1 //===-- WebAssemblyAsmPrinter.cpp - WebAssembly LLVM assembly writer ------===//
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 /// \file
10 /// This file contains a printer that converts from our internal
11 /// representation of machine-dependent LLVM code to the WebAssembly assembly
12 /// language.
13 ///
14 //===----------------------------------------------------------------------===//
15 
16 #include "WebAssemblyAsmPrinter.h"
17 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
18 #include "MCTargetDesc/WebAssemblyTargetStreamer.h"
19 #include "TargetInfo/WebAssemblyTargetInfo.h"
20 #include "Utils/WebAssemblyTypeUtilities.h"
21 #include "Utils/WebAssemblyUtilities.h"
22 #include "WebAssembly.h"
23 #include "WebAssemblyMCInstLower.h"
24 #include "WebAssemblyMachineFunctionInfo.h"
25 #include "WebAssemblyRegisterInfo.h"
26 #include "WebAssemblyTargetMachine.h"
27 #include "llvm/ADT/SmallSet.h"
28 #include "llvm/ADT/StringExtras.h"
29 #include "llvm/BinaryFormat/Wasm.h"
30 #include "llvm/CodeGen/Analysis.h"
31 #include "llvm/CodeGen/AsmPrinter.h"
32 #include "llvm/CodeGen/MachineConstantPool.h"
33 #include "llvm/CodeGen/MachineInstr.h"
34 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
35 #include "llvm/IR/DataLayout.h"
36 #include "llvm/IR/DebugInfoMetadata.h"
37 #include "llvm/IR/GlobalVariable.h"
38 #include "llvm/IR/Metadata.h"
39 #include "llvm/MC/MCContext.h"
40 #include "llvm/MC/MCSectionWasm.h"
41 #include "llvm/MC/MCStreamer.h"
42 #include "llvm/MC/MCSymbol.h"
43 #include "llvm/MC/MCSymbolWasm.h"
44 #include "llvm/Support/Debug.h"
45 #include "llvm/Support/TargetRegistry.h"
46 #include "llvm/Support/raw_ostream.h"
47 
48 using namespace llvm;
49 
50 #define DEBUG_TYPE "asm-printer"
51 
52 extern cl::opt<bool> WasmKeepRegisters;
53 extern cl::opt<bool> EnableEmException;
54 extern cl::opt<bool> EnableEmSjLj;
55 
56 //===----------------------------------------------------------------------===//
57 // Helpers.
58 //===----------------------------------------------------------------------===//
59 
60 MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
61   const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
62   const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
63   for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
64                 MVT::v4i32, MVT::v2i64, MVT::v4f32, MVT::v2f64})
65     if (TRI->isTypeLegalForClass(*TRC, T))
66       return T;
67   LLVM_DEBUG(errs() << "Unknown type for register number: " << RegNo);
68   llvm_unreachable("Unknown register type");
69   return MVT::Other;
70 }
71 
72 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
73   Register RegNo = MO.getReg();
74   assert(Register::isVirtualRegister(RegNo) &&
75          "Unlowered physical register encountered during assembly printing");
76   assert(!MFI->isVRegStackified(RegNo));
77   unsigned WAReg = MFI->getWAReg(RegNo);
78   assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
79   return '$' + utostr(WAReg);
80 }
81 
82 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
83   MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
84   return static_cast<WebAssemblyTargetStreamer *>(TS);
85 }
86 
87 // Emscripten exception handling helpers
88 //
89 // This converts invoke names generated by LowerEmscriptenEHSjLj to real names
90 // that are expected by JavaScript glue code. The invoke names generated by
91 // Emscripten JS glue code are based on their argument and return types; for
92 // example, for a function that takes an i32 and returns nothing, it is
93 // 'invoke_vi'. But the format of invoke generated by LowerEmscriptenEHSjLj pass
94 // contains a mangled string generated from their IR types, for example,
95 // "__invoke_void_%struct.mystruct*_int", because final wasm types are not
96 // available in the IR pass. So we convert those names to the form that
97 // Emscripten JS code expects.
98 //
99 // Refer to LowerEmscriptenEHSjLj pass for more details.
100 
101 // Returns true if the given function name is an invoke name generated by
102 // LowerEmscriptenEHSjLj pass.
