1 //===- StackMaps.cpp ------------------------------------------------------===//
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 #include "llvm/CodeGen/StackMaps.h"
10 #include "llvm/ADT/DenseMapInfo.h"
11 #include "llvm/ADT/STLExtras.h"
12 #include "llvm/ADT/Twine.h"
13 #include "llvm/CodeGen/AsmPrinter.h"
14 #include "llvm/CodeGen/MachineFrameInfo.h"
15 #include "llvm/CodeGen/MachineFunction.h"
16 #include "llvm/CodeGen/MachineInstr.h"
17 #include "llvm/CodeGen/MachineOperand.h"
18 #include "llvm/CodeGen/TargetOpcodes.h"
19 #include "llvm/CodeGen/TargetRegisterInfo.h"
20 #include "llvm/CodeGen/TargetSubtargetInfo.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCObjectFileInfo.h"
25 #include "llvm/MC/MCRegisterInfo.h"
26 #include "llvm/MC/MCStreamer.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/MathExtras.h"
31 #include "llvm/Support/raw_ostream.h"
32 #include <algorithm>
33 #include <cassert>
34 #include <cstdint>
35 #include <iterator>
36 #include <utility>
37 
38 using namespace llvm;
39 
40 #define DEBUG_TYPE "stackmaps"
41 
42 static cl::opt<int> StackMapVersion(
43     "stackmap-version", cl::init(3), cl::Hidden,
44     cl::desc("Specify the stackmap encoding version (default = 3)"));
45 
46 const char *StackMaps::WSMP = "Stack Maps: ";
47 
48 StackMapOpers::StackMapOpers(const MachineInstr *MI)
49   : MI(MI) {
50   assert(getVarIdx() <= MI->getNumOperands() &&
51          "invalid stackmap definition");
52 }
53 
54 PatchPointOpers::PatchPointOpers(const MachineInstr *MI)
55     : MI(MI), HasDef(MI->getOperand(0).isReg() && MI->getOperand(0).isDef() &&
56                      !MI->getOperand(0).isImplicit()) {
57 #ifndef NDEBUG
58   unsigned CheckStartIdx = 0, e = MI->getNumOperands();
59   while (CheckStartIdx < e && MI->getOperand(CheckStartIdx).isReg() &&
60          MI->getOperand(CheckStartIdx).isDef() &&
61          !MI->getOperand(CheckStartIdx).isImplicit())
62     ++CheckStartIdx;
63 
64   assert(getMetaIdx() == CheckStartIdx &&
65          "Unexpected additional definition in Patchpoint intrinsic.");
66 #endif
67 }
68 
69 unsigned PatchPointOpers::getNextScratchIdx(unsigned StartIdx) const {
70   if (!StartIdx)
71     StartIdx = getVarIdx();
72 
73   // Find the next scratch register (implicit def and early clobber)
74   unsigned ScratchIdx = StartIdx, e = MI->getNumOperands();
75   while (ScratchIdx < e &&
76          !(MI->getOperand(ScratchIdx).isReg() &&
77            MI->getOperand(ScratchIdx).isDef() &&
78            MI->getOperand(ScratchIdx).isImplicit() &&
79            MI->getOperand(ScratchIdx).isEarlyClobber()))
80     ++ScratchIdx;
81 
82   assert(ScratchIdx != e && "No scratch register available");
83   return ScratchIdx;
84 }
85 
86 StackMaps::StackMaps(AsmPrinter &AP) : AP(AP) {
87   if (StackMapVersion != 3)
88     llvm_unreachable("Unsupported stackmap version!");
89 }
90 
91 /// Go up the super-register chain until we hit a valid dwarf register number.
