1//===- InterferenceCache.cpp - Caching per-block interference -------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// InterferenceCache remembers per-block interference in LiveIntervalUnions.
10//
11//===----------------------------------------------------------------------===//
12
13#include "InterferenceCache.h"
14#include "llvm/ADT/ArrayRef.h"
15#include "llvm/CodeGen/LiveIntervals.h"
16#include "llvm/CodeGen/MachineBasicBlock.h"
17#include "llvm/CodeGen/MachineFunction.h"
18#include "llvm/CodeGen/MachineOperand.h"
19#include "llvm/CodeGen/TargetRegisterInfo.h"
20#include "llvm/MC/MCRegisterInfo.h"
21#include "llvm/Support/ErrorHandling.h"
22#include <cassert>
23#include <cstdint>
24#include <tuple>
25
26using namespace llvm;
27
28#define DEBUG_TYPE "regalloc"
29
30// Static member used for null interference cursors.
31const InterferenceCache::BlockInterference
32 InterferenceCache::Cursor::NoInterference;
33
34// Initializes PhysRegEntries (instead of a SmallVector, PhysRegEntries is a
35// buffer of size NumPhysRegs to speed up alloc/clear for targets with large
36// reg files). Calloced memory is used for good form, and quites tools like
37// Valgrind too, but zero initialized memory is not required by the algorithm:
38// this is because PhysRegEntries works like a SparseSet and its entries are
39// only valid when there is a corresponding CacheEntries assignment. There is
40// also support for when pass managers are reused for targets with different
41// numbers of PhysRegs: in this case PhysRegEntries is freed and reinitialized.
42void InterferenceCache::reinitPhysRegEntries() {
43 if (PhysRegEntriesCount == TRI->getNumRegs()) return;
44 free(ptr: PhysRegEntries);
45 PhysRegEntriesCount = TRI->getNumRegs();
46 PhysRegEntries = static_cast<unsigned char*>(
47 safe_calloc(Count: PhysRegEntriesCount, Sz: sizeof(unsigned char)));
48}
49
50void InterferenceCache::init(MachineFunction *mf,
51 LiveIntervalUnion *liuarray,
52 SlotIndexes *indexes,
53 LiveIntervals *lis,
54 const TargetRegisterInfo *tri) {
55 MF = mf;
56 LIUArray = liuarray;
57 TRI = tri;
58 reinitPhysRegEntries();
59 for (Entry &E : Entries)
60 E.clear(mf, indexes, lis);
61}
62
63InterferenceCache::Entry *InterferenceCache::get(MCRegister PhysReg) {
64 unsigned char E = PhysRegEntries[PhysReg.id()];
65 if (E < CacheEntries && Entries[E].getPhysReg() == PhysReg) {
66 if (!Entries[E].valid(LIUArray, TRI))
67 Entries[E].revalidate(LIUArray, TRI);
68 return &Entries[E];
69 }
70 // No valid entry exists, pick the next round-robin entry.
71 E = RoundRobin;
72 if (++RoundRobin == CacheEntries)
73 RoundRobin = 0;
74 for (unsigned i = 0; i != CacheEntries; ++i) {
75 // Skip entries that are in use.
76 if (Entries[E].hasRefs()) {
77 if (++E == CacheEntries)
78 E = 0;
79 continue;
80 }
81 Entries[E].reset(physReg: PhysReg, LIUArray, TRI, MF);
82 PhysRegEntries[PhysReg] = E;
83 return &Entries[E];
84 }
85 llvm_unreachable("Ran out of interference cache entries.");
86}
87
88/// revalidate - LIU contents have changed, update tags.
89void InterferenceCache::Entry::revalidate(LiveIntervalUnion *LIUArray,
90 const TargetRegisterInfo *TRI) {
91 // Invalidate all block entries.
92 ++Tag;
93 // Invalidate all iterators.
94 PrevPos = SlotIndex();
95 unsigned i = 0;
96 for (MCRegUnit Unit : TRI->regunits(Reg: PhysReg))
97 RegUnits[i++].VirtTag = LIUArray[Unit].getTag();
98}
99
100void InterferenceCache::Entry::reset(MCRegister physReg,
101 LiveIntervalUnion *LIUArray,
102 const TargetRegisterInfo *TRI,
103 const MachineFunction *MF) {
104 assert(!hasRefs() && "Cannot reset cache entry with references");
105 // LIU's changed, invalidate cache.
106 ++Tag;
107 PhysReg = physReg;
108 Blocks.resize(N: MF->getNumBlockIDs());
109
110 // Reset iterators.
111 PrevPos = SlotIndex();
112 RegUnits.clear();
113 for (MCRegUnit Unit : TRI->regunits(Reg: PhysReg)) {
114 RegUnits.push_back(Elt: LIUArray[Unit]);
115 RegUnits.back().Fixed = &LIS->getRegUnit(Unit);
116 }
117}
118
119bool InterferenceCache::Entry::valid(LiveIntervalUnion *LIUArray,
120 const TargetRegisterInfo *TRI) {
121 unsigned i = 0, e = RegUnits.size();
122 for (MCRegUnit Unit : TRI->regunits(Reg: PhysReg)) {
123 if (i == e)
124 return false;
125 if (LIUArray[Unit].changedSince(tag: RegUnits[i].VirtTag))
126 return false;
127 ++i;
128 }
129 return i == e;
130}
131
132void InterferenceCache::Entry::update(unsigned MBBNum) {
133 SlotIndex Start, Stop;
134 std::tie(args&: Start, args&: Stop) = Indexes->getMBBRange(Num: MBBNum);
135
136 // Use advanceTo only when possible.
