1 //===-- RegAllocIterativeScan.cpp - Iterative Scan register allocator -----===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements an iterative scan register
11 // allocator. Iterative scan is a linear scan variant with the
12 // following difference:
14 // It performs linear scan and keeps a list of the registers it cannot
15 // allocate. It then spills all those registers and repeats the
16 // process until allocation succeeds.
18 //===----------------------------------------------------------------------===//
20 #define DEBUG_TYPE "regalloc"
21 #include "llvm/Function.h"
22 #include "llvm/CodeGen/LiveVariables.h"
23 #include "llvm/CodeGen/MachineFunctionPass.h"
24 #include "llvm/CodeGen/MachineInstr.h"
25 #include "llvm/CodeGen/Passes.h"
26 #include "llvm/CodeGen/SSARegMap.h"
27 #include "llvm/Target/MRegisterInfo.h"
28 #include "llvm/Target/TargetMachine.h"
29 #include "Support/Debug.h"
30 #include "Support/Statistic.h"
31 #include "Support/STLExtras.h"
32 #include "LiveIntervals.h"
33 #include "PhysRegTracker.h"
34 #include "VirtRegMap.h"
44 Statistic<double> efficiency
45 ("regalloc", "Ratio of intervals processed over total intervals");
47 static unsigned numIterations = 0;
48 static unsigned numIntervals = 0;
50 class RA : public MachineFunctionPass {
53 const TargetMachine* tm_;
54 const MRegisterInfo* mri_;
56 typedef std::list<LiveInterval*> IntervalPtrs;
57 IntervalPtrs unhandled_, fixed_, active_, inactive_, handled_, spilled_;
59 std::auto_ptr<PhysRegTracker> prt_;
60 std::auto_ptr<VirtRegMap> vrm_;
61 std::auto_ptr<Spiller> spiller_;
63 typedef std::vector<float> SpillWeights;
64 SpillWeights spillWeights_;
67 virtual const char* getPassName() const {
68 return "Linear Scan Register Allocator";
71 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
72 AU.addRequired<LiveVariables>();
73 AU.addRequired<LiveIntervals>();
74 MachineFunctionPass::getAnalysisUsage(AU);
77 /// runOnMachineFunction - register allocate the whole function
78 bool runOnMachineFunction(MachineFunction&);
83 /// linearScan - the linear scan algorithm. Returns a boolean
84 /// indicating if there were any spills
87 /// initIntervalSets - initializes the four interval sets:
88 /// unhandled, fixed, active and inactive
89 void initIntervalSets(LiveIntervals::Intervals& li);
91 /// processActiveIntervals - expire old intervals and move
92 /// non-overlapping ones to the incative list
93 void processActiveIntervals(IntervalPtrs::value_type cur);
95 /// processInactiveIntervals - expire old intervals and move
96 /// overlapping ones to the active list
97 void processInactiveIntervals(IntervalPtrs::value_type cur);
99 /// updateSpillWeights - updates the spill weights of the
100 /// specifed physical register and its weight
101 void updateSpillWeights(unsigned reg, SpillWeights::value_type weight);
103 /// assignRegOrStackSlotAtInterval - assign a register if one
104 /// is available, or spill.