92 static unsigned getDwarfRegNum(unsigned Reg, const TargetRegisterInfo *TRI) {
93   int RegNum = TRI->getDwarfRegNum(Reg, false);
94   for (MCSuperRegIterator SR(Reg, TRI); SR.isValid() && RegNum < 0; ++SR)
95     RegNum = TRI->getDwarfRegNum(*SR, false);
96 
97   assert(RegNum >= 0 && "Invalid Dwarf register number.");
98   return (unsigned)RegNum;
99 }
100 
101 MachineInstr::const_mop_iterator
102 StackMaps::parseOperand(MachineInstr::const_mop_iterator MOI,
103                         MachineInstr::const_mop_iterator MOE, LocationVec &Locs,
104                         LiveOutVec &LiveOuts) const {
105   const TargetRegisterInfo *TRI = AP.MF->getSubtarget().getRegisterInfo();
106   if (MOI->isImm()) {
107     switch (MOI->getImm()) {
108     default:
109       llvm_unreachable("Unrecognized operand type.");
110     case StackMaps::DirectMemRefOp: {
111       auto &DL = AP.MF->getDataLayout();
112 
113       unsigned Size = DL.getPointerSizeInBits();
114       assert((Size % 8) == 0 && "Need pointer size in bytes.");
115       Size /= 8;
116       unsigned Reg = (++MOI)->getReg();
117       int64_t Imm = (++MOI)->getImm();
118       Locs.emplace_back(StackMaps::Location::Direct, Size,
119                         getDwarfRegNum(Reg, TRI), Imm);
120       break;
121     }
122     case StackMaps::IndirectMemRefOp: {
123       int64_t Size = (++MOI)->getImm();
124       assert(Size > 0 && "Need a valid size for indirect memory locations.");
125       unsigned Reg = (++MOI)->getReg();
126       int64_t Imm = (++MOI)->getImm();
127       Locs.emplace_back(StackMaps::Location::Indirect, Size,
128                         getDwarfRegNum(Reg, TRI), Imm);
129       break;
130     }
131     case StackMaps::ConstantOp: {
132       ++MOI;
133       assert(MOI->isImm() && "Expected constant operand.");
134       int64_t Imm = MOI->getImm();
135       Locs.emplace_back(Location::Constant, sizeof(int64_t), 0, Imm);
136       break;
137     }
138     }
139     return ++MOI;
140   }
141 
142   // The physical register number will ultimately be encoded as a DWARF regno.
143   // The stack map also records the size of a spill slot that can hold the
144   // register content. (The runtime can track the actual size of the data type
145   // if it needs to.)
146   if (MOI->isReg()) {
147     // Skip implicit registers (this includes our scratch registers)
148     if (MOI->isImplicit())
149       return ++MOI;
150 
151     assert(TargetRegisterInfo::isPhysicalRegister(MOI->getReg()) &&
152            "Virtreg operands should have been rewritten before now.");
153     const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(MOI->getReg());
154     assert(!MOI->getSubReg() && "Physical subreg still around.");
155 
156     unsigned Offset = 0;
157     unsigned DwarfRegNum = getDwarfRegNum(MOI->getReg(), TRI);
158     unsigned LLVMRegNum = TRI->getLLVMRegNum(DwarfRegNum, false);
159     unsigned SubRegIdx = TRI->getSubRegIndex(LLVMRegNum, MOI->getReg());
160     if (SubRegIdx)
161       Offset = TRI->getSubRegIdxOffset(SubRegIdx);
162 
163     Locs.emplace_back(Location::Register, TRI->getSpillSize(*RC),
164                       DwarfRegNum, Offset);
165     return ++MOI;
166   }
167 
168   if (MOI->isRegLiveOut())
169     LiveOuts = parseRegisterLiveOutMask(MOI->getRegLiveOut());
170 
171   return ++MOI;
172 }
173 
174 void StackMaps::print(raw_ostream &OS) {
175   const TargetRegisterInfo *TRI =
176       AP.MF ? AP.MF->getSubtarget().getRegisterInfo() : nullptr;
177   OS << WSMP << "callsites:\n";
178   for (const auto &CSI : CSInfos) {
179     const LocationVec &CSLocs = CSI.Locations;
180     const LiveOutVec &LiveOuts = CSI.LiveOuts;
181 
182     OS << WSMP << "callsite " << CSI.ID << "\n";
183     OS << WSMP << "  has " << CSLocs.size() << " locations\n";
184 
185     unsigned Idx = 0;
186     for (const auto &Loc : CSLocs) {
187       OS << WSMP << "\t\tLoc " << Idx << ": ";
188       switch (Loc.Type) {
189       case Location::Unprocessed:
190         OS << "<Unprocessed operand>";
191         break;
192       case Location::Register:
193         OS << "Register ";
194         if (TRI)
195           OS << printReg(Loc.Reg, TRI);
196         else
197           OS << Loc.Reg;
198         break;
199       case Location::Direct:
