1 //===-- llvm/CodeGen/VirtRegMap.cpp - Virtual Register Map ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the VirtRegMap class.
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
17 //===----------------------------------------------------------------------===//
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"
43 #define DEBUG_TYPE "regalloc"
45 STATISTIC(NumSpillSlots, "Number of spill slots allocated");
46 STATISTIC(NumIdCopies, "Number of identity moves eliminated after rewriting");
48 //===----------------------------------------------------------------------===//
49 // VirtRegMap implementation
50 //===----------------------------------------------------------------------===//
52 char VirtRegMap::ID = 0;
54 INITIALIZE_PASS(VirtRegMap, "virtregmap", "Virtual Register Map", false, false)
56 bool VirtRegMap::runOnMachineFunction(MachineFunction &mf) {
57 MRI = &mf.getRegInfo();
58 TII = mf.getSubtarget().getInstrInfo();
59 TRI = mf.getSubtarget().getRegisterInfo();
63 Virt2StackSlotMap.clear();
64 Virt2SplitMap.clear();
70 void VirtRegMap::grow() {
71 unsigned NumRegs = MF->getRegInfo().getNumVirtRegs();
72 Virt2PhysMap.resize(NumRegs);
73 Virt2StackSlotMap.resize(NumRegs);
74 Virt2SplitMap.resize(NumRegs);
77 unsigned VirtRegMap::createSpillSlot(const TargetRegisterClass *RC) {
78 int SS = MF->getFrameInfo()->CreateSpillStackObject(RC->getSize(),
84 bool VirtRegMap::hasPreferredPhys(unsigned VirtReg) {
85 unsigned Hint = MRI->getSimpleHint(VirtReg);
88 if (TargetRegisterInfo::isVirtualRegister(Hint))
90 return getPhys(VirtReg) == Hint;
93 bool VirtRegMap::hasKnownPreference(unsigned VirtReg) {
94 std::pair<unsigned, unsigned> Hint = MRI->getRegAllocationHint(VirtReg);
95 if (TargetRegisterInfo::isPhysicalRegister(Hint.second))
97 if (TargetRegisterInfo::isVirtualRegister(Hint.second))
98 return hasPhys(Hint.second);
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);
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");
115 (SS >= MF->getFrameInfo()->getObjectIndexBegin())) &&
116 "illegal fixed frame index");
117 Virt2StackSlotMap[virtReg] = SS;
120 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";
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";
141 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
142 void VirtRegMap::dump() const {
147 //===----------------------------------------------------------------------===//
149 //===----------------------------------------------------------------------===//
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.
157 class VirtRegRewriter : public MachineFunctionPass {
159 const TargetMachine *TM;
160 const TargetRegisterInfo *TRI;
161 const TargetInstrInfo *TII;
162 MachineRegisterInfo *MRI;
163 SlotIndexes *Indexes;
166 SparseSet<unsigned> PhysRegs;
169 void addMBBLiveIns();
170 bool readsUndefSubreg(const MachineOperand &MO) const;
173 VirtRegRewriter() : MachineFunctionPass(ID) {}
175 void getAnalysisUsage(AnalysisUsage &AU) const override;
177 bool runOnMachineFunction(MachineFunction&) override;
179 } // end anonymous namespace
181 char &llvm::VirtRegRewriterID = VirtRegRewriter::ID;
183 INITIALIZE_PASS_BEGIN(VirtRegRewriter, "virtregrewriter",
184 "Virtual Register Rewriter", false, false)
185 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
186 INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
187 INITIALIZE_PASS_DEPENDENCY(LiveDebugVariables)
188 INITIALIZE_PASS_DEPENDENCY(LiveStacks)
189 INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
190 INITIALIZE_PASS_END(VirtRegRewriter, "virtregrewriter",
191 "Virtual Register Rewriter", false, false)
193 char VirtRegRewriter::ID = 0;
195 void VirtRegRewriter::getAnalysisUsage(AnalysisUsage &AU) const {
196 AU.setPreservesCFG();
197 AU.addRequired<LiveIntervals>();
198 AU.addRequired<SlotIndexes>();
199 AU.addPreserved<SlotIndexes>();
200 AU.addRequired<LiveDebugVariables>();
201 AU.addRequired<LiveStacks>();
202 AU.addPreserved<LiveStacks>();
203 AU.addRequired<VirtRegMap>();
204 MachineFunctionPass::getAnalysisUsage(AU);
207 bool VirtRegRewriter::runOnMachineFunction(MachineFunction &fn) {
209 TM = &MF->getTarget();
210 TRI = MF->getSubtarget().getRegisterInfo();
211 TII = MF->getSubtarget().getInstrInfo();
212 MRI = &MF->getRegInfo();
213 Indexes = &getAnalysis<SlotIndexes>();
214 LIS = &getAnalysis<LiveIntervals>();
215 VRM = &getAnalysis<VirtRegMap>();
216 DEBUG(dbgs() << "********** REWRITE VIRTUAL REGISTERS **********\n"
217 << "********** Function: "
218 << MF->getName() << '\n');
221 // Add kill flags while we still have virtual registers.
