LiveIntervalAnalysis.cpp revision dd2cc65f34f9b7bfda1cd0c42becedfc361d46f8 
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/CodeGen/LiveVariables.h"
22#include "llvm/CodeGen/MachineFrameInfo.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/TargetInstrInfo.h"
29#include "llvm/Target/TargetMachine.h"
30#include "llvm/Target/TargetRegInfo.h"
31#include "llvm/Support/CFG.h"
32#include "Support/Debug.h"
33#include "Support/DepthFirstIterator.h"
34#include "Support/Statistic.h"
35#include <iostream>
36
37using namespace llvm;
38
39namespace {
40    RegisterAnalysis<LiveIntervals> X("liveintervals",
41                                      "Live Interval Analysis");
42
43    Statistic<> numIntervals("liveintervals", "Number of intervals");
44};
45
46void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const
47{
48    AU.addPreserved<LiveVariables>();
49    AU.addRequired<LiveVariables>();
50    AU.addPreservedID(PHIEliminationID);
51    AU.addRequiredID(PHIEliminationID);
52    MachineFunctionPass::getAnalysisUsage(AU);
53}
54
55/// runOnMachineFunction - Register allocate the whole function
56///
57bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
58    DEBUG(std::cerr << "Machine Function\n");
59    mf_ = &fn;
60    tm_ = &fn.getTarget();
61    mri_ = tm_->getRegisterInfo();
62    lv_ = &getAnalysis<LiveVariables>();
63    allocatableRegisters_.clear();
64    mbbi2mbbMap_.clear();
65    mi2iMap_.clear();
66    r2iMap_.clear();
67    r2iMap_.clear();
68    intervals_.clear();
69
70    // mark allocatable registers
71    allocatableRegisters_.resize(MRegisterInfo::FirstVirtualRegister);
72    // Loop over all of the register classes...
73    for (MRegisterInfo::regclass_iterator
74             rci = mri_->regclass_begin(), rce = mri_->regclass_end();
75         rci != rce; ++rci) {
76        // Loop over all of the allocatable registers in the function...
77        for (TargetRegisterClass::iterator
78                 i = (*rci)->allocation_order_begin(*mf_),
79                 e = (*rci)->allocation_order_end(*mf_); i != e; ++i) {
80            allocatableRegisters_[*i] = true;  // The reg is allocatable!
81        }
82    }
83
84    // number MachineInstrs
85    unsigned miIndex = 0;
86    for (MachineFunction::iterator mbb = mf_->begin(), mbbEnd = mf_->end();
87         mbb != mbbEnd; ++mbb) {
88        const std::pair<MachineBasicBlock*, unsigned>& entry =
89            lv_->getMachineBasicBlockInfo(&*mbb);
90        bool inserted = mbbi2mbbMap_.insert(std::make_pair(entry.second,
91                                                           entry.first)).second;
92        assert(inserted && "multiple index -> MachineBasicBlock");
93
94        for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
95             mi != miEnd; ++mi) {
96            inserted = mi2iMap_.insert(std::make_pair(*mi, miIndex)).second;
97            assert(inserted && "multiple MachineInstr -> index mappings");
98            ++miIndex;
99        }
100    }
101
102    computeIntervals();
103
104    return true;
105}
106
107void LiveIntervals::printRegName(unsigned reg) const
108{
109    if (reg < MRegisterInfo::FirstVirtualRegister)
110        std::cerr << mri_->getName(reg);
111    else
112        std::cerr << '%' << reg;
113}
114
115void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
116                                             MachineBasicBlock::iterator mi,
117                                             unsigned reg)
118{
119    DEBUG(std::cerr << "\t\t\tregister: ";printRegName(reg); std::cerr << '\n');
120
121    unsigned instrIndex = getInstructionIndex(*mi);
122
123    LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
124
125    Interval* interval = 0;
126    Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
127    if (r2iit == r2iMap_.end()) {
128        // add new interval
129        intervals_.push_back(Interval(reg));
130        // update interval index for this register
131        r2iMap_[reg] = intervals_.size() - 1;
132        interval = &intervals_.back();
133    }
134    else {
135        interval = &intervals_[r2iit->second];
136    }
137
138    for (MbbIndex2MbbMap::iterator
139             it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
140         it != itEnd; ++it) {
141        unsigned liveBlockIndex = it->first;
142        MachineBasicBlock* liveBlock = it->second;
143        if (liveBlockIndex < vi.AliveBlocks.size() &&
144            vi.AliveBlocks[liveBlockIndex]) {
145            unsigned start =  getInstructionIndex(liveBlock->front());
146            unsigned end = getInstructionIndex(liveBlock->back()) + 1;
147            interval->addRange(start, end);
148        }
149    }
150
151    bool killedInDefiningBasicBlock = false;
152    for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
153        MachineBasicBlock* killerBlock = vi.Kills[i].first;
154        MachineInstr* killerInstr = vi.Kills[i].second;
155        killedInDefiningBasicBlock |= mbb == killerBlock;
156        unsigned start = (mbb == killerBlock ?
