llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

   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 "WebAssemblyRuntimeLibcallSignatures.h"
  27 #include "WebAssemblyTargetMachine.h"
  28 #include "llvm/ADT/SmallSet.h"
  29 #include "llvm/ADT/StringExtras.h"
  30 #include "llvm/BinaryFormat/Wasm.h"
  31 #include "llvm/CodeGen/Analysis.h"
  32 #include "llvm/CodeGen/AsmPrinter.h"
  33 #include "llvm/CodeGen/MachineConstantPool.h"
  34 #include "llvm/CodeGen/MachineInstr.h"
  35 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
  36 #include "llvm/IR/DataLayout.h"
  37 #include "llvm/IR/DebugInfoMetadata.h"
  38 #include "llvm/IR/GlobalVariable.h"
  39 #include "llvm/IR/Metadata.h"
  40 #include "llvm/MC/MCContext.h"
  41 #include "llvm/MC/MCSectionWasm.h"
  42 #include "llvm/MC/MCStreamer.h"
  43 #include "llvm/MC/MCSymbol.h"
  44 #include "llvm/MC/MCSymbolWasm.h"
  45 #include "llvm/Support/Debug.h"
  46 #include "llvm/Support/TargetRegistry.h"
  47 #include "llvm/Support/raw_ostream.h"
  48
  49 using namespace llvm;
  50
  51 #define DEBUG_TYPE "asm-printer"
  52
  53 extern cl::opt<bool> WasmKeepRegisters;
  54 extern cl::opt<bool> WasmEnableEmException;
  55 extern cl::opt<bool> WasmEnableEmSjLj;
  56
  57 //===----------------------------------------------------------------------===//
  58 // Helpers.
  59 //===----------------------------------------------------------------------===//
  60
  61 MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
  62   const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
  63   const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
  64   for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
  65                 MVT::v4i32, MVT::v2i64, MVT::v4f32, MVT::v2f64})
  66     if (TRI->isTypeLegalForClass(*TRC, T))
  67       return T;
  68   LLVM_DEBUG(errs() << "Unknown type for register number: " << RegNo);
  69   llvm_unreachable("Unknown register type");
  70   return MVT::Other;
  71 }
  72
  73 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
  74   Register RegNo = MO.getReg();
  75   assert(Register::isVirtualRegister(RegNo) &&
  76          "Unlowered physical register encountered during assembly printing");
  77   assert(!MFI->isVRegStackified(RegNo));
  78   unsigned WAReg = MFI->getWAReg(RegNo);
  79   assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
  80   return '$' + utostr(WAReg);
  81 }
  82
  83 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
  84   MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
  85   return static_cast<WebAssemblyTargetStreamer *>(TS);
  86 }
  87
  88 // Emscripten exception handling helpers
  89 //
  90 // This converts invoke names generated by LowerEmscriptenEHSjLj to real names
  91 // that are expected by JavaScript glue code. The invoke names generated by
  92 // Emscripten JS glue code are based on their argument and return types; for
  93 // example, for a function that takes an i32 and returns nothing, it is
  94 // 'invoke_vi'. But the format of invoke generated by LowerEmscriptenEHSjLj pass
  95 // contains a mangled string generated from their IR types, for example,
  96 // "__invoke_void_%struct.mystruct*_int", because final wasm types are not
  97 // available in the IR pass. So we convert those names to the form that
  98 // Emscripten JS code expects.
  99 //
 100 // Refer to LowerEmscriptenEHSjLj pass for more details.
 101
 102 // Returns true if the given function name is an invoke name generated by
 103 // LowerEmscriptenEHSjLj pass.
 104 static bool isEmscriptenInvokeName(StringRef Name) {
 105   if (Name.front() == '"' && Name.back() == '"')
 106     Name = Name.substr(1, Name.size() - 2);
 107   return Name.startswith("__invoke_");
 108 }
 109
 110 // Returns a character that represents the given wasm value type in invoke
 111 // signatures.
