WebAssemblyAsmPrinter.cpp revision 353358 
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/WebAssemblyInstPrinter.h"
18#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
19#include "MCTargetDesc/WebAssemblyTargetStreamer.h"
20#include "TargetInfo/WebAssemblyTargetInfo.h"
21#include "WebAssembly.h"
22#include "WebAssemblyMCInstLower.h"
23#include "WebAssemblyMachineFunctionInfo.h"
24#include "WebAssemblyRegisterInfo.h"
25#include "WebAssemblyTargetMachine.h"
26#include "llvm/ADT/SmallSet.h"
27#include "llvm/ADT/StringExtras.h"
28#include "llvm/BinaryFormat/Wasm.h"
29#include "llvm/CodeGen/Analysis.h"
30#include "llvm/CodeGen/AsmPrinter.h"
31#include "llvm/CodeGen/MachineConstantPool.h"
32#include "llvm/CodeGen/MachineInstr.h"
33#include "llvm/CodeGen/MachineModuleInfoImpls.h"
34#include "llvm/IR/DataLayout.h"
35#include "llvm/IR/DebugInfoMetadata.h"
36#include "llvm/IR/GlobalVariable.h"
37#include "llvm/IR/Metadata.h"
38#include "llvm/MC/MCContext.h"
39#include "llvm/MC/MCSectionWasm.h"
40#include "llvm/MC/MCStreamer.h"
41#include "llvm/MC/MCSymbol.h"
42#include "llvm/MC/MCSymbolWasm.h"
43#include "llvm/Support/Debug.h"
44#include "llvm/Support/TargetRegistry.h"
45#include "llvm/Support/raw_ostream.h"
46
47using namespace llvm;
48
49#define DEBUG_TYPE "asm-printer"
50
51extern cl::opt<bool> WasmKeepRegisters;
52
53//===----------------------------------------------------------------------===//
54// Helpers.
55//===----------------------------------------------------------------------===//
56
57MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
58  const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
59  const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
60  for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
61                MVT::v4i32, MVT::v2i64, MVT::v4f32, MVT::v2f64})
62    if (TRI->isTypeLegalForClass(*TRC, T))
63      return T;
64  LLVM_DEBUG(errs() << "Unknown type for register number: " << RegNo);
65  llvm_unreachable("Unknown register type");
66  return MVT::Other;
67}
68
69std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
70  unsigned RegNo = MO.getReg();
71  assert(TargetRegisterInfo::isVirtualRegister(RegNo) &&
72         "Unlowered physical register encountered during assembly printing");
73  assert(!MFI->isVRegStackified(RegNo));
74  unsigned WAReg = MFI->getWAReg(RegNo);
75  assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
76  return '$' + utostr(WAReg);
77}
78
79WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
80  MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
81  return static_cast<WebAssemblyTargetStreamer *>(TS);
82}
83
84//===----------------------------------------------------------------------===//
85// WebAssemblyAsmPrinter Implementation.
86//===----------------------------------------------------------------------===//
87
88void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
89  for (auto &It : OutContext.getSymbols()) {
90    // Emit a .globaltype and .eventtype declaration.
91    auto Sym = cast<MCSymbolWasm>(It.getValue());
92    if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_GLOBAL)
93      getTargetStreamer()->emitGlobalType(Sym);
94    else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_EVENT)
95      getTargetStreamer()->emitEventType(Sym);
96  }
97
98  for (const auto &F : M) {
99    // Emit function type info for all undefined functions
100    if (F.isDeclarationForLinker() && !F.isIntrinsic()) {
101      SmallVector<MVT, 4> Results;
102      SmallVector<MVT, 4> Params;
103      computeSignatureVTs(F.getFunctionType(), F, TM, Params, Results);
104      auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
105      Sym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
106      if (!Sym->getSignature()) {
107        auto Signature = signatureFromMVTs(Results, Params);
108        Sym->setSignature(Signature.get());
109        addSignature(std::move(Signature));
110      }
111      // FIXME: this was originally intended for post-linking and was only used
112      // for imports that were only called indirectly (i.e. s2wasm could not
113      // infer the type from a call). With object files it applies to all
114      // imports. so fix the names and the tests, or rethink how import
115      // delcarations work in asm files.
