LiveIntervalAnalysis.cpp revision 0b8cb2bc47a6bee59c8c3f46d4cc047badf7f8ac 
1//===-- LiveIntervals.cpp - Live Interval Analysis ------------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
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.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the LiveInterval analysis pass which is used
11// by the Linear Scan Register allocator. This pass linearizes the
12// basic blocks of the function in DFS order and uses the
13// LiveVariables pass to conservatively compute live intervals for
14// each virtual and physical register.
15//
16//===----------------------------------------------------------------------===//
17
18#define DEBUG_TYPE "liveintervals"
19#include "llvm/CodeGen/LiveIntervals.h"
20#include "llvm/Analysis/LoopInfo.h"
21#include "llvm/CodeGen/LiveVariables.h"
22#include "llvm/CodeGen/MachineFrameInfo.h"
23#include "llvm/CodeGen/MachineInstr.h"
24#include "llvm/CodeGen/Passes.h"
25#include "llvm/CodeGen/SSARegMap.h"
26#include "llvm/Target/MRegisterInfo.h"
27#include "llvm/Target/TargetInstrInfo.h"
28#include "llvm/Target/TargetMachine.h"
29#include "llvm/Support/CFG.h"
30#include "Support/CommandLine.h"
31#include "Support/Debug.h"
32#include "Support/Statistic.h"
33#include <cmath>
34#include <iostream>
35#include <limits>
36
37using namespace llvm;
38
39namespace {
40    RegisterAnalysis<LiveIntervals> X("liveintervals",
41                                      "Live Interval Analysis");
42
43    Statistic<> numIntervals("liveintervals", "Number of intervals");
44    Statistic<> numJoined   ("liveintervals", "Number of joined intervals");
45
46    cl::opt<bool>
47    join("join-liveintervals",
48         cl::desc("Join compatible live intervals"),
49         cl::init(true));
50};
51
52void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const
53{
54    AU.addPreserved<LiveVariables>();
55    AU.addRequired<LiveVariables>();
56    AU.addPreservedID(PHIEliminationID);
57    AU.addRequiredID(PHIEliminationID);
58    AU.addRequiredID(TwoAddressInstructionPassID);
59    AU.addRequired<LoopInfo>();
60    MachineFunctionPass::getAnalysisUsage(AU);
61}
62
63void LiveIntervals::releaseMemory()
64{
65    mbbi2mbbMap_.clear();
66    mi2iMap_.clear();
67    r2iMap_.clear();
68    r2iMap_.clear();
69    r2rMap_.clear();
70    intervals_.clear();
71}
72
73
74/// runOnMachineFunction - Register allocate the whole function
75///
76bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
77    DEBUG(std::cerr << "Machine Function\n");
78    mf_ = &fn;
79    tm_ = &fn.getTarget();
80    mri_ = tm_->getRegisterInfo();
81    lv_ = &getAnalysis<LiveVariables>();
82
83    // number MachineInstrs
84    unsigned miIndex = 0;
85    for (MachineFunction::iterator mbb = mf_->begin(), mbbEnd = mf_->end();
86         mbb != mbbEnd; ++mbb) {
87        const std::pair<MachineBasicBlock*, unsigned>& entry =
88            lv_->getMachineBasicBlockInfo(mbb);
89        bool inserted = mbbi2mbbMap_.insert(std::make_pair(entry.second,
90                                                           entry.first)).second;
91        assert(inserted && "multiple index -> MachineBasicBlock");
92
93        for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
94             mi != miEnd; ++mi) {
95            inserted = mi2iMap_.insert(std::make_pair(*mi, miIndex)).second;
96            assert(inserted && "multiple MachineInstr -> index mappings");
97            miIndex += 2;
98        }
99    }
100
101    computeIntervals();
102
103    // compute spill weights
104    const LoopInfo& loopInfo = getAnalysis<LoopInfo>();