 112 static char getInvokeSig(wasm::ValType VT) {
 113   switch (VT) {
 114   case wasm::ValType::I32:
 115     return 'i';
 116   case wasm::ValType::I64:
 117     return 'j';
 118   case wasm::ValType::F32:
 119     return 'f';
 120   case wasm::ValType::F64:
 121     return 'd';
 122   case wasm::ValType::V128:
 123     return 'V';
 124   case wasm::ValType::FUNCREF:
 125     return 'F';
 126   case wasm::ValType::EXTERNREF:
 127     return 'X';
 128   }
 129   llvm_unreachable("Unhandled wasm::ValType enum");
 130 }
 131
 132 // Given the wasm signature, generate the invoke name in the format JS glue code
 133 // expects.
 134 static std::string getEmscriptenInvokeSymbolName(wasm::WasmSignature *Sig) {
 135   assert(Sig->Returns.size() <= 1);
 136   std::string Ret = "invoke_";
 137   if (!Sig->Returns.empty())
 138     for (auto VT : Sig->Returns)
 139       Ret += getInvokeSig(VT);
 140   else
 141     Ret += 'v';
 142   // Invokes' first argument is a pointer to the original function, so skip it
 143   for (unsigned I = 1, E = Sig->Params.size(); I < E; I++)
 144     Ret += getInvokeSig(Sig->Params[I]);
 145   return Ret;
 146 }
 147
 148 //===----------------------------------------------------------------------===//
 149 // WebAssemblyAsmPrinter Implementation.
 150 //===----------------------------------------------------------------------===//
 151
 152 MCSymbolWasm *WebAssemblyAsmPrinter::getMCSymbolForFunction(
 153     const Function *F, bool EnableEmEH, wasm::WasmSignature *Sig,
 154     bool &InvokeDetected) {
 155   MCSymbolWasm *WasmSym = nullptr;
 156   if (EnableEmEH && isEmscriptenInvokeName(F->getName())) {
 157     assert(Sig);
 158     InvokeDetected = true;
 159     if (Sig->Returns.size() > 1) {
 160       std::string Msg =
 161           "Emscripten EH/SjLj does not support multivalue returns: " +
 162           std::string(F->getName()) + ": " +
 163           WebAssembly::signatureToString(Sig);
 164       report_fatal_error(Msg);
 165     }
 166     WasmSym = cast<MCSymbolWasm>(
 167         GetExternalSymbolSymbol(getEmscriptenInvokeSymbolName(Sig)));
 168   } else {
 169     WasmSym = cast<MCSymbolWasm>(getSymbol(F));
 170   }
 171   return WasmSym;
 172 }
 173
 174 void WebAssemblyAsmPrinter::emitGlobalVariable(const GlobalVariable *GV) {
 175   if (!WebAssembly::isWasmVarAddressSpace(GV->getAddressSpace())) {
 176     AsmPrinter::emitGlobalVariable(GV);
 177     return;
 178   }
 179
 180   assert(!GV->isThreadLocal());
 181
 182   MCSymbolWasm *Sym = cast<MCSymbolWasm>(getSymbol(GV));
 183
 184   if (!Sym->getType()) {
 185     const WebAssemblyTargetLowering &TLI = *Subtarget->getTargetLowering();
 186     SmallVector<EVT, 1> VTs;
 187     ComputeValueVTs(TLI, GV->getParent()->getDataLayout(), GV->getValueType(),
 188                     VTs);
 189     if (VTs.size() != 1 ||
 190         TLI.getNumRegisters(GV->getParent()->getContext(), VTs[0]) != 1)
 191       report_fatal_error("Aggregate globals not yet implemented");
 192     MVT VT = TLI.getRegisterType(GV->getParent()->getContext(), VTs[0]);
 193     bool Mutable = true;
 194     wasm::ValType Type = WebAssembly::toValType(VT);
 195     Sym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
 196     Sym->setGlobalType(wasm::WasmGlobalType{uint8_t(Type), Mutable});
 197   }
 198
 199   emitVisibility(Sym, GV->getVisibility(), !GV->isDeclaration());
 200   if (GV->hasInitializer()) {
 201     assert(getSymbolPreferLocal(*GV) == Sym);
 202     emitLinkage(GV, Sym);
 203     getTargetStreamer()->emitGlobalType(Sym);
 204     OutStreamer->emitLabel(Sym);
 205     // TODO: Actually emit the initializer value.  Otherwise the global has the
 206     // default value for its type (0, ref.null, etc).
