LiveIntervalAnalysis.cpp revision af25473d5e99e0c0968746e12d8827e4b712bd31 
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                intervals_[r2iit->second].weight += pow(10.0F, loopDepth);
118            }
119        }
120    }
121
122    return true;
123}
124
125void LiveIntervals::printRegName(unsigned reg) const
126{
127    if (reg < MRegisterInfo::FirstVirtualRegister)
128        std::cerr << mri_->getName(reg);
129    else
130        std::cerr << '%' << reg;
131}
132
133void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
134                                             MachineBasicBlock::iterator mi,
135                                             unsigned reg)
136{
137    DEBUG(std::cerr << "\t\tregister: ";printRegName(reg); std::cerr << '\n');
138
139    unsigned instrIndex = getInstructionIndex(*mi);
140
141    LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
142
143    Interval* interval = 0;
144    Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
145    if (r2iit == r2iMap_.end()) {
146        // add new interval
147        intervals_.push_back(Interval(reg));
148        // update interval index for this register
149        r2iMap_[reg] = intervals_.size() - 1;
150        interval = &intervals_.back();
151    }
152    else {
153        interval = &intervals_[r2iit->second];
154    }
155
156    for (MbbIndex2MbbMap::iterator
157             it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
158         it != itEnd; ++it) {
159        unsigned liveBlockIndex = it->first;
160        MachineBasicBlock* liveBlock = it->second;
161        if (liveBlockIndex < vi.AliveBlocks.size() &&
162            vi.AliveBlocks[liveBlockIndex] &&
163            !liveBlock->empty()) {
164            unsigned start =  getInstructionIndex(liveBlock->front());
165            unsigned end = getInstructionIndex(liveBlock->back()) + 1;
166            interval->addRange(start, end);
167        }
168    }
169
170    bool killedInDefiningBasicBlock = false;
171    for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
172        MachineBasicBlock* killerBlock = vi.Kills[i].first;
173        MachineInstr* killerInstr = vi.Kills[i].second;
174        unsigned start = (mbb == killerBlock ?
175                          instrIndex :
176                          getInstructionIndex(killerBlock->front()));
177        unsigned end = getInstructionIndex(killerInstr) + 1;
178        if (start < end) {
179            killedInDefiningBasicBlock |= mbb == killerBlock;
180            interval->addRange(start, end);
181        }
182    }
183
184    if (!killedInDefiningBasicBlock) {
185        unsigned end = getInstructionIndex(mbb->back()) + 1;
186        interval->addRange(instrIndex, end);
187    }
188}
189
190void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
191                                              MachineBasicBlock::iterator mi,
192                                              unsigned reg)
193{
194    DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
195
196    unsigned start = getInstructionIndex(*mi);
197    unsigned end = start;
198
199    // register can be dead by the instruction defining it but it can
200    // only be killed by subsequent instructions
201
202    for (LiveVariables::killed_iterator
203             ki = lv_->dead_begin(*mi),
204             ke = lv_->dead_end(*mi);
205         ki != ke; ++ki) {
206        if (reg == ki->second) {
207            end = getInstructionIndex(ki->first) + 1;
208            DEBUG(std::cerr << " dead\n");
209            goto exit;
210        }
211    }
212    ++mi;
213
214    for (MachineBasicBlock::iterator e = mbb->end(); mi != e; ++mi) {
215        for (LiveVariables::killed_iterator
216                 ki = lv_->dead_begin(*mi),
217                 ke = lv_->dead_end(*mi);
218             ki != ke; ++ki) {
219            if (reg == ki->second) {
220                end = getInstructionIndex(ki->first) + 1;
221                DEBUG(std::cerr << " dead\n");
222                goto exit;
223            }
224        }
225
226        for (LiveVariables::killed_iterator
227                 ki = lv_->killed_begin(*mi),
228                 ke = lv_->killed_end(*mi);
229             ki != ke; ++ki) {
230            if (reg == ki->second) {
231                end = getInstructionIndex(ki->first) + 1;
232                DEBUG(std::cerr << " killed\n");
233                goto exit;
234            }
235        }
236    }
237exit:
238    assert(start < end && "did not find end of interval?");
239
240    Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
241    if (r2iit != r2iMap_.end()) {
242        unsigned ii = r2iit->second;
243        Interval& interval = intervals_[ii];
244        interval.addRange(start, end);
245    }
246    else {
247        intervals_.push_back(Interval(reg));
248        Interval& interval = intervals_.back();
249        // update interval index for this register
250        r2iMap_[reg] = intervals_.size() - 1;
251        interval.addRange(start, end);
252    }
253}
254
255void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
256                                      MachineBasicBlock::iterator mi,
257                                      unsigned reg)
258{
259    if (reg < MRegisterInfo::FirstVirtualRegister) {