116      getTargetStreamer()->emitFunctionType(Sym);
117
118      if (TM.getTargetTriple().isOSBinFormatWasm() &&
119          F.hasFnAttribute("wasm-import-module")) {
120        StringRef Name =
121            F.getFnAttribute("wasm-import-module").getValueAsString();
122        Sym->setImportModule(Name);
123        getTargetStreamer()->emitImportModule(Sym, Name);
124      }
125      if (TM.getTargetTriple().isOSBinFormatWasm() &&
126          F.hasFnAttribute("wasm-import-name")) {
127        StringRef Name =
128            F.getFnAttribute("wasm-import-name").getValueAsString();
129        Sym->setImportName(Name);
130        getTargetStreamer()->emitImportName(Sym, Name);
131      }
132    }
133  }
134
135  for (const auto &G : M.globals()) {
136    if (!G.hasInitializer() && G.hasExternalLinkage()) {
137      if (G.getValueType()->isSized()) {
138        uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
139        OutStreamer->emitELFSize(getSymbol(&G),
140                                 MCConstantExpr::create(Size, OutContext));
141      }
142    }
143  }
144
145  if (const NamedMDNode *Named = M.getNamedMetadata("wasm.custom_sections")) {
146    for (const Metadata *MD : Named->operands()) {
147      const auto *Tuple = dyn_cast<MDTuple>(MD);
148      if (!Tuple || Tuple->getNumOperands() != 2)
149        continue;
150      const MDString *Name = dyn_cast<MDString>(Tuple->getOperand(0));
151      const MDString *Contents = dyn_cast<MDString>(Tuple->getOperand(1));
152      if (!Name || !Contents)
153        continue;
154
155      OutStreamer->PushSection();
156      std::string SectionName = (".custom_section." + Name->getString()).str();
157      MCSectionWasm *MySection =
158          OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
159      OutStreamer->SwitchSection(MySection);
160      OutStreamer->EmitBytes(Contents->getString());
161      OutStreamer->PopSection();
162    }
163  }
164
165  EmitProducerInfo(M);
166  EmitTargetFeatures(M);
167}
168
169void WebAssemblyAsmPrinter::EmitProducerInfo(Module &M) {
170  llvm::SmallVector<std::pair<std::string, std::string>, 4> Languages;
171  if (const NamedMDNode *Debug = M.getNamedMetadata("llvm.dbg.cu")) {
172    llvm::SmallSet<StringRef, 4> SeenLanguages;
173    for (size_t I = 0, E = Debug->getNumOperands(); I < E; ++I) {
174      const auto *CU = cast<DICompileUnit>(Debug->getOperand(I));
175      StringRef Language = dwarf::LanguageString(CU->getSourceLanguage());
176      Language.consume_front("DW_LANG_");
177      if (SeenLanguages.insert(Language).second)
178        Languages.emplace_back(Language.str(), "");
179    }
180  }
181
182  llvm::SmallVector<std::pair<std::string, std::string>, 4> Tools;
183  if (const NamedMDNode *Ident = M.getNamedMetadata("llvm.ident")) {
184    llvm::SmallSet<StringRef, 4> SeenTools;
185    for (size_t I = 0, E = Ident->getNumOperands(); I < E; ++I) {
186      const auto *S = cast<MDString>(Ident->getOperand(I)->getOperand(0));
187      std::pair<StringRef, StringRef> Field = S->getString().split("version");
188      StringRef Name = Field.first.trim();
189      StringRef Version = Field.second.trim();
190      if (SeenTools.insert(Name).second)
191        Tools.emplace_back(Name.str(), Version.str());
192    }
193  }
194
195  int FieldCount = int(!Languages.empty()) + int(!Tools.empty());
196  if (FieldCount != 0) {
197    MCSectionWasm *Producers = OutContext.getWasmSection(
198        ".custom_section.producers", SectionKind::getMetadata());
199    OutStreamer->PushSection();
200    OutStreamer->SwitchSection(Producers);
201    OutStreamer->EmitULEB128IntValue(FieldCount);
202    for (auto &Producers : {std::make_pair("language", &Languages),
203            std::make_pair("processed-by", &Tools)}) {
204      if (Producers.second->empty())
205        continue;
206      OutStreamer->EmitULEB128IntValue(strlen(Producers.first));
207      OutStreamer->EmitBytes(Producers.first);
208      OutStreamer->EmitULEB128IntValue(Producers.second->size());
209      for (auto &Producer : *Producers.second) {
210        OutStreamer->EmitULEB128IntValue(Producer.first.size());
211        OutStreamer->EmitBytes(Producer.first);
212        OutStreamer->EmitULEB128IntValue(Producer.second.size());
213        OutStreamer->EmitBytes(Producer.second);