103 static bool isEmscriptenInvokeName(StringRef Name) {
104   if (Name.front() == '"' && Name.back() == '"')
105     Name = Name.substr(1, Name.size() - 2);
106   return Name.startswith("__invoke_");
107 }
108 
109 // Returns a character that represents the given wasm value type in invoke
110 // signatures.
111 static char getInvokeSig(wasm::ValType VT) {
112   switch (VT) {
113   case wasm::ValType::I32:
114     return 'i';
115   case wasm::ValType::I64:
116     return 'j';
117   case wasm::ValType::F32:
118     return 'f';
119   case wasm::ValType::F64:
120     return 'd';
121   case wasm::ValType::V128:
122     return 'V';
123   case wasm::ValType::FUNCREF:
124     return 'F';
125   case wasm::ValType::EXTERNREF:
126     return 'X';
127   }
128   llvm_unreachable("Unhandled wasm::ValType enum");
129 }
130 
131 // Given the wasm signature, generate the invoke name in the format JS glue code
132 // expects.
133 static std::string getEmscriptenInvokeSymbolName(wasm::WasmSignature *Sig) {
134   assert(Sig->Returns.size() <= 1);
135   std::string Ret = "invoke_";
136   if (!Sig->Returns.empty())
137     for (auto VT : Sig->Returns)
138       Ret += getInvokeSig(VT);
139   else
140     Ret += 'v';
141   // Invokes' first argument is a pointer to the original function, so skip it
142   for (unsigned I = 1, E = Sig->Params.size(); I < E; I++)
143     Ret += getInvokeSig(Sig->Params[I]);
144   return Ret;
145 }
146 
147 //===----------------------------------------------------------------------===//
148 // WebAssemblyAsmPrinter Implementation.
149 //===----------------------------------------------------------------------===//
150 
151 MCSymbolWasm *WebAssemblyAsmPrinter::getMCSymbolForFunction(
152     const Function *F, bool EnableEmEH, wasm::WasmSignature *Sig,
153     bool &InvokeDetected) {
154   MCSymbolWasm *WasmSym = nullptr;
155   if (EnableEmEH && isEmscriptenInvokeName(F->getName())) {
156     assert(Sig);
157     InvokeDetected = true;
158     if (Sig->Returns.size() > 1) {
159       std::string Msg =
160           "Emscripten EH/SjLj does not support multivalue returns: " +
161           std::string(F->getName()) + ": " +
162           WebAssembly::signatureToString(Sig);
163       report_fatal_error(Msg);
164     }
165     WasmSym = cast<MCSymbolWasm>(
166         GetExternalSymbolSymbol(getEmscriptenInvokeSymbolName(Sig)));
167   } else {
168     WasmSym = cast<MCSymbolWasm>(getSymbol(F));
169   }
170   return WasmSym;
171 }
172 
173 void WebAssemblyAsmPrinter::emitGlobalVariable(const GlobalVariable *GV) {
174   if (!WebAssembly::isWasmVarAddressSpace(GV->getAddressSpace())) {
175     AsmPrinter::emitGlobalVariable(GV);
176     return;
177   }
178 
179   assert(!GV->isThreadLocal());
180 
181   MCSymbolWasm *Sym = cast<MCSymbolWasm>(getSymbol(GV));
182 
183   if (!Sym->getType()) {
184     const WebAssemblyTargetLowering &TLI = *Subtarget->getTargetLowering();
185     SmallVector<EVT, 1> VTs;
186     ComputeValueVTs(TLI, GV->getParent()->getDataLayout(), GV->getValueType(),
187                     VTs);
188     if (VTs.size() != 1 ||
189         TLI.getNumRegisters(GV->getParent()->getContext(), VTs[0]) != 1)
190       report_fatal_error("Aggregate globals not yet implemented");
191     MVT VT = TLI.getRegisterType(GV->getParent()->getContext(), VTs[0]);
192     bool Mutable = true;
193     wasm::ValType Type = WebAssembly::toValType(VT);
194     Sym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
195     Sym->setGlobalType(wasm::WasmGlobalType{uint8_t(Type), Mutable});
196   }
197 
198   emitVisibility(Sym, GV->getVisibility(), !GV->isDeclaration());
199   if (GV->hasInitializer()) {
200     assert(getSymbolPreferLocal(*GV) == Sym);
201     emitLinkage(GV, Sym);
202     getTargetStreamer()->emitGlobalType(Sym);
203     OutStreamer->emitLabel(Sym);
204     // TODO: Actually emit the initializer value.  Otherwise the global has the
205     // default value for its type (0, ref.null, etc).
