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 
47 using namespace llvm;
48 
49 #define DEBUG_TYPE "asm-printer"
50 
51 extern cl::opt<bool> WasmKeepRegisters;
52 
53 //===----------------------------------------------------------------------===//
54 // Helpers.
55 //===----------------------------------------------------------------------===//
56 
57 MVT 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 
69 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
70   Register RegNo = MO.getReg();
71   assert(Register::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 
79 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
80   MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
81   return static_cast<WebAssemblyTargetStreamer *>(TS);
82 }
83 
84 //===----------------------------------------------------------------------===//
85 // WebAssemblyAsmPrinter Implementation.
86 //===----------------------------------------------------------------------===//
87 
88 void 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     if (F.isIntrinsic())
100       continue;
101 
102     // Emit function type info for all undefined functions
103     if (F.isDeclarationForLinker()) {
104       SmallVector<MVT, 4> Results;
105       SmallVector<MVT, 4> Params;
106       computeSignatureVTs(F.getFunctionType(), &F, F, TM, Params, Results);
107       auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
108       Sym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
109       if (!Sym->getSignature()) {
110         auto Signature = signatureFromMVTs(Results, Params);
111         Sym->setSignature(Signature.get());
112         addSignature(std::move(Signature));
113       }
114       // FIXME: this was originally intended for post-linking and was only used
115       // for imports that were only called indirectly (i.e. s2wasm could not
116       // infer the type from a call). With object files it applies to all
117       // imports. so fix the names and the tests, or rethink how import
118       // delcarations work in asm files.
119       getTargetStreamer()->emitFunctionType(Sym);
120 
121       if (TM.getTargetTriple().isOSBinFormatWasm() &&
122           F.hasFnAttribute("wasm-import-module")) {
123         StringRef Name =
124             F.getFnAttribute("wasm-import-module").getValueAsString();
125         Sym->setImportModule(storeName(Name));
126         getTargetStreamer()->emitImportModule(Sym, Name);
127       }
128       if (TM.getTargetTriple().isOSBinFormatWasm() &&
129           F.hasFnAttribute("wasm-import-name")) {
130         StringRef Name =
131             F.getFnAttribute("wasm-import-name").getValueAsString();
132         Sym->setImportName(storeName(Name));
133         getTargetStreamer()->emitImportName(Sym, Name);
134       }
135     }
136 
137     if (F.hasFnAttribute("wasm-export-name")) {
138       auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
139       StringRef Name = F.getFnAttribute("wasm-export-name").getValueAsString();
140       Sym->setExportName(storeName(Name));
141       getTargetStreamer()->emitExportName(Sym, Name);
142     }
143   }
144 
145   for (const auto &G : M.globals()) {
146     if (!G.hasInitializer() && G.hasExternalLinkage()) {
147       if (G.getValueType()->isSized()) {
148         uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
149         OutStreamer->emitELFSize(getSymbol(&G),
150                                  MCConstantExpr::create(Size, OutContext));
151       }
152     }
153   }
154 
155   if (const NamedMDNode *Named = M.getNamedMetadata("wasm.custom_sections")) {
156     for (const Metadata *MD : Named->operands()) {
157       const auto *Tuple = dyn_cast<MDTuple>(MD);
158       if (!Tuple || Tuple->getNumOperands() != 2)
159         continue;
160       const MDString *Name = dyn_cast<MDString>(Tuple->getOperand(0));
161       const MDString *Contents = dyn_cast<MDString>(Tuple->getOperand(1));
162       if (!Name || !Contents)
163         continue;
164 
165       OutStreamer->PushSection();
166       std::string SectionName = (".custom_section." + Name->getString()).str();
167       MCSectionWasm *MySection =
168           OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
169       OutStreamer->SwitchSection(MySection);
170       OutStreamer->emitBytes(Contents->getString());
171       OutStreamer->PopSection();
172     }
173   }
174 
175   EmitProducerInfo(M);
176   EmitTargetFeatures(M);
177 }
178 
179 void WebAssemblyAsmPrinter::EmitProducerInfo(Module &M) {
180   llvm::SmallVector<std::pair<std::string, std::string>, 4> Languages;
181   if (const NamedMDNode *Debug = M.getNamedMetadata("llvm.dbg.cu")) {
182     llvm::SmallSet<StringRef, 4> SeenLanguages;
183     for (size_t I = 0, E = Debug->getNumOperands(); I < E; ++I) {
184       const auto *CU = cast<DICompileUnit>(Debug->getOperand(I));