260        if (lv_->getAllocatablePhysicalRegisters()[reg]) {
261            handlePhysicalRegisterDef(mbb, mi, reg);
262            for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
263                handlePhysicalRegisterDef(mbb, mi, *as);
264        }
265    }
266    else {
267        handleVirtualRegisterDef(mbb, mi, reg);
268    }
269}
270
271unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
272{
273    assert(mi2iMap_.find(instr) != mi2iMap_.end() &&
274           "instruction not assigned a number");
275    return mi2iMap_.find(instr)->second;
276}
277
278/// computeIntervals - computes the live intervals for virtual
279/// registers. for some ordering of the machine instructions [1,N] a
280/// live interval is an interval [i, j] where 1 <= i <= j <= N for
281/// which a variable is live
282void LiveIntervals::computeIntervals()
283{
284    DEBUG(std::cerr << "computing live intervals:\n");
285
286    for (MbbIndex2MbbMap::iterator
287             it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
288         it != itEnd; ++it) {
289        MachineBasicBlock* mbb = it->second;
290        DEBUG(std::cerr << "machine basic block: "
291              << mbb->getBasicBlock()->getName() << "\n");
292
293        for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
294             mi != miEnd; ++mi) {
295            MachineInstr* instr = *mi;
296            const TargetInstrDescriptor& tid =
297                tm_->getInstrInfo().get(instr->getOpcode());
298            DEBUG(std::cerr << "\t[" << getInstructionIndex(instr) << "] ";
299                  instr->print(std::cerr, *tm_););
300
301            // handle implicit defs
302            for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
303                handleRegisterDef(mbb, mi, *id);
304
305            // handle explicit defs
306            for (int i = instr->getNumOperands() - 1; i >= 0; --i) {
307                MachineOperand& mop = instr->getOperand(i);
308
309                if (!mop.isRegister())
310                    continue;
311
312                // handle defs - build intervals
313                if (mop.isDef())
314                    handleRegisterDef(mbb, mi, mop.getAllocatedRegNum());
315            }
316        }
317    }
318
319    std::sort(intervals_.begin(), intervals_.end(), StartPointComp());
320    DEBUG(std::copy(intervals_.begin(), intervals_.end(),
321                    std::ostream_iterator<Interval>(std::cerr, "\n")));
322}
323
324LiveIntervals::Interval::Interval(unsigned r)
325    : reg(r), hint(0),
326      weight((r < MRegisterInfo::FirstVirtualRegister ?
327              std::numeric_limits<float>::max() : 0.0F))
328{
329
330}
331
332void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
333{
334    DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
335    //assert(start < end && "invalid range?");
336    Range range = std::make_pair(start, end);
337    Ranges::iterator it =
338        ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
339                      range);
340
341    mergeRangesForward(it);
342    mergeRangesBackward(it);
343    DEBUG(std::cerr << *this << '\n');
344}
345
346void LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
347{
348    for (Ranges::iterator next = it + 1;
349         next != ranges.end() && it->second >= next->first; ) {
350        it->second = std::max(it->second, next->second);
351        next = ranges.erase(next);
352    }
353}
354
355void LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
356{
357    for (Ranges::iterator prev = it - 1;
358         it != ranges.begin() && it->first <= prev->second; ) {
359        it->first = std::min(it->first, prev->first);
360        it->second = std::max(it->second, prev->second);
361        it = ranges.erase(prev);
362        prev = it - 1;
363    }
364}
365
366bool LiveIntervals::Interval::liveAt(unsigned index) const
367{
368    Ranges::const_iterator r = ranges.begin();
369    while (r != ranges.end() && index < r->second) {
370        if (index >= r->first)
371            return true;
372        ++r;
373    }
374    return false;
375}
376
377bool LiveIntervals::Interval::overlaps(const Interval& other) const
378{
379    Ranges::const_iterator i = ranges.begin();
380    Ranges::const_iterator j = other.ranges.begin();
381
382    while (i != ranges.end() && j != other.ranges.end()) {
383        if (i->first < j->first) {
384            if (i->second > j->first) {
385                return true;
386            }
387            else {
388                ++i;
389            }
390        }
391        else if (j->first < i->first) {
392            if (j->second > i->first) {
393                return true;
394            }
395            else {
396                ++j;
397            }
398        }
399        else {
400            return true;
401        }
402    }
403
404    return false;
405}
406
407std::ostream& llvm::operator<<(std::ostream& os,
408                               const LiveIntervals::Interval& li)
409{
410    os << "%reg" << li.reg << ',' << li.weight << " = ";
411    for (LiveIntervals::Interval::Ranges::const_iterator
412             i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
413        os << "[" << i->first << "," << i->second << ")";
414    }
415    return os;
416}
417