206     OutStreamer->AddBlankLine();
207   }
208 }
209 
210 void WebAssemblyAsmPrinter::emitEndOfAsmFile(Module &M) {
211   for (auto &It : OutContext.getSymbols()) {
212     // Emit .globaltype, .eventtype, or .tabletype declarations.
213     auto Sym = cast<MCSymbolWasm>(It.getValue());
214     if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_GLOBAL) {
215       // .globaltype already handled by emitGlobalVariable for defined
216       // variables; here we make sure the types of external wasm globals get
217       // written to the file.
218       if (Sym->isUndefined())
219         getTargetStreamer()->emitGlobalType(Sym);
220     } else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_EVENT)
221       getTargetStreamer()->emitEventType(Sym);
222     else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_TABLE)
223       getTargetStreamer()->emitTableType(Sym);
224   }
225 
226   DenseSet<MCSymbol *> InvokeSymbols;
227   bool HasAddressTakenFunction = false;
228   for (const auto &F : M) {
229     if (F.isIntrinsic())
230       continue;
231 
232     if (F.hasAddressTaken())
233       HasAddressTakenFunction = true;
234 
235     // Emit function type info for all undefined functions
236     if (F.isDeclarationForLinker()) {
237       SmallVector<MVT, 4> Results;
238       SmallVector<MVT, 4> Params;
239       computeSignatureVTs(F.getFunctionType(), &F, F, TM, Params, Results);
240       // At this point these MCSymbols may or may not have been created already
241       // and thus also contain a signature, but we need to get the signature
242       // anyway here in case it is an invoke that has not yet been created. We
243       // will discard it later if it turns out not to be necessary.
244       auto Signature = signatureFromMVTs(Results, Params);
245       bool InvokeDetected = false;
246       auto *Sym = getMCSymbolForFunction(&F, EnableEmException || EnableEmSjLj,
247                                          Signature.get(), InvokeDetected);
248 
249       // Multiple functions can be mapped to the same invoke symbol. For
250       // example, two IR functions '__invoke_void_i8*' and '__invoke_void_i32'
251       // are both mapped to '__invoke_vi'. We keep them in a set once we emit an
252       // Emscripten EH symbol so we don't emit the same symbol twice.
253       if (InvokeDetected && !InvokeSymbols.insert(Sym).second)
254         continue;
255 
256       Sym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
257       if (!Sym->getSignature()) {
258         Sym->setSignature(Signature.get());
259         addSignature(std::move(Signature));
260       } else {
261         // This symbol has already been created and had a signature. Discard it.
262         Signature.reset();
263       }
264 
265       getTargetStreamer()->emitFunctionType(Sym);
266 
267       if (F.hasFnAttribute("wasm-import-module")) {
268         StringRef Name =
269             F.getFnAttribute("wasm-import-module").getValueAsString();
270         Sym->setImportModule(storeName(Name));
271         getTargetStreamer()->emitImportModule(Sym, Name);
272       }
273       if (F.hasFnAttribute("wasm-import-name")) {
274         // If this is a converted Emscripten EH/SjLj symbol, we shouldn't use
275         // the original function name but the converted symbol name.
276         StringRef Name =
277             InvokeDetected
278                 ? Sym->getName()
279                 : F.getFnAttribute("wasm-import-name").getValueAsString();
280         Sym->setImportName(storeName(Name));
281         getTargetStreamer()->emitImportName(Sym, Name);
282       }
283     }
284 
285     if (F.hasFnAttribute("wasm-export-name")) {
286       auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
287       StringRef Name = F.getFnAttribute("wasm-export-name").getValueAsString();
288       Sym->setExportName(storeName(Name));
289       getTargetStreamer()->emitExportName(Sym, Name);
290     }
291   }
292 
293   // When a function's address is taken, a TABLE_INDEX relocation is emitted
294   // against the function symbol at the use site.  However the relocation
295   // doesn't explicitly refer to the table.  In the future we may want to
296   // define a new kind of reloc against both the function and the table, so
297   // that the linker can see that the function symbol keeps the table alive,
298   // but for now manually mark the table as live.