105 void assignRegOrSpillAtInterval(IntervalPtrs::value_type cur);
108 /// register handling helpers
111 /// getFreePhysReg - return a free physical register for this
112 /// virtual register interval if we have one, otherwise return
114 unsigned getFreePhysReg(IntervalPtrs::value_type cur);
116 /// assignVirt2StackSlot - assigns this virtual register to a
117 /// stack slot. returns the stack slot
118 int assignVirt2StackSlot(unsigned virtReg);
120 void printIntervals(const char* const str,
121 RA::IntervalPtrs::const_iterator i,
122 RA::IntervalPtrs::const_iterator e) const {
123 if (str) std::cerr << str << " intervals:\n";
124 for (; i != e; ++i) {
125 std::cerr << "\t" << **i << " -> ";
126 unsigned reg = (*i)->reg;
127 if (MRegisterInfo::isVirtualRegister(reg)) {
128 reg = vrm_->getPhys(reg);
130 std::cerr << mri_->getName(reg) << '\n';
136 void RA::releaseMemory()
146 bool RA::runOnMachineFunction(MachineFunction &fn) {
148 tm_ = &fn.getTarget();
149 mri_ = tm_->getRegisterInfo();
150 li_ = &getAnalysis<LiveIntervals>();
151 if (!prt_.get()) prt_.reset(new PhysRegTracker(*mri_));
152 vrm_.reset(new VirtRegMap(*mf_));
153 if (!spiller_.get()) spiller_.reset(createSpiller());
155 initIntervalSets(li_->getIntervals());
157 numIntervals += li_->getIntervals().size();
159 while (linearScan()) {
160 // we spilled some registers, so we need to add intervals for
161 // the spill code and restart the algorithm
162 std::set<unsigned> spilledRegs;
163 for (IntervalPtrs::iterator
164 i = spilled_.begin(); i != spilled_.end(); ) {
165 int slot = vrm_->assignVirt2StackSlot((*i)->reg);
166 std::vector<LiveInterval*> added =
167 li_->addIntervalsForSpills(**i, *vrm_, slot);
168 std::copy(added.begin(), added.end(), std::back_inserter(handled_));
169 spilledRegs.insert((*i)->reg);
170 i = spilled_.erase(i);
172 for (IntervalPtrs::iterator
173 i = handled_.begin(); i != handled_.end(); )
174 if (spilledRegs.count((*i)->reg))
175 i = handled_.erase(i);
178 handled_.swap(unhandled_);
179 vrm_->clearAllVirt();
182 efficiency = double(numIterations) / double(numIntervals);
184 DEBUG(std::cerr << *vrm_);
186 spiller_->runOnMachineFunction(*mf_, *vrm_);
191 bool RA::linearScan()
193 // linear scan algorithm
194 DEBUG(std::cerr << "********** LINEAR SCAN **********\n");
195 DEBUG(std::cerr << "********** Function: "
196 << mf_->getFunction()->getName() << '\n');
199 unhandled_.sort(less_ptr<LiveInterval>());
200 DEBUG(printIntervals("unhandled", unhandled_.begin(), unhandled_.end()));
201 DEBUG(printIntervals("fixed", fixed_.begin(), fixed_.end()));
202 DEBUG(printIntervals("active", active_.begin(), active_.end()));
203 DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
205 while (!unhandled_.empty()) {
206 // pick the interval with the earliest start point
207 IntervalPtrs::value_type cur = unhandled_.front();
208 unhandled_.pop_front();
210 DEBUG(std::cerr << "\n*** CURRENT ***: " << *cur << '\n');
212 processActiveIntervals(cur);
213 processInactiveIntervals(cur);
215 // if this register is fixed we are done
216 if (MRegisterInfo::isPhysicalRegister(cur->reg)) {
217 prt_->addRegUse(cur->reg);
218 active_.push_back(cur);
219 handled_.push_back(cur);
221 // otherwise we are allocating a virtual register. try to find
222 // a free physical register or spill an interval in order to
223 // assign it one (we could spill the current though).
