1 //===-- llvm/CodeGen/VirtRegMap.cpp - Virtual Register Map ----------------===//
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 // This file implements the VirtRegMap class.
11 //
12 // It also contains implementations of the Spiller interface, which, given a
13 // virtual register map and a machine function, eliminates all virtual
14 // references by replacing them with physical register references - adding spill
15 // code as necessary.
16 //
17 //===----------------------------------------------------------------------===//
18
19 #include "llvm/CodeGen/VirtRegMap.h"
20 #include "LiveDebugVariables.h"
21 #include "llvm/ADT/STLExtras.h"
22 #include "llvm/ADT/SparseSet.h"
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
25 #include "llvm/CodeGen/LiveStackAnalysis.h"
26 #include "llvm/CodeGen/MachineFrameInfo.h"
27 #include "llvm/CodeGen/MachineFunction.h"
28 #include "llvm/CodeGen/MachineInstrBuilder.h"
29 #include "llvm/CodeGen/MachineRegisterInfo.h"
30 #include "llvm/CodeGen/Passes.h"
31 #include "llvm/IR/Function.h"
32 #include "llvm/Support/CommandLine.h"
33 #include "llvm/Support/Compiler.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/raw_ostream.h"
36 #include "llvm/Target/TargetInstrInfo.h"
37 #include "llvm/Target/TargetMachine.h"
38 #include "llvm/Target/TargetRegisterInfo.h"
39 #include "llvm/Target/TargetSubtargetInfo.h"
40 #include <algorithm>
41 using namespace llvm;
42
43 #define DEBUG_TYPE "regalloc"
44
45 STATISTIC(NumSpillSlots, "Number of spill slots allocated");
46 STATISTIC(NumIdCopies, "Number of identity moves eliminated after rewriting");
47
48 //===----------------------------------------------------------------------===//
49 // VirtRegMap implementation
50 //===----------------------------------------------------------------------===//
51
52 char VirtRegMap::ID = 0;
53
54 INITIALIZE_PASS(VirtRegMap, "virtregmap", "Virtual Register Map", false, false)
55
runOnMachineFunction(MachineFunction & mf)56 bool VirtRegMap::runOnMachineFunction(MachineFunction &mf) {
57 MRI = &mf.getRegInfo();
58 TII = mf.getSubtarget().getInstrInfo();
59 TRI = mf.getSubtarget().getRegisterInfo();
60 MF = &mf;
61
62 Virt2PhysMap.clear();
63 Virt2StackSlotMap.clear();
64 Virt2SplitMap.clear();
65
66 grow();
67 return false;
68 }
69
grow()70 void VirtRegMap::grow() {
71 unsigned NumRegs = MF->getRegInfo().getNumVirtRegs();
72 Virt2PhysMap.resize(NumRegs);
73 Virt2StackSlotMap.resize(NumRegs);
74 Virt2SplitMap.resize(NumRegs);
75 }
76
createSpillSlot(const TargetRegisterClass * RC)77 unsigned VirtRegMap::createSpillSlot(const TargetRegisterClass *RC) {
78 int SS = MF->getFrameInfo()->CreateSpillStackObject(RC->getSize(),
79 RC->getAlignment());
80 ++NumSpillSlots;
81 return SS;
82 }
83
hasPreferredPhys(unsigned VirtReg)84 bool VirtRegMap::hasPreferredPhys(unsigned VirtReg) {
85 unsigned Hint = MRI->getSimpleHint(VirtReg);
86 if (!Hint)
87 return 0;
88 if (TargetRegisterInfo::isVirtualRegister(Hint))
89 Hint = getPhys(Hint);
90 return getPhys(VirtReg) == Hint;
91 }
92
hasKnownPreference(unsigned VirtReg)93 bool VirtRegMap::hasKnownPreference(unsigned VirtReg) {
94 std::pair<unsigned, unsigned> Hint = MRI->getRegAllocationHint(VirtReg);
95 if (TargetRegisterInfo::isPhysicalRegister(Hint.second))
96 return true;