200         OS << "Direct ";
201         if (TRI)
202           OS << printReg(Loc.Reg, TRI);
203         else
204           OS << Loc.Reg;
205         if (Loc.Offset)
206           OS << " + " << Loc.Offset;
207         break;
208       case Location::Indirect:
209         OS << "Indirect ";
210         if (TRI)
211           OS << printReg(Loc.Reg, TRI);
212         else
213           OS << Loc.Reg;
214         OS << "+" << Loc.Offset;
215         break;
216       case Location::Constant:
217         OS << "Constant " << Loc.Offset;
218         break;
219       case Location::ConstantIndex:
220         OS << "Constant Index " << Loc.Offset;
221         break;
222       }
223       OS << "\t[encoding: .byte " << Loc.Type << ", .byte 0"
224          << ", .short " << Loc.Size << ", .short " << Loc.Reg << ", .short 0"
225          << ", .int " << Loc.Offset << "]\n";
226       Idx++;
227     }
228 
229     OS << WSMP << "\thas " << LiveOuts.size() << " live-out registers\n";
230 
231     Idx = 0;
232     for (const auto &LO : LiveOuts) {
233       OS << WSMP << "\t\tLO " << Idx << ": ";
234       if (TRI)
235         OS << printReg(LO.Reg, TRI);
236       else
237         OS << LO.Reg;
238       OS << "\t[encoding: .short " << LO.DwarfRegNum << ", .byte 0, .byte "
239          << LO.Size << "]\n";
240       Idx++;
241     }
242   }
243 }
244 
245 /// Create a live-out register record for the given register Reg.
246 StackMaps::LiveOutReg
247 StackMaps::createLiveOutReg(unsigned Reg, const TargetRegisterInfo *TRI) const {
248   unsigned DwarfRegNum = getDwarfRegNum(Reg, TRI);
249   unsigned Size = TRI->getSpillSize(*TRI->getMinimalPhysRegClass(Reg));
250   return LiveOutReg(Reg, DwarfRegNum, Size);
251 }
252 
253 /// Parse the register live-out mask and return a vector of live-out registers
254 /// that need to be recorded in the stackmap.
255 StackMaps::LiveOutVec
256 StackMaps::parseRegisterLiveOutMask(const uint32_t *Mask) const {
257   assert(Mask && "No register mask specified");
258   const TargetRegisterInfo *TRI = AP.MF->getSubtarget().getRegisterInfo();
259   LiveOutVec LiveOuts;
260 
261   // Create a LiveOutReg for each bit that is set in the register mask.
262   for (unsigned Reg = 0, NumRegs = TRI->getNumRegs(); Reg != NumRegs; ++Reg)
263     if ((Mask[Reg / 32] >> Reg % 32) & 1)
264       LiveOuts.push_back(createLiveOutReg(Reg, TRI));
265 
266   // We don't need to keep track of a register if its super-register is already
267   // in the list. Merge entries that refer to the same dwarf register and use
268   // the maximum size that needs to be spilled.
269 
270   llvm::sort(LiveOuts, [](const LiveOutReg &LHS, const LiveOutReg &RHS) {
271     // Only sort by the dwarf register number.
272     return LHS.DwarfRegNum < RHS.DwarfRegNum;
273   });
274 
275   for (auto I = LiveOuts.begin(), E = LiveOuts.end(); I != E; ++I) {
276     for (auto II = std::next(I); II != E; ++II) {
277       if (I->DwarfRegNum != II->DwarfRegNum) {
278         // Skip all the now invalid entries.
279         I = --II;
280         break;
281       }
282       I->Size = std::max(I->Size, II->Size);
283       if (TRI->isSuperRegister(I->Reg, II->Reg))
284         I->Reg = II->Reg;
285       II->Reg = 0; // mark for deletion.
286     }
287   }
288 
289   LiveOuts.erase(
290       llvm::remove_if(LiveOuts,
291                       [](const LiveOutReg &LO) { return LO.Reg == 0; }),
292       LiveOuts.end());
293 
294   return LiveOuts;
295 }
296 
297 void StackMaps::recordStackMapOpers(const MachineInstr &MI, uint64_t ID,
298                                     MachineInstr::const_mop_iterator MOI,
299                                     MachineInstr::const_mop_iterator MOE,
300                                     bool recordResult) {
301   MCContext &OutContext = AP.OutStreamer->getContext();
302   MCSymbol *MILabel = OutContext.createTempSymbol();
303   AP.OutStreamer->EmitLabel(MILabel);
304 
305   LocationVec Locations;
306   LiveOutVec LiveOuts;
307 
308   if (recordResult) {
309     assert(PatchPointOpers(&MI).hasDef() && "Stackmap has no return value.");
310     parseOperand(MI.operands_begin(), std::next(MI.operands_begin()), Locations,
311                  LiveOuts);
312   }
313 
314   // Parse operands.