222 LIS->addKillFlags(VRM);
224 // Live-in lists on basic blocks are required for physregs.
227 // Rewrite virtual registers.
230 // Write out new DBG_VALUE instructions.
231 getAnalysis<LiveDebugVariables>().emitDebugValues(VRM);
233 // All machine operands and other references to virtual registers have been
234 // replaced. Remove the virtual registers and release all the transient data.
236 MRI->clearVirtRegs();
240 // Compute MBB live-in lists from virtual register live ranges and their
242 void VirtRegRewriter::addMBBLiveIns() {
243 SmallVector<MachineBasicBlock*, 16> LiveIn;
244 for (unsigned Idx = 0, IdxE = MRI->getNumVirtRegs(); Idx != IdxE; ++Idx) {
245 unsigned VirtReg = TargetRegisterInfo::index2VirtReg(Idx);
246 if (MRI->reg_nodbg_empty(VirtReg))
248 LiveInterval &LI = LIS->getInterval(VirtReg);
249 if (LI.empty() || LIS->intervalIsInOneMBB(LI))
251 // This is a virtual register that is live across basic blocks. Its
252 // assigned PhysReg must be marked as live-in to those blocks.
253 unsigned PhysReg = VRM->getPhys(VirtReg);
254 assert(PhysReg != VirtRegMap::NO_PHYS_REG && "Unmapped virtual register.");
256 if (LI.hasSubRanges()) {
257 for (LiveInterval::SubRange &S : LI.subranges()) {
258 for (const auto &Seg : S.segments) {
259 if (!Indexes->findLiveInMBBs(Seg.start, Seg.end, LiveIn))
261 for (MCSubRegIndexIterator SR(PhysReg, TRI); SR.isValid(); ++SR) {
262 unsigned SubReg = SR.getSubReg();
263 unsigned SubRegIndex = SR.getSubRegIndex();
264 unsigned SubRegLaneMask = TRI->getSubRegIndexLaneMask(SubRegIndex);
265 if ((SubRegLaneMask & S.LaneMask) == 0)
267 for (unsigned i = 0, e = LiveIn.size(); i != e; ++i) {
268 LiveIn[i]->addLiveIn(SubReg);
275 // Scan the segments of LI.
276 for (const auto &Seg : LI.segments) {
277 if (!Indexes->findLiveInMBBs(Seg.start, Seg.end, LiveIn))
279 for (unsigned i = 0, e = LiveIn.size(); i != e; ++i)
280 LiveIn[i]->addLiveIn(PhysReg);
286 // Sort and unique MBB LiveIns as we've not checked if SubReg/PhysReg were in
287 // each MBB's LiveIns set before calling addLiveIn on them.
288 for (MachineBasicBlock &MBB : *MF)
289 MBB.sortUniqueLiveIns();
292 /// Returns true if the given machine operand \p MO only reads undefined lanes.