97 if (TargetRegisterInfo::isVirtualRegister(Hint.second))
98 return hasPhys(Hint.second);
99 return false;
100 }
101
assignVirt2StackSlot(unsigned virtReg)102 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {
103 assert(TargetRegisterInfo::isVirtualRegister(virtReg));
104 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
105 "attempt to assign stack slot to already spilled register");
106 const TargetRegisterClass* RC = MF->getRegInfo().getRegClass(virtReg);
107 return Virt2StackSlotMap[virtReg] = createSpillSlot(RC);
108 }
109
assignVirt2StackSlot(unsigned virtReg,int SS)110 void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int SS) {
111 assert(TargetRegisterInfo::isVirtualRegister(virtReg));
112 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
113 "attempt to assign stack slot to already spilled register");
114 assert((SS >= 0 ||
115 (SS >= MF->getFrameInfo()->getObjectIndexBegin())) &&
116 "illegal fixed frame index");
117 Virt2StackSlotMap[virtReg] = SS;
118 }
119
print(raw_ostream & OS,const Module *) const120 void VirtRegMap::print(raw_ostream &OS, const Module*) const {
121 OS << "********** REGISTER MAP **********\n";
122 for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
123 unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
124 if (Virt2PhysMap[Reg] != (unsigned)VirtRegMap::NO_PHYS_REG) {
125 OS << '[' << PrintReg(Reg, TRI) << " -> "
126 << PrintReg(Virt2PhysMap[Reg], TRI) << "] "
127 << TRI->getRegClassName(MRI->getRegClass(Reg)) << "\n";
128 }
129 }
130
131 for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
132 unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
133 if (Virt2StackSlotMap[Reg] != VirtRegMap::NO_STACK_SLOT) {
134 OS << '[' << PrintReg(Reg, TRI) << " -> fi#" << Virt2StackSlotMap[Reg]
135 << "] " << TRI->getRegClassName(MRI->getRegClass(Reg)) << "\n";
136 }
137 }
138 OS << '\n';
139 }
140
141 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
dump() const142 void VirtRegMap::dump() const {
143 print(dbgs());
144 }
145 #endif
146
147 //===----------------------------------------------------------------------===//
148 // VirtRegRewriter
149 //===----------------------------------------------------------------------===//
150 //
151 // The VirtRegRewriter is the last of the register allocator passes.
152 // It rewrites virtual registers to physical registers as specified in the
153 // VirtRegMap analysis. It also updates live-in information on basic blocks
154 // according to LiveIntervals.
155 //
156 namespace {
157 class VirtRegRewriter : public MachineFunctionPass {
158 MachineFunction *MF;
159 const TargetMachine *TM;
160 const TargetRegisterInfo *TRI;
161 const TargetInstrInfo *TII;
162 MachineRegisterInfo *MRI;
163 SlotIndexes *Indexes;
164 LiveIntervals *LIS;
165 VirtRegMap *VRM;
166
167 void rewrite();
168 void addMBBLiveIns();
169 bool readsUndefSubreg(const MachineOperand &MO) const;
170 void addLiveInsForSubRanges(const LiveInterval &LI, unsigned PhysReg) const;
171
172 public:
173 static char ID;
VirtRegRewriter()174 VirtRegRewriter() : MachineFunctionPass(ID) {}
175
176 void getAnalysisUsage(AnalysisUsage &AU) const override;
177
178 bool runOnMachineFunction(MachineFunction&) override;
179 };
180 } // end anonymous namespace
181
182 char &llvm::VirtRegRewriterID = VirtRegRewriter::ID;
183