299   if (HasAddressTakenFunction) {
300     MCSymbolWasm *FunctionTable =
301         WebAssembly::getOrCreateFunctionTableSymbol(OutContext, Subtarget);
302     OutStreamer->emitSymbolAttribute(FunctionTable, MCSA_NoDeadStrip);
303   }
304 
305   for (const auto &G : M.globals()) {
306     if (!G.hasInitializer() && G.hasExternalLinkage() &&
307         !WebAssembly::isWasmVarAddressSpace(G.getAddressSpace()) &&
308         G.getValueType()->isSized()) {
309       uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
310       OutStreamer->emitELFSize(getSymbol(&G),
311                                MCConstantExpr::create(Size, OutContext));
312     }
313   }
314 
315   if (const NamedMDNode *Named = M.getNamedMetadata("wasm.custom_sections")) {
316     for (const Metadata *MD : Named->operands()) {
317       const auto *Tuple = dyn_cast<MDTuple>(MD);
318       if (!Tuple || Tuple->getNumOperands() != 2)
319         continue;
320       const MDString *Name = dyn_cast<MDString>(Tuple->getOperand(0));
321       const MDString *Contents = dyn_cast<MDString>(Tuple->getOperand(1));
322       if (!Name || !Contents)
323         continue;
324 
325       OutStreamer->PushSection();
326       std::string SectionName = (".custom_section." + Name->getString()).str();
327       MCSectionWasm *MySection =
328           OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
329       OutStreamer->SwitchSection(MySection);
330       OutStreamer->emitBytes(Contents->getString());
331       OutStreamer->PopSection();
332     }
333   }
334 
335   EmitProducerInfo(M);
336   EmitTargetFeatures(M);
337 }
338 
339 void WebAssemblyAsmPrinter::EmitProducerInfo(Module &M) {
340   llvm::SmallVector<std::pair<std::string, std::string>, 4> Languages;
341   if (const NamedMDNode *Debug = M.getNamedMetadata("llvm.dbg.cu")) {
342     llvm::SmallSet<StringRef, 4> SeenLanguages;
343     for (size_t I = 0, E = Debug->getNumOperands(); I < E; ++I) {
344       const auto *CU = cast<DICompileUnit>(Debug->getOperand(I));
345       StringRef Language = dwarf::LanguageString(CU->getSourceLanguage());
346       Language.consume_front("DW_LANG_");
347       if (SeenLanguages.insert(Language).second)
348         Languages.emplace_back(Language.str(), "");
349     }
350   }
351 
352   llvm::SmallVector<std::pair<std::string, std::string>, 4> Tools;
353   if (const NamedMDNode *Ident = M.getNamedMetadata("llvm.ident")) {
354     llvm::SmallSet<StringRef, 4> SeenTools;
355     for (size_t I = 0, E = Ident->getNumOperands(); I < E; ++I) {
356       const auto *S = cast<MDString>(Ident->getOperand(I)->getOperand(0));
357       std::pair<StringRef, StringRef> Field = S->getString().split("version");
358       StringRef Name = Field.first.trim();
359       StringRef Version = Field.second.trim();
360       if (SeenTools.insert(Name).second)
361         Tools.emplace_back(Name.str(), Version.str());
362     }
363   }
364 
365   int FieldCount = int(!Languages.empty()) + int(!Tools.empty());
366   if (FieldCount != 0) {
367     MCSectionWasm *Producers = OutContext.getWasmSection(
368         ".custom_section.producers", SectionKind::getMetadata());
369     OutStreamer->PushSection();
370     OutStreamer->SwitchSection(Producers);
371     OutStreamer->emitULEB128IntValue(FieldCount);
372     for (auto &Producers : {std::make_pair("language", &Languages),
373             std::make_pair("processed-by", &Tools)}) {
374       if (Producers.second->empty())
375         continue;
