1 //===-- WebAssemblyAsmPrinter.cpp - WebAssembly LLVM assembly writer ------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 ///
10 /// \file
11 /// This file contains a printer that converts from our internal
12 /// representation of machine-dependent LLVM code to the WebAssembly assembly
13 /// language.
14 ///
15 //===----------------------------------------------------------------------===//
16 
17 #include "WebAssemblyAsmPrinter.h"
18 #include "InstPrinter/WebAssemblyInstPrinter.h"
19 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
20 #include "MCTargetDesc/WebAssemblyTargetStreamer.h"
21 #include "WebAssembly.h"
22 #include "WebAssemblyMCInstLower.h"
23 #include "WebAssemblyMachineFunctionInfo.h"
24 #include "WebAssemblyRegisterInfo.h"
25 #include "llvm/ADT/StringExtras.h"
26 #include "llvm/CodeGen/Analysis.h"
27 #include "llvm/CodeGen/AsmPrinter.h"
28 #include "llvm/CodeGen/MachineConstantPool.h"
29 #include "llvm/CodeGen/MachineInstr.h"
30 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
31 #include "llvm/IR/DataLayout.h"
32 #include "llvm/IR/GlobalVariable.h"
33 #include "llvm/MC/MCContext.h"
34 #include "llvm/MC/MCSectionWasm.h"
35 #include "llvm/MC/MCStreamer.h"
36 #include "llvm/MC/MCSymbol.h"
37 #include "llvm/MC/MCSymbolWasm.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/TargetRegistry.h"
40 #include "llvm/Support/raw_ostream.h"
41 using namespace llvm;
42 
43 #define DEBUG_TYPE "asm-printer"
44 
45 //===----------------------------------------------------------------------===//
46 // Helpers.
47 //===----------------------------------------------------------------------===//
48 
49 MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
50   const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
51   const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
52   for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
53                 MVT::v4i32, MVT::v2i64, MVT::v4f32, MVT::v2f64})
54     if (TRI->isTypeLegalForClass(*TRC, T))
55       return T;
56   LLVM_DEBUG(errs() << "Unknown type for register number: " << RegNo);
57   llvm_unreachable("Unknown register type");
58   return MVT::Other;
59 }
60 
61 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
62   unsigned RegNo = MO.getReg();
63   assert(TargetRegisterInfo::isVirtualRegister(RegNo) &&
64          "Unlowered physical register encountered during assembly printing");
65   assert(!MFI->isVRegStackified(RegNo));
66   unsigned WAReg = MFI->getWAReg(RegNo);
67   assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
68   return '$' + utostr(WAReg);
69 }
70 
71 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
72   MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
73   return static_cast<WebAssemblyTargetStreamer *>(TS);
74 }
75 
76 //===----------------------------------------------------------------------===//
77 // WebAssemblyAsmPrinter Implementation.
78 //===----------------------------------------------------------------------===//
79 
80 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
81   for (const auto &F : M) {
82     // Emit function type info for all undefined functions
83     if (F.isDeclarationForLinker() && !F.isIntrinsic()) {
84       SmallVector<MVT, 4> Results;
85       SmallVector<MVT, 4> Params;
86       ComputeSignatureVTs(F, TM, Params, Results);
87       MCSymbol *Sym = getSymbol(&F);
88       getTargetStreamer()->emitIndirectFunctionType(Sym, Params, Results);
89 
90       if (TM.getTargetTriple().isOSBinFormatWasm() &&
91           F.hasFnAttribute("wasm-import-module")) {
92         MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Sym);
93         StringRef Name = F.getFnAttribute("wasm-import-module")
94                              .getValueAsString();
95         getTargetStreamer()->emitImportModule(WasmSym, Name);
96       }
97     }
98   }
99   for (const auto &G : M.globals()) {
100     if (!G.hasInitializer() && G.hasExternalLinkage()) {
101       if (G.getValueType()->isSized()) {
102         uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
103         OutStreamer->emitELFSize(getSymbol(&G),
104                                  MCConstantExpr::create(Size, OutContext));
105       }
106     }
107   }
108 
109   if (const NamedMDNode *Named = M.getNamedMetadata("wasm.custom_sections")) {
110     for (const Metadata *MD : Named->operands()) {
111       const MDTuple *Tuple = dyn_cast<MDTuple>(MD);
112       if (!Tuple || Tuple->getNumOperands() != 2)
113         continue;
114       const MDString *Name = dyn_cast<MDString>(Tuple->getOperand(0));
115       const MDString *Contents = dyn_cast<MDString>(Tuple->getOperand(1));
116       if (!Name || !Contents)
117         continue;
118 
119       OutStreamer->PushSection();
120       std::string SectionName = (".custom_section." + Name->getString()).str();
121       MCSectionWasm *mySection =
122           OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
123       OutStreamer->SwitchSection(mySection);
124       OutStreamer->EmitBytes(Contents->getString());
125       OutStreamer->PopSection();
126     }
127   }
128 }
129 
130 void WebAssemblyAsmPrinter::EmitConstantPool() {
131   assert(MF->getConstantPool()->getConstants().empty() &&
132          "WebAssembly disables constant pools");
133 }
134 
135 void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
136   // Nothing to do; jump tables are incorporated into the instruction stream.
137 }
138 
139 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
140   getTargetStreamer()->emitParam(CurrentFnSym, MFI->getParams());
141 
142   SmallVector<MVT, 4> ResultVTs;
143   const Function &F = MF->getFunction();
144 
145   // Emit the function index.
