPassRegistry());
initializePreAllocSplittingPass(*PassRegistry::getPassRegistry());
initializeLiveStacksPass(*PassRegistry::getPassRegistry());
initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
// Initialize the queue to record recently-used registers.
if (NumRecentlyUsedRegs > 0)
RecentRegs.resize(NumRecentlyUsedRegs, 0);
RecentNext = RecentRegs.begin();
}
typedef std::pair<LiveInterval*, LiveInterval::iterator> IntervalPtr;
typedef SmallVector<IntervalPtr, 32> IntervalPtrs;
private:
/// RelatedRegClasses - This structure is built the first time a function is
/// compiled, and keeps track of which register classes have registers that
/// belong to multiple classes or have aliases that are in other classes.
EquivalenceClasses<const TargetRegisterClass*> RelatedRegClasses;
DenseMap<unsigned, const TargetRegisterClass*> OneClassForEachPhysReg;
// NextReloadMap - For each register in the map, it maps to the another
// register which is defined by a reload from the same stack slot and
// both reloads are in the same basic block.
DenseMap<unsigned, unsigned> NextReloadMap;
// DowngradedRegs - A set of registers which are being "downgraded", i.e.
// un-favored for allocation.
SmallSet<unsigned, 8> DowngradedRegs;
// DowngradeMap - A map from virtual registers to physical registers being
// downgraded for the virtual registers.
DenseMap<unsigned, unsigned> DowngradeMap;
MachineFunction* mf_;
MachineRegisterInfo* mri_;
const TargetMachine* tm_;
const TargetRegisterInfo* tri_;
const TargetInstrInfo* tii_;
BitVector allocatableRegs_;
BitVector reservedRegs_;
LiveIntervals* li_;
MachineLoopInfo *loopInfo;
/// handled_ - Intervals are added to the handled_ set in the order of their
/// start value. This is uses for backtracking.
std::vector<LiveInterval*> handled_;
/// fixed_ - Intervals that correspond to machine registers.
///
IntervalPtrs fixed_;
/// active_ - Intervals that are currently being processed, and which have a
/// live range active for the current point.
IntervalPtrs active_;
/// inactive_ - Intervals that are currently being processed, but which have
/// a hold at the current point.
IntervalPtrs inactive_;
typedef std::priority_queue<LiveInterval*,
SmallVector<LiveInterval*, 64>,
greater_ptr<LiveInterval> > IntervalHeap;
IntervalHeap unhandled_;
/// regUse_ - Tracks register usage.
SmallVector<unsigned, 32> regUse_;
SmallVector<unsigned, 32> regUseBackUp_;
/// vrm_ - Tracks register assignments.
VirtRegMap* vrm_;
std::auto_ptr<VirtRegRewriter> rewriter_;
std::auto_ptr<Spiller> spiller_;
// The queue of recently-used registers.
SmallVector<unsigned, 4> RecentRegs;
SmallVector<unsigned, 4>::iterator RecentNext;
// Record that we just picked this register.
void recordRecentlyUsed(unsigned reg) {
assert(reg != 0 && "Recently used register is NOREG!");
if (!RecentRegs.empty()) {
*RecentNext++ = reg;
if (RecentNext == RecentRegs.end())
RecentNext = RecentRegs.begin();
}
}
public:
virtual const char* getPassName() const {
return "Linear Scan Register Allocator";
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<AliasAnalysis>();
AU.addPreserved<AliasAnalysis>();
AU.addRequired<LiveIntervals>();
AU.addPreserved<SlotIndexes>();
if (StrongPHIElim)
AU.addRequiredID(StrongPHIEliminationID);
// Make sure PassManager knows which analyses to make available
// to coalescing and which analyses coalescing invalidates.
AU.addRequiredTransitive<RegisterCoalescer>();
AU.addRequired<CalculateSpillWeights>();
if (PreSplitIntervals)
AU.addRequiredID(PreAllocSplittingID);
AU.addRequiredID(LiveStacksID);
AU.addPreservedID(LiveStacksID);
AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineLoopInfo>();
AU.addRequired<VirtRegMap>();
AU.addPreserved<VirtRegMap>();
AU.addRequired<LiveDebugVariables>();
AU.addPreserved<LiveDebugVariables>();
AU.addRequiredID(MachineDominatorsID);
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
/// runOnMachineFunction - register allocate the whole function
bool runOnMachineFunction(MachineFunction&);
// Determine if we skip this register due to its being recently used.
bool isRecentlyUsed(unsigned reg) const {
return std::find(RecentRegs.begin(), RecentRegs.end(), reg) !=
RecentRegs.end();
}
private:
/// linearScan - the linear scan algorithm
void linearScan();
/// initIntervalSets - initialize the interval sets.
///
void initIntervalSets();
/// processActiveIntervals - expire old intervals and move non-overlapping
/// ones to the inactive list.
void processActiveIntervals(SlotIndex CurPoint);
/// processInactiveIntervals - expire old intervals and move overlapping
/// ones to the active list.
void processInactiveIntervals(SlotIndex CurPoint);
/// hasNextReloadInterval - Return the next liveinterval that's being
/// defined by a reload from the same SS as the specified one.
LiveInterval *hasNextReloadInterval(LiveInterval *cur);
/// DowngradeRegister - Downgrade a register for allocation.
void DowngradeRegister(LiveInterval *li, unsigned Reg);
/// UpgradeRegister - Upgrade a register for allocation.
void UpgradeRegister(unsigned Reg);
/// assignRegOrStackSlotAtInterval - assign a register if one
/// is available, or spill.
void assignRegOrStackSlotAtInterval(LiveInterval* cur);
void updateSpillWeights(std::vector<float> &Weights,
unsigned reg, float weight,
const TargetRegisterClass *RC);
/// findIntervalsToSpill - Determine the intervals to spill for the
/// specified interval. It's passed the physical registers whose spill
/// weight is the lowest among all the registers whose live intervals
/// conflict with the interval.
void findIntervalsToSpill(LiveInterval *cur,
std::vector<std::pair<unsigned,float> > &Candidates,
unsigned NumCands,
SmallVector<LiveInterval*, 8> &SpillIntervals);
/// attemptTrivialCoalescing - If a simple interval is defined by a copy,
/// try to allocate the definition to the same register as the source,
/// if the register is not defined during the life time of the interval.
/// This eliminates a copy, and is used to coalesce copies which were not
/// coalesced away before allocation either due to dest and src being in
/// different register classes or because the coalescer was overly
/// conservative.
unsigned attemptTrivialCoalescing(LiveInterval &cur, unsigned Reg);
///
/// Register usage / availability tracking helpers.