184 INITIALIZE_PASS_BEGIN(VirtRegRewriter, "virtregrewriter",
185 "Virtual Register Rewriter", false, false)
186 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
187 INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
188 INITIALIZE_PASS_DEPENDENCY(LiveDebugVariables)
189 INITIALIZE_PASS_DEPENDENCY(LiveStacks)
190 INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
191 INITIALIZE_PASS_END(VirtRegRewriter, "virtregrewriter",
192 "Virtual Register Rewriter", false, false)
193
194 char VirtRegRewriter::ID = 0;
195
getAnalysisUsage(AnalysisUsage & AU) const196 void VirtRegRewriter::getAnalysisUsage(AnalysisUsage &AU) const {
197 AU.setPreservesCFG();
198 AU.addRequired<LiveIntervals>();
199 AU.addRequired<SlotIndexes>();
200 AU.addPreserved<SlotIndexes>();
201 AU.addRequired<LiveDebugVariables>();
202 AU.addRequired<LiveStacks>();
203 AU.addPreserved<LiveStacks>();
204 AU.addRequired<VirtRegMap>();
205 MachineFunctionPass::getAnalysisUsage(AU);
206 }
207
runOnMachineFunction(MachineFunction & fn)208 bool VirtRegRewriter::runOnMachineFunction(MachineFunction &fn) {
209 MF = &fn;
210 TM = &MF->getTarget();
211 TRI = MF->getSubtarget().getRegisterInfo();
212 TII = MF->getSubtarget().getInstrInfo();
213 MRI = &MF->getRegInfo();
214 Indexes = &getAnalysis<SlotIndexes>();
215 LIS = &getAnalysis<LiveIntervals>();
216 VRM = &getAnalysis<VirtRegMap>();
217 DEBUG(dbgs() << "********** REWRITE VIRTUAL REGISTERS **********\n"
218 << "********** Function: "
219 << MF->getName() << '\n');
220 DEBUG(VRM->dump());
221
222 // Add kill flags while we still have virtual registers.
223 LIS->addKillFlags(VRM);
224
225 // Live-in lists on basic blocks are required for physregs.
226 addMBBLiveIns();
227
228 // Rewrite virtual registers.
229 rewrite();
230
231 // Write out new DBG_VALUE instructions.
232 getAnalysis<LiveDebugVariables>().emitDebugValues(VRM);
233
234 // All machine operands and other references to virtual registers have been
235 // replaced. Remove the virtual registers and release all the transient data.
236 VRM->clearAllVirt();
237 MRI->clearVirtRegs();
238 return true;
239 }
240
addLiveInsForSubRanges(const LiveInterval & LI,unsigned PhysReg) const241 void VirtRegRewriter::addLiveInsForSubRanges(const LiveInterval &LI,
242 unsigned PhysReg) const {
243 assert(!LI.empty());
244 assert(LI.hasSubRanges());
245
246 typedef std::pair<const LiveInterval::SubRange *,
247 LiveInterval::const_iterator> SubRangeIteratorPair;
248 SmallVector<SubRangeIteratorPair, 4> SubRanges;
249 SlotIndex First;
250 SlotIndex Last;
251 for (const LiveInterval::SubRange &SR : LI.subranges()) {
252 SubRanges.push_back(std::make_pair(&SR, SR.begin()));
253 if (!First.isValid() || SR.segments.front().start < First)
254 First = SR.segments.front().start;
255 if (!Last.isValid() || SR.segments.back().end > Last)
256 Last = SR.segments.back().end;
257 }
258
259 // Check all mbb start positions between First and Last while
260 // simulatenously advancing an iterator for each subrange.
261 for (SlotIndexes::MBBIndexIterator MBBI = Indexes->findMBBIndex(First);
262 MBBI != Indexes->MBBIndexEnd() && MBBI->first <= Last; ++MBBI) {
263 SlotIndex MBBBegin = MBBI->first;
264 // Advance all subrange iterators so that their end position is just
265 // behind MBBBegin (or the iterator is at the end).