214      }
215    }
216    OutStreamer->PopSection();
217  }
218}
219
220void WebAssemblyAsmPrinter::EmitTargetFeatures(Module &M) {
221  struct FeatureEntry {
222    uint8_t Prefix;
223    StringRef Name;
224  };
225
226  // Read target features and linkage policies from module metadata
227  SmallVector<FeatureEntry, 4> EmittedFeatures;
228  for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
229    std::string MDKey = (StringRef("wasm-feature-") + KV.Key).str();
230    Metadata *Policy = M.getModuleFlag(MDKey);
231    if (Policy == nullptr)
232      continue;
233
234    FeatureEntry Entry;
235    Entry.Prefix = 0;
236    Entry.Name = KV.Key;
237
238    if (auto *MD = cast<ConstantAsMetadata>(Policy))
239      if (auto *I = cast<ConstantInt>(MD->getValue()))
240        Entry.Prefix = I->getZExtValue();
241
242    // Silently ignore invalid metadata
243    if (Entry.Prefix != wasm::WASM_FEATURE_PREFIX_USED &&
244        Entry.Prefix != wasm::WASM_FEATURE_PREFIX_REQUIRED &&
245        Entry.Prefix != wasm::WASM_FEATURE_PREFIX_DISALLOWED)
246      continue;
247
248    EmittedFeatures.push_back(Entry);
249  }
250
251  if (EmittedFeatures.size() == 0)
252    return;
253
254  // Emit features and linkage policies into the "target_features" section
255  MCSectionWasm *FeaturesSection = OutContext.getWasmSection(
256      ".custom_section.target_features", SectionKind::getMetadata());
257  OutStreamer->PushSection();
258  OutStreamer->SwitchSection(FeaturesSection);
259
260  OutStreamer->EmitULEB128IntValue(EmittedFeatures.size());
261  for (auto &F : EmittedFeatures) {
262    OutStreamer->EmitIntValue(F.Prefix, 1);
263    OutStreamer->EmitULEB128IntValue(F.Name.size());
264    OutStreamer->EmitBytes(F.Name);
265  }
266
267  OutStreamer->PopSection();
268}
269
270void WebAssemblyAsmPrinter::EmitConstantPool() {
271  assert(MF->getConstantPool()->getConstants().empty() &&
272         "WebAssembly disables constant pools");
273}
274
275void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
276  // Nothing to do; jump tables are incorporated into the instruction stream.
277}
278
279void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
280  const Function &F = MF->getFunction();
281  SmallVector<MVT, 1> ResultVTs;
282  SmallVector<MVT, 4> ParamVTs;
283  computeSignatureVTs(F.getFunctionType(), F, TM, ParamVTs, ResultVTs);
284  auto Signature = signatureFromMVTs(ResultVTs, ParamVTs);
285  auto *WasmSym = cast<MCSymbolWasm>(CurrentFnSym);
286  WasmSym->setSignature(Signature.get());
287  addSignature(std::move(Signature));
288  WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
289
290  // FIXME: clean up how params and results are emitted (use signatures)
291  getTargetStreamer()->emitFunctionType(WasmSym);
292
293  // Emit the function index.
294  if (MDNode *Idx = F.getMetadata("wasm.index")) {
295    assert(Idx->getNumOperands() == 1);
296
297    getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
298        cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
299  }
300
301  SmallVector<wasm::ValType, 16> Locals;
302  valTypesFromMVTs(MFI->getLocals(), Locals);
303  getTargetStreamer()->emitLocal(Locals);
304
305  AsmPrinter::EmitFunctionBodyStart();
306}
307
308void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
309  LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
310
311  switch (MI->getOpcode()) {
312  case WebAssembly::ARGUMENT_i32:
313  case WebAssembly::ARGUMENT_i32_S:
314  case WebAssembly::ARGUMENT_i64:
315  case WebAssembly::ARGUMENT_i64_S:
316  case WebAssembly::ARGUMENT_f32:
317  case WebAssembly::ARGUMENT_f32_S:
318  case WebAssembly::ARGUMENT_f64:
319  case WebAssembly::ARGUMENT_f64_S:
320  case WebAssembly::ARGUMENT_v16i8:
321  case WebAssembly::ARGUMENT_v16i8_S:
322  case WebAssembly::ARGUMENT_v8i16:
323  case WebAssembly::ARGUMENT_v8i16_S:
324  case WebAssembly::ARGUMENT_v4i32:
325  case WebAssembly::ARGUMENT_v4i32_S:
326  case WebAssembly::ARGUMENT_v2i64:
327  case WebAssembly::ARGUMENT_v2i64_S:
328  case WebAssembly::ARGUMENT_v4f32:
329  case WebAssembly::ARGUMENT_v4f32_S:
330  case WebAssembly::ARGUMENT_v2f64:
331  case WebAssembly::ARGUMENT_v2f64_S:
332    // These represent values which are live into the function entry, so there's
333    // no instruction to emit.