293 /// The function only works for use operands with a subregister set.
294 bool VirtRegRewriter::readsUndefSubreg(const MachineOperand &MO) const {
295 // Shortcut if the operand is already marked undef.
299 unsigned Reg = MO.getReg();
300 const LiveInterval &LI = LIS->getInterval(Reg);
301 const MachineInstr &MI = *MO.getParent();
302 SlotIndex BaseIndex = LIS->getInstructionIndex(&MI);
303 // This code is only meant to handle reading undefined subregisters which
304 // we couldn't properly detect before.
305 assert(LI.liveAt(BaseIndex) &&
306 "Reads of completely dead register should be marked undef already");
307 unsigned SubRegIdx = MO.getSubReg();
308 unsigned UseMask = TRI->getSubRegIndexLaneMask(SubRegIdx);
309 // See if any of the relevant subregister liveranges is defined at this point.
310 for (const LiveInterval::SubRange &SR : LI.subranges()) {
311 if ((SR.LaneMask & UseMask) != 0 && SR.liveAt(BaseIndex))
317 void VirtRegRewriter::rewrite() {
318 bool NoSubRegLiveness = !MRI->subRegLivenessEnabled();
319 SmallVector<unsigned, 8> SuperDeads;
320 SmallVector<unsigned, 8> SuperDefs;
321 SmallVector<unsigned, 8> SuperKills;
322 SmallPtrSet<const MachineInstr *, 4> NoReturnInsts;
324 // Here we have a SparseSet to hold which PhysRegs are actually encountered
325 // in the MF we are about to iterate over so that later when we call
326 // setPhysRegUsed, we are only doing it for physRegs that were actually found
327 // in the program and not for all of the possible physRegs for the given
328 // target architecture. If the target has a lot of physRegs, then for a small
329 // program there will be a significant compile time reduction here.
331 PhysRegs.setUniverse(TRI->getNumRegs());
333 // The function with uwtable should guarantee that the stack unwinder
334 // can unwind the stack to the previous frame. Thus, we can't apply the
335 // noreturn optimization if the caller function has uwtable attribute.
336 bool HasUWTable = MF->getFunction()->hasFnAttribute(Attribute::UWTable);
338 for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
339 MBBI != MBBE; ++MBBI) {
340 DEBUG(MBBI->print(dbgs(), Indexes));
341 bool IsExitBB = MBBI->succ_empty();
342 for (MachineBasicBlock::instr_iterator
343 MII = MBBI->instr_begin(), MIE = MBBI->instr_end(); MII != MIE;) {
344 MachineInstr *MI = MII;
347 // Check if this instruction is a call to a noreturn function. If this
348 // is a call to noreturn function and we don't need the stack unwinding
349 // functionality (i.e. this function does not have uwtable attribute and
350 // the callee function has the nounwind attribute), then we can ignore
351 // the definitions set by this instruction.
352 if (!HasUWTable && IsExitBB && MI->isCall()) {
353 for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
354 MOE = MI->operands_end(); MOI != MOE; ++MOI) {
355 MachineOperand &MO = *MOI;
358 const Function *Func = dyn_cast<Function>(MO.getGlobal());
359 if (!Func || !Func->hasFnAttribute(Attribute::NoReturn) ||
360 // We need to keep correct unwind information
361 // even if the function will not return, since the
362 // runtime may need it.
363 !Func->hasFnAttribute(Attribute::NoUnwind))
365 NoReturnInsts.insert(MI);
370 for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
371 MOE = MI->operands_end(); MOI != MOE; ++MOI) {
372 MachineOperand &MO = *MOI;
374 // Make sure MRI knows about registers clobbered by regmasks.
376 MRI->addPhysRegsUsedFromRegMask(MO.getRegMask());
378 // If we encounter a VirtReg or PhysReg then get at the PhysReg and add
379 // it to the physreg bitset. Later we use only the PhysRegs that were
380 // actually encountered in the MF to populate the MRI's used physregs.