///
void initRegUses() {
regUse_.resize(tri_->getNumRegs(), 0);
regUseBackUp_.resize(tri_->getNumRegs(), 0);
}
void finalizeRegUses() {
#ifndef NDEBUG
// Verify all the registers are "freed".
bool Error = false;
for (unsigned i = 0, e = tri_->getNumRegs(); i != e; ++i) {
if (regUse_[i] != 0) {
dbgs() << tri_->getName(i) << " is still in use!\n";
Error = true;
}
}
if (Error)
llvm_unreachable(0);
#endif
regUse_.clear();
regUseBackUp_.clear();
}
void addRegUse(unsigned physReg) {
assert(TargetRegisterInfo::isPhysicalRegister(physReg) &&
"should be physical register!");
++regUse_[physReg];
for (const unsigned* as = tri_->getAliasSet(physReg); *as; ++as)
++regUse_[*as];
}
void delRegUse(unsigned physReg) {
assert(TargetRegisterInfo::isPhysicalRegister(physReg) &&
"should be physical register!");
assert(regUse_[physReg] != 0);
--regUse_[physReg];
for (const unsigned* as = tri_->getAliasSet(physReg); *as; ++as) {
assert(regUse_[*as] != 0);
--regUse_[*as];
}
}
bool isRegAvail(unsigned physReg) const {
assert(TargetRegisterInfo::isPhysicalRegister(physReg) &&
"should be physical register!");
return regUse_[physReg] == 0;
}
void backUpRegUses() {
regUseBackUp_ = regUse_;
}
void restoreRegUses() {
regUse_ = regUseBackUp_;
}
///
/// Register handling helpers.
///
/// getFreePhysReg - return a free physical register for this virtual
/// register interval if we have one, otherwise return 0.
unsigned getFreePhysReg(LiveInterval* cur);
unsigned getFreePhysReg(LiveInterval* cur,
const TargetRegisterClass *RC,
unsigned MaxInactiveCount,
SmallVector<unsigned, 256> &inactiveCounts,
bool SkipDGRegs);
/// getFirstNonReservedPhysReg - return the first non-reserved physical
/// register in the register class.
unsigned getFirstNonReservedPhysReg(const TargetRegisterClass *RC) {
TargetRegisterClass::iterator aoe = RC->allocation_order_end(*mf_);
TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_);
while (i != aoe && reservedRegs_.test(*i))
++i;
assert(i != aoe && "All registers reserved?!");
return *i;
}
void ComputeRelatedRegClasses();
template <typename ItTy>
void printIntervals(const char* const str, ItTy i, ItTy e) const {
DEBUG({
if (str)
dbgs() << str << " intervals:\n";
for (; i != e; ++i) {
dbgs() << "\t" << *i->first << " -> ";
unsigned reg = i->first->reg;
if (TargetRegisterInfo::isVirtualRegister(reg))
reg = vrm_->getPhys(reg);
dbgs() << tri_->getName(reg) << '\n';
}
});
}
};
char RALinScan::ID = 0;
}
INITIALIZE_PASS_BEGIN(RALinScan, "linearscan-regalloc",
"Linear Scan Register Allocator", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_DEPENDENCY(StrongPHIElimination)
INITIALIZE_PASS_DEPENDENCY(CalculateSpillWeights)
INITIALIZE_PASS_DEPENDENCY(PreAllocSplitting)
INITIALIZE_PASS_DEPENDENCY(LiveStacks)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
INITIALIZE_AG_DEPENDENCY(RegisterCoalescer)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(RALinScan, "linearscan-regalloc",
"Linear Scan Register Allocator", false, false)
void RALinScan::ComputeRelatedRegClasses() {
// First pass, add all reg classes to the union, and determine at least one
// reg class that each register is in.
bool HasAliases = false;
for (TargetRegisterInfo::regclass_iterator RCI = tri_->regclass_begin(),
E = tri_->regclass_end(); RCI != E; ++RCI) {
RelatedRegClasses.insert(*RCI);
for (TargetRegisterClass::iterator I = (*RCI)->begin(), E = (*RCI)->end();
I != E; ++I) {
HasAliases = HasAliases || *tri_->getAliasSet(*I) != 0;
const TargetRegisterClass *&PRC = OneClassForEachPhysReg[*I];
if (PRC) {
// Already processed this register. Just make sure we know that
// multiple register classes share a register.
RelatedRegClasses.unionSets(PRC, *RCI);
} else {
PRC = *RCI;
}
}
}
// Second pass, now that we know conservatively what register classes each reg
// belongs to, add info about aliases. We don't need to do this for targets
// without register aliases.
if (HasAliases)
for (DenseMap<unsigned, const TargetRegisterClass*>::iterator
I = OneClassForEachPhysReg.begin(), E = OneClassForEachPhysReg.end();
I != E; ++I)
for (const unsigned *AS = tri_->getAliasSet(I->first); *AS; ++AS)
RelatedRegClasses.unionSets(I->second, OneClassForEachPhysReg[*AS]);
}
/// attemptTrivialCoalescing - If a simple interval is defined by a copy, try
/// allocate the definition the same register as the source register if the
/// register is not defined during live time of the interval. If the interval is
/// killed by a copy, try to use the destination register. This eliminates a
/// copy. This is used to coalesce copies which were not coalesced away before
/// allocation either due to dest and src being in different register classes or
/// because the coalescer was overly conservative.
unsigned RALinScan::attemptTrivialCoalescing(LiveInterval &cur, unsigned Reg) {
unsigned Preference = vrm_->getRegAllocPref(cur.reg);
if ((Preference && Preference == Reg) || !cur.containsOneValue())
return Reg;
// We cannot handle complicated live ranges. Simple linear stuff only.
if (cur.ranges.size() != 1)
return Reg;
const LiveRange &range = cur.ranges.front();
VNInfo *vni = range.valno;
if (vni->isUnused())
return Reg;
unsigned CandReg;
{
MachineInstr *CopyMI;
if ((CopyMI = li_->getInstructionFromIndex(vni->def)) && CopyMI->isCopy())
// Defined by a copy, try to extend SrcReg forward
CandReg = CopyMI->getOperand(1).getReg();
else if (TrivCoalesceEnds &&
(CopyMI = li_->getInstructionFromIndex(range.end.getBaseIndex())) &&
CopyMI->isCopy() && cur.reg == CopyMI->getOperand(1).getReg())
// Only used by a copy, try to extend DstReg backwards
CandReg = CopyMI->getOperand(0).getReg();
else
return Reg;
// If the target of the copy is a sub-register then don't coalesce.
if(CopyMI->getOperand(0).getSubReg())
return Reg;
}
if (TargetRegisterInfo::isVirtualRegister(CandReg)) {
if (!vrm_->isAssignedReg(CandReg))
return Reg;
CandReg = vrm_->getPhys(CandReg);
}
if (Reg == CandReg)
return Reg;
const TargetRegisterClass *RC = mri_->getRegClass(cur.reg);
if (!RC->contains(CandReg))
return Reg;
if (li_->conflictsWithPhysReg(cur, *vrm_, CandReg))
return Reg;
// Try to coalesce.