 207     OutStreamer->AddBlankLine();
 208   }
 209 }
 210
 211 MCSymbol *WebAssemblyAsmPrinter::getOrCreateWasmSymbol(StringRef Name) {
 212   auto *WasmSym = cast<MCSymbolWasm>(GetExternalSymbolSymbol(Name));
 213
 214   // May be called multiple times, so early out.
 215   if (WasmSym->getType().hasValue())
 216     return WasmSym;
 217
 218   const WebAssemblySubtarget &Subtarget = getSubtarget();
 219
 220   // Except for certain known symbols, all symbols used by CodeGen are
 221   // functions. It's OK to hardcode knowledge of specific symbols here; this
 222   // method is precisely there for fetching the signatures of known
 223   // Clang-provided symbols.
 224   if (Name == "__stack_pointer" || Name == "__tls_base" ||
 225       Name == "__memory_base" || Name == "__table_base" ||
 226       Name == "__tls_size" || Name == "__tls_align") {
 227     bool Mutable =
 228         Name == "__stack_pointer" || Name == "__tls_base";
 229     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
 230     WasmSym->setGlobalType(wasm::WasmGlobalType{
 231         uint8_t(Subtarget.hasAddr64() ? wasm::WASM_TYPE_I64
 232                                       : wasm::WASM_TYPE_I32),
 233         Mutable});
 234     return WasmSym;
 235   }
 236
 237   SmallVector<wasm::ValType, 4> Returns;
 238   SmallVector<wasm::ValType, 4> Params;
 239   if (Name == "__cpp_exception") {
 240     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_TAG);
 241     // We can't confirm its signature index for now because there can be
 242     // imported exceptions. Set it to be 0 for now.
 243     WasmSym->setTagType(
 244         {wasm::WASM_TAG_ATTRIBUTE_EXCEPTION, /* SigIndex */ 0});
 245     // We may have multiple C++ compilation units to be linked together, each of
 246     // which defines the exception symbol. To resolve them, we declare them as
 247     // weak.
 248     WasmSym->setWeak(true);
 249     WasmSym->setExternal(true);
 250
 251     // All C++ exceptions are assumed to have a single i32 (for wasm32) or i64
 252     // (for wasm64) param type and void return type. The reaon is, all C++
 253     // exception values are pointers, and to share the type section with
 254     // functions, exceptions are assumed to have void return type.
 255     Params.push_back(Subtarget.hasAddr64() ? wasm::ValType::I64
 256                                            : wasm::ValType::I32);
 257   } else { // Function symbols
 258     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
 259     getLibcallSignature(Subtarget, Name, Returns, Params);
 260   }
 261   auto Signature = std::make_unique<wasm::WasmSignature>(std::move(Returns),
 262                                                          std::move(Params));
 263   WasmSym->setSignature(Signature.get());
 264   addSignature(std::move(Signature));
 265
 266   return WasmSym;
 267 }
 268
 269 void WebAssemblyAsmPrinter::emitExternalDecls(const Module &M) {
 270   if (signaturesEmitted)
 271     return;
 272   signaturesEmitted = true;
 273
 274   // Normally symbols for globals get discovered as the MI gets lowered,
 275   // but we need to know about them ahead of time.
 276   MachineModuleInfoWasm &MMIW = MMI->getObjFileInfo<MachineModuleInfoWasm>();
 277   for (const auto &Name : MMIW.MachineSymbolsUsed) {
 278     getOrCreateWasmSymbol(Name.getKey());
 279   }
 280
 281   for (auto &It : OutContext.getSymbols()) {
 282     // Emit .globaltype, .tagtype, or .tabletype declarations.
 283     auto Sym = cast<MCSymbolWasm>(It.getValue());
 284     if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_GLOBAL) {
 285       // .globaltype already handled by emitGlobalVariable for defined
 286       // variables; here we make sure the types of external wasm globals get
 287       // written to the file.
