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 /// \brief 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 "WebAssembly.h"
18 #include "WebAssemblyMachineFunctionInfo.h"
19 #include "WebAssemblyRegisterInfo.h"
20 #include "WebAssemblySubtarget.h"
21 #include "InstPrinter/WebAssemblyInstPrinter.h"
22 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
23 
24 #include "llvm/ADT/SmallString.h"
25 #include "llvm/CodeGen/AsmPrinter.h"
26 #include "llvm/CodeGen/MachineConstantPool.h"
27 #include "llvm/CodeGen/MachineInstr.h"
28 #include "llvm/IR/DataLayout.h"
29 #include "llvm/IR/DebugInfo.h"
30 #include "llvm/MC/MCStreamer.h"
31 #include "llvm/MC/MCSymbol.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/TargetRegistry.h"
34 #include "llvm/Support/raw_ostream.h"
35 
36 using namespace llvm;
37 
38 #define DEBUG_TYPE "asm-printer"
39 
40 namespace {
41 
42 class WebAssemblyAsmPrinter final : public AsmPrinter {
43   const WebAssemblyInstrInfo *TII;
44 
45 public:
46   WebAssemblyAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
47       : AsmPrinter(TM, std::move(Streamer)), TII(nullptr) {}
48 
49 private:
50   const char *getPassName() const override {
51     return "WebAssembly Assembly Printer";
52   }
53 
54   //===------------------------------------------------------------------===//
55   // MachineFunctionPass Implementation.
56   //===------------------------------------------------------------------===//
57 
58   void getAnalysisUsage(AnalysisUsage &AU) const override {
59     AsmPrinter::getAnalysisUsage(AU);
60   }
61 
62   bool runOnMachineFunction(MachineFunction &MF) override {
63     const auto &Subtarget = MF.getSubtarget<WebAssemblySubtarget>();
64     TII = Subtarget.getInstrInfo();
65     return AsmPrinter::runOnMachineFunction(MF);
66   }
67 
68   //===------------------------------------------------------------------===//
69   // AsmPrinter Implementation.
70   //===------------------------------------------------------------------===//
71 
72   void EmitGlobalVariable(const GlobalVariable *GV) override;
73 
74   void EmitJumpTableInfo() override;
75   void EmitConstantPool() override;
76   void EmitFunctionEntryLabel() override;
77   void EmitFunctionBodyStart() override;
78   void EmitFunctionBodyEnd() override;
79 
80   void EmitInstruction(const MachineInstr *MI) override;
81 
82   static std::string toString(const APFloat &APF);
83   const char *toString(Type *Ty) const;
84 };
85 
86 } // end anonymous namespace
87 
88 //===----------------------------------------------------------------------===//
89 // Helpers.
90 //===----------------------------------------------------------------------===//
91 
92 // Untyped, lower-case version of the opcode's name matching the names
93 // WebAssembly opcodes are expected to have. The tablegen names are uppercase
94 // and suffixed with their type (after an underscore).
95 static SmallString<32> OpcodeName(const WebAssemblyInstrInfo *TII,
96                                   const MachineInstr *MI) {
97   std::string N(StringRef(TII->getName(MI->getOpcode())).lower());
98   std::string::size_type End = N.rfind('_');
99   End = std::string::npos == End ? N.length() : End;
100   return SmallString<32>(&N[0], &N[End]);
101 }
102 
103 static std::string toSymbol(StringRef S) { return ("$" + S).str(); }
104 
105 std::string WebAssemblyAsmPrinter::toString(const APFloat &FP) {
106   static const size_t BufBytes = 128;
107   char buf[BufBytes];
108   if (FP.isNaN())
109     assert((FP.bitwiseIsEqual(APFloat::getQNaN(FP.getSemantics())) ||
110             FP.bitwiseIsEqual(
111                 APFloat::getQNaN(FP.getSemantics(), /*Negative=*/true))) &&
112            "convertToHexString handles neither SNaN nor NaN payloads");
113   // Use C99's hexadecimal floating-point representation.
114   auto Written = FP.convertToHexString(
115       buf, /*hexDigits=*/0, /*upperCase=*/false, APFloat::rmNearestTiesToEven);
116   (void)Written;
117   assert(Written != 0);
118   assert(Written < BufBytes);
119   return buf;
120 }
121 
122 const char *WebAssemblyAsmPrinter::toString(Type *Ty) const {
123   switch (Ty->getTypeID()) {
124   default:
125     break;
126   // Treat all pointers as the underlying integer into linear memory.
127   case Type::PointerTyID:
128     switch (getPointerSize()) {
129     case 4:
130       return "i32";
131     case 8:
132       return "i64";
133     default:
134       llvm_unreachable("unsupported pointer size");
135     }
136     break;
137   case Type::FloatTyID:
138     return "f32";
139   case Type::DoubleTyID:
140     return "f64";
141   case Type::IntegerTyID:
142     switch (Ty->getIntegerBitWidth()) {
143     case 8:
144       return "i8";
145     case 16:
146       return "i16";
147     case 32:
148       return "i32";
149     case 64:
150       return "i64";
151     default:
152       break;
153     }
154   }
155   DEBUG(dbgs() << "Invalid type "; Ty->print(dbgs()); dbgs() << '\n');
156   llvm_unreachable("invalid type");
157   return "<invalid>";
158 }
159 
160 //===----------------------------------------------------------------------===//
161 // WebAssemblyAsmPrinter Implementation.