315   while (MOI != MOE) {
316     MOI = parseOperand(MOI, MOE, Locations, LiveOuts);
317   }
318 
319   // Move large constants into the constant pool.
320   for (auto &Loc : Locations) {
321     // Constants are encoded as sign-extended integers.
322     // -1 is directly encoded as .long 0xFFFFFFFF with no constant pool.
323     if (Loc.Type == Location::Constant && !isInt<32>(Loc.Offset)) {
324       Loc.Type = Location::ConstantIndex;
325       // ConstPool is intentionally a MapVector of 'uint64_t's (as
326       // opposed to 'int64_t's).  We should never be in a situation
327       // where we have to insert either the tombstone or the empty
328       // keys into a map, and for a DenseMap<uint64_t, T> these are
329       // (uint64_t)0 and (uint64_t)-1.  They can be and are
330       // represented using 32 bit integers.
331       assert((uint64_t)Loc.Offset != DenseMapInfo<uint64_t>::getEmptyKey() &&
332              (uint64_t)Loc.Offset !=
333                  DenseMapInfo<uint64_t>::getTombstoneKey() &&
334              "empty and tombstone keys should fit in 32 bits!");
335       auto Result = ConstPool.insert(std::make_pair(Loc.Offset, Loc.Offset));
336       Loc.Offset = Result.first - ConstPool.begin();
337     }
338   }
339 
340   // Create an expression to calculate the offset of the callsite from function
341   // entry.
342   const MCExpr *CSOffsetExpr = MCBinaryExpr::createSub(
343       MCSymbolRefExpr::create(MILabel, OutContext),
344       MCSymbolRefExpr::create(AP.CurrentFnSymForSize, OutContext), OutContext);
345 
346   CSInfos.emplace_back(CSOffsetExpr, ID, std::move(Locations),
347                        std::move(LiveOuts));
348 
349   // Record the stack size of the current function and update callsite count.
350   const MachineFrameInfo &MFI = AP.MF->getFrameInfo();
351   const TargetRegisterInfo *RegInfo = AP.MF->getSubtarget().getRegisterInfo();
352   bool HasDynamicFrameSize =
353       MFI.hasVarSizedObjects() || RegInfo->needsStackRealignment(*(AP.MF));
354   uint64_t FrameSize = HasDynamicFrameSize ? UINT64_MAX : MFI.getStackSize();
355 
356   auto CurrentIt = FnInfos.find(AP.CurrentFnSym);
357   if (CurrentIt != FnInfos.end())
358     CurrentIt->second.RecordCount++;
359   else
360     FnInfos.insert(std::make_pair(AP.CurrentFnSym, FunctionInfo(FrameSize)));
361 }
362 
363 void StackMaps::recordStackMap(const MachineInstr &MI) {
364   assert(MI.getOpcode() == TargetOpcode::STACKMAP && "expected stackmap");
365 
366   StackMapOpers opers(&MI);
367   const int64_t ID = MI.getOperand(PatchPointOpers::IDPos).getImm();
368   recordStackMapOpers(MI, ID, std::next(MI.operands_begin(), opers.getVarIdx()),
369                       MI.operands_end());
370 }
371 
372 void StackMaps::recordPatchPoint(const MachineInstr &MI) {
373   assert(MI.getOpcode() == TargetOpcode::PATCHPOINT && "expected patchpoint");
374 
375   PatchPointOpers opers(&MI);
376   const int64_t ID = opers.getID();
377   auto MOI = std::next(MI.operands_begin(), opers.getStackMapStartIdx());
378   recordStackMapOpers(MI, ID, MOI, MI.operands_end(),
379                       opers.isAnyReg() && opers.hasDef());
380 
381 #ifndef NDEBUG
382   // verify anyregcc
383   auto &Locations = CSInfos.back().Locations;
384   if (opers.isAnyReg()) {
385     unsigned NArgs = opers.getNumCallArgs();
386     for (unsigned i = 0, e = (opers.hasDef() ? NArgs + 1 : NArgs); i != e; ++i)
387       assert(Locations[i].Type == Location::Register &&
388              "anyreg arg must be in reg.");
389   }
390 #endif
391 }
392 
393 void StackMaps::recordStatepoint(const MachineInstr &MI) {
394   assert(MI.getOpcode() == TargetOpcode::STATEPOINT && "expected statepoint");
395 
396   StatepointOpers opers(&MI);
397   // Record all the deopt and gc operands (they're contiguous and run from the
398   // initial index to the end of the operand list)
399   const unsigned StartIdx = opers.getVarIdx();
400   recordStackMapOpers(MI, opers.getID(), MI.operands_begin() + StartIdx,
401                       MI.operands_end(), false);
402 }
403 
404 /// Emit the stackmap header.