185       StringRef Language = dwarf::LanguageString(CU->getSourceLanguage());
186       Language.consume_front("DW_LANG_");
187       if (SeenLanguages.insert(Language).second)
188         Languages.emplace_back(Language.str(), "");
189     }
190   }
191 
192   llvm::SmallVector<std::pair<std::string, std::string>, 4> Tools;
193   if (const NamedMDNode *Ident = M.getNamedMetadata("llvm.ident")) {
194     llvm::SmallSet<StringRef, 4> SeenTools;
195     for (size_t I = 0, E = Ident->getNumOperands(); I < E; ++I) {
196       const auto *S = cast<MDString>(Ident->getOperand(I)->getOperand(0));
197       std::pair<StringRef, StringRef> Field = S->getString().split("version");
198       StringRef Name = Field.first.trim();
199       StringRef Version = Field.second.trim();
200       if (SeenTools.insert(Name).second)
201         Tools.emplace_back(Name.str(), Version.str());
202     }
203   }
204 
205   int FieldCount = int(!Languages.empty()) + int(!Tools.empty());
206   if (FieldCount != 0) {
207     MCSectionWasm *Producers = OutContext.getWasmSection(
208         ".custom_section.producers", SectionKind::getMetadata());
209     OutStreamer->PushSection();
210     OutStreamer->SwitchSection(Producers);
211     OutStreamer->emitULEB128IntValue(FieldCount);
212     for (auto &Producers : {std::make_pair("language", &Languages),
213             std::make_pair("processed-by", &Tools)}) {
214       if (Producers.second->empty())
215         continue;
216       OutStreamer->emitULEB128IntValue(strlen(Producers.first));
217       OutStreamer->emitBytes(Producers.first);
218       OutStreamer->emitULEB128IntValue(Producers.second->size());
219       for (auto &Producer : *Producers.second) {
220         OutStreamer->emitULEB128IntValue(Producer.first.size());
221         OutStreamer->emitBytes(Producer.first);
222         OutStreamer->emitULEB128IntValue(Producer.second.size());
223         OutStreamer->emitBytes(Producer.second);
224       }
225     }
226     OutStreamer->PopSection();
227   }
228 }
229 
230 void WebAssemblyAsmPrinter::EmitTargetFeatures(Module &M) {
231   struct FeatureEntry {
232     uint8_t Prefix;
233     StringRef Name;
234   };
235 
236   // Read target features and linkage policies from module metadata
237   SmallVector<FeatureEntry, 4> EmittedFeatures;
238   for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
239     std::string MDKey = (StringRef("wasm-feature-") + KV.Key).str();
240     Metadata *Policy = M.getModuleFlag(MDKey);
241     if (Policy == nullptr)
242       continue;
243 
244     FeatureEntry Entry;
245     Entry.Prefix = 0;
246     Entry.Name = KV.Key;
247 
248     if (auto *MD = cast<ConstantAsMetadata>(Policy))
249       if (auto *I = cast<ConstantInt>(MD->getValue()))
250         Entry.Prefix = I->getZExtValue();
251 
252     // Silently ignore invalid metadata
253     if (Entry.Prefix != wasm::WASM_FEATURE_PREFIX_USED &&
254         Entry.Prefix != wasm::WASM_FEATURE_PREFIX_REQUIRED &&
255         Entry.Prefix != wasm::WASM_FEATURE_PREFIX_DISALLOWED)
256       continue;
257 
258     EmittedFeatures.push_back(Entry);
259   }
260 
261   if (EmittedFeatures.size() == 0)
262     return;
263 
264   // Emit features and linkage policies into the "target_features" section
265   MCSectionWasm *FeaturesSection = OutContext.getWasmSection(
266       ".custom_section.target_features", SectionKind::getMetadata());
267   OutStreamer->PushSection();
268   OutStreamer->SwitchSection(FeaturesSection);
269 
270   OutStreamer->emitULEB128IntValue(EmittedFeatures.size());
271   for (auto &F : EmittedFeatures) {
272     OutStreamer->emitIntValue(F.Prefix, 1);
273     OutStreamer->emitULEB128IntValue(F.Name.size());
274     OutStreamer->emitBytes(F.Name);
275   }
276 
277   OutStreamer->PopSection();
278 }
279 
280 void WebAssemblyAsmPrinter::emitConstantPool() {
281   assert(MF->getConstantPool()->getConstants().empty() &&
282          "WebAssembly disables constant pools");
283 }
284 
285 void WebAssemblyAsmPrinter::emitJumpTableInfo() {
286   // Nothing to do; jump tables are incorporated into the instruction stream.
287 }
288 
289 void WebAssemblyAsmPrinter::emitFunctionBodyStart() {
290   const Function &F = MF->getFunction();
291   SmallVector<MVT, 1> ResultVTs;
292   SmallVector<MVT, 4> ParamVTs;
293   computeSignatureVTs(F.getFunctionType(), &F, F, TM, ParamVTs, ResultVTs);
294 
295   auto Signature = signatureFromMVTs(ResultVTs, ParamVTs);
296   auto *WasmSym = cast<MCSymbolWasm>(CurrentFnSym);
297   WasmSym->setSignature(Signature.get());
298   addSignature(std::move(Signature));
299   WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
300 
301   // FIXME: clean up how params and results are emitted (use signatures)
302   getTargetStreamer()->emitFunctionType(WasmSym);
303 
304   // Emit the function index.