DEBUG(dbgs() << "Coalescing: " << cur << " -> " << tri_->getName(CandReg)
<< '\n');
vrm_->clearVirt(cur.reg);
vrm_->assignVirt2Phys(cur.reg, CandReg);
++NumCoalesce;
return CandReg;
}
bool RALinScan::runOnMachineFunction(MachineFunction &fn) {
mf_ = &fn;
mri_ = &fn.getRegInfo();
tm_ = &fn.getTarget();
tri_ = tm_->getRegisterInfo();
tii_ = tm_->getInstrInfo();
allocatableRegs_ = tri_->getAllocatableSet(fn);
reservedRegs_ = tri_->getReservedRegs(fn);
li_ = &getAnalysis<LiveIntervals>();
loopInfo = &getAnalysis<MachineLoopInfo>();
// We don't run the coalescer here because we have no reason to
// interact with it. If the coalescer requires interaction, it
// won't do anything. If it doesn't require interaction, we assume
// it was run as a separate pass.
// If this is the first function compiled, compute the related reg classes.
if (RelatedRegClasses.empty())
ComputeRelatedRegClasses();
// Also resize register usage trackers.
initRegUses();
vrm_ = &getAnalysis<VirtRegMap>();
if (!rewriter_.get()) rewriter_.reset(createVirtRegRewriter());
spiller_.reset(createSpiller(*this, *mf_, *vrm_));
initIntervalSets();
linearScan();
// Rewrite spill code and update the PhysRegsUsed set.
rewriter_->runOnMachineFunction(*mf_, *vrm_, li_);
// Write out new DBG_VALUE instructions.
getAnalysis<LiveDebugVariables>().emitDebugValues(vrm_);
assert(unhandled_.empty() && "Unhandled live intervals remain!");
finalizeRegUses();
fixed_.clear();
active_.clear();
inactive_.clear();
handled_.clear();
NextReloadMap.clear();
DowngradedRegs.clear();
DowngradeMap.clear();
spiller_.reset(0);
return true;
}
/// initIntervalSets - initialize the interval sets.
///
void RALinScan::initIntervalSets()
{
assert(unhandled_.empty() && fixed_.empty() &&
active_.empty() && inactive_.empty() &&
"interval sets should be empty on initialization");
handled_.reserve(li_->getNumIntervals());
for (LiveIntervals::iterator i = li_->begin(), e = li_->end(); i != e; ++i) {
if (TargetRegisterInfo::isPhysicalRegister(i->second->reg)) {
if (!i->second->empty()) {
mri_->setPhysRegUsed(i->second->reg);
fixed_.push_back(std::make_pair(i->second, i->second->begin()));
}
} else {
if (i->second->empty()) {
assignRegOrStackSlotAtInterval(i->second);
}
else
unhandled_.push(i->second);
}
}
}
void RALinScan::linearScan() {
// linear scan algorithm
DEBUG({
dbgs() << "********** LINEAR SCAN **********\n"
<< "********** Function: "
<< mf_->getFunction()->getName() << '\n';
printIntervals("fixed", fixed_.begin(), fixed_.end());
});
while (!unhandled_.empty()) {
// pick the interval with the earliest start point
LiveInterval* cur = unhandled_.top();
unhandled_.pop();
++NumIters;
DEBUG(dbgs() << "\n*** CURRENT ***: " << *cur << '\n');
assert(!cur->empty() && "Empty interval in unhandled set.");
processActiveIntervals(cur->beginIndex());
processInactiveIntervals(cur->beginIndex());
assert(TargetRegisterInfo::isVirtualRegister(cur->reg) &&
"Can only allocate virtual registers!");
// Allocating a virtual register. try to find a free
// physical register or spill an interval (possibly this one) in order to
// assign it one.
assignRegOrStackSlotAtInterval(cur);
DEBUG({
printIntervals("active", active_.begin(), active_.end());
printIntervals("inactive", inactive_.begin(), inactive_.end());
});
}
// Expire any remaining active intervals
while (!active_.empty()) {
IntervalPtr &IP = active_.back();
unsigned reg = IP.first->reg;
DEBUG(dbgs() << "\tinterval " << *IP.first << " expired\n");
assert(TargetRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
delRegUse(reg);
active_.pop_back();
}
// Expire any remaining inactive intervals
DEBUG({
for (IntervalPtrs::reverse_iterator
i = inactive_.rbegin(); i != inactive_.rend(); ++i)
dbgs() << "\tinterval " << *i->first << " expired\n";
});
inactive_.clear();
// Add live-ins to every BB except for entry. Also perform trivial coalescing.
MachineFunction::iterator EntryMBB = mf_->begin();
SmallVector<MachineBasicBlock*, 8> LiveInMBBs;
for (LiveIntervals::iterator i = li_->begin(), e = li_->end(); i != e; ++i) {
LiveInterval &cur = *i->second;
unsigned Reg = 0;
bool isPhys = TargetRegisterInfo::isPhysicalRegister(cur.reg);
if (isPhys)
Reg = cur.reg;
else if (vrm_->isAssignedReg(cur.reg))
Reg = attemptTrivialCoalescing(cur, vrm_->getPhys(cur.reg));
if (!Reg)
continue;
// Ignore splited live intervals.
if (!isPhys && vrm_->getPreSplitReg(cur.reg))
continue;
for (LiveInterval::Ranges::const_iterator I = cur.begin(), E = cur.end();
I != E; ++I) {
const LiveRange &LR = *I;
if (li_->findLiveInMBBs(LR.start, LR.end, LiveInMBBs)) {
for (unsigned i = 0, e = LiveInMBBs.size(); i != e; ++i)
if (LiveInMBBs[i] != EntryMBB) {
assert(TargetRegisterInfo::isPhysicalRegister(Reg) &&
"Adding a virtual register to livein set?");
LiveInMBBs[i]->addLiveIn(Reg);
}
LiveInMBBs.clear();
}
}
}
DEBUG(dbgs() << *vrm_);
// Look for physical registers that end up not being allocated even though
// register allocator had to spill other registers in its register class.
if (!vrm_->FindUnusedRegisters(li_))
return;
}
/// processActiveIntervals - expire old intervals and move non-overlapping ones
/// to the inactive list.
void RALinScan::processActiveIntervals(SlotIndex CurPoint)
{
DEBUG(dbgs() << "\tprocessing active intervals:\n");
for (unsigned i = 0, e = active_.size(); i != e; ++i) {
LiveInterval *Interval = active_[i].first;
LiveInterval::iterator IntervalPos = active_[i].second;
unsigned reg = Interval->reg;
IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
if (IntervalPos == Interval->end()) { // Remove expired intervals.