405 ///
406 /// Header {
407 ///   uint8  : Stack Map Version (currently 2)
408 ///   uint8  : Reserved (expected to be 0)
409 ///   uint16 : Reserved (expected to be 0)
410 /// }
411 /// uint32 : NumFunctions
412 /// uint32 : NumConstants
413 /// uint32 : NumRecords
414 void StackMaps::emitStackmapHeader(MCStreamer &OS) {
415   // Header.
416   OS.EmitIntValue(StackMapVersion, 1); // Version.
417   OS.EmitIntValue(0, 1);               // Reserved.
418   OS.EmitIntValue(0, 2);               // Reserved.
419 
420   // Num functions.
421   LLVM_DEBUG(dbgs() << WSMP << "#functions = " << FnInfos.size() << '\n');
422   OS.EmitIntValue(FnInfos.size(), 4);
423   // Num constants.
424   LLVM_DEBUG(dbgs() << WSMP << "#constants = " << ConstPool.size() << '\n');
425   OS.EmitIntValue(ConstPool.size(), 4);
426   // Num callsites.
427   LLVM_DEBUG(dbgs() << WSMP << "#callsites = " << CSInfos.size() << '\n');
428   OS.EmitIntValue(CSInfos.size(), 4);
429 }
430 
431 /// Emit the function frame record for each function.
432 ///
433 /// StkSizeRecord[NumFunctions] {
434 ///   uint64 : Function Address
435 ///   uint64 : Stack Size
436 ///   uint64 : Record Count
437 /// }
438 void StackMaps::emitFunctionFrameRecords(MCStreamer &OS) {
439   // Function Frame records.
440   LLVM_DEBUG(dbgs() << WSMP << "functions:\n");
441   for (auto const &FR : FnInfos) {
442     LLVM_DEBUG(dbgs() << WSMP << "function addr: " << FR.first
443                       << " frame size: " << FR.second.StackSize
444                       << " callsite count: " << FR.second.RecordCount << '\n');
445     OS.EmitSymbolValue(FR.first, 8);
446     OS.EmitIntValue(FR.second.StackSize, 8);
447     OS.EmitIntValue(FR.second.RecordCount, 8);
448   }
449 }
450 
451 /// Emit the constant pool.
452 ///
453 /// int64  : Constants[NumConstants]
454 void StackMaps::emitConstantPoolEntries(MCStreamer &OS) {
455   // Constant pool entries.
456   LLVM_DEBUG(dbgs() << WSMP << "constants:\n");
457   for (const auto &ConstEntry : ConstPool) {
458     LLVM_DEBUG(dbgs() << WSMP << ConstEntry.second << '\n');
459     OS.EmitIntValue(ConstEntry.second, 8);
460   }
461 }
462 
463 /// Emit the callsite info for each callsite.
464 ///
465 /// StkMapRecord[NumRecords] {
466 ///   uint64 : PatchPoint ID
467 ///   uint32 : Instruction Offset
468 ///   uint16 : Reserved (record flags)
469 ///   uint16 : NumLocations
470 ///   Location[NumLocations] {
471 ///     uint8  : Register | Direct | Indirect | Constant | ConstantIndex
472 ///     uint8  : Size in Bytes
473 ///     uint16 : Dwarf RegNum
474 ///     int32  : Offset
475 ///   }
476 ///   uint16 : Padding
477 ///   uint16 : NumLiveOuts
478 ///   LiveOuts[NumLiveOuts] {
479 ///     uint16 : Dwarf RegNum
480 ///     uint8  : Reserved
481 ///     uint8  : Size in Bytes
482 ///   }
483 ///   uint32 : Padding (only if required to align to 8 byte)
484 /// }
485 ///
486 /// Location Encoding, Type, Value:
487 ///   0x1, Register, Reg                 (value in register)
488 ///   0x2, Direct, Reg + Offset          (frame index)
489 ///   0x3, Indirect, [Reg + Offset]      (spilled value)
490 ///   0x4, Constant, Offset              (small constant)
491 ///   0x5, ConstIndex, Constants[Offset] (large constant)
492 void StackMaps::emitCallsiteEntries(MCStreamer &OS) {
493   LLVM_DEBUG(print(dbgs()));
494   // Callsite entries.