225 assignRegOrSpillAtInterval(cur);
228 DEBUG(printIntervals("active", active_.begin(), active_.end()));
229 DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
232 // expire any remaining active intervals
233 for (IntervalPtrs::iterator i = active_.begin(); i != active_.end(); ) {
234 unsigned reg = (*i)->reg;
235 DEBUG(std::cerr << "\tinterval " << **i << " expired\n");
236 if (MRegisterInfo::isVirtualRegister(reg))
237 reg = vrm_->getPhys(reg);
238 prt_->delRegUse(reg);
239 i = active_.erase(i);
242 // expire any remaining inactive intervals
243 for (IntervalPtrs::iterator
244 i = inactive_.begin(); i != inactive_.end(); ) {
245 DEBUG(std::cerr << "\tinterval " << **i << " expired\n");
246 i = inactive_.erase(i);
249 // return true if we spilled anything
250 return !spilled_.empty();
253 void RA::initIntervalSets(LiveIntervals::Intervals& li)
255 assert(unhandled_.empty() && fixed_.empty() &&
256 active_.empty() && inactive_.empty() &&
257 "interval sets should be empty on initialization");
259 for (LiveIntervals::Intervals::iterator i = li.begin(), e = li.end();
261 unhandled_.push_back(&*i);
262 if (MRegisterInfo::isPhysicalRegister(i->reg))
263 fixed_.push_back(&*i);
267 void RA::processActiveIntervals(IntervalPtrs::value_type cur)
269 DEBUG(std::cerr << "\tprocessing active intervals:\n");
270 for (IntervalPtrs::iterator i = active_.begin(); i != active_.end();) {
271 unsigned reg = (*i)->reg;
272 // remove expired intervals
273 if ((*i)->expiredAt(cur->start())) {
274 DEBUG(std::cerr << "\t\tinterval " << **i << " expired\n");
275 if (MRegisterInfo::isVirtualRegister(reg))
276 reg = vrm_->getPhys(reg);
277 prt_->delRegUse(reg);
278 // remove from active
279 i = active_.erase(i);
281 // move inactive intervals to inactive list
282 else if (!(*i)->liveAt(cur->start())) {
283 DEBUG(std::cerr << "\t\tinterval " << **i << " inactive\n");
284 if (MRegisterInfo::isVirtualRegister(reg))
285 reg = vrm_->getPhys(reg);
286 prt_->delRegUse(reg);
288 inactive_.push_back(*i);
289 // remove from active
290 i = active_.erase(i);
298 void RA::processInactiveIntervals(IntervalPtrs::value_type cur)
300 DEBUG(std::cerr << "\tprocessing inactive intervals:\n");
301 for (IntervalPtrs::iterator i = inactive_.begin(); i != inactive_.end();) {
302 unsigned reg = (*i)->reg;
304 // remove expired intervals
305 if ((*i)->expiredAt(cur->start())) {
306 DEBUG(std::cerr << "\t\tinterval " << **i << " expired\n");
307 // remove from inactive
308 i = inactive_.erase(i);
310 // move re-activated intervals in active list
311 else if ((*i)->liveAt(cur->start())) {
312 DEBUG(std::cerr << "\t\tinterval " << **i << " active\n");
313 if (MRegisterInfo::isVirtualRegister(reg))
314 reg = vrm_->getPhys(reg);
315 prt_->addRegUse(reg);
317 active_.push_back(*i);
318 // remove from inactive
319 i = inactive_.erase(i);
327 void RA::updateSpillWeights(unsigned reg, SpillWeights::value_type weight)
329 spillWeights_[reg] += weight;
330 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
331 spillWeights_[*as] += weight;
334 void RA::assignRegOrSpillAtInterval(IntervalPtrs::value_type cur)
336 DEBUG(std::cerr << "\tallocating current interval: ");
338 PhysRegTracker backupPrt = *prt_;
340 spillWeights_.assign(mri_->getNumRegs(), 0.0);
342 // for each interval in active update spill weights
343 for (IntervalPtrs::const_iterator i = active_.begin(), e = active_.end();
345 unsigned reg = (*i)->reg;
346 if (MRegisterInfo::isVirtualRegister(reg))
347 reg = vrm_->getPhys(reg);
348 updateSpillWeights(reg, (*i)->weight);
351 // for every interval in inactive we overlap with, mark the