376       OutStreamer->emitULEB128IntValue(strlen(Producers.first));
377       OutStreamer->emitBytes(Producers.first);
378       OutStreamer->emitULEB128IntValue(Producers.second->size());
379       for (auto &Producer : *Producers.second) {
380         OutStreamer->emitULEB128IntValue(Producer.first.size());
381         OutStreamer->emitBytes(Producer.first);
382         OutStreamer->emitULEB128IntValue(Producer.second.size());
383         OutStreamer->emitBytes(Producer.second);
384       }
385     }
386     OutStreamer->PopSection();
387   }
388 }
389 
390 void WebAssemblyAsmPrinter::EmitTargetFeatures(Module &M) {
391   struct FeatureEntry {
392     uint8_t Prefix;
393     std::string Name;
394   };
395 
396   // Read target features and linkage policies from module metadata
397   SmallVector<FeatureEntry, 4> EmittedFeatures;
398   auto EmitFeature = [&](std::string Feature) {
399     std::string MDKey = (StringRef("wasm-feature-") + Feature).str();
400     Metadata *Policy = M.getModuleFlag(MDKey);
401     if (Policy == nullptr)
402       return;
403 
404     FeatureEntry Entry;
405     Entry.Prefix = 0;
406     Entry.Name = Feature;
407 
408     if (auto *MD = cast<ConstantAsMetadata>(Policy))
409       if (auto *I = cast<ConstantInt>(MD->getValue()))
410         Entry.Prefix = I->getZExtValue();
411 
412     // Silently ignore invalid metadata
413     if (Entry.Prefix != wasm::WASM_FEATURE_PREFIX_USED &&
414         Entry.Prefix != wasm::WASM_FEATURE_PREFIX_REQUIRED &&
415         Entry.Prefix != wasm::WASM_FEATURE_PREFIX_DISALLOWED)
416       return;
417 
418     EmittedFeatures.push_back(Entry);
419   };
420 
421   for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
422     EmitFeature(KV.Key);
423   }
424   // This pseudo-feature tells the linker whether shared memory would be safe
425   EmitFeature("shared-mem");
426 
427   if (EmittedFeatures.size() == 0)
428     return;
429 
430   // Emit features and linkage policies into the "target_features" section
431   MCSectionWasm *FeaturesSection = OutContext.getWasmSection(
432       ".custom_section.target_features", SectionKind::getMetadata());
433   OutStreamer->PushSection();
434   OutStreamer->SwitchSection(FeaturesSection);
435 
436   OutStreamer->emitULEB128IntValue(EmittedFeatures.size());
437   for (auto &F : EmittedFeatures) {
438     OutStreamer->emitIntValue(F.Prefix, 1);
439     OutStreamer->emitULEB128IntValue(F.Name.size());
440     OutStreamer->emitBytes(F.Name);
441   }
442 
443   OutStreamer->PopSection();
444 }
445 
446 void WebAssemblyAsmPrinter::emitConstantPool() {
447   assert(MF->getConstantPool()->getConstants().empty() &&
448          "WebAssembly disables constant pools");
449 }
450 
451 void WebAssemblyAsmPrinter::emitJumpTableInfo() {
452   // Nothing to do; jump tables are incorporated into the instruction stream.
453 }
454 
455 void WebAssemblyAsmPrinter::emitFunctionBodyStart() {
456   const Function &F = MF->getFunction();
457   SmallVector<MVT, 1> ResultVTs;
458   SmallVector<MVT, 4> ParamVTs;
459   computeSignatureVTs(F.getFunctionType(), &F, F, TM, ParamVTs, ResultVTs);
460 
461   auto Signature = signatureFromMVTs(ResultVTs, ParamVTs);
462   auto *WasmSym = cast<MCSymbolWasm>(CurrentFnSym);
463   WasmSym->setSignature(Signature.get());
464   addSignature(std::move(Signature));
465   WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
466 
467   getTargetStreamer()->emitFunctionType(WasmSym);
468 
469   // Emit the function index.