305   if (MDNode *Idx = F.getMetadata("wasm.index")) {
306     assert(Idx->getNumOperands() == 1);
307 
308     getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
309         cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
310   }
311 
312   SmallVector<wasm::ValType, 16> Locals;
313   valTypesFromMVTs(MFI->getLocals(), Locals);
314   getTargetStreamer()->emitLocal(Locals);
315 
316   AsmPrinter::emitFunctionBodyStart();
317 }
318 
319 void WebAssemblyAsmPrinter::emitInstruction(const MachineInstr *MI) {
320   LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
321 
322   switch (MI->getOpcode()) {
323   case WebAssembly::ARGUMENT_i32:
324   case WebAssembly::ARGUMENT_i32_S:
325   case WebAssembly::ARGUMENT_i64:
326   case WebAssembly::ARGUMENT_i64_S:
327   case WebAssembly::ARGUMENT_f32:
328   case WebAssembly::ARGUMENT_f32_S:
329   case WebAssembly::ARGUMENT_f64:
330   case WebAssembly::ARGUMENT_f64_S:
331   case WebAssembly::ARGUMENT_v16i8:
332   case WebAssembly::ARGUMENT_v16i8_S:
333   case WebAssembly::ARGUMENT_v8i16:
334   case WebAssembly::ARGUMENT_v8i16_S:
335   case WebAssembly::ARGUMENT_v4i32:
336   case WebAssembly::ARGUMENT_v4i32_S:
337   case WebAssembly::ARGUMENT_v2i64:
338   case WebAssembly::ARGUMENT_v2i64_S:
339   case WebAssembly::ARGUMENT_v4f32:
340   case WebAssembly::ARGUMENT_v4f32_S:
341   case WebAssembly::ARGUMENT_v2f64:
342   case WebAssembly::ARGUMENT_v2f64_S:
343     // These represent values which are live into the function entry, so there's
344     // no instruction to emit.
345     break;
346   case WebAssembly::FALLTHROUGH_RETURN: {
347     // These instructions represent the implicit return at the end of a
348     // function body.
349     if (isVerbose()) {
350       OutStreamer->AddComment("fallthrough-return");
351       OutStreamer->AddBlankLine();
352     }
353     break;
354   }
355   case WebAssembly::COMPILER_FENCE:
356     // This is a compiler barrier that prevents instruction reordering during
357     // backend compilation, and should not be emitted.
358     break;
359   case WebAssembly::EXTRACT_EXCEPTION_I32:
360   case WebAssembly::EXTRACT_EXCEPTION_I32_S:
361     // These are pseudo instructions that simulates popping values from stack.
362     // We print these only when we have -wasm-keep-registers on for assembly
363     // readability.
364     if (!WasmKeepRegisters)
365       break;
366     LLVM_FALLTHROUGH;
367   default: {
368     WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
369     MCInst TmpInst;
370     MCInstLowering.lower(MI, TmpInst);
371     EmitToStreamer(*OutStreamer, TmpInst);
372     break;
373   }
374   }
375 }
376 
377 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
378                                             unsigned OpNo,
379                                             const char *ExtraCode,
380                                             raw_ostream &OS) {
381   // First try the generic code, which knows about modifiers like 'c' and 'n'.
382   if (!AsmPrinter::PrintAsmOperand(MI, OpNo, ExtraCode, OS))
383     return false;
384 
385   if (!ExtraCode) {
386     const MachineOperand &MO = MI->getOperand(OpNo);
387     switch (MO.getType()) {
388     case MachineOperand::MO_Immediate:
389       OS << MO.getImm();
390       return false;
391     case MachineOperand::MO_Register:
392       // FIXME: only opcode that still contains registers, as required by
393       // MachineInstr::getDebugVariable().
394       assert(MI->getOpcode() == WebAssembly::INLINEASM);
395       OS << regToString(MO);
396       return false;
397     case MachineOperand::MO_GlobalAddress:
398       PrintSymbolOperand(MO, OS);
399       return false;
400     case MachineOperand::MO_ExternalSymbol:
401       GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
402       printOffset(MO.getOffset(), OS);
403       return false;
404     case MachineOperand::MO_MachineBasicBlock:
405       MO.getMBB()->getSymbol()->print(OS, MAI);
406       return false;
407     default:
408       break;
409     }
410   }
411 
412   return true;
413 }
414 
415 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
416                                                   unsigned OpNo,
417                                                   const char *ExtraCode,
418                                                   raw_ostream &OS) {
419   // The current approach to inline asm is that "r" constraints are expressed
420   // as local indices, rather than values on the operand stack. This simplifies
421   // using "r" as it eliminates the need to push and pop the values in a
422   // particular order, however it also makes it impossible to have an "m"
423   // constraint. So we don't support it.
424 
425   return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, ExtraCode, OS);
426 }
427 
428 // Force static initialization.
429 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeWebAssemblyAsmPrinter() {
430   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
431   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
432 }
433