157                          instrIndex :
158                          getInstructionIndex(killerBlock->front()));
159        unsigned end = getInstructionIndex(killerInstr) + 1;
160    }
161
162    if (!killedInDefiningBasicBlock) {
163        unsigned end = getInstructionIndex(mbb->back()) + 1;
164        interval->addRange(instrIndex, end);
165    }
166}
167
168void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
169                                              MachineBasicBlock::iterator mi,
170                                              unsigned reg)
171{
172    DEBUG(std::cerr << "\t\t\tregister: ";printRegName(reg); std::cerr << '\n');
173    if (!lv_->getAllocatablePhysicalRegisters()[reg]) {
174        DEBUG(std::cerr << "\t\t\t\tnon allocatable register: ignoring\n");
175        return;
176    }
177
178    unsigned start = getInstructionIndex(*mi);
179    unsigned end = start;
180
181    for (MachineBasicBlock::iterator e = mbb->end(); mi != e; ++mi) {
182        for (LiveVariables::killed_iterator
183                 ki = lv_->dead_begin(*mi),
184                 ke = lv_->dead_end(*mi);
185             ki != ke; ++ki) {
186            if (reg == ki->second) {
187                end = getInstructionIndex(ki->first) + 1;
188                goto exit;
189            }
190        }
191
192        for (LiveVariables::killed_iterator
193                 ki = lv_->killed_begin(*mi),
194                 ke = lv_->killed_end(*mi);
195             ki != ke; ++ki) {
196            if (reg == ki->second) {
197                end = getInstructionIndex(ki->first) + 1;
198                goto exit;
199            }
200        }
201    }
202exit:
203    assert(start < end && "did not find end of interval?");
204
205    Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
206    if (r2iit != r2iMap_.end()) {
207        unsigned ii = r2iit->second;
208        Interval& interval = intervals_[ii];
209        interval.addRange(start, end);
210    }
211    else {
212        intervals_.push_back(Interval(reg));
213        Interval& interval = intervals_.back();
214        // update interval index for this register
215        r2iMap_[reg] = intervals_.size() - 1;
216        interval.addRange(start, end);
217    }
218}
219
220void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
221                                      MachineBasicBlock::iterator mi,
222                                      unsigned reg)
223{
224    if (reg < MRegisterInfo::FirstVirtualRegister) {
225        if (allocatableRegisters_[reg]) {
226            handlePhysicalRegisterDef(mbb, mi, reg);
227        }
228    }
229    else {
230        handleVirtualRegisterDef(mbb, mi, reg);
231    }
232}
233
234unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
235{
236    assert(mi2iMap_.find(instr) != mi2iMap_.end() &&
237           "instruction not assigned a number");
238    return mi2iMap_.find(instr)->second;
239}
240
241/// computeIntervals - computes the live intervals for virtual
242/// registers. for some ordering of the machine instructions [1,N] a
243/// live interval is an interval [i, j] where 1 <= i <= j <= N for
244/// which a variable is live
245void LiveIntervals::computeIntervals()
246{
247    DEBUG(std::cerr << "computing live intervals:\n");
248
249    for (MbbIndex2MbbMap::iterator
250             it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
251         it != itEnd; ++it) {
252        MachineBasicBlock* mbb = it->second;
253        DEBUG(std::cerr << "machine basic block: "
254              << mbb->getBasicBlock()->getName() << "\n");
255        for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
256             mi != miEnd; ++mi) {
257            MachineInstr* instr = *mi;
258            const TargetInstrDescriptor& tid =
259                tm_->getInstrInfo().get(instr->getOpcode());
260            DEBUG(std::cerr << "\t\tinstruction["
261                  << getInstructionIndex(instr) << "]: ";
262                  instr->print(std::cerr, *tm_););
263
264            // handle implicit defs
265            for (const unsigned* id = tid.ImplicitDefs; *id; ++id) {
266                unsigned physReg = *id;
267                handlePhysicalRegisterDef(mbb, mi, physReg);
268            }
269
270            // handle explicit defs
271            for (int i = instr->getNumOperands() - 1; i >= 0; --i) {
272                MachineOperand& mop = instr->getOperand(i);
273
274                if (!mop.isRegister())
275                    continue;
276
277                if (mop.isDef()) {
278                    unsigned reg = mop.getAllocatedRegNum();
279                    if (reg < MRegisterInfo::FirstVirtualRegister)
280                        handlePhysicalRegisterDef(mbb, mi, reg);
281                    else
282                        handleVirtualRegisterDef(mbb, mi, reg);
283                }
284            }
285        }
286    }
287
288    std::sort(intervals_.begin(), intervals_.end(), StartPointComp());
289    DEBUG(std::copy(intervals_.begin(), intervals_.end(),
290                    std::ostream_iterator<Interval>(std::cerr, "\n")));
291}
292
293void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
294{
295    DEBUG(std::cerr << "\t\t\t\tadding range: [" << start <<','<< end << "]\n");
296    //assert(start < end && "invalid range?");
297    Range range = std::make_pair(start, end);
298    Ranges::iterator it =
299        ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
300                      range);
301
302    DEBUG(std::cerr << "\t\t\t\tbefore merge forward: " << *this << '\n');
303    mergeRangesForward(it);
304    DEBUG(std::cerr << "\t\t\t\tbefore merge backward: " << *this << '\n');
305    mergeRangesBackward(it);
306    DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
307}
308
309void LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
310{
311    for (Ranges::iterator next = it + 1;
312         next != ranges.end() && it->second >= next->first; ) {
313        it->second = std::max(it->second, next->second);
314        next = ranges.erase(next);
315    }
316}
317
318void LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
319{
320    for (Ranges::iterator prev = it - 1;
321         it != ranges.begin() && it->first <= prev->second; ) {
322        it->first = std::min(it->first, prev->first);
323        it->second = std::max(it->second, prev->second);
324        it = ranges.erase(prev);
325        prev = it - 1;
326    }
327}
328
329std::ostream& llvm::operator<<(std::ostream& os,
330                               const LiveIntervals::Interval& li)
331{
332    os << "%reg" << li.reg << " = ";
333    for (LiveIntervals::Interval::Ranges::const_iterator
334             i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
335        os << "[" << i->first << "," << i->second << "]";
336    }
337    return os;
338}
339