DEBUG(dbgs() << "\t\tinterval " << *Interval << " expired\n");
assert(TargetRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
delRegUse(reg);
// Pop off the end of the list.
active_[i] = active_.back();
active_.pop_back();
--i; --e;
} else if (IntervalPos->start > CurPoint) {
// Move inactive intervals to inactive list.
DEBUG(dbgs() << "\t\tinterval " << *Interval << " inactive\n");
assert(TargetRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
delRegUse(reg);
// add to inactive.
inactive_.push_back(std::make_pair(Interval, IntervalPos));
// Pop off the end of the list.
active_[i] = active_.back();
active_.pop_back();
--i; --e;
} else {
// Otherwise, just update the iterator position.
active_[i].second = IntervalPos;
}
}
}
/// processInactiveIntervals - expire old intervals and move overlapping
/// ones to the active list.
void RALinScan::processInactiveIntervals(SlotIndex CurPoint)
{
DEBUG(dbgs() << "\tprocessing inactive intervals:\n");
for (unsigned i = 0, e = inactive_.size(); i != e; ++i) {
LiveInterval *Interval = inactive_[i].first;
LiveInterval::iterator IntervalPos = inactive_[i].second;
unsigned reg = Interval->reg;
IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
if (IntervalPos == Interval->end()) { // remove expired intervals.
DEBUG(dbgs() << "\t\tinterval " << *Interval << " expired\n");
// Pop off the end of the list.
inactive_[i] = inactive_.back();
inactive_.pop_back();
--i; --e;
} else if (IntervalPos->start <= CurPoint) {
// move re-activated intervals in active list
DEBUG(dbgs() << "\t\tinterval " << *Interval << " active\n");
assert(TargetRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
addRegUse(reg);
// add to active
active_.push_back(std::make_pair(Interval, IntervalPos));
// Pop off the end of the list.
inactive_[i] = inactive_.back();
inactive_.pop_back();
--i; --e;
} else {
// Otherwise, just update the iterator position.
inactive_[i].second = IntervalPos;
}
}
}
/// updateSpillWeights - updates the spill weights of the specifed physical
/// register and its weight.
void RALinScan::updateSpillWeights(std::vector<float> &Weights,
unsigned reg, float weight,
const TargetRegisterClass *RC) {
SmallSet<unsigned, 4> Processed;
SmallSet<unsigned, 4> SuperAdded;
SmallVector<unsigned, 4> Supers;
Weights[reg] += weight;
Processed.insert(reg);
for (const unsigned* as = tri_->getAliasSet(reg); *as; ++as) {
Weights[*as] += weight;
Processed.insert(*as);
if (tri_->isSubRegister(*as, reg) &&
SuperAdded.insert(*as) &&
RC->contains(*as)) {
Supers.push_back(*as);
}
}
// If the alias is a super-register, and the super-register is in the
// register class we are trying to allocate. Then add the weight to all
// sub-registers of the super-register even if they are not aliases.
// e.g. allocating for GR32, bh is not used, updating bl spill weight.
// bl should get the same spill weight otherwise it will be choosen
// as a spill candidate since spilling bh doesn't make ebx available.
for (unsigned i = 0, e = Supers.size(); i != e; ++i) {
for (const unsigned *sr = tri_->getSubRegisters(Supers[i]); *sr; ++sr)
if (!Processed.count(*sr))
Weights[*sr] += weight;
}
}
static
RALinScan::IntervalPtrs::iterator
FindIntervalInVector(RALinScan::IntervalPtrs &IP, LiveInterval *LI) {
for (RALinScan::IntervalPtrs::iterator I = IP.begin(), E = IP.end();
I != E; ++I)
if (I->first == LI) return I;
return IP.end();
}
static void RevertVectorIteratorsTo(RALinScan::IntervalPtrs &V,
SlotIndex Point){
for (unsigned i = 0, e = V.size(); i != e; ++i) {
RALinScan::IntervalPtr &IP = V[i];
LiveInterval::iterator I = std::upper_bound(IP.first->begin(),
IP.second, Point);
if (I != IP.first->begin()) --I;
IP.second = I;
}
}
/// getConflictWeight - Return the number of conflicts between cur
/// live interval and defs and uses of Reg weighted by loop depthes.
static
float getConflictWeight(LiveInterval *cur, unsigned Reg, LiveIntervals *li_,
MachineRegisterInfo *mri_,
MachineLoopInfo *loopInfo) {
float Conflicts = 0;
for (MachineRegisterInfo::reg_iterator I = mri_->reg_begin(Reg),
E = mri_->reg_end(); I != E; ++I) {
MachineInstr *MI = &*I;
if (cur->liveAt(li_->getInstructionIndex(MI))) {
unsigned loopDepth = loopInfo->getLoopDepth(MI->getParent());
Conflicts += std::pow(10.0f, (float)loopDepth);
}
}
return Conflicts;
}
/// findIntervalsToSpill - Determine the intervals to spill for the
/// specified interval. It's passed the physical registers whose spill
/// weight is the lowest among all the registers whose live intervals
/// conflict with the interval.
void RALinScan::findIntervalsToSpill(LiveInterval *cur,
std::vector<std::pair<unsigned,float> > &Candidates,
unsigned NumCands,
SmallVector<LiveInterval*, 8> &SpillIntervals) {
// We have figured out the *best* register to spill. But there are other
// registers that are pretty good as well (spill weight within 3%). Spill
// the one that has fewest defs and uses that conflict with cur.
float Conflicts[3] = { 0.0f, 0.0f, 0.0f };
SmallVector<LiveInterval*, 8> SLIs[3];
DEBUG({
dbgs() << "\tConsidering " << NumCands << " candidates: ";
for (unsigned i = 0; i != NumCands; ++i)
dbgs() << tri_->getName(Candidates[i].first) << " ";
dbgs() << "\n";
});
// Calculate the number of conflicts of each candidate.