105    const TargetInstrInfo& tii = tm_->getInstrInfo();
106
107    for (MachineFunction::const_iterator mbbi = mf_->begin(),
108             mbbe = mf_->end(); mbbi != mbbe; ++mbbi) {
109        const MachineBasicBlock* mbb = mbbi;
110        unsigned loopDepth = loopInfo.getLoopDepth(mbb->getBasicBlock());
111
112        for (MachineBasicBlock::const_iterator mii = mbb->begin(),
113                 mie = mbb->end(); mii != mie; ++mii) {
114            MachineInstr* mi = *mii;
115
116            for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
117                MachineOperand& mop = mi->getOperand(i);
118                if (mop.isVirtualRegister()) {
119                    unsigned reg = mop.getAllocatedRegNum();
120                    Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
121                    assert(r2iit != r2iMap_.end());
122                    r2iit->second->weight += pow(10.0F, loopDepth);
123                }
124            }
125        }
126    }
127
128    // join intervals if requested
129    if (join) joinIntervals();
130
131    numIntervals += intervals_.size();
132
133    intervals_.sort(StartPointComp());
134    DEBUG(std::copy(intervals_.begin(), intervals_.end(),
135                    std::ostream_iterator<Interval>(std::cerr, "\n")));
136    return true;
137}
138
139void LiveIntervals::printRegName(unsigned reg) const
140{
141    if (MRegisterInfo::isPhysicalRegister(reg))
142        std::cerr << mri_->getName(reg);
143    else
144        std::cerr << '%' << reg;
145}
146
147void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
148                                             MachineBasicBlock::iterator mi,
149                                             unsigned reg)
150{
151    DEBUG(std::cerr << "\t\tregister: ";printRegName(reg); std::cerr << '\n');
152
153    LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
154
155    Interval* interval = 0;
156    Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
157    if (r2iit == r2iMap_.end() || r2iit->first != reg) {
158        // add new interval
159        intervals_.push_back(Interval(reg));
160        // update interval index for this register
161        r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
162        interval = &intervals_.back();
163
164        // iterate over all of the blocks that the variable is
165        // completely live in, adding them to the live
166        // interval. obviously we only need to do this once.
167        for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
168            if (vi.AliveBlocks[i]) {
169                MachineBasicBlock* mbb = lv_->getIndexMachineBasicBlock(i);
170                if (!mbb->empty()) {
171                    interval->addRange(getInstructionIndex(mbb->front()),
172                                       getInstructionIndex(mbb->back()) + 1);
173                }
174            }
175        }
176    }
177    else {
178        interval = &*r2iit->second;
179    }
180
181    // we consider defs to happen at the second time slot of the
182    // instruction
183    unsigned instrIndex = getInstructionIndex(*mi) + 1;
184
185    bool killedInDefiningBasicBlock = false;
186    for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
187        MachineBasicBlock* killerBlock = vi.Kills[i].first;
188        MachineInstr* killerInstr = vi.Kills[i].second;
189        unsigned start = (mbb == killerBlock ?
190                          instrIndex :
191                          getInstructionIndex(killerBlock->front()));
192        unsigned end = (killerInstr == *mi ?
