1 //===-- RenameIndependentSubregs.cpp - Live Interval Analysis -------------===//
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 /// Rename independent subregisters looks for virtual registers with
11 /// independently used subregisters and renames them to new virtual registers.
12 /// Example: In the following:
13 /// %0:sub0<read-undef> = ...
19 /// sub0 and sub1 are never used together, and we have two independent sub0
20 /// definitions. This pass will rename to:
21 /// %0:sub0<read-undef> = ...
22 /// %1:sub1<read-undef> = ...
24 /// %2:sub1<read-undef> = ...
28 //===----------------------------------------------------------------------===//
30 #include "LiveRangeUtils.h"
31 #include "PHIEliminationUtils.h"
32 #include "llvm/CodeGen/LiveInterval.h"
33 #include "llvm/CodeGen/LiveIntervals.h"
34 #include "llvm/CodeGen/MachineFunctionPass.h"
35 #include "llvm/CodeGen/MachineInstrBuilder.h"
36 #include "llvm/CodeGen/MachineRegisterInfo.h"
37 #include "llvm/CodeGen/Passes.h"
38 #include "llvm/CodeGen/TargetInstrInfo.h"
42 #define DEBUG_TYPE "rename-independent-subregs"
46 class RenameIndependentSubregs : public MachineFunctionPass {
49 RenameIndependentSubregs() : MachineFunctionPass(ID) {}
51 StringRef getPassName() const override {
52 return "Rename Disconnected Subregister Components";
55 void getAnalysisUsage(AnalysisUsage &AU) const override {
57 AU.addRequired<LiveIntervals>();
58 AU.addPreserved<LiveIntervals>();
59 AU.addRequired<SlotIndexes>();
60 AU.addPreserved<SlotIndexes>();
61 MachineFunctionPass::getAnalysisUsage(AU);
64 bool runOnMachineFunction(MachineFunction &MF) override;
68 ConnectedVNInfoEqClasses ConEQ;
69 LiveInterval::SubRange *SR;
72 SubRangeInfo(LiveIntervals &LIS, LiveInterval::SubRange &SR,
74 : ConEQ(LIS), SR(&SR), Index(Index) {}
77 /// Split unrelated subregister components and rename them to new vregs.
78 bool renameComponents(LiveInterval &LI) const;
80 /// \brief Build a vector of SubRange infos and a union find set of
81 /// equivalence classes.
82 /// Returns true if more than 1 equivalence class was found.
83 bool findComponents(IntEqClasses &Classes,
84 SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
85 LiveInterval &LI) const;
87 /// \brief Distribute the LiveInterval segments into the new LiveIntervals
88 /// belonging to their class.
89 void distribute(const IntEqClasses &Classes,
90 const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
91 const SmallVectorImpl<LiveInterval*> &Intervals) const;
93 /// \brief Constructs main liverange and add missing undef+dead flags.
94 void computeMainRangesFixFlags(const IntEqClasses &Classes,
95 const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
96 const SmallVectorImpl<LiveInterval*> &Intervals) const;
98 /// Rewrite Machine Operands to use the new vreg belonging to their class.
99 void rewriteOperands(const IntEqClasses &Classes,
100 const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
101 const SmallVectorImpl<LiveInterval*> &Intervals) const;
105 MachineRegisterInfo *MRI;
106 const TargetInstrInfo *TII;
109 } // end anonymous namespace
111 char RenameIndependentSubregs::ID;
113 char &llvm::RenameIndependentSubregsID = RenameIndependentSubregs::ID;
115 INITIALIZE_PASS_BEGIN(RenameIndependentSubregs, DEBUG_TYPE,
116 "Rename Independent Subregisters", false, false)
117 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
118 INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
119 INITIALIZE_PASS_END(RenameIndependentSubregs, DEBUG_TYPE,
120 "Rename Independent Subregisters", false, false)
122 bool RenameIndependentSubregs::renameComponents(LiveInterval &LI) const {
123 // Shortcut: We cannot have split components with a single definition.