381 if (MO.isReg() && MO.getReg())
383 TargetRegisterInfo::isVirtualRegister(MO.getReg()) ?
384 VRM->getPhys(MO.getReg()) :
387 if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
389 unsigned VirtReg = MO.getReg();
390 unsigned PhysReg = VRM->getPhys(VirtReg);
391 assert(PhysReg != VirtRegMap::NO_PHYS_REG &&
392 "Instruction uses unmapped VirtReg");
393 assert(!MRI->isReserved(PhysReg) && "Reserved register assignment");
395 // Preserve semantics of sub-register operands.
396 unsigned SubReg = MO.getSubReg();
398 if (NoSubRegLiveness) {
399 // A virtual register kill refers to the whole register, so we may
400 // have to add <imp-use,kill> operands for the super-register. A
401 // partial redef always kills and redefines the super-register.
402 if (MO.readsReg() && (MO.isDef() || MO.isKill()))
403 SuperKills.push_back(PhysReg);
406 // Also add implicit defs for the super-register.
408 SuperDeads.push_back(PhysReg);
410 SuperDefs.push_back(PhysReg);
414 if (readsUndefSubreg(MO))
415 // We need to add an <undef> flag if the subregister is
416 // completely undefined (and we are not adding super-register
419 } else if (!MO.isDead()) {
421 // Things get tricky when we ran out of lane mask bits and
422 // merged multiple lanes into the overflow bit: In this case
423 // our subregister liveness tracking isn't precise and we can't
424 // know what subregister parts are undefined, fall back to the
425 // implicit super-register def then.
426 unsigned LaneMask = TRI->getSubRegIndexLaneMask(SubReg);
427 if (TargetRegisterInfo::isImpreciseLaneMask(LaneMask))
428 SuperDefs.push_back(PhysReg);
432 // The <def,undef> flag only makes sense for sub-register defs, and
433 // we are substituting a full physreg. An <imp-use,kill> operand
434 // from the SuperKills list will represent the partial read of the
437 MO.setIsUndef(false);
439 // PhysReg operands cannot have subregister indexes.
440 PhysReg = TRI->getSubReg(PhysReg, SubReg);
441 assert(PhysReg && "Invalid SubReg for physical register");
444 // Rewrite. Note we could have used MachineOperand::substPhysReg(), but
445 // we need the inlining here.
449 // Add any missing super-register kills after rewriting the whole
451 while (!SuperKills.empty())
452 MI->addRegisterKilled(SuperKills.pop_back_val(), TRI, true);
454 while (!SuperDeads.empty())
455 MI->addRegisterDead(SuperDeads.pop_back_val(), TRI, true);
457 while (!SuperDefs.empty())
458 MI->addRegisterDefined(SuperDefs.pop_back_val(), TRI);
460 DEBUG(dbgs() << "> " << *MI);
462 // Finally, remove any identity copies.
463 if (MI->isIdentityCopy()) {
465 DEBUG(dbgs() << "Deleting identity copy.\n");
467 Indexes->removeMachineInstrFromMaps(MI);
468 // It's safe to erase MI because MII has already been incremented.
469 MI->eraseFromParent();
474 // Tell MRI about physical registers in use.
475 if (NoReturnInsts.empty()) {
476 for (SparseSet<unsigned>::iterator
477 RegI = PhysRegs.begin(), E = PhysRegs.end(); RegI != E; ++RegI)
478 if (!MRI->reg_nodbg_empty(*RegI))
479 MRI->setPhysRegUsed(*RegI);
481 for (SparseSet<unsigned>::iterator
482 I = PhysRegs.begin(), E = PhysRegs.end(); I != E; ++I) {
484 if (MRI->reg_nodbg_empty(Reg))
486 // Check if this register has a use that will impact the rest of the
487 // code. Uses in debug and noreturn instructions do not impact the
489 for (MachineInstr &It : MRI->reg_nodbg_instructions(Reg)) {
490 if (!NoReturnInsts.count(&It)) {
491 MRI->setPhysRegUsed(Reg);