193                        instrIndex + 1 : // dead
194                        getInstructionIndex(killerInstr) + 1); // killed
195        // we do not want to add invalid ranges. these can happen when
196        // a variable has its latest use and is redefined later on in
197        // the same basic block (common with variables introduced by
198        // PHI elimination)
199        if (start < end) {
200            killedInDefiningBasicBlock |= mbb == killerBlock;
201            interval->addRange(start, end);
202        }
203    }
204
205    if (!killedInDefiningBasicBlock) {
206        unsigned end = getInstructionIndex(mbb->back()) + 1;
207        interval->addRange(instrIndex, end);
208    }
209}
210
211void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
212                                              MachineBasicBlock::iterator mi,
213                                              unsigned reg)
214{
215    typedef LiveVariables::killed_iterator KillIter;
216
217    DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
218
219    MachineBasicBlock::iterator e = mbb->end();
220    // we consider defs to happen at the second time slot of the
221    // instruction
222    unsigned start, end;
223    start = end = getInstructionIndex(*mi) + 1;
224
225    // a variable can be dead by the instruction defining it
226    for (KillIter ki = lv_->dead_begin(*mi), ke = lv_->dead_end(*mi);
227         ki != ke; ++ki) {
228        if (reg == ki->second) {
229            DEBUG(std::cerr << " dead\n");
230            ++end;
231            goto exit;
232        }
233    }
234
235    // a variable can only be killed by subsequent instructions
236    do {
237        ++mi;
238        end += 2;
239        for (KillIter ki = lv_->killed_begin(*mi), ke = lv_->killed_end(*mi);
240             ki != ke; ++ki) {
241            if (reg == ki->second) {
242                DEBUG(std::cerr << " killed\n");
243                goto exit;
244            }
245        }
246    } while (mi != e);
247
248exit:
249    assert(start < end && "did not find end of interval?");
250
251    Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
252    if (r2iit != r2iMap_.end() && r2iit->first == reg) {
253        r2iit->second->addRange(start, end);
254    }
255    else {
256        intervals_.push_back(Interval(reg));
257        // update interval index for this register
258        r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
259        intervals_.back().addRange(start, end);
260    }
261}
262
263void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
264                                      MachineBasicBlock::iterator mi,
265                                      unsigned reg)
266{
267    if (MRegisterInfo::isPhysicalRegister(reg)) {
268        if (lv_->getAllocatablePhysicalRegisters()[reg]) {
269            handlePhysicalRegisterDef(mbb, mi, reg);
270            for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
271                handlePhysicalRegisterDef(mbb, mi, *as);
272        }
273    }
274    else {
275        handleVirtualRegisterDef(mbb, mi, reg);
276    }
277}
278
279unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
280{
281    assert(mi2iMap_.find(instr) != mi2iMap_.end() &&
282           "instruction not assigned a number");
283    return mi2iMap_.find(instr)->second;
284}
285
286/// computeIntervals - computes the live intervals for virtual
287/// registers. for some ordering of the machine instructions [1,N] a
288/// live interval is an interval [i, j) where 1 <= i <= j < N for
289/// which a variable is live
290void LiveIntervals::computeIntervals()
291{
292    DEBUG(std::cerr << "computing live intervals:\n");
293
294    for (MbbIndex2MbbMap::iterator
295             it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
296         it != itEnd; ++it) {
297        MachineBasicBlock* mbb = it->second;
298        DEBUG(std::cerr << "machine basic block: "
299              << mbb->getBasicBlock()->getName() << "\n");
300
301        for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
302             mi != miEnd; ++mi) {
303            MachineInstr* instr = *mi;
304            const TargetInstrDescriptor& tid =
305                tm_->getInstrInfo().get(instr->getOpcode());
306            DEBUG(std::cerr << "\t[" << getInstructionIndex(instr) << "] ";
307                  instr->print(std::cerr, *tm_););
308
309            // handle implicit defs
310            for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
311                handleRegisterDef(mbb, mi, *id);
312
313            // handle explicit defs
314            for (int i = instr->getNumOperands() - 1; i >= 0; --i) {
315                MachineOperand& mop = instr->getOperand(i);
316                // handle register defs - build intervals
317                if (mop.isRegister() && mop.isDef())
318                    handleRegisterDef(mbb, mi, mop.getAllocatedRegNum());
319            }
320        }
321    }
322}
323
324unsigned LiveIntervals::rep(unsigned reg)
325{
326    Reg2RegMap::iterator it = r2rMap_.find(reg);
327    if (it != r2rMap_.end())
328        return it->second = rep(it->second);
329    return reg;
330}
331
332void LiveIntervals::joinIntervals()
333{
334    DEBUG(std::cerr << "joining compatible intervals:\n");