124 if (LI.valnos.size() < 2)
127 SmallVector<SubRangeInfo, 4> SubRangeInfos;
128 IntEqClasses Classes;
129 if (!findComponents(Classes, SubRangeInfos, LI))
132 // Create a new VReg for each class.
133 unsigned Reg = LI.reg;
134 const TargetRegisterClass *RegClass = MRI->getRegClass(Reg);
135 SmallVector<LiveInterval*, 4> Intervals;
136 Intervals.push_back(&LI);
137 DEBUG(dbgs() << printReg(Reg) << ": Found " << Classes.getNumClasses()
138 << " equivalence classes.\n");
139 DEBUG(dbgs() << printReg(Reg) << ": Splitting into newly created:");
140 for (unsigned I = 1, NumClasses = Classes.getNumClasses(); I < NumClasses;
142 unsigned NewVReg = MRI->createVirtualRegister(RegClass);
143 LiveInterval &NewLI = LIS->createEmptyInterval(NewVReg);
144 Intervals.push_back(&NewLI);
145 DEBUG(dbgs() << ' ' << printReg(NewVReg));
147 DEBUG(dbgs() << '\n');
149 rewriteOperands(Classes, SubRangeInfos, Intervals);
150 distribute(Classes, SubRangeInfos, Intervals);
151 computeMainRangesFixFlags(Classes, SubRangeInfos, Intervals);
155 bool RenameIndependentSubregs::findComponents(IntEqClasses &Classes,
156 SmallVectorImpl<RenameIndependentSubregs::SubRangeInfo> &SubRangeInfos,
157 LiveInterval &LI) const {
158 // First step: Create connected components for the VNInfos inside the
159 // subranges and count the global number of such components.
160 unsigned NumComponents = 0;
161 for (LiveInterval::SubRange &SR : LI.subranges()) {
162 SubRangeInfos.push_back(SubRangeInfo(*LIS, SR, NumComponents));
163 ConnectedVNInfoEqClasses &ConEQ = SubRangeInfos.back().ConEQ;
165 unsigned NumSubComponents = ConEQ.Classify(SR);
166 NumComponents += NumSubComponents;
168 // Shortcut: With only 1 subrange, the normal separate component tests are
169 // enough and we do not need to perform the union-find on the subregister
171 if (SubRangeInfos.size() < 2)
174 // Next step: Build union-find structure over all subranges and merge classes
175 // across subranges when they are affected by the same MachineOperand.
176 const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
177 Classes.grow(NumComponents);
178 unsigned Reg = LI.reg;
179 for (const MachineOperand &MO : MRI->reg_nodbg_operands(Reg)) {
180 if (!MO.isDef() && !MO.readsReg())
182 unsigned SubRegIdx = MO.getSubReg();
183 LaneBitmask LaneMask = TRI.getSubRegIndexLaneMask(SubRegIdx);
184 unsigned MergedID = ~0u;
185 for (RenameIndependentSubregs::SubRangeInfo &SRInfo : SubRangeInfos) {
186 const LiveInterval::SubRange &SR = *SRInfo.SR;
187 if ((SR.LaneMask & LaneMask).none())
189 SlotIndex Pos = LIS->getInstructionIndex(*MO.getParent());
190 Pos = MO.isDef() ? Pos.getRegSlot(MO.isEarlyClobber())
191 : Pos.getBaseIndex();
192 const VNInfo *VNI = SR.getVNInfoAt(Pos);
196 // Map to local representant ID.
197 unsigned LocalID = SRInfo.ConEQ.getEqClass(VNI);
199 unsigned ID = LocalID + SRInfo.Index;
201 MergedID = MergedID == ~0u ? ID : Classes.join(MergedID, ID);
205 // Early exit if we ended up with a single equivalence class.
