LiveIntervalAnalysis.cpp revision 1893a05b28bf03e0ded1ed651cc1d71c7854ad93 
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/Function.h"
21#include "llvm/Analysis/LoopInfo.h"
22#include "llvm/CodeGen/LiveVariables.h"
23#include "llvm/CodeGen/MachineFrameInfo.h"
24#include "llvm/CodeGen/MachineFunctionPass.h"
25#include "llvm/CodeGen/MachineInstr.h"
26#include "llvm/CodeGen/Passes.h"
27#include "llvm/CodeGen/SSARegMap.h"
28#include "llvm/Target/MRegisterInfo.h"
29#include "llvm/Target/TargetInstrInfo.h"
30#include "llvm/Target/TargetMachine.h"
31#include "llvm/Target/TargetRegInfo.h"
32#include "llvm/Support/CFG.h"
33#include "Support/Debug.h"
34#include "Support/DepthFirstIterator.h"
35#include "Support/Statistic.h"
36#include <cmath>
37#include <iostream>
38#include <limits>
39
40using namespace llvm;
41
42namespace {
43    RegisterAnalysis<LiveIntervals> X("liveintervals",
44                                      "Live Interval Analysis");
45
46    Statistic<> numIntervals("liveintervals", "Number of intervals");
47};
48
49void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const
50{
51    AU.addPreserved<LiveVariables>();
52    AU.addRequired<LiveVariables>();
53    AU.addPreservedID(PHIEliminationID);
54    AU.addRequiredID(PHIEliminationID);
55    AU.addRequiredID(TwoAddressInstructionPassID);
56    AU.addRequired<LoopInfo>();
57    MachineFunctionPass::getAnalysisUsage(AU);
58}
59
60/// runOnMachineFunction - Register allocate the whole function
61///
62bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
63    DEBUG(std::cerr << "Machine Function\n");
64    mf_ = &fn;
65    tm_ = &fn.getTarget();
66    mri_ = tm_->getRegisterInfo();
67    lv_ = &getAnalysis<LiveVariables>();
68    mbbi2mbbMap_.clear();
69    mi2iMap_.clear();
70    r2iMap_.clear();
71    r2iMap_.clear();
72    intervals_.clear();
73
74    // number MachineInstrs
75    unsigned miIndex = 0;
76    for (MachineFunction::iterator mbb = mf_->begin(), mbbEnd = mf_->end();
77         mbb != mbbEnd; ++mbb) {
78        const std::pair<MachineBasicBlock*, unsigned>& entry =
79            lv_->getMachineBasicBlockInfo(&*mbb);
80        bool inserted = mbbi2mbbMap_.insert(std::make_pair(entry.second,
81                                                           entry.first)).second;
82        assert(inserted && "multiple index -> MachineBasicBlock");
83
84        for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
85             mi != miEnd; ++mi) {
86            inserted = mi2iMap_.insert(std::make_pair(*mi, miIndex)).second;
87            assert(inserted && "multiple MachineInstr -> index mappings");
88            ++miIndex;
89        }
90    }
91
92    computeIntervals();
93
94    // compute spill weights
95    const LoopInfo& loopInfo = getAnalysis<LoopInfo>();
96    const TargetInstrInfo& tii = tm_->getInstrInfo();
97
98    for (MbbIndex2MbbMap::iterator
99             it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
100         it != itEnd; ++it) {
101        MachineBasicBlock* mbb = it->second;
102
103        unsigned loopDepth = loopInfo.getLoopDepth(mbb->getBasicBlock());
104
105        for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
106             mi != miEnd; ++mi) {
107            MachineInstr* instr = *mi;
108            for (int i = instr->getNumOperands() - 1; i >= 0; --i) {
109                MachineOperand& mop = instr->getOperand(i);
110
111                if (!mop.isVirtualRegister())
112                    continue;
113
114                unsigned reg = mop.getAllocatedRegNum();
115                Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
116                assert(r2iit != r2iMap_.end());
117                r2iit->second->weight += pow(10.0F, loopDepth);
118            }
119        }
120    }
121
122    numIntervals += intervals_.size();
123
124    return true;
125}
126
127void LiveIntervals::printRegName(unsigned reg) const
128{
129    if (reg < MRegisterInfo::FirstVirtualRegister)
130        std::cerr << mri_->getName(reg);
131    else
132        std::cerr << '%' << reg;
133}
134
135void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
136                                             MachineBasicBlock::iterator mi,
137                                             unsigned reg)
138{
139    DEBUG(std::cerr << "\t\tregister: ";printRegName(reg); std::cerr << '\n');
140
141    unsigned instrIndex = getInstructionIndex(*mi);
142
143    LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
144
145    Interval* interval = 0;
146    Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
147    if (r2iit == r2iMap_.end()) {
148        // add new interval
149        intervals_.push_back(Interval(reg));
150        // update interval index for this register