for (IntervalPtrs::iterator i = active_.begin(); i != active_.end(); ++i) {
unsigned Reg = i->first->reg;
unsigned PhysReg = vrm_->getPhys(Reg);
if (!cur->overlapsFrom(*i->first, i->second))
continue;
for (unsigned j = 0; j < NumCands; ++j) {
unsigned Candidate = Candidates[j].first;
if (tri_->regsOverlap(PhysReg, Candidate)) {
if (NumCands > 1)
Conflicts[j] += getConflictWeight(cur, Reg, li_, mri_, loopInfo);
SLIs[j].push_back(i->first);
}
}
}
for (IntervalPtrs::iterator i = inactive_.begin(); i != inactive_.end(); ++i){
unsigned Reg = i->first->reg;
unsigned PhysReg = vrm_->getPhys(Reg);
if (!cur->overlapsFrom(*i->first, i->second-1))
continue;
for (unsigned j = 0; j < NumCands; ++j) {
unsigned Candidate = Candidates[j].first;
if (tri_->regsOverlap(PhysReg, Candidate)) {
if (NumCands > 1)
Conflicts[j] += getConflictWeight(cur, Reg, li_, mri_, loopInfo);
SLIs[j].push_back(i->first);
}
}
}
// Which is the best candidate?
unsigned BestCandidate = 0;
float MinConflicts = Conflicts[0];
for (unsigned i = 1; i != NumCands; ++i) {
if (Conflicts[i] < MinConflicts) {
BestCandidate = i;
MinConflicts = Conflicts[i];
}
}
std::copy(SLIs[BestCandidate].begin(), SLIs[BestCandidate].end(),
std::back_inserter(SpillIntervals));
}
namespace {
struct WeightCompare {
private:
const RALinScan &Allocator;
public:
WeightCompare(const RALinScan &Alloc) : Allocator(Alloc) {}
typedef std::pair<unsigned, float> RegWeightPair;
bool operator()(const RegWeightPair &LHS, const RegWeightPair &RHS) const {
return LHS.second < RHS.second && !Allocator.isRecentlyUsed(LHS.first);
}
};
}
static bool weightsAreClose(float w1, float w2) {
if (!NewHeuristic)
return false;
float diff = w1 - w2;
if (diff <= 0.02f) // Within 0.02f
return true;
return (diff / w2) <= 0.05f; // Within 5%.
}
LiveInterval *RALinScan::hasNextReloadInterval(LiveInterval *cur) {
DenseMap<unsigned, unsigned>::iterator I = NextReloadMap.find(cur->reg);
if (I == NextReloadMap.end())
return 0;
return &li_->getInterval(I->second);
}
void RALinScan::DowngradeRegister(LiveInterval *li, unsigned Reg) {
bool isNew = DowngradedRegs.insert(Reg);
(void)isNew; // Silence compiler warning.
assert(isNew && "Multiple reloads holding the same register?");
DowngradeMap.insert(std::make_pair(li->reg, Reg));
for (const unsigned *AS = tri_->getAliasSet(Reg); *AS; ++AS) {
isNew = DowngradedRegs.insert(*AS);
isNew = isNew; // Silence compiler warning.
assert(isNew && "Multiple reloads holding the same register?");
DowngradeMap.insert(std::make_pair(li->reg, *AS));
}
++NumDowngrade;
}
void RALinScan::UpgradeRegister(unsigned Reg) {
if (Reg) {
DowngradedRegs.erase(Reg);
for (const unsigned *AS = tri_->getAliasSet(Reg); *AS; ++AS)
DowngradedRegs.erase(*AS);
}
}
namespace {
struct LISorter {
bool operator()(LiveInterval* A, LiveInterval* B) {
return A->beginIndex() < B->beginIndex();
}
};
}
/// assignRegOrStackSlotAtInterval - assign a register if one is available, or
/// spill.
void RALinScan::assignRegOrStackSlotAtInterval(LiveInterval* cur) {
const TargetRegisterClass *RC = mri_->getRegClass(cur->reg);
DEBUG(dbgs() << "\tallocating current interval from "
<< RC->getName() << ": ");
// This is an implicitly defined live interval, just assign any register.
if (cur->empty()) {
unsigned physReg = vrm_->getRegAllocPref(cur->reg);
if (!physReg)
physReg = getFirstNonReservedPhysReg(RC);
DEBUG(dbgs() << tri_->getName(physReg) << '\n');
// Note the register is not really in use.
vrm_->assignVirt2Phys(cur->reg, physReg);
return;
}
backUpRegUses();
std::vector<std::pair<unsigned, float> > SpillWeightsToAdd;
SlotIndex StartPosition = cur->beginIndex();
const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
// If start of this live interval is defined by a move instruction and its
// source is assigned a physical register that is compatible with the target
// register class, then we should try to assign it the same register.
// This can happen when the move is from a larger register class to a smaller
// one, e.g. X86::mov32to32_. These move instructions are not coalescable.
if (!vrm_->getRegAllocPref(cur->reg) && cur->hasAtLeastOneValue()) {
VNInfo *vni = cur->begin()->valno;
if (!vni->isUnused()) {
MachineInstr *CopyMI = li_->getInstructionFromIndex(vni->def);
if (CopyMI && CopyMI->isCopy()) {
unsigned DstSubReg = CopyMI->getOperand(0).getSubReg();
unsigned SrcReg = CopyMI->getOperand(1).getReg();
unsigned SrcSubReg = CopyMI->getOperand(1).getSubReg();
unsigned Reg = 0;
if (TargetRegisterInfo::isPhysicalRegister(SrcReg))
Reg = SrcReg;
else if (vrm_->isAssignedReg(SrcReg))
Reg = vrm_->getPhys(SrcReg);
if (Reg) {
if (SrcSubReg)
Reg = tri_->getSubReg(Reg, SrcSubReg);
if (DstSubReg)
Reg = tri_->getMatchingSuperReg(Reg, DstSubReg, RC);
if (Reg && allocatableRegs_[Reg] && RC->contains(Reg))
mri_->setRegAllocationHint(cur->reg, 0, Reg);
}
}
}
}
// For every interval in inactive we overlap with, mark the
// register as not free and update spill weights.
for (IntervalPtrs::const_iterator i = inactive_.begin(),
e = inactive_.end(); i != e; ++i) {
unsigned Reg = i->first->reg;
assert(TargetRegisterInfo::isVirtualRegister(Reg) &&
"Can only allocate virtual registers!");
const TargetRegisterClass *RegRC = mri_->getRegClass(Reg);
// If this is not in a related reg class to the register we're allocating,
// don't check it.
if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&
cur->overlapsFrom(*i->first, i->second-1)) {
Reg = vrm_->getPhys(Reg);
addRegUse(Reg);
SpillWeightsToAdd.push_back(std::make_pair(Reg, i->first->weight));
}
}
// Speculatively check to see if we can get a register right now. If not,
// we know we won't be able to by adding more constraints. If so, we can
// check to see if it is valid. Doing an exhaustive search of the fixed_ list
// is very bad (it contains all callee clobbered registers for any functions
// with a call), so we want to avoid doing that if possible.
unsigned physReg = getFreePhysReg(cur);
unsigned BestPhysReg = physReg;
if (physReg) {
// We got a register. However, if it's in the fixed_ list, we might
// conflict with it. Check to see if we conflict with it or any of its
// aliases.