266 LaneBitmask LaneMask = 0;
267 for (auto &RangeIterPair : SubRanges) {
268 const LiveInterval::SubRange *SR = RangeIterPair.first;
269 LiveInterval::const_iterator &SRI = RangeIterPair.second;
270 while (SRI != SR->end() && SRI->end <= MBBBegin)
271 ++SRI;
272 if (SRI == SR->end())
273 continue;
274 if (SRI->start <= MBBBegin)
275 LaneMask |= SR->LaneMask;
276 }
277 if (LaneMask == 0)
278 continue;
279 MachineBasicBlock *MBB = MBBI->second;
280 MBB->addLiveIn(PhysReg, LaneMask);
281 }
282 }
283
284 // Compute MBB live-in lists from virtual register live ranges and their
285 // assignments.
addMBBLiveIns()286 void VirtRegRewriter::addMBBLiveIns() {
287 for (unsigned Idx = 0, IdxE = MRI->getNumVirtRegs(); Idx != IdxE; ++Idx) {
288 unsigned VirtReg = TargetRegisterInfo::index2VirtReg(Idx);
289 if (MRI->reg_nodbg_empty(VirtReg))
290 continue;
291 LiveInterval &LI = LIS->getInterval(VirtReg);
292 if (LI.empty() || LIS->intervalIsInOneMBB(LI))
293 continue;
294 // This is a virtual register that is live across basic blocks. Its
295 // assigned PhysReg must be marked as live-in to those blocks.
296 unsigned PhysReg = VRM->getPhys(VirtReg);
297 assert(PhysReg != VirtRegMap::NO_PHYS_REG && "Unmapped virtual register.");
298
299 if (LI.hasSubRanges()) {
300 addLiveInsForSubRanges(LI, PhysReg);
301 } else {
302 // Go over MBB begin positions and see if we have segments covering them.
303 // The following works because segments and the MBBIndex list are both
304 // sorted by slot indexes.
305 SlotIndexes::MBBIndexIterator I = Indexes->MBBIndexBegin();
306 for (const auto &Seg : LI) {
307 I = Indexes->advanceMBBIndex(I, Seg.start);
308 for (; I != Indexes->MBBIndexEnd() && I->first < Seg.end; ++I) {
309 MachineBasicBlock *MBB = I->second;
310 MBB->addLiveIn(PhysReg);
311 }
312 }
313 }
314 }
315
316 // Sort and unique MBB LiveIns as we've not checked if SubReg/PhysReg were in
317 // each MBB's LiveIns set before calling addLiveIn on them.
318 for (MachineBasicBlock &MBB : *MF)
319 MBB.sortUniqueLiveIns();
320 }
321
322 /// Returns true if the given machine operand \p MO only reads undefined lanes.
323 /// The function only works for use operands with a subregister set.
readsUndefSubreg(const MachineOperand & MO) const324 bool VirtRegRewriter::readsUndefSubreg(const MachineOperand &MO) const {
325 // Shortcut if the operand is already marked undef.
326 if (MO.isUndef())
327 return true;
328
329 unsigned Reg = MO.getReg();
330 const LiveInterval &LI = LIS->getInterval(Reg);
331 const MachineInstr &MI = *MO.getParent();
332 SlotIndex BaseIndex = LIS->getInstructionIndex(&MI);
333 // This code is only meant to handle reading undefined subregisters which
334 // we couldn't properly detect before.
335 assert(LI.liveAt(BaseIndex) &&
336 "Reads of completely dead register should be marked undef already");
337 unsigned SubRegIdx = MO.getSubReg();
338 LaneBitmask UseMask = TRI->getSubRegIndexLaneMask(SubRegIdx);
339 // See if any of the relevant subregister liveranges is defined at this point.