 288       if (Sym->isUndefined())
 289         getTargetStreamer()->emitGlobalType(Sym);
 290     } else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_TAG)
 291       getTargetStreamer()->emitTagType(Sym);
 292     else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_TABLE)
 293       getTargetStreamer()->emitTableType(Sym);
 294   }
 295
 296   DenseSet<MCSymbol *> InvokeSymbols;
 297   for (const auto &F : M) {
 298     if (F.isIntrinsic())
 299       continue;
 300
 301     // Emit function type info for all undefined functions
 302     if (F.isDeclarationForLinker()) {
 303       SmallVector<MVT, 4> Results;
 304       SmallVector<MVT, 4> Params;
 305       computeSignatureVTs(F.getFunctionType(), &F, F, TM, Params, Results);
 306       // At this point these MCSymbols may or may not have been created already
 307       // and thus also contain a signature, but we need to get the signature
 308       // anyway here in case it is an invoke that has not yet been created. We
 309       // will discard it later if it turns out not to be necessary.
 310       auto Signature = signatureFromMVTs(Results, Params);
 311       bool InvokeDetected = false;
 312       auto *Sym =
 313           getMCSymbolForFunction(&F, WasmEnableEmException || WasmEnableEmSjLj,
 314                                  Signature.get(), InvokeDetected);
 315
 316       // Multiple functions can be mapped to the same invoke symbol. For
 317       // example, two IR functions '__invoke_void_i8*' and '__invoke_void_i32'
 318       // are both mapped to '__invoke_vi'. We keep them in a set once we emit an
 319       // Emscripten EH symbol so we don't emit the same symbol twice.
 320       if (InvokeDetected && !InvokeSymbols.insert(Sym).second)
 321         continue;
 322
 323       Sym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
 324       if (!Sym->getSignature()) {
 325         Sym->setSignature(Signature.get());
 326         addSignature(std::move(Signature));
 327       } else {
 328         // This symbol has already been created and had a signature. Discard it.
 329         Signature.reset();
 330       }
 331
 332       getTargetStreamer()->emitFunctionType(Sym);
 333
 334       if (F.hasFnAttribute("wasm-import-module")) {
 335         StringRef Name =
 336             F.getFnAttribute("wasm-import-module").getValueAsString();
 337         Sym->setImportModule(storeName(Name));
 338         getTargetStreamer()->emitImportModule(Sym, Name);
 339       }
 340       if (F.hasFnAttribute("wasm-import-name")) {
 341         // If this is a converted Emscripten EH/SjLj symbol, we shouldn't use
 342         // the original function name but the converted symbol name.
 343         StringRef Name =
 344             InvokeDetected
 345                 ? Sym->getName()
 346                 : F.getFnAttribute("wasm-import-name").getValueAsString();
 347         Sym->setImportName(storeName(Name));
 348         getTargetStreamer()->emitImportName(Sym, Name);
 349       }
 350     }
 351
 352     if (F.hasFnAttribute("wasm-export-name")) {
 353       auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
 354       StringRef Name = F.getFnAttribute("wasm-export-name").getValueAsString();
 355       Sym->setExportName(storeName(Name));
 356       getTargetStreamer()->emitExportName(Sym, Name);
 357     }
 358   }
 359 }
 360
 361 void WebAssemblyAsmPrinter::emitEndOfAsmFile(Module &M) {
 362   emitExternalDecls(M);
 363
 364   // When a function's address is taken, a TABLE_INDEX relocation is emitted
 365   // against the function symbol at the use site.  However the relocation
 366   // doesn't explicitly refer to the table.  In the future we may want to
 367   // define a new kind of reloc against both the function and the table, so
 368   // that the linker can see that the function symbol keeps the table alive,
 369   // but for now manually mark the table as live.