151        bool inserted =
152            r2iMap_.insert(std::make_pair(reg, --intervals_.end())).second;
153        assert(inserted);
154        interval = &intervals_.back();
155    }
156    else {
157        interval = &*r2iit->second;
158    }
159
160    for (MbbIndex2MbbMap::iterator
161             it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
162         it != itEnd; ++it) {
163        unsigned liveBlockIndex = it->first;
164        MachineBasicBlock* liveBlock = it->second;
165        if (liveBlockIndex < vi.AliveBlocks.size() &&
166            vi.AliveBlocks[liveBlockIndex] &&
167            !liveBlock->empty()) {
168            unsigned start =  getInstructionIndex(liveBlock->front());
169            unsigned end = getInstructionIndex(liveBlock->back()) + 1;
170            interval->addRange(start, end);
171        }
172    }
173
174    bool killedInDefiningBasicBlock = false;
175    for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
176        MachineBasicBlock* killerBlock = vi.Kills[i].first;
177        MachineInstr* killerInstr = vi.Kills[i].second;
178        unsigned start = (mbb == killerBlock ?
179                          instrIndex :
180                          getInstructionIndex(killerBlock->front()));
181        unsigned end = getInstructionIndex(killerInstr) + 1;
182        if (start < end) {
183            killedInDefiningBasicBlock |= mbb == killerBlock;
184            interval->addRange(start, end);
185        }
186    }
187
188    if (!killedInDefiningBasicBlock) {
189        unsigned end = getInstructionIndex(mbb->back()) + 1;
190        interval->addRange(instrIndex, end);
191    }
192}
193
194void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
195                                              MachineBasicBlock::iterator mi,
196                                              unsigned reg)
197{
198    DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
199
200    unsigned start = getInstructionIndex(*mi);
201    unsigned end = start;
202
203    // register can be dead by the instruction defining it but it can
204    // only be killed by subsequent instructions
205
206    for (LiveVariables::killed_iterator
207             ki = lv_->dead_begin(*mi),
208             ke = lv_->dead_end(*mi);
209         ki != ke; ++ki) {
210        if (reg == ki->second) {
211            end = getInstructionIndex(ki->first) + 1;
212            DEBUG(std::cerr << " dead\n");
213            goto exit;
214        }
215    }
216    ++mi;
217
218    for (MachineBasicBlock::iterator e = mbb->end(); mi != e; ++mi) {
219        for (LiveVariables::killed_iterator
220                 ki = lv_->dead_begin(*mi),
221                 ke = lv_->dead_end(*mi);
222             ki != ke; ++ki) {
223            if (reg == ki->second) {
224                end = getInstructionIndex(ki->first) + 1;
225                DEBUG(std::cerr << " dead\n");
226                goto exit;
227            }
228        }
229
230        for (LiveVariables::killed_iterator
231                 ki = lv_->killed_begin(*mi),
232                 ke = lv_->killed_end(*mi);
233             ki != ke; ++ki) {
234            if (reg == ki->second) {
235                end = getInstructionIndex(ki->first) + 1;
236                DEBUG(std::cerr << " killed\n");
237                goto exit;
238            }
239        }
240    }
241exit:
242    assert(start < end && "did not find end of interval?");
243
244    Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
245    if (r2iit != r2iMap_.end()) {
246        Interval& interval = *r2iit->second;
247        interval.addRange(start, end);
248    }
249    else {
250        intervals_.push_back(Interval(reg));
251        Interval& interval = intervals_.back();
252        // update interval index for this register
253        bool inserted =
254            r2iMap_.insert(std::make_pair(reg, --intervals_.end())).second;
255        assert(inserted);
256        interval.addRange(start, end);
257    }
258}
259
260void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
261                                      MachineBasicBlock::iterator mi,
262                                      unsigned reg)
263{
264    if (reg < MRegisterInfo::FirstVirtualRegister) {
265        if (lv_->getAllocatablePhysicalRegisters()[reg]) {
266            handlePhysicalRegisterDef(mbb, mi, reg);
267            for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
268                handlePhysicalRegisterDef(mbb, mi, *as);
269        }
270    }
271    else {
272        handleVirtualRegisterDef(mbb, mi, reg);
273    }
274}
275
276unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
277{
278    assert(mi2iMap_.find(instr) != mi2iMap_.end() &&
279           "instruction not assigned a number");