335
336    const TargetInstrInfo& tii = tm_->getInstrInfo();
337
338    for (MachineFunction::const_iterator mbbi = mf_->begin(),
339             mbbe = mf_->end(); mbbi != mbbe; ++mbbi) {
340        const MachineBasicBlock* mbb = mbbi;
341        DEBUG(std::cerr << "machine basic block: "
342              << mbb->getBasicBlock()->getName() << "\n");
343
344        for (MachineBasicBlock::const_iterator mii = mbb->begin(),
345                 mie = mbb->end(); mii != mie; ++mii) {
346            MachineInstr* mi = *mii;
347            const TargetInstrDescriptor& tid =
348                tm_->getInstrInfo().get(mi->getOpcode());
349            DEBUG(std::cerr << "\t\tinstruction["
350                  << getInstructionIndex(mi) << "]: ";
351                  mi->print(std::cerr, *tm_););
352
353            // we only join virtual registers with allocatable
354            // physical registers since we do not have liveness information
355            // on not allocatable physical registers
356            unsigned regA, regB;
357            if (tii.isMoveInstr(*mi, regA, regB) &&
358                (MRegisterInfo::isVirtualRegister(regA) ||
359                 lv_->getAllocatablePhysicalRegisters()[regA]) &&
360                (MRegisterInfo::isVirtualRegister(regB) ||
361                 lv_->getAllocatablePhysicalRegisters()[regB])) {
362
363                // get representative registers
364                regA = rep(regA);
365                regB = rep(regB);
366
367                // if they are already joined we continue
368                if (regA == regB)
369                    continue;
370
371                Reg2IntervalMap::iterator r2iA = r2iMap_.find(regA);
372                assert(r2iA != r2iMap_.end());
373                Reg2IntervalMap::iterator r2iB = r2iMap_.find(regB);
374                assert(r2iB != r2iMap_.end());
375
376                Intervals::iterator intA = r2iA->second;
377                Intervals::iterator intB = r2iB->second;
378
379                // both A and B are virtual registers
380                if (MRegisterInfo::isVirtualRegister(intA->reg) &&
381                    MRegisterInfo::isVirtualRegister(intB->reg)) {
382
383                    const TargetRegisterClass *rcA, *rcB;
384                    rcA = mf_->getSSARegMap()->getRegClass(intA->reg);
385                    rcB = mf_->getSSARegMap()->getRegClass(intB->reg);
386                    assert(rcA == rcB && "registers must be of the same class");
387
388                    // if their intervals do not overlap we join them
389                    if (!intB->overlaps(*intA)) {
390                        intA->join(*intB);
391                        r2iB->second = r2iA->second;
392                        r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
393                        intervals_.erase(intB);
394                        ++numJoined;
395                    }
396                }
397                else if (MRegisterInfo::isPhysicalRegister(intA->reg) ^
398                         MRegisterInfo::isPhysicalRegister(intB->reg)) {
399                    if (MRegisterInfo::isPhysicalRegister(intB->reg)) {
400                        std::swap(regA, regB);
401                        std::swap(intA, intB);
402                        std::swap(r2iA, r2iB);
403                    }
404
405                    assert(MRegisterInfo::isPhysicalRegister(intA->reg) &&
406                           MRegisterInfo::isVirtualRegister(intB->reg) &&
407                           "A must be physical and B must be virtual");
408
409                    if (!intA->overlaps(*intB) &&
410                         !overlapsAliases(*intA, *intB)) {
411                        intA->join(*intB);
412                        r2iB->second = r2iA->second;
413                        r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
414                        intervals_.erase(intB);
415                        ++numJoined;
416                    }
417                }
418            }
419        }
420    }
421}
422
423bool LiveIntervals::overlapsAliases(const Interval& lhs,
424                                    const Interval& rhs) const
425{
426    assert(MRegisterInfo::isPhysicalRegister(lhs.reg) &&
427           "first interval must describe a physical register");
428
429    for (const unsigned* as = mri_->getAliasSet(lhs.reg); *as; ++as) {
430        Reg2IntervalMap::const_iterator r2i = r2iMap_.find(*as);
431        assert(r2i != r2iMap_.end() && "alias does not have interval?");
432        if (rhs.overlaps(*r2i->second))
433            return true;
434    }
435
436    return false;
437}
438
439LiveIntervals::Interval::Interval(unsigned r)
440    : reg(r),
441      weight((MRegisterInfo::isPhysicalRegister(r) ?
442              std::numeric_limits<float>::max() : 0.0F))
443{
444
445}
446
447// An example for liveAt():
448//
449// this = [1,2), liveAt(0) will return false. The instruction defining
450// this spans slots [0,1]. Since it is a definition we say that it is
451// live in the second slot onwards. By ending the lifetime of this
452// interval at 2 it means that it is not used at all. liveAt(1)
453// returns true which means that this clobbers a register at
454// instruction at 0.