 370   for (const auto &F : M) {
 371     if (!F.isIntrinsic() && F.hasAddressTaken()) {
 372       MCSymbolWasm *FunctionTable =
 373           WebAssembly::getOrCreateFunctionTableSymbol(OutContext, Subtarget);
 374       OutStreamer->emitSymbolAttribute(FunctionTable, MCSA_NoDeadStrip);
 375       break;
 376     }
 377   }
 378
 379   for (const auto &G : M.globals()) {
 380     if (!G.hasInitializer() && G.hasExternalLinkage() &&
 381         !WebAssembly::isWasmVarAddressSpace(G.getAddressSpace()) &&
 382         G.getValueType()->isSized()) {
 383       uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
 384       OutStreamer->emitELFSize(getSymbol(&G),
 385                                MCConstantExpr::create(Size, OutContext));
 386     }
 387   }
 388
 389   if (const NamedMDNode *Named = M.getNamedMetadata("wasm.custom_sections")) {
 390     for (const Metadata *MD : Named->operands()) {
 391       const auto *Tuple = dyn_cast<MDTuple>(MD);
 392       if (!Tuple || Tuple->getNumOperands() != 2)
 393         continue;
 394       const MDString *Name = dyn_cast<MDString>(Tuple->getOperand(0));
 395       const MDString *Contents = dyn_cast<MDString>(Tuple->getOperand(1));
 396       if (!Name || !Contents)
 397         continue;
 398
 399       OutStreamer->PushSection();
 400       std::string SectionName = (".custom_section." + Name->getString()).str();
 401       MCSectionWasm *MySection =
 402           OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
 403       OutStreamer->SwitchSection(MySection);
 404       OutStreamer->emitBytes(Contents->getString());
 405       OutStreamer->PopSection();
 406     }
 407   }
 408
 409   EmitProducerInfo(M);
 410   EmitTargetFeatures(M);
 411 }
 412
 413 void WebAssemblyAsmPrinter::EmitProducerInfo(Module &M) {
 414   llvm::SmallVector<std::pair<std::string, std::string>, 4> Languages;
 415   if (const NamedMDNode *Debug = M.getNamedMetadata("llvm.dbg.cu")) {
 416     llvm::SmallSet<StringRef, 4> SeenLanguages;
 417     for (size_t I = 0, E = Debug->getNumOperands(); I < E; ++I) {
 418       const auto *CU = cast<DICompileUnit>(Debug->getOperand(I));
 419       StringRef Language = dwarf::LanguageString(CU->getSourceLanguage());
 420       Language.consume_front("DW_LANG_");
 421       if (SeenLanguages.insert(Language).second)
 422         Languages.emplace_back(Language.str(), "");
 423     }
 424   }
 425
 426   llvm::SmallVector<std::pair<std::string, std::string>, 4> Tools;
 427   if (const NamedMDNode *Ident = M.getNamedMetadata("llvm.ident")) {
 428     llvm::SmallSet<StringRef, 4> SeenTools;
 429     for (size_t I = 0, E = Ident->getNumOperands(); I < E; ++I) {
 430       const auto *S = cast<MDString>(Ident->getOperand(I)->getOperand(0));
 431       std::pair<StringRef, StringRef> Field = S->getString().split("version");
 432       StringRef Name = Field.first.trim();
 433       StringRef Version = Field.second.trim();
 434       if (SeenTools.insert(Name).second)
 435         Tools.emplace_back(Name.str(), Version.str());
 436     }
 437   }
 438
 439   int FieldCount = int(!Languages.empty()) + int(!Tools.empty());
 440   if (FieldCount != 0) {
 441     MCSectionWasm *Producers = OutContext.getWasmSection(
 442         ".custom_section.producers", SectionKind::getMetadata());
 443     OutStreamer->PushSection();
 444     OutStreamer->SwitchSection(Producers);
 445     OutStreamer->emitULEB128IntValue(FieldCount);
 446     for (auto &Producers : {std::make_pair("language", &Languages),
 447             std::make_pair("processed-by", &Tools)}) {
 448       if (Producers.second->empty())
 449         continue;
 450       OutStreamer->emitULEB128IntValue(strlen(Producers.first));
 451       OutStreamer->emitBytes(Producers.first);
 452       OutStreamer->emitULEB128IntValue(Producers.second->size());