SmallSet<unsigned, 8> RegAliases;
for (const unsigned *AS = tri_->getAliasSet(physReg); *AS; ++AS)
RegAliases.insert(*AS);
bool ConflictsWithFixed = false;
for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
IntervalPtr &IP = fixed_[i];
if (physReg == IP.first->reg || RegAliases.count(IP.first->reg)) {
// Okay, this reg is on the fixed list. Check to see if we actually
// conflict.
LiveInterval *I = IP.first;
if (I->endIndex() > StartPosition) {
LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
IP.second = II;
if (II != I->begin() && II->start > StartPosition)
--II;
if (cur->overlapsFrom(*I, II)) {
ConflictsWithFixed = true;
break;
}
}
}
}
// Okay, the register picked by our speculative getFreePhysReg call turned
// out to be in use. Actually add all of the conflicting fixed registers to
// regUse_ so we can do an accurate query.
if (ConflictsWithFixed) {
// For every interval in fixed we overlap with, mark the register as not
// free and update spill weights.
for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
IntervalPtr &IP = fixed_[i];
LiveInterval *I = IP.first;
const TargetRegisterClass *RegRC = OneClassForEachPhysReg[I->reg];
if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&
I->endIndex() > StartPosition) {
LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
IP.second = II;
if (II != I->begin() && II->start > StartPosition)
--II;
if (cur->overlapsFrom(*I, II)) {
unsigned reg = I->reg;
addRegUse(reg);
SpillWeightsToAdd.push_back(std::make_pair(reg, I->weight));
}
}
}
// Using the newly updated regUse_ object, which includes conflicts in the
// future, see if there are any registers available.
physReg = getFreePhysReg(cur);
}
}
// Restore the physical register tracker, removing information about the
// future.
restoreRegUses();
// If we find a free register, we are done: assign this virtual to
// the free physical register and add this interval to the active
// list.
if (physReg) {
DEBUG(dbgs() << tri_->getName(physReg) << '\n');
vrm_->assignVirt2Phys(cur->reg, physReg);
addRegUse(physReg);
active_.push_back(std::make_pair(cur, cur->begin()));
handled_.push_back(cur);
// "Upgrade" the physical register since it has been allocated.
UpgradeRegister(physReg);
if (LiveInterval *NextReloadLI = hasNextReloadInterval(cur)) {
// "Downgrade" physReg to try to keep physReg from being allocated until
// the next reload from the same SS is allocated.
mri_->setRegAllocationHint(NextReloadLI->reg, 0, physReg);
DowngradeRegister(cur, physReg);
}
return;
}
DEBUG(dbgs() << "no free registers\n");
// Compile the spill weights into an array that is better for scanning.
std::vector<float> SpillWeights(tri_->getNumRegs(), 0.0f);
for (std::vector<std::pair<unsigned, float> >::iterator
I = SpillWeightsToAdd.begin(), E = SpillWeightsToAdd.end(); I != E; ++I)
updateSpillWeights(SpillWeights, I->first, I->second, RC);
// for each interval in active, update spill weights.
for (IntervalPtrs::const_iterator i = active_.begin(), e = active_.end();
i != e; ++i) {
unsigned reg = i->first->reg;
assert(TargetRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
updateSpillWeights(SpillWeights, reg, i->first->weight, RC);
}
DEBUG(dbgs() << "\tassigning stack slot at interval "<< *cur << ":\n");
// Find a register to spill.
float minWeight = HUGE_VALF;
unsigned minReg = 0;
bool Found = false;
std::vector<std::pair<unsigned,float> > RegsWeights;
if (!minReg || SpillWeights[minReg] == HUGE_VALF)
for (TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_),
e = RC->allocation_order_end(*mf_); i != e; ++i) {
unsigned reg = *i;
float regWeight = SpillWeights[reg];
// Don't even consider reserved regs.
if (reservedRegs_.test(reg))
continue;
// Skip recently allocated registers and reserved registers.
if (minWeight > regWeight && !isRecentlyUsed(reg))
Found = true;
RegsWeights.push_back(std::make_pair(reg, regWeight));
}
// If we didn't find a register that is spillable, try aliases?
if (!Found) {
for (TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_),
e = RC->allocation_order_end(*mf_); i != e; ++i) {
unsigned reg = *i;
if (reservedRegs_.test(reg))
continue;
// No need to worry about if the alias register size < regsize of RC.
// We are going to spill all registers that alias it anyway.
for (const unsigned* as = tri_->getAliasSet(reg); *as; ++as)
RegsWeights.push_back(std::make_pair(*as, SpillWeights[*as]));
}
}
// Sort all potential spill candidates by weight.
std::sort(RegsWeights.begin(), RegsWeights.end(), WeightCompare(*this));
minReg = RegsWeights[0].first;
minWeight = RegsWeights[0].second;
if (minWeight == HUGE_VALF) {
// All registers must have inf weight. Just grab one!
minReg = BestPhysReg ? BestPhysReg : getFirstNonReservedPhysReg(RC);
if (cur->weight == HUGE_VALF ||
li_->getApproximateInstructionCount(*cur) == 0) {
// Spill a physical register around defs and uses.
if (li_->spillPhysRegAroundRegDefsUses(*cur, minReg, *vrm_)) {
// spillPhysRegAroundRegDefsUses may have invalidated iterator stored
// in fixed_. Reset them.
for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
IntervalPtr &IP = fixed_[i];
LiveInterval *I = IP.first;
if (I->reg == minReg || tri_->isSubRegister(minReg, I->reg))
IP.second = I->advanceTo(I->begin(), StartPosition);
}
DowngradedRegs.clear();
assignRegOrStackSlotAtInterval(cur);
} else {
assert(false && "Ran out of registers during register allocation!");
report_fatal_error("Ran out of registers during register allocation!");
}
return;
}
}
// Find up to 3 registers to consider as spill candidates.