137 if (PrevPos != Start) {
138 if (!PrevPos.isValid() || Start < PrevPos) {
139 for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
140 RegUnitInfo &RUI = RegUnits[i];
141 RUI.VirtI.find(x: Start);
142 RUI.FixedI = RUI.Fixed->find(Pos: Start);
143 }
144 } else {
145 for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
146 RegUnitInfo &RUI = RegUnits[i];
147 RUI.VirtI.advanceTo(x: Start);
148 if (RUI.FixedI != RUI.Fixed->end())
149 RUI.FixedI = RUI.Fixed->advanceTo(I: RUI.FixedI, Pos: Start);
150 }
151 }
152 PrevPos = Start;
153 }
154
155 MachineFunction::const_iterator MFI =
156 MF->getBlockNumbered(N: MBBNum)->getIterator();
157 BlockInterference *BI = &Blocks[MBBNum];
158 ArrayRef<SlotIndex> RegMaskSlots;
159 ArrayRef<const uint32_t*> RegMaskBits;
160 while (true) {
161 BI->Tag = Tag;
162 BI->First = BI->Last = SlotIndex();
163
164 // Check for first interference from virtregs.
165 for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
166 LiveIntervalUnion::SegmentIter &I = RegUnits[i].VirtI;
167 if (!I.valid())
168 continue;
169 SlotIndex StartI = I.start();
170 if (StartI >= Stop)
171 continue;
172 if (!BI->First.isValid() || StartI < BI->First)
173 BI->First = StartI;
174 }
175
176 // Same thing for fixed interference.
177 for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
178 LiveInterval::const_iterator I = RegUnits[i].FixedI;
179 LiveInterval::const_iterator E = RegUnits[i].Fixed->end();
180 if (I == E)
181 continue;
182 SlotIndex StartI = I->start;
183 if (StartI >= Stop)
184 continue;
185 if (!BI->First.isValid() || StartI < BI->First)
186 BI->First = StartI;
187 }
188
189 // Also check for register mask interference.
190 RegMaskSlots = LIS->getRegMaskSlotsInBlock(MBBNum);
191 RegMaskBits = LIS->getRegMaskBitsInBlock(MBBNum);
192 SlotIndex Limit = BI->First.isValid() ? BI->First : Stop;
193 for (unsigned i = 0, e = RegMaskSlots.size();
194 i != e && RegMaskSlots[i] < Limit; ++i)
195 if (MachineOperand::clobbersPhysReg(RegMask: RegMaskBits[i], PhysReg)) {
196 // Register mask i clobbers PhysReg before the LIU interference.
197 BI->First = RegMaskSlots[i];
198 break;
199 }
200
201 PrevPos = Stop;
202 if (BI->First.isValid())
203 break;
204
205 // No interference in this block? Go ahead and precompute the next block.
206 if (++MFI == MF->end())
207 return;
208 MBBNum = MFI->getNumber();
209 BI = &Blocks[MBBNum];
210 if (BI->Tag == Tag)
211 return;
212 std::tie(args&: Start, args&: Stop) = Indexes->getMBBRange(Num: MBBNum);
213 }
214
215 // Check for last interference in block.
216 for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
217 LiveIntervalUnion::SegmentIter &I = RegUnits[i].VirtI;
218 if (!I.valid() || I.start() >= Stop)
219 continue;
220 I.advanceTo(x: Stop);
221 bool Backup = !I.valid() || I.start() >= Stop;
222 if (Backup)
223 --I;
224 SlotIndex StopI = I.stop();
225 if (!BI->Last.isValid() || StopI > BI->Last)
226 BI->Last = StopI;
227 if (Backup)
228 ++I;
229 }
230
231 // Fixed interference.
232 for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
233 LiveInterval::iterator &I = RegUnits[i].FixedI;
234 LiveRange *LR = RegUnits[i].Fixed;
235 if (I == LR->end() || I->start >= Stop)
236 continue;
237 I = LR->advanceTo(I, Pos: Stop);
238 bool Backup = I == LR->end() || I->start >= Stop;
239 if (Backup)
240 --I;
241 SlotIndex StopI = I->end;
242 if (!BI->Last.isValid() || StopI > BI->Last)
243 BI->Last = StopI;
244 if (Backup)
245 ++I;
246 }
247
248 // Also check for register mask interference.
249 SlotIndex Limit = BI->Last.isValid() ? BI->Last : Start;
250 for (unsigned i = RegMaskSlots.size();
251 i && RegMaskSlots[i-1].getDeadSlot() > Limit; --i)
252 if (MachineOperand::clobbersPhysReg(RegMask: RegMaskBits[i-1], PhysReg)) {
253 // Register mask i-1 clobbers PhysReg after the LIU interference.
254 // Model the regmask clobber as a dead def.
255 BI->Last = RegMaskSlots[i-1].getDeadSlot();
256 break;
257 }
258}
259

source code of llvm/lib/CodeGen/InterferenceCache.cpp