 453       for (auto &Producer : *Producers.second) {
 454         OutStreamer->emitULEB128IntValue(Producer.first.size());
 455         OutStreamer->emitBytes(Producer.first);
 456         OutStreamer->emitULEB128IntValue(Producer.second.size());
 457         OutStreamer->emitBytes(Producer.second);
 458       }
 459     }
 460     OutStreamer->PopSection();
 461   }
 462 }
 463
 464 void WebAssemblyAsmPrinter::EmitTargetFeatures(Module &M) {
 465   struct FeatureEntry {
 466     uint8_t Prefix;
 467     std::string Name;
 468   };
 469
 470   // Read target features and linkage policies from module metadata
 471   SmallVector<FeatureEntry, 4> EmittedFeatures;
 472   auto EmitFeature = [&](std::string Feature) {
 473     std::string MDKey = (StringRef("wasm-feature-") + Feature).str();
 474     Metadata *Policy = M.getModuleFlag(MDKey);
 475     if (Policy == nullptr)
 476       return;
 477
 478     FeatureEntry Entry;
 479     Entry.Prefix = 0;
 480     Entry.Name = Feature;
 481
 482     if (auto *MD = cast<ConstantAsMetadata>(Policy))
 483       if (auto *I = cast<ConstantInt>(MD->getValue()))
 484         Entry.Prefix = I->getZExtValue();
 485
 486     // Silently ignore invalid metadata
 487     if (Entry.Prefix != wasm::WASM_FEATURE_PREFIX_USED &&
 488         Entry.Prefix != wasm::WASM_FEATURE_PREFIX_REQUIRED &&
 489         Entry.Prefix != wasm::WASM_FEATURE_PREFIX_DISALLOWED)
 490       return;
 491
 492     EmittedFeatures.push_back(Entry);
 493   };
 494
 495   for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
 496     EmitFeature(KV.Key);
 497   }
 498   // This pseudo-feature tells the linker whether shared memory would be safe
 499   EmitFeature("shared-mem");
 500
 501   if (EmittedFeatures.size() == 0)
 502     return;
 503
 504   // Emit features and linkage policies into the "target_features" section
 505   MCSectionWasm *FeaturesSection = OutContext.getWasmSection(
 506       ".custom_section.target_features", SectionKind::getMetadata());
 507   OutStreamer->PushSection();
 508   OutStreamer->SwitchSection(FeaturesSection);
 509
 510   OutStreamer->emitULEB128IntValue(EmittedFeatures.size());
 511   for (auto &F : EmittedFeatures) {
 512     OutStreamer->emitIntValue(F.Prefix, 1);
 513     OutStreamer->emitULEB128IntValue(F.Name.size());
 514     OutStreamer->emitBytes(F.Name);
 515   }
 516
 517   OutStreamer->PopSection();
 518 }
 519
 520 void WebAssemblyAsmPrinter::emitConstantPool() {
 521   assert(MF->getConstantPool()->getConstants().empty() &&
 522          "WebAssembly disables constant pools");
 523 }
 524
 525 void WebAssemblyAsmPrinter::emitJumpTableInfo() {
 526   // Nothing to do; jump tables are incorporated into the instruction stream.
 527 }
 528
 529 void WebAssemblyAsmPrinter::emitLinkage(const GlobalValue *GV, MCSymbol *Sym)
 530   const {
 531   AsmPrinter::emitLinkage(GV, Sym);
 532   // This gets called before the function label and type are emitted.
 533   // We use it to emit signatures of external functions.
 534   // FIXME casts!
 535   const_cast<WebAssemblyAsmPrinter *>(this)
 536     ->emitExternalDecls(*MMI->getModule());
 537 }
 538
 539
 540 void WebAssemblyAsmPrinter::emitFunctionBodyStart() {
 541   const Function &F = MF->getFunction();
 542   SmallVector<MVT, 1> ResultVTs;
 543   SmallVector<MVT, 4> ParamVTs;
 544   computeSignatureVTs(F.getFunctionType(), &F, F, TM, ParamVTs, ResultVTs);
 545
 546   auto Signature = signatureFromMVTs(ResultVTs, ParamVTs);
 547   auto *WasmSym = cast<MCSymbolWasm>(CurrentFnSym);
 548   WasmSym->setSignature(Signature.get());
 549   addSignature(std::move(Signature));
 550   WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
 551
 552   getTargetStreamer()->emitFunctionType(WasmSym);
 553
 554   // Emit the function index.