207 unsigned NumClasses = Classes.getNumClasses();
208 return NumClasses > 1;
211 void RenameIndependentSubregs::rewriteOperands(const IntEqClasses &Classes,
212 const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
213 const SmallVectorImpl<LiveInterval*> &Intervals) const {
214 const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
215 unsigned Reg = Intervals[0]->reg;
216 for (MachineRegisterInfo::reg_nodbg_iterator I = MRI->reg_nodbg_begin(Reg),
217 E = MRI->reg_nodbg_end(); I != E; ) {
218 MachineOperand &MO = *I++;
219 if (!MO.isDef() && !MO.readsReg())
222 SlotIndex Pos = LIS->getInstructionIndex(*MO.getParent());
223 Pos = MO.isDef() ? Pos.getRegSlot(MO.isEarlyClobber())
224 : Pos.getBaseIndex();
225 unsigned SubRegIdx = MO.getSubReg();
226 LaneBitmask LaneMask = TRI.getSubRegIndexLaneMask(SubRegIdx);
229 for (const SubRangeInfo &SRInfo : SubRangeInfos) {
230 const LiveInterval::SubRange &SR = *SRInfo.SR;
231 if ((SR.LaneMask & LaneMask).none())
233 const VNInfo *VNI = SR.getVNInfoAt(Pos);
237 // Map to local representant ID.
238 unsigned LocalID = SRInfo.ConEQ.getEqClass(VNI);
240 ID = Classes[LocalID + SRInfo.Index];
244 unsigned VReg = Intervals[ID]->reg;
247 if (MO.isTied() && Reg != VReg) {
248 /// Undef use operands are not tracked in the equivalence class but need
249 /// to be update if they are tied.
250 MO.getParent()->substituteRegister(Reg, VReg, 0, TRI);
252 // substituteRegister breaks the iterator, so restart.
253 I = MRI->reg_nodbg_begin(Reg);
256 // TODO: We could attempt to recompute new register classes while visiting
257 // the operands: Some of the split register may be fine with less constraint
258 // classes than the original vreg.
261 void RenameIndependentSubregs::distribute(const IntEqClasses &Classes,
262 const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
263 const SmallVectorImpl<LiveInterval*> &Intervals) const {
264 unsigned NumClasses = Classes.getNumClasses();
265 SmallVector<unsigned, 8> VNIMapping;
266 SmallVector<LiveInterval::SubRange*, 8> SubRanges;
267 BumpPtrAllocator &Allocator = LIS->getVNInfoAllocator();
268 for (const SubRangeInfo &SRInfo : SubRangeInfos) {
269 LiveInterval::SubRange &SR = *SRInfo.SR;
270 unsigned NumValNos = SR.valnos.size();
272 VNIMapping.reserve(NumValNos);
274 SubRanges.resize(NumClasses-1, nullptr);
275 for (unsigned I = 0; I < NumValNos; ++I) {
276 const VNInfo &VNI = *SR.valnos[I];
277 unsigned LocalID = SRInfo.ConEQ.getEqClass(&VNI);
278 unsigned ID = Classes[LocalID + SRInfo.Index];
279 VNIMapping.push_back(ID);
280 if (ID > 0 && SubRanges[ID-1] == nullptr)
281 SubRanges[ID-1] = Intervals[ID]->createSubRange(Allocator, SR.LaneMask);
283 DistributeRange(SR, SubRanges.data(), VNIMapping);
287 static bool subRangeLiveAt(const LiveInterval &LI, SlotIndex Pos) {
288 for (const LiveInterval::SubRange &SR : LI.subranges()) {
295 void RenameIndependentSubregs::computeMainRangesFixFlags(
296 const IntEqClasses &Classes,
297 const SmallVectorImpl<SubRangeInfo> &SubRangeInfos,
298 const SmallVectorImpl<LiveInterval*> &Intervals) const {
299 BumpPtrAllocator &Allocator = LIS->getVNInfoAllocator();
300 const SlotIndexes &Indexes = *LIS->getSlotIndexes();
301 for (size_t I = 0, E = Intervals.size(); I < E; ++I) {
302 LiveInterval &LI = *Intervals[I];
303 unsigned Reg = LI.reg;
305 LI.removeEmptySubRanges();
307 // There must be a def (or live-in) before every use. Splitting vregs may
308 // violate this principle as the splitted vreg may not have a definition on
309 // every path. Fix this by creating IMPLICIT_DEF instruction as necessary.