unsigned LastCandidate = RegsWeights.size() >= 3 ? 3 : 1;
while (LastCandidate > 1) {
if (weightsAreClose(RegsWeights[LastCandidate-1].second, minWeight))
break;
--LastCandidate;
}
DEBUG({
dbgs() << "\t\tregister(s) with min weight(s): ";
for (unsigned i = 0; i != LastCandidate; ++i)
dbgs() << tri_->getName(RegsWeights[i].first)
<< " (" << RegsWeights[i].second << ")\n";
});
// If the current has the minimum weight, we need to spill it and
// add any added intervals back to unhandled, and restart
// linearscan.
if (cur->weight != HUGE_VALF && cur->weight <= minWeight) {
DEBUG(dbgs() << "\t\t\tspilling(c): " << *cur << '\n');
SmallVector<LiveInterval*, 8> spillIs, added;
spiller_->spill(cur, added, spillIs);
std::sort(added.begin(), added.end(), LISorter());
if (added.empty())
return; // Early exit if all spills were folded.
// Merge added with unhandled. Note that we have already sorted
// intervals returned by addIntervalsForSpills by their starting
// point.
// This also update the NextReloadMap. That is, it adds mapping from a
// register defined by a reload from SS to the next reload from SS in the
// same basic block.
MachineBasicBlock *LastReloadMBB = 0;
LiveInterval *LastReload = 0;
int LastReloadSS = VirtRegMap::NO_STACK_SLOT;
for (unsigned i = 0, e = added.size(); i != e; ++i) {
LiveInterval *ReloadLi = added[i];
if (ReloadLi->weight == HUGE_VALF &&
li_->getApproximateInstructionCount(*ReloadLi) == 0) {
SlotIndex ReloadIdx = ReloadLi->beginIndex();
MachineBasicBlock *ReloadMBB = li_->getMBBFromIndex(ReloadIdx);
int ReloadSS = vrm_->getStackSlot(ReloadLi->reg);
if (LastReloadMBB == ReloadMBB && LastReloadSS == ReloadSS) {
// Last reload of same SS is in the same MBB. We want to try to
// allocate both reloads the same register and make sure the reg
// isn't clobbered in between if at all possible.
assert(LastReload->beginIndex() < ReloadIdx);
NextReloadMap.insert(std::make_pair(LastReload->reg, ReloadLi->reg));
}
LastReloadMBB = ReloadMBB;
LastReload = ReloadLi;
LastReloadSS = ReloadSS;
}
unhandled_.push(ReloadLi);
}
return;
}
++NumBacktracks;
// Push the current interval back to unhandled since we are going
// to re-run at least this iteration. Since we didn't modify it it
// should go back right in the front of the list
unhandled_.push(cur);
assert(TargetRegisterInfo::isPhysicalRegister(minReg) &&
"did not choose a register to spill?");
// We spill all intervals aliasing the register with
// minimum weight, rollback to the interval with the earliest
// start point and let the linear scan algorithm run again
SmallVector<LiveInterval*, 8> spillIs;
// Determine which intervals have to be spilled.
findIntervalsToSpill(cur, RegsWeights, LastCandidate, spillIs);
// Set of spilled vregs (used later to rollback properly)
SmallSet<unsigned, 8> spilled;
// The earliest start of a Spilled interval indicates up to where
// in handled we need to roll back
assert(!spillIs.empty() && "No spill intervals?");
SlotIndex earliestStart = spillIs[0]->beginIndex();
// Spill live intervals of virtual regs mapped to the physical register we
// want to clear (and its aliases). We only spill those that overlap with the
// current interval as the rest do not affect its allocation. we also keep
// track of the earliest start of all spilled live intervals since this will
// mark our rollback point.
SmallVector<LiveInterval*, 8> added;
while (!spillIs.empty()) {
LiveInterval *sli = spillIs.back();
spillIs.pop_back();
DEBUG(dbgs() << "\t\t\tspilling(a): " << *sli << '\n');
if (sli->beginIndex() < earliestStart)
earliestStart = sli->beginIndex();
spiller_->spill(sli, added, spillIs);
spilled.insert(sli->reg);
}
// Include any added intervals in earliestStart.
for (unsigned i = 0, e = added.size(); i != e; ++i) {
SlotIndex SI = added[i]->beginIndex();
if (SI < earliestStart)
earliestStart = SI;
}
DEBUG(dbgs() << "\t\trolling back to: " << earliestStart << '\n');
// Scan handled in reverse order up to the earliest start of a
// spilled live interval and undo each one, restoring the state of
// unhandled.
while (!handled_.empty()) {
LiveInterval* i = handled_.back();
// If this interval starts before t we are done.
if (!i->empty() && i->beginIndex() < earliestStart)
break;
DEBUG(dbgs() << "\t\t\tundo changes for: " << *i << '\n');
handled_.pop_back();
// When undoing a live interval allocation we must know if it is active or
// inactive to properly update regUse_ and the VirtRegMap.
IntervalPtrs::iterator it;
if ((it = FindIntervalInVector(active_, i)) != active_.end()) {
active_.erase(it);
assert(!TargetRegisterInfo::isPhysicalRegister(i->reg));
if (!spilled.count(i->reg))
unhandled_.push(i);
delRegUse(vrm_->getPhys(i->reg));
vrm_->clearVirt(i->reg);
} else if ((it = FindIntervalInVector(inactive_, i)) != inactive_.end()) {
inactive_.erase(it);
assert(!TargetRegisterInfo::isPhysicalRegister(i->reg));
if (!spilled.count(i->reg))
unhandled_.push(i);
vrm_->clearVirt(i->reg);
} else {
assert(TargetRegisterInfo::isVirtualRegister(i->reg) &&
"Can only allocate virtual registers!");
vrm_->clearVirt(i->reg);
unhandled_.push(i);
}
DenseMap<unsigned, unsigned>::iterator ii = DowngradeMap.find(i->reg);
if (ii == DowngradeMap.end())
// It interval has a preference, it must be defined by a copy. Clear the
// preference now since the source interval allocation may have been
// undone as well.
mri_->setRegAllocationHint(i->reg, 0, 0);
else {
UpgradeRegister(ii->second);
}
}
// Rewind the iterators in the active, inactive, and fixed lists back to the
// point we reverted to.