 555   if (MDNode *Idx = F.getMetadata("wasm.index")) {
 556     assert(Idx->getNumOperands() == 1);
 557
 558     getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
 559         cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
 560   }
 561
 562   SmallVector<wasm::ValType, 16> Locals;
 563   valTypesFromMVTs(MFI->getLocals(), Locals);
 564   getTargetStreamer()->emitLocal(Locals);
 565
 566   AsmPrinter::emitFunctionBodyStart();
 567 }
 568
 569 void WebAssemblyAsmPrinter::emitInstruction(const MachineInstr *MI) {
 570   LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
 571
 572   switch (MI->getOpcode()) {
 573   case WebAssembly::ARGUMENT_i32:
 574   case WebAssembly::ARGUMENT_i32_S:
 575   case WebAssembly::ARGUMENT_i64:
 576   case WebAssembly::ARGUMENT_i64_S:
 577   case WebAssembly::ARGUMENT_f32:
 578   case WebAssembly::ARGUMENT_f32_S:
 579   case WebAssembly::ARGUMENT_f64:
 580   case WebAssembly::ARGUMENT_f64_S:
 581   case WebAssembly::ARGUMENT_v16i8:
 582   case WebAssembly::ARGUMENT_v16i8_S:
 583   case WebAssembly::ARGUMENT_v8i16:
 584   case WebAssembly::ARGUMENT_v8i16_S:
 585   case WebAssembly::ARGUMENT_v4i32:
 586   case WebAssembly::ARGUMENT_v4i32_S:
 587   case WebAssembly::ARGUMENT_v2i64:
 588   case WebAssembly::ARGUMENT_v2i64_S:
 589   case WebAssembly::ARGUMENT_v4f32:
 590   case WebAssembly::ARGUMENT_v4f32_S:
 591   case WebAssembly::ARGUMENT_v2f64:
 592   case WebAssembly::ARGUMENT_v2f64_S:
 593     // These represent values which are live into the function entry, so there's
 594     // no instruction to emit.
 595     break;
 596   case WebAssembly::FALLTHROUGH_RETURN: {
 597     // These instructions represent the implicit return at the end of a
 598     // function body.
 599     if (isVerbose()) {
 600       OutStreamer->AddComment("fallthrough-return");
 601       OutStreamer->AddBlankLine();
 602     }
 603     break;
 604   }
 605   case WebAssembly::COMPILER_FENCE:
 606     // This is a compiler barrier that prevents instruction reordering during
 607     // backend compilation, and should not be emitted.
 608     break;
 609   default: {
 610     WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
 611     MCInst TmpInst;
 612     MCInstLowering.lower(MI, TmpInst);
 613     EmitToStreamer(*OutStreamer, TmpInst);
 614     break;
 615   }
 616   }
 617 }
 618
 619 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
 620                                             unsigned OpNo,
 621                                             const char *ExtraCode,
 622                                             raw_ostream &OS) {
 623   // First try the generic code, which knows about modifiers like 'c' and 'n'.
 624   if (!AsmPrinter::PrintAsmOperand(MI, OpNo, ExtraCode, OS))
 625     return false;
 626
 627   if (!ExtraCode) {
 628     const MachineOperand &MO = MI->getOperand(OpNo);
 629     switch (MO.getType()) {
 630     case MachineOperand::MO_Immediate:
 631       OS << MO.getImm();
 632       return false;
 633     case MachineOperand::MO_Register:
 634       // FIXME: only opcode that still contains registers, as required by
 635       // MachineInstr::getDebugVariable().
 636       assert(MI->getOpcode() == WebAssembly::INLINEASM);
 637       OS << regToString(MO);
 638       return false;
 639     case MachineOperand::MO_GlobalAddress:
 640       PrintSymbolOperand(MO, OS);
 641       return false;
 642     case MachineOperand::MO_ExternalSymbol:
 643       GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
 644       printOffset(MO.getOffset(), OS);
 645       return false;
 646     case MachineOperand::MO_MachineBasicBlock:
 647       MO.getMBB()->getSymbol()->print(OS, MAI);
 648       return false;
 649     default:
 650       break;
 651     }
 652   }
 653
 654   return true;
 655 }
 656
 657 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
 658                                                   unsigned OpNo,
 659                                                   const char *ExtraCode,
 660                                                   raw_ostream &OS) {
 661   // The current approach to inline asm is that "r" constraints are expressed
 662   // as local indices, rather than values on the operand stack. This simplifies
 663   // using "r" as it eliminates the need to push and pop the values in a
 664   // particular order, however it also makes it impossible to have an "m"
 665   // constraint. So we don't support it.
 666
 667   return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, ExtraCode, OS);
 668 }
 669
 670 // Force static initialization.
 671 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeWebAssemblyAsmPrinter() {
 672   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
 673   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
 674 }