310 for (const LiveInterval::SubRange &SR : LI.subranges()) {
311 // Search for "PHI" value numbers in the subranges. We must find a live
312 // value in each predecessor block, add an IMPLICIT_DEF where it is
314 for (unsigned I = 0; I < SR.valnos.size(); ++I) {
315 const VNInfo &VNI = *SR.valnos[I];
316 if (VNI.isUnused() || !VNI.isPHIDef())
319 SlotIndex Def = VNI.def;
320 MachineBasicBlock &MBB = *Indexes.getMBBFromIndex(Def);
321 for (MachineBasicBlock *PredMBB : MBB.predecessors()) {
322 SlotIndex PredEnd = Indexes.getMBBEndIdx(PredMBB);
323 if (subRangeLiveAt(LI, PredEnd.getPrevSlot()))
326 MachineBasicBlock::iterator InsertPos =
327 llvm::findPHICopyInsertPoint(PredMBB, &MBB, Reg);
328 const MCInstrDesc &MCDesc = TII->get(TargetOpcode::IMPLICIT_DEF);
329 MachineInstrBuilder ImpDef = BuildMI(*PredMBB, InsertPos,
330 DebugLoc(), MCDesc, Reg);
331 SlotIndex DefIdx = LIS->InsertMachineInstrInMaps(*ImpDef);
332 SlotIndex RegDefIdx = DefIdx.getRegSlot();
333 for (LiveInterval::SubRange &SR : LI.subranges()) {
334 VNInfo *SRVNI = SR.getNextValue(RegDefIdx, Allocator);
335 SR.addSegment(LiveRange::Segment(RegDefIdx, PredEnd, SRVNI));
341 for (MachineOperand &MO : MRI->reg_nodbg_operands(Reg)) {
344 unsigned SubRegIdx = MO.getSubReg();
347 // After assigning the new vreg we may not have any other sublanes living
348 // in and out of the instruction anymore. We need to add new dead and
349 // undef flags in these cases.
351 SlotIndex Pos = LIS->getInstructionIndex(*MO.getParent());
352 if (!subRangeLiveAt(LI, Pos))
356 SlotIndex Pos = LIS->getInstructionIndex(*MO.getParent()).getDeadSlot();
357 if (!subRangeLiveAt(LI, Pos))
364 LIS->constructMainRangeFromSubranges(LI);
365 // A def of a subregister may be a use of other register lanes. Replacing
366 // such a def with a def of a different register will eliminate the use,
367 // and may cause the recorded live range to be larger than the actual
368 // liveness in the program IR.
369 LIS->shrinkToUses(&LI);
373 bool RenameIndependentSubregs::runOnMachineFunction(MachineFunction &MF) {
374 // Skip renaming if liveness of subregister is not tracked.
375 MRI = &MF.getRegInfo();
376 if (!MRI->subRegLivenessEnabled())
379 DEBUG(dbgs() << "Renaming independent subregister live ranges in "
380 << MF.getName() << '\n');
382 LIS = &getAnalysis<LiveIntervals>();
383 TII = MF.getSubtarget().getInstrInfo();
385 // Iterate over all vregs. Note that we query getNumVirtRegs() the newly
386 // created vregs end up with higher numbers but do not need to be visited as
387 // there can't be any further splitting.
388 bool Changed = false;
389 for (size_t I = 0, E = MRI->getNumVirtRegs(); I < E; ++I) {
390 unsigned Reg = TargetRegisterInfo::index2VirtReg(I);
391 if (!LIS->hasInterval(Reg))
393 LiveInterval &LI = LIS->getInterval(Reg);
394 if (!LI.hasSubRanges())
397 Changed |= renameComponents(LI);