495   for (const auto &CSI : CSInfos) {
496     const LocationVec &CSLocs = CSI.Locations;
497     const LiveOutVec &LiveOuts = CSI.LiveOuts;
498 
499     // Verify stack map entry. It's better to communicate a problem to the
500     // runtime than crash in case of in-process compilation. Currently, we do
501     // simple overflow checks, but we may eventually communicate other
502     // compilation errors this way.
503     if (CSLocs.size() > UINT16_MAX || LiveOuts.size() > UINT16_MAX) {
504       OS.EmitIntValue(UINT64_MAX, 8); // Invalid ID.
505       OS.EmitValue(CSI.CSOffsetExpr, 4);
506       OS.EmitIntValue(0, 2); // Reserved.
507       OS.EmitIntValue(0, 2); // 0 locations.
508       OS.EmitIntValue(0, 2); // padding.
509       OS.EmitIntValue(0, 2); // 0 live-out registers.
510       OS.EmitIntValue(0, 4); // padding.
511       continue;
512     }
513 
514     OS.EmitIntValue(CSI.ID, 8);
515     OS.EmitValue(CSI.CSOffsetExpr, 4);
516 
517     // Reserved for flags.
518     OS.EmitIntValue(0, 2);
519     OS.EmitIntValue(CSLocs.size(), 2);
520 
521     for (const auto &Loc : CSLocs) {
522       OS.EmitIntValue(Loc.Type, 1);
523       OS.EmitIntValue(0, 1);  // Reserved
524       OS.EmitIntValue(Loc.Size, 2);
525       OS.EmitIntValue(Loc.Reg, 2);
526       OS.EmitIntValue(0, 2);  // Reserved
527       OS.EmitIntValue(Loc.Offset, 4);
528     }
529 
530     // Emit alignment to 8 byte.
531     OS.EmitValueToAlignment(8);
532 
533     // Num live-out registers and padding to align to 4 byte.
534     OS.EmitIntValue(0, 2);
535     OS.EmitIntValue(LiveOuts.size(), 2);
536 
537     for (const auto &LO : LiveOuts) {
538       OS.EmitIntValue(LO.DwarfRegNum, 2);
539       OS.EmitIntValue(0, 1);
540       OS.EmitIntValue(LO.Size, 1);
541     }
542     // Emit alignment to 8 byte.
543     OS.EmitValueToAlignment(8);
544   }
545 }
546 
547 /// Serialize the stackmap data.
548 void StackMaps::serializeToStackMapSection() {
549   (void)WSMP;
550   // Bail out if there's no stack map data.
551   assert((!CSInfos.empty() || ConstPool.empty()) &&
552          "Expected empty constant pool too!");
553   assert((!CSInfos.empty() || FnInfos.empty()) &&
554          "Expected empty function record too!");
555   if (CSInfos.empty())
556     return;
557 
558   MCContext &OutContext = AP.OutStreamer->getContext();
559   MCStreamer &OS = *AP.OutStreamer;
560 
561   // Create the section.
562   MCSection *StackMapSection =
563       OutContext.getObjectFileInfo()->getStackMapSection();
564   OS.SwitchSection(StackMapSection);
565 
566   // Emit a dummy symbol to force section inclusion.
567   OS.EmitLabel(OutContext.getOrCreateSymbol(Twine("__LLVM_StackMaps")));
568 
569   // Serialize data.
570   LLVM_DEBUG(dbgs() << "********** Stack Map Output **********\n");
571   emitStackmapHeader(OS);
572   emitFunctionFrameRecords(OS);
573   emitConstantPoolEntries(OS);
574   emitCallsiteEntries(OS);
575   OS.AddBlankLine();
576 
577   // Clean up.
578   CSInfos.clear();
579   ConstPool.clear();
580 }
581