340 for (const LiveInterval::SubRange &SR : LI.subranges()) {
341 if ((SR.LaneMask & UseMask) != 0 && SR.liveAt(BaseIndex))
342 return false;
343 }
344 return true;
345 }
346
rewrite()347 void VirtRegRewriter::rewrite() {
348 bool NoSubRegLiveness = !MRI->subRegLivenessEnabled();
349 SmallVector<unsigned, 8> SuperDeads;
350 SmallVector<unsigned, 8> SuperDefs;
351 SmallVector<unsigned, 8> SuperKills;
352
353 for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
354 MBBI != MBBE; ++MBBI) {
355 DEBUG(MBBI->print(dbgs(), Indexes));
356 for (MachineBasicBlock::instr_iterator
357 MII = MBBI->instr_begin(), MIE = MBBI->instr_end(); MII != MIE;) {
358 MachineInstr *MI = &*MII;
359 ++MII;
360
361 for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
362 MOE = MI->operands_end(); MOI != MOE; ++MOI) {
363 MachineOperand &MO = *MOI;
364
365 // Make sure MRI knows about registers clobbered by regmasks.
366 if (MO.isRegMask())
367 MRI->addPhysRegsUsedFromRegMask(MO.getRegMask());
368
369 if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
370 continue;
371 unsigned VirtReg = MO.getReg();
372 unsigned PhysReg = VRM->getPhys(VirtReg);
373 assert(PhysReg != VirtRegMap::NO_PHYS_REG &&
374 "Instruction uses unmapped VirtReg");
375 assert(!MRI->isReserved(PhysReg) && "Reserved register assignment");
376
377 // Preserve semantics of sub-register operands.
378 unsigned SubReg = MO.getSubReg();
379 if (SubReg != 0) {
380 if (NoSubRegLiveness) {
381 // A virtual register kill refers to the whole register, so we may
382 // have to add <imp-use,kill> operands for the super-register. A
383 // partial redef always kills and redefines the super-register.
384 if (MO.readsReg() && (MO.isDef() || MO.isKill()))
385 SuperKills.push_back(PhysReg);
386
387 if (MO.isDef()) {
388 // Also add implicit defs for the super-register.
389 if (MO.isDead())
390 SuperDeads.push_back(PhysReg);
391 else
392 SuperDefs.push_back(PhysReg);
393 }
394 } else {
395 if (MO.isUse()) {
396 if (readsUndefSubreg(MO))
397 // We need to add an <undef> flag if the subregister is
398 // completely undefined (and we are not adding super-register
399 // defs).
400 MO.setIsUndef(true);
401 } else if (!MO.isDead()) {
402 assert(MO.isDef());
403 }
404 }
405
406 // The <def,undef> flag only makes sense for sub-register defs, and
407 // we are substituting a full physreg. An <imp-use,kill> operand
408 // from the SuperKills list will represent the partial read of the
409 // super-register.
410 if (MO.isDef())
411 MO.setIsUndef(false);
412
413 // PhysReg operands cannot have subregister indexes.
414 PhysReg = TRI->getSubReg(PhysReg, SubReg);
415 assert(PhysReg && "Invalid SubReg for physical register");
416 MO.setSubReg(0);
417 }
418 // Rewrite. Note we could have used MachineOperand::substPhysReg(), but
419 // we need the inlining here.
420 MO.setReg(PhysReg);
421 }
422
423 // Add any missing super-register kills after rewriting the whole
424 // instruction.
425 while (!SuperKills.empty())
426 MI->addRegisterKilled(SuperKills.pop_back_val(), TRI, true);
427
428 while (!SuperDeads.empty())
429 MI->addRegisterDead(SuperDeads.pop_back_val(), TRI, true);
430
431 while (!SuperDefs.empty())
432 MI->addRegisterDefined(SuperDefs.pop_back_val(), TRI);
433
434 DEBUG(dbgs() << "> " << *MI);
435
436 // Finally, remove any identity copies.
437 if (MI->isIdentityCopy()) {
438 ++NumIdCopies;
439 DEBUG(dbgs() << "Deleting identity copy.\n");
440 if (Indexes)
441 Indexes->removeMachineInstrFromMaps(MI);
442 // It's safe to erase MI because MII has already been incremented.
443 MI->eraseFromParent();
444 }
445 }
446 }
447 }
448
449