352 // register as not free and update spill weights
353 for (IntervalPtrs::const_iterator i = inactive_.begin(),
354 e = inactive_.end(); i != e; ++i) {
355 if (cur->overlaps(**i)) {
356 unsigned reg = (*i)->reg;
357 if (MRegisterInfo::isVirtualRegister(reg))
358 reg = vrm_->getPhys(reg);
359 prt_->addRegUse(reg);
360 updateSpillWeights(reg, (*i)->weight);
364 // for every interval in fixed we overlap with,
365 // mark the register as not free and update spill weights
366 for (IntervalPtrs::const_iterator i = fixed_.begin(),
367 e = fixed_.end(); i != e; ++i) {
368 if (cur->overlaps(**i)) {
369 unsigned reg = (*i)->reg;
370 prt_->addRegUse(reg);
371 updateSpillWeights(reg, (*i)->weight);
375 unsigned physReg = getFreePhysReg(cur);
376 // restore the physical register tracker
378 // if we find a free register, we are done: assign this virtual to
379 // the free physical register and add this interval to the active
382 DEBUG(std::cerr << mri_->getName(physReg) << '\n');
383 vrm_->assignVirt2Phys(cur->reg, physReg);
384 prt_->addRegUse(physReg);
385 active_.push_back(cur);
386 handled_.push_back(cur);
389 DEBUG(std::cerr << "no free registers\n");
391 DEBUG(std::cerr << "\tassigning stack slot at interval "<< *cur << ":\n");
393 float minWeight = HUGE_VAL;
395 const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
396 for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
397 i != rc->allocation_order_end(*mf_); ++i) {
399 if (minWeight > spillWeights_[reg]) {
400 minWeight = spillWeights_[reg];
404 DEBUG(std::cerr << "\t\tregister with min weight: "
405 << mri_->getName(minReg) << " (" << minWeight << ")\n");
407 // if the current has the minimum weight, we spill it and move on
408 if (cur->weight <= minWeight) {
409 DEBUG(std::cerr << "\t\t\tspilling(c): " << *cur << '\n');
410 spilled_.push_back(cur);
414 // otherwise we spill all intervals aliasing the register with
415 // minimum weight, assigned the newly cleared register to the
416 // current interval and continue
417 std::vector<LiveInterval*> added;
418 assert(MRegisterInfo::isPhysicalRegister(minReg) &&
419 "did not choose a register to spill?");
420 std::vector<bool> toSpill(mri_->getNumRegs(), false);
421 toSpill[minReg] = true;
422 for (const unsigned* as = mri_->getAliasSet(minReg); *as; ++as)
424 unsigned earliestStart = cur->start();
426 std::set<unsigned> spilled;
428 for (IntervalPtrs::iterator i = active_.begin(); i != active_.end(); ) {
429 unsigned reg = (*i)->reg;
430 if (MRegisterInfo::isVirtualRegister(reg) &&
431 toSpill[vrm_->getPhys(reg)] &&
432 cur->overlaps(**i)) {
433 DEBUG(std::cerr << "\t\t\tspilling(a): " << **i << '\n');
434 spilled_.push_back(*i);
435 prt_->delRegUse(vrm_->getPhys(reg));
436 vrm_->clearVirt(reg);
437 i = active_.erase(i);
442 for (IntervalPtrs::iterator i = inactive_.begin(); i != inactive_.end(); ) {
443 unsigned reg = (*i)->reg;
444 if (MRegisterInfo::isVirtualRegister(reg) &&
445 toSpill[vrm_->getPhys(reg)] &&
446 cur->overlaps(**i)) {
447 DEBUG(std::cerr << "\t\t\tspilling(i): " << **i << '\n');
448 spilled_.push_back(*i);
449 vrm_->clearVirt(reg);
450 i = inactive_.erase(i);
456 vrm_->assignVirt2Phys(cur->reg, minReg);
457 prt_->addRegUse(minReg);
458 active_.push_back(cur);
459 handled_.push_back(cur);
463 unsigned RA::getFreePhysReg(IntervalPtrs::value_type cur)
465 const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
467 for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
468 i != rc->allocation_order_end(*mf_); ++i) {
470 if (prt_->isRegAvail(reg))
476 FunctionPass* llvm::createIterativeScanRegisterAllocator() {