RevertVectorIteratorsTo(active_, earliestStart);
RevertVectorIteratorsTo(inactive_, earliestStart);
RevertVectorIteratorsTo(fixed_, earliestStart);
// Scan the rest and undo each interval that expired after t and
// insert it in active (the next iteration of the algorithm will
// put it in inactive if required)
for (unsigned i = 0, e = handled_.size(); i != e; ++i) {
LiveInterval *HI = handled_[i];
if (!HI->expiredAt(earliestStart) &&
HI->expiredAt(cur->beginIndex())) {
DEBUG(dbgs() << "\t\t\tundo changes for: " << *HI << '\n');
active_.push_back(std::make_pair(HI, HI->begin()));
assert(!TargetRegisterInfo::isPhysicalRegister(HI->reg));
addRegUse(vrm_->getPhys(HI->reg));
}
}
// Merge added with unhandled.
// This also update the NextReloadMap. That is, it adds mapping from a
// register defined by a reload from SS to the next reload from SS in the
// same basic block.
MachineBasicBlock *LastReloadMBB = 0;
LiveInterval *LastReload = 0;
int LastReloadSS = VirtRegMap::NO_STACK_SLOT;
std::sort(added.begin(), added.end(), LISorter());
for (unsigned i = 0, e = added.size(); i != e; ++i) {
LiveInterval *ReloadLi = added[i];
if (ReloadLi->weight == HUGE_VALF &&
li_->getApproximateInstructionCount(*ReloadLi) == 0) {
SlotIndex ReloadIdx = ReloadLi->beginIndex();
MachineBasicBlock *ReloadMBB = li_->getMBBFromIndex(ReloadIdx);
int ReloadSS = vrm_->getStackSlot(ReloadLi->reg);
if (LastReloadMBB == ReloadMBB && LastReloadSS == ReloadSS) {
// Last reload of same SS is in the same MBB. We want to try to
// allocate both reloads the same register and make sure the reg
// isn't clobbered in between if at all possible.
assert(LastReload->beginIndex() < ReloadIdx);
NextReloadMap.insert(std::make_pair(LastReload->reg, ReloadLi->reg));
}
LastReloadMBB = ReloadMBB;
LastReload = ReloadLi;
LastReloadSS = ReloadSS;
}
unhandled_.push(ReloadLi);
}
}
unsigned RALinScan::getFreePhysReg(LiveInterval* cur,
const TargetRegisterClass *RC,
unsigned MaxInactiveCount,
SmallVector<unsigned, 256> &inactiveCounts,
bool SkipDGRegs) {
unsigned FreeReg = 0;
unsigned FreeRegInactiveCount = 0;
std::pair<unsigned, unsigned> Hint = mri_->getRegAllocationHint(cur->reg);
// Resolve second part of the hint (if possible) given the current allocation.
unsigned physReg = Hint.second;
if (physReg &&
TargetRegisterInfo::isVirtualRegister(physReg) && vrm_->hasPhys(physReg))
physReg = vrm_->getPhys(physReg);
TargetRegisterClass::iterator I, E;
tie(I, E) = tri_->getAllocationOrder(RC, Hint.first, physReg, *mf_);
assert(I != E && "No allocatable register in this register class!");
// Scan for the first available register.
for (; I != E; ++I) {
unsigned Reg = *I;
// Ignore "downgraded" registers.
if (SkipDGRegs && DowngradedRegs.count(Reg))
continue;
// Skip reserved registers.
if (reservedRegs_.test(Reg))
continue;
// Skip recently allocated registers.
if (isRegAvail(Reg) && !isRecentlyUsed(Reg)) {
FreeReg = Reg;
if (FreeReg < inactiveCounts.size())
FreeRegInactiveCount = inactiveCounts[FreeReg];
else
FreeRegInactiveCount = 0;
break;
}
}
// If there are no free regs, or if this reg has the max inactive count,
// return this register.
if (FreeReg == 0 || FreeRegInactiveCount == MaxInactiveCount) {
// Remember what register we picked so we can skip it next time.
if (FreeReg != 0) recordRecentlyUsed(FreeReg);
return FreeReg;
}
// Continue scanning the registers, looking for the one with the highest
// inactive count. Alkis found that this reduced register pressure very
// slightly on X86 (in rev 1.94 of this file), though this should probably be
// reevaluated now.
for (; I != E; ++I) {
unsigned Reg = *I;
// Ignore "downgraded" registers.
if (SkipDGRegs && DowngradedRegs.count(Reg))
continue;
// Skip reserved registers.
if (reservedRegs_.test(Reg))
continue;
if (isRegAvail(Reg) && Reg < inactiveCounts.size() &&
FreeRegInactiveCount < inactiveCounts[Reg] && !isRecentlyUsed(Reg)) {
FreeReg = Reg;
FreeRegInactiveCount = inactiveCounts[Reg];
if (FreeRegInactiveCount == MaxInactiveCount)
break; // We found the one with the max inactive count.
}
}
// Remember what register we picked so we can skip it next time.
recordRecentlyUsed(FreeReg);
return FreeReg;
}
/// getFreePhysReg - return a free physical register for this virtual register
/// interval if we have one, otherwise return 0.
unsigned RALinScan::getFreePhysReg(LiveInterval *cur) {
SmallVector<unsigned, 256> inactiveCounts;
unsigned MaxInactiveCount = 0;
const TargetRegisterClass *RC = mri_->getRegClass(cur->reg);
const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
for (IntervalPtrs::iterator i = inactive_.begin(), e = inactive_.end();
i != e; ++i) {
unsigned reg = i->first->reg;
assert(TargetRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
// If this is not in a related reg class to the register we're allocating,
// don't check it.
const TargetRegisterClass *RegRC = mri_->getRegClass(reg);
if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader) {
reg = vrm_->getPhys(reg);
if (inactiveCounts.size() <= reg)
inactiveCounts.resize(reg+1);
++inactiveCounts[reg];
MaxInactiveCount = std::max(MaxInactiveCount, inactiveCounts[reg]);
}
}
// If copy coalescer has assigned a "preferred" register, check if it's
// available first.
unsigned Preference = vrm_->getRegAllocPref(cur->reg);
if (Preference) {
DEBUG(dbgs() << "(preferred: " << tri_->getName(Preference) << ") ");
if (isRegAvail(Preference) &&
RC->contains(Preference))
return Preference;
}
if (!DowngradedRegs.empty()) {
unsigned FreeReg = getFreePhysReg(cur, RC, MaxInactiveCount, inactiveCounts,
true);
if (FreeReg)
return FreeReg;
}
return getFreePhysReg(cur, RC, MaxInactiveCount, inactiveCounts, false);
}
FunctionPass* llvm::createLinearScanRegisterAllocator() {
return new RALinScan();
}
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