146   if (MDNode *Idx = F.getMetadata("wasm.index")) {
147     assert(Idx->getNumOperands() == 1);
148 
149     getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
150         cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
151   }
152 
153   ComputeLegalValueVTs(F, TM, F.getReturnType(), ResultVTs);
154 
155   // If the return type needs to be legalized it will get converted into
156   // passing a pointer.
157   if (ResultVTs.size() == 1)
158     getTargetStreamer()->emitResult(CurrentFnSym, ResultVTs);
159   else
160     getTargetStreamer()->emitResult(CurrentFnSym, ArrayRef<MVT>());
161 
162   getTargetStreamer()->emitLocal(MFI->getLocals());
163 
164   AsmPrinter::EmitFunctionBodyStart();
165 }
166 
167 void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
168   LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
169 
170   switch (MI->getOpcode()) {
171   case WebAssembly::ARGUMENT_I32:
172   case WebAssembly::ARGUMENT_I64:
173   case WebAssembly::ARGUMENT_F32:
174   case WebAssembly::ARGUMENT_F64:
175   case WebAssembly::ARGUMENT_v16i8:
176   case WebAssembly::ARGUMENT_v8i16:
177   case WebAssembly::ARGUMENT_v4i32:
178   case WebAssembly::ARGUMENT_v2i64:
179   case WebAssembly::ARGUMENT_v4f32:
180   case WebAssembly::ARGUMENT_v2f64:
181     // These represent values which are live into the function entry, so there's
182     // no instruction to emit.
183     break;
184   case WebAssembly::FALLTHROUGH_RETURN_I32:
185   case WebAssembly::FALLTHROUGH_RETURN_I64:
186   case WebAssembly::FALLTHROUGH_RETURN_F32:
187   case WebAssembly::FALLTHROUGH_RETURN_F64:
188   case WebAssembly::FALLTHROUGH_RETURN_v16i8:
189   case WebAssembly::FALLTHROUGH_RETURN_v8i16:
190   case WebAssembly::FALLTHROUGH_RETURN_v4i32:
191   case WebAssembly::FALLTHROUGH_RETURN_v2i64:
192   case WebAssembly::FALLTHROUGH_RETURN_v4f32:
193   case WebAssembly::FALLTHROUGH_RETURN_v2f64: {
194     // These instructions represent the implicit return at the end of a
195     // function body. The operand is always a pop.
196     assert(MFI->isVRegStackified(MI->getOperand(0).getReg()));
197 
198     if (isVerbose()) {
199       OutStreamer->AddComment("fallthrough-return: $pop" +
200                               Twine(MFI->getWARegStackId(
201                                   MFI->getWAReg(MI->getOperand(0).getReg()))));
202       OutStreamer->AddBlankLine();
203     }
204     break;
205   }
206   case WebAssembly::FALLTHROUGH_RETURN_VOID:
207     // This instruction represents the implicit return at the end of a
208     // function body with no return value.
209     if (isVerbose()) {
210       OutStreamer->AddComment("fallthrough-return");
211       OutStreamer->AddBlankLine();
212     }
213     break;
214   default: {
215     WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
216     MCInst TmpInst;
217     MCInstLowering.Lower(MI, TmpInst);
218     EmitToStreamer(*OutStreamer, TmpInst);
219     break;
220   }
221   }
222 }
223 
224 const MCExpr *WebAssemblyAsmPrinter::lowerConstant(const Constant *CV) {
225   if (const GlobalValue *GV = dyn_cast<GlobalValue>(CV))
226     if (GV->getValueType()->isFunctionTy()) {
227       return MCSymbolRefExpr::create(
228           getSymbol(GV), MCSymbolRefExpr::VK_WebAssembly_FUNCTION, OutContext);
229     }
230   return AsmPrinter::lowerConstant(CV);
231 }
232 
233 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
234                                             unsigned OpNo, unsigned AsmVariant,
235                                             const char *ExtraCode,
236                                             raw_ostream &OS) {
237   if (AsmVariant != 0)
238     report_fatal_error("There are no defined alternate asm variants");
239 
240   // First try the generic code, which knows about modifiers like 'c' and 'n'.
241   if (!AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, OS))
242     return false;
243 
244   if (!ExtraCode) {
245     const MachineOperand &MO = MI->getOperand(OpNo);
246     switch (MO.getType()) {
247     case MachineOperand::MO_Immediate:
248       OS << MO.getImm();
249       return false;
250     case MachineOperand::MO_Register:
251       OS << regToString(MO);
252       return false;
253     case MachineOperand::MO_GlobalAddress:
254       getSymbol(MO.getGlobal())->print(OS, MAI);
255       printOffset(MO.getOffset(), OS);
256       return false;
257     case MachineOperand::MO_ExternalSymbol:
258       GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
259       printOffset(MO.getOffset(), OS);
260       return false;
261     case MachineOperand::MO_MachineBasicBlock:
262       MO.getMBB()->getSymbol()->print(OS, MAI);
263       return false;
264     default:
265       break;
266     }
267   }
268 
269   return true;
270 }
271 
272 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
273                                                   unsigned OpNo,
274                                                   unsigned AsmVariant,
275                                                   const char *ExtraCode,
276                                                   raw_ostream &OS) {
277   if (AsmVariant != 0)
278     report_fatal_error("There are no defined alternate asm variants");
279 
280   // The current approach to inline asm is that "r" constraints are expressed
281   // as local indices, rather than values on the operand stack. This simplifies
282   // using "r" as it eliminates the need to push and pop the values in a
283   // particular order, however it also makes it impossible to have an "m"
284   // constraint. So we don't support it.
285 
286   return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, AsmVariant, ExtraCode, OS);
287 }
288 
289 // Force static initialization.
290 extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
291   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
292   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
293 }
294