455//
456// this = [1,4), liveAt(0) will return false and liveAt(2) will return
457// true.  The variable is defined at instruction 0 and last used at 2.
458bool LiveIntervals::Interval::liveAt(unsigned index) const
459{
460    Range dummy(index, index+1);
461    Ranges::const_iterator r = std::upper_bound(ranges.begin(),
462                                                ranges.end(),
463                                                dummy);
464    if (r == ranges.begin())
465        return false;
466
467    --r;
468    return index >= r->first && index < r->second;
469}
470
471// An example for overlaps():
472//
473// 0: A = ...
474// 2: B = ...
475// 4: C = A + B ;; last use of A
476//
477// The live intervals should look like:
478//
479// A = [1, 5)
480// B = [3, x)
481// C = [5, y)
482//
483// A->overlaps(C) should return false since we want to be able to join
484// A and C.
485bool LiveIntervals::Interval::overlaps(const Interval& other) const
486{
487    Ranges::const_iterator i = ranges.begin();
488    Ranges::const_iterator ie = ranges.end();
489    Ranges::const_iterator j = other.ranges.begin();
490    Ranges::const_iterator je = other.ranges.end();
491    if (i->first < j->first) {
492        i = std::upper_bound(i, ie, *j);
493        if (i != ranges.begin()) --i;
494    }
495    else if (j->first < i->first) {
496        j = std::upper_bound(j, je, *i);
497        if (j != other.ranges.begin()) --j;
498    }
499
500    while (i != ie && j != je) {
501        if (i->first == j->first) {
502            return true;
503        }
504        else {
505            if (i->first > j->first) {
506                swap(i, j);
507                swap(ie, je);
508            }
509            assert(i->first < j->first);
510
511            if (i->second > j->first) {
512                return true;
513            }
514            else {
515                ++i;
516            }
517        }
518    }
519
520    return false;
521}
522
523void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
524{
525    assert(start < end && "Invalid range to add!");
526    DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
527    //assert(start < end && "invalid range?");
528    Range range = std::make_pair(start, end);
529    Ranges::iterator it =
530        ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
531                      range);
532
533    it = mergeRangesForward(it);
534    it = mergeRangesBackward(it);
535    DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
536}
537
538void LiveIntervals::Interval::join(const LiveIntervals::Interval& other)
539{
540    DEBUG(std::cerr << "\t\t\t\tjoining intervals: "
541          << other << " and " << *this << '\n');
542    Ranges::iterator cur = ranges.begin();
543
544    for (Ranges::const_iterator i = other.ranges.begin(),
545             e = other.ranges.end(); i != e; ++i) {
546        cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
547        cur = mergeRangesForward(cur);
548        cur = mergeRangesBackward(cur);
549    }
550    if (MRegisterInfo::isVirtualRegister(reg))
551        weight += other.weight;
552
553    DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
554}
555
556LiveIntervals::Interval::Ranges::iterator
557LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
558{
559    for (Ranges::iterator next = it + 1;
560         next != ranges.end() && it->second >= next->first; ) {
561        it->second = std::max(it->second, next->second);
562        next = ranges.erase(next);
563    }
564    return it;
565}
566
567LiveIntervals::Interval::Ranges::iterator
568LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
569{
570    while (it != ranges.begin()) {
571        Ranges::iterator prev = it - 1;
572        if (it->first > prev->second) break;
573
574        it->first = std::min(it->first, prev->first);
575        it->second = std::max(it->second, prev->second);
576        it = ranges.erase(prev);
577    }
578
579    return it;
580}
581
582std::ostream& llvm::operator<<(std::ostream& os,
583                               const LiveIntervals::Interval& li)
584{
585    os << "%reg" << li.reg << ',' << li.weight << " = ";
586    for (LiveIntervals::Interval::Ranges::const_iterator
587             i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
588        os << "[" << i->first << "," << i->second << ")";
589    }
590    return os;
591}
592