334    break;
335  case WebAssembly::FALLTHROUGH_RETURN_I32:
336  case WebAssembly::FALLTHROUGH_RETURN_I32_S:
337  case WebAssembly::FALLTHROUGH_RETURN_I64:
338  case WebAssembly::FALLTHROUGH_RETURN_I64_S:
339  case WebAssembly::FALLTHROUGH_RETURN_F32:
340  case WebAssembly::FALLTHROUGH_RETURN_F32_S:
341  case WebAssembly::FALLTHROUGH_RETURN_F64:
342  case WebAssembly::FALLTHROUGH_RETURN_F64_S:
343  case WebAssembly::FALLTHROUGH_RETURN_v16i8:
344  case WebAssembly::FALLTHROUGH_RETURN_v16i8_S:
345  case WebAssembly::FALLTHROUGH_RETURN_v8i16:
346  case WebAssembly::FALLTHROUGH_RETURN_v8i16_S:
347  case WebAssembly::FALLTHROUGH_RETURN_v4i32:
348  case WebAssembly::FALLTHROUGH_RETURN_v4i32_S:
349  case WebAssembly::FALLTHROUGH_RETURN_v2i64:
350  case WebAssembly::FALLTHROUGH_RETURN_v2i64_S:
351  case WebAssembly::FALLTHROUGH_RETURN_v4f32:
352  case WebAssembly::FALLTHROUGH_RETURN_v4f32_S:
353  case WebAssembly::FALLTHROUGH_RETURN_v2f64:
354  case WebAssembly::FALLTHROUGH_RETURN_v2f64_S: {
355    // These instructions represent the implicit return at the end of a
356    // function body. Always pops one value off the stack.
357    if (isVerbose()) {
358      OutStreamer->AddComment("fallthrough-return-value");
359      OutStreamer->AddBlankLine();
360    }
361    break;
362  }
363  case WebAssembly::FALLTHROUGH_RETURN_VOID:
364  case WebAssembly::FALLTHROUGH_RETURN_VOID_S:
365    // This instruction represents the implicit return at the end of a
366    // function body with no return value.
367    if (isVerbose()) {
368      OutStreamer->AddComment("fallthrough-return-void");
369      OutStreamer->AddBlankLine();
370    }
371    break;
372  case WebAssembly::COMPILER_FENCE:
373    // This is a compiler barrier that prevents instruction reordering during
374    // backend compilation, and should not be emitted.
375    break;
376  case WebAssembly::EXTRACT_EXCEPTION_I32:
377  case WebAssembly::EXTRACT_EXCEPTION_I32_S:
378    // These are pseudo instructions that simulates popping values from stack.
379    // We print these only when we have -wasm-keep-registers on for assembly
380    // readability.
381    if (!WasmKeepRegisters)
382      break;
383    LLVM_FALLTHROUGH;
384  default: {
385    WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
386    MCInst TmpInst;
387    MCInstLowering.lower(MI, TmpInst);
388    EmitToStreamer(*OutStreamer, TmpInst);
389    break;
390  }
391  }
392}
393
394bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
395                                            unsigned OpNo,
396                                            const char *ExtraCode,
397                                            raw_ostream &OS) {
398  // First try the generic code, which knows about modifiers like 'c' and 'n'.
399  if (!AsmPrinter::PrintAsmOperand(MI, OpNo, ExtraCode, OS))
400    return false;
401
402  if (!ExtraCode) {
403    const MachineOperand &MO = MI->getOperand(OpNo);
404    switch (MO.getType()) {
405    case MachineOperand::MO_Immediate:
406      OS << MO.getImm();
407      return false;
408    case MachineOperand::MO_Register:
409      // FIXME: only opcode that still contains registers, as required by
410      // MachineInstr::getDebugVariable().
411      assert(MI->getOpcode() == WebAssembly::INLINEASM);
412      OS << regToString(MO);
413      return false;
414    case MachineOperand::MO_GlobalAddress:
415      PrintSymbolOperand(MO, OS);
416      return false;
417    case MachineOperand::MO_ExternalSymbol:
418      GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
419      printOffset(MO.getOffset(), OS);
420      return false;
421    case MachineOperand::MO_MachineBasicBlock:
422      MO.getMBB()->getSymbol()->print(OS, MAI);
423      return false;
424    default:
425      break;
426    }
427  }
428
429  return true;
430}
431
432bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
433                                                  unsigned OpNo,
434                                                  const char *ExtraCode,
435                                                  raw_ostream &OS) {
436  // The current approach to inline asm is that "r" constraints are expressed
437  // as local indices, rather than values on the operand stack. This simplifies
438  // using "r" as it eliminates the need to push and pop the values in a
439  // particular order, however it also makes it impossible to have an "m"
440  // constraint. So we don't support it.
441
442  return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, ExtraCode, OS);
443}
444
445// Force static initialization.
446extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
447  RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
448  RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
449}
450