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1 //===-- InterferenceCache.h - Caching per-block interference ---*- C++ -*--===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // InterferenceCache remembers per-block interference in LiveIntervalUnions.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #define DEBUG_TYPE "regalloc"
15 #include "InterferenceCache.h"
16 #include "llvm/Target/TargetRegisterInfo.h"
17 #include "llvm/Support/ErrorHandling.h"
18 
19 using namespace llvm;
20 
21 // Static member used for null interference cursors.
22 InterferenceCache::BlockInterference InterferenceCache::Cursor::NoInterference;
23 
init(MachineFunction * mf,LiveIntervalUnion * liuarray,SlotIndexes * indexes,const TargetRegisterInfo * tri)24 void InterferenceCache::init(MachineFunction *mf,
25                              LiveIntervalUnion *liuarray,
26                              SlotIndexes *indexes,
27                              const TargetRegisterInfo *tri) {
28   MF = mf;
29   LIUArray = liuarray;
30   TRI = tri;
31   PhysRegEntries.assign(TRI->getNumRegs(), 0);
32   for (unsigned i = 0; i != CacheEntries; ++i)
33     Entries[i].clear(mf, indexes);
34 }
35 
get(unsigned PhysReg)36 InterferenceCache::Entry *InterferenceCache::get(unsigned PhysReg) {
37   unsigned E = PhysRegEntries[PhysReg];
38   if (E < CacheEntries && Entries[E].getPhysReg() == PhysReg) {
39     if (!Entries[E].valid(LIUArray, TRI))
40       Entries[E].revalidate();
41     return &Entries[E];
42   }
43   // No valid entry exists, pick the next round-robin entry.
44   E = RoundRobin;
45   if (++RoundRobin == CacheEntries)
46     RoundRobin = 0;
47   for (unsigned i = 0; i != CacheEntries; ++i) {
48     // Skip entries that are in use.
49     if (Entries[E].hasRefs()) {
50       if (++E == CacheEntries)
51         E = 0;
52       continue;
53     }
54     Entries[E].reset(PhysReg, LIUArray, TRI, MF);
55     PhysRegEntries[PhysReg] = E;
56     return &Entries[E];
57   }
58   llvm_unreachable("Ran out of interference cache entries.");
59 }
60 
61 /// revalidate - LIU contents have changed, update tags.
revalidate()62 void InterferenceCache::Entry::revalidate() {
63   // Invalidate all block entries.
64   ++Tag;
65   // Invalidate all iterators.
66   PrevPos = SlotIndex();
67   for (unsigned i = 0, e = Aliases.size(); i != e; ++i)
68     Aliases[i].second = Aliases[i].first->getTag();
69 }
70 
reset(unsigned physReg,LiveIntervalUnion * LIUArray,const TargetRegisterInfo * TRI,const MachineFunction * MF)71 void InterferenceCache::Entry::reset(unsigned physReg,
72                                      LiveIntervalUnion *LIUArray,
73                                      const TargetRegisterInfo *TRI,
74                                      const MachineFunction *MF) {
75   assert(!hasRefs() && "Cannot reset cache entry with references");
76   // LIU's changed, invalidate cache.
77   ++Tag;
78   PhysReg = physReg;
79   Blocks.resize(MF->getNumBlockIDs());
80   Aliases.clear();
81   for (const unsigned *AS = TRI->getOverlaps(PhysReg); *AS; ++AS) {
82     LiveIntervalUnion *LIU = LIUArray + *AS;
83     Aliases.push_back(std::make_pair(LIU, LIU->getTag()));
84   }
85 
86   // Reset iterators.
87   PrevPos = SlotIndex();
88   unsigned e = Aliases.size();
89   Iters.resize(e);
90   for (unsigned i = 0; i != e; ++i)
91     Iters[i].setMap(Aliases[i].first->getMap());
92 }
93 
valid(LiveIntervalUnion * LIUArray,const TargetRegisterInfo * TRI)94 bool InterferenceCache::Entry::valid(LiveIntervalUnion *LIUArray,
95                                      const TargetRegisterInfo *TRI) {
96   unsigned i = 0, e = Aliases.size();
97   for (const unsigned *AS = TRI->getOverlaps(PhysReg); *AS; ++AS, ++i) {
98     LiveIntervalUnion *LIU = LIUArray + *AS;
99     if (i == e ||  Aliases[i].first != LIU)
100       return false;
101     if (LIU->changedSince(Aliases[i].second))
102       return false;
103   }
104   return i == e;
105 }
106 
update(unsigned MBBNum)107 void InterferenceCache::Entry::update(unsigned MBBNum) {
108   SlotIndex Start, Stop;
109   tie(Start, Stop) = Indexes->getMBBRange(MBBNum);
110 
111   // Use advanceTo only when possible.
112   if (PrevPos != Start) {
113     if (!PrevPos.isValid() || Start < PrevPos)
114       for (unsigned i = 0, e = Iters.size(); i != e; ++i)
115         Iters[i].find(Start);
116     else
117       for (unsigned i = 0, e = Iters.size(); i != e; ++i)
118         Iters[i].advanceTo(Start);
119     PrevPos = Start;
120   }
121 
122   MachineFunction::const_iterator MFI = MF->getBlockNumbered(MBBNum);
123   BlockInterference *BI = &Blocks[MBBNum];
124   for (;;) {
125     BI->Tag = Tag;
126     BI->First = BI->Last = SlotIndex();
127 
128     // Check for first interference.
129     for (unsigned i = 0, e = Iters.size(); i != e; ++i) {
130       Iter &I = Iters[i];
131       if (!I.valid())
132         continue;
133       SlotIndex StartI = I.start();
134       if (StartI >= Stop)
135         continue;
136       if (!BI->First.isValid() || StartI < BI->First)
137         BI->First = StartI;
138     }
139 
140     PrevPos = Stop;
141     if (BI->First.isValid())
142       break;
143 
144     // No interference in this block? Go ahead and precompute the next block.
145     if (++MFI == MF->end())
146       return;
147     MBBNum = MFI->getNumber();
148     BI = &Blocks[MBBNum];
149     if (BI->Tag == Tag)
150       return;
151     tie(Start, Stop) = Indexes->getMBBRange(MBBNum);
152   }
153 
154   // Check for last interference in block.
155   for (unsigned i = 0, e = Iters.size(); i != e; ++i) {
156     Iter &I = Iters[i];
157     if (!I.valid() || I.start() >= Stop)
158       continue;
159     I.advanceTo(Stop);
160     bool Backup = !I.valid() || I.start() >= Stop;
161     if (Backup)
162       --I;
163     SlotIndex StopI = I.stop();
164     if (!BI->Last.isValid() || StopI > BI->Last)
165       BI->Last = StopI;
166     if (Backup)
167       ++I;
168   }
169 }
170