470   if (MDNode *Idx = F.getMetadata("wasm.index")) {
471     assert(Idx->getNumOperands() == 1);
472 
473     getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
474         cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
475   }
476 
477   SmallVector<wasm::ValType, 16> Locals;
478   valTypesFromMVTs(MFI->getLocals(), Locals);
479   getTargetStreamer()->emitLocal(Locals);
480 
481   AsmPrinter::emitFunctionBodyStart();
482 }
483 
484 void WebAssemblyAsmPrinter::emitInstruction(const MachineInstr *MI) {
485   LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
486 
487   switch (MI->getOpcode()) {
488   case WebAssembly::ARGUMENT_i32:
489   case WebAssembly::ARGUMENT_i32_S:
490   case WebAssembly::ARGUMENT_i64:
491   case WebAssembly::ARGUMENT_i64_S:
492   case WebAssembly::ARGUMENT_f32:
493   case WebAssembly::ARGUMENT_f32_S:
494   case WebAssembly::ARGUMENT_f64:
495   case WebAssembly::ARGUMENT_f64_S:
496   case WebAssembly::ARGUMENT_v16i8:
497   case WebAssembly::ARGUMENT_v16i8_S:
498   case WebAssembly::ARGUMENT_v8i16:
499   case WebAssembly::ARGUMENT_v8i16_S:
500   case WebAssembly::ARGUMENT_v4i32:
501   case WebAssembly::ARGUMENT_v4i32_S:
502   case WebAssembly::ARGUMENT_v2i64:
503   case WebAssembly::ARGUMENT_v2i64_S:
504   case WebAssembly::ARGUMENT_v4f32:
505   case WebAssembly::ARGUMENT_v4f32_S:
506   case WebAssembly::ARGUMENT_v2f64:
507   case WebAssembly::ARGUMENT_v2f64_S:
508     // These represent values which are live into the function entry, so there's
509     // no instruction to emit.
510     break;
511   case WebAssembly::FALLTHROUGH_RETURN: {
512     // These instructions represent the implicit return at the end of a
513     // function body.
514     if (isVerbose()) {
515       OutStreamer->AddComment("fallthrough-return");
516       OutStreamer->AddBlankLine();
517     }
518     break;
519   }
520   case WebAssembly::COMPILER_FENCE:
521     // This is a compiler barrier that prevents instruction reordering during
522     // backend compilation, and should not be emitted.
523     break;
524   default: {
525     WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
526     MCInst TmpInst;
527     MCInstLowering.lower(MI, TmpInst);
528     EmitToStreamer(*OutStreamer, TmpInst);
529     break;
530   }
531   }
532 }
533 
534 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
535                                             unsigned OpNo,
536                                             const char *ExtraCode,
537                                             raw_ostream &OS) {
538   // First try the generic code, which knows about modifiers like 'c' and 'n'.
539   if (!AsmPrinter::PrintAsmOperand(MI, OpNo, ExtraCode, OS))
540     return false;
541 
542   if (!ExtraCode) {
543     const MachineOperand &MO = MI->getOperand(OpNo);
544     switch (MO.getType()) {
545     case MachineOperand::MO_Immediate:
546       OS << MO.getImm();
547       return false;
548     case MachineOperand::MO_Register:
549       // FIXME: only opcode that still contains registers, as required by
550       // MachineInstr::getDebugVariable().
551       assert(MI->getOpcode() == WebAssembly::INLINEASM);
552       OS << regToString(MO);
553       return false;
554     case MachineOperand::MO_GlobalAddress:
555       PrintSymbolOperand(MO, OS);
556       return false;
557     case MachineOperand::MO_ExternalSymbol:
558       GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
559       printOffset(MO.getOffset(), OS);
560       return false;
561     case MachineOperand::MO_MachineBasicBlock:
562       MO.getMBB()->getSymbol()->print(OS, MAI);
563       return false;
564     default:
565       break;
566     }
567   }
568 
569   return true;
570 }
571 
572 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
573                                                   unsigned OpNo,
574                                                   const char *ExtraCode,
575                                                   raw_ostream &OS) {
576   // The current approach to inline asm is that "r" constraints are expressed
577   // as local indices, rather than values on the operand stack. This simplifies
578   // using "r" as it eliminates the need to push and pop the values in a
579   // particular order, however it also makes it impossible to have an "m"
580   // constraint. So we don't support it.
581 
582   return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, ExtraCode, OS);
583 }
584 
585 // Force static initialization.
586 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeWebAssemblyAsmPrinter() {
587   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
588   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
589 }
590