280    return mi2iMap_.find(instr)->second;
281}
282
283/// computeIntervals - computes the live intervals for virtual
284/// registers. for some ordering of the machine instructions [1,N] a
285/// live interval is an interval [i, j] where 1 <= i <= j <= N for
286/// which a variable is live
287void LiveIntervals::computeIntervals()
288{
289    DEBUG(std::cerr << "computing live intervals:\n");
290
291    for (MbbIndex2MbbMap::iterator
292             it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
293         it != itEnd; ++it) {
294        MachineBasicBlock* mbb = it->second;
295        DEBUG(std::cerr << "machine basic block: "
296              << mbb->getBasicBlock()->getName() << "\n");
297
298        for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
299             mi != miEnd; ++mi) {
300            MachineInstr* instr = *mi;
301            const TargetInstrDescriptor& tid =
302                tm_->getInstrInfo().get(instr->getOpcode());
303            DEBUG(std::cerr << "\t[" << getInstructionIndex(instr) << "] ";
304                  instr->print(std::cerr, *tm_););
305
306            // handle implicit defs
307            for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
308                handleRegisterDef(mbb, mi, *id);
309
310            // handle explicit defs
311            for (int i = instr->getNumOperands() - 1; i >= 0; --i) {
312                MachineOperand& mop = instr->getOperand(i);
313
314                if (!mop.isRegister())
315                    continue;
316
317                // handle defs - build intervals
318                if (mop.isDef())
319                    handleRegisterDef(mbb, mi, mop.getAllocatedRegNum());
320            }
321        }
322    }
323
324    intervals_.sort(StartPointComp());
325    DEBUG(std::copy(intervals_.begin(), intervals_.end(),
326                    std::ostream_iterator<Interval>(std::cerr, "\n")));
327}
328
329LiveIntervals::Interval::Interval(unsigned r)
330    : reg(r), hint(0),
331      weight((r < MRegisterInfo::FirstVirtualRegister ?
332              std::numeric_limits<float>::max() : 0.0F))
333{
334
335}
336
337void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
338{
339    DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
340    //assert(start < end && "invalid range?");
341    Range range = std::make_pair(start, end);
342    Ranges::iterator it =
343        ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
344                      range);
345
346    mergeRangesForward(it);
347    mergeRangesBackward(it);
348    DEBUG(std::cerr << *this << '\n');
349}
350
351void LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
352{
353    for (Ranges::iterator next = it + 1;
354         next != ranges.end() && it->second >= next->first; ) {
355        it->second = std::max(it->second, next->second);
356        next = ranges.erase(next);
357    }
358}
359
360void LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
361{
362    for (Ranges::iterator prev = it - 1;
363         it != ranges.begin() && it->first <= prev->second; ) {
364        it->first = std::min(it->first, prev->first);
365        it->second = std::max(it->second, prev->second);
366        it = ranges.erase(prev);
367        prev = it - 1;
368    }
369}
370
371bool LiveIntervals::Interval::liveAt(unsigned index) const
372{
373    Ranges::const_iterator r = ranges.begin();
374    while (r != ranges.end() && index < (r->second - 1)) {
375        if (index >= r->first)
376            return true;
377        ++r;
378    }
379    return false;
380}
381
382bool LiveIntervals::Interval::overlaps(const Interval& other) const
383{
384    Ranges::const_iterator i = ranges.begin();
385    Ranges::const_iterator j = other.ranges.begin();
386
387    while (i != ranges.end() && j != other.ranges.end()) {
388        if (i->first < j->first) {
389            if ((i->second - 1) > j->first) {
390                return true;
391            }
392            else {
393                ++i;
394            }
395        }
396        else if (j->first < i->first) {
397            if ((j->second - 1) > i->first) {
398                return true;
399            }
400            else {
401                ++j;
402            }
403        }
404        else {
405            return true;
406        }
407    }
408
409    return false;
410}
411
412std::ostream& llvm::operator<<(std::ostream& os,
413                               const LiveIntervals::Interval& li)
414{
415    os << "%reg" << li.reg << ',' << li.weight << " = ";
416    for (LiveIntervals::Interval::Ranges::const_iterator
417             i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
418        os << "[" << i->first << "," << i->second << ")";
419    }
420    return os;
421}
422