162 //===----------------------------------------------------------------------===//
163 
164 void WebAssemblyAsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
165   SmallString<128> Str;
166   raw_svector_ostream OS(Str);
167   StringRef Name = GV->getName();
168   DEBUG(dbgs() << "Global " << Name << '\n');
169 
170   if (!GV->hasInitializer()) {
171     DEBUG(dbgs() << "  Skipping declaration.\n");
172     return;
173   }
174 
175   // Check to see if this is a special global used by LLVM.
176   static const char *Ignored[] = {"llvm.used", "llvm.metadata"};
177   for (const char *I : Ignored)
178     if (Name == I)
179       return;
180   // FIXME: Handle the following globals.
181   static const char *Unhandled[] = {"llvm.global_ctors", "llvm.global_dtors"};
182   for (const char *U : Unhandled)
183     if (Name == U)
184       report_fatal_error("Unhandled global");
185   if (Name.startswith("llvm."))
186     report_fatal_error("Unknown LLVM-internal global");
187 
188   if (GV->isThreadLocal())
189     report_fatal_error("TLS isn't yet supported by WebAssembly");
190 
191   const DataLayout &DL = getDataLayout();
192   const Constant *Init = GV->getInitializer();
193   if (isa<UndefValue>(Init))
194     Init = Constant::getNullValue(Init->getType());
195   unsigned Align = DL.getPrefTypeAlignment(Init->getType());
196 
197   switch (GV->getLinkage()) {
198   case GlobalValue::InternalLinkage:
199   case GlobalValue::PrivateLinkage:
200     break;
201   case GlobalValue::AppendingLinkage:
202   case GlobalValue::LinkOnceAnyLinkage:
203   case GlobalValue::LinkOnceODRLinkage:
204   case GlobalValue::WeakAnyLinkage:
205   case GlobalValue::WeakODRLinkage:
206   case GlobalValue::ExternalLinkage:
207   case GlobalValue::CommonLinkage:
208     report_fatal_error("Linkage types other than internal and private aren't "
209                        "supported by WebAssembly yet");
210   default:
211     llvm_unreachable("Unknown linkage type");
212     return;
213   }
214 
215   OS << "(global " << toSymbol(Name) << ' ' << toString(Init->getType()) << ' ';
216   if (const auto *C = dyn_cast<ConstantInt>(Init)) {
217     assert(C->getBitWidth() <= 64 && "Printing wider types unimplemented");
218     OS << C->getZExtValue();
219   } else if (const auto *C = dyn_cast<ConstantFP>(Init)) {
220     OS << toString(C->getValueAPF());
221   } else {
222     assert(false && "Only integer and floating-point constants are supported");
223   }
224   OS << ") ;; align " << Align;
225   OutStreamer->EmitRawText(OS.str());
226 }
227 
228 void WebAssemblyAsmPrinter::EmitConstantPool() {
229   assert(MF->getConstantPool()->getConstants().empty() &&
230          "WebAssembly disables constant pools");
231 }
232 
233 void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
234   // Nothing to do; jump tables are incorporated into the instruction stream.
235 }
236 
237 void WebAssemblyAsmPrinter::EmitFunctionEntryLabel() {
238   SmallString<128> Str;
239   raw_svector_ostream OS(Str);
240 
241   CurrentFnSym->redefineIfPossible();
242 
243   // The function label could have already been emitted if two symbols end up
244   // conflicting due to asm renaming.  Detect this and emit an error.
245   if (CurrentFnSym->isVariable())
246     report_fatal_error("'" + Twine(CurrentFnSym->getName()) +
247                        "' is a protected alias");
248   if (CurrentFnSym->isDefined())
249     report_fatal_error("'" + Twine(CurrentFnSym->getName()) +
250                        "' label emitted multiple times to assembly file");
251 
252   OS << "(func " << toSymbol(CurrentFnSym->getName());
253   OutStreamer->EmitRawText(OS.str());
254 }
255 
256 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
257   SmallString<128> Str;
258   raw_svector_ostream OS(Str);
259   const Function *F = MF->getFunction();
260   Type *Rt = F->getReturnType();
261   if (!Rt->isVoidTy() || !F->arg_empty()) {
262     for (const Argument &A : F->args())
263       OS << " (param " << toString(A.getType()) << ')';
264     if (!Rt->isVoidTy())
265       OS << " (result " << toString(Rt) << ')';
266     OutStreamer->EmitRawText(OS.str());
267   }
268 }
269 
270 void WebAssemblyAsmPrinter::EmitFunctionBodyEnd() {
271   SmallString<128> Str;
272   raw_svector_ostream OS(Str);
273   OS << ") ;; end func " << toSymbol(CurrentFnSym->getName());
274   OutStreamer->EmitRawText(OS.str());
275 }
276 
277 void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
278   DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
279   SmallString<128> Str;
280   raw_svector_ostream OS(Str);
281 
282   unsigned NumDefs = MI->getDesc().getNumDefs();
283   assert(NumDefs <= 1 &&
284          "Instructions with multiple result values not implemented");
285 
286   OS << '\t';
287 
288   if (NumDefs != 0) {
289     const MachineOperand &MO = MI->getOperand(0);
290     unsigned Reg = MO.getReg();
291     OS << "(setlocal @" << TargetRegisterInfo::virtReg2Index(Reg) << ' ';
292   }
293 
294   if (MI->getOpcode() == WebAssembly::COPY) {
295     OS << '@' << TargetRegisterInfo::virtReg2Index(MI->getOperand(1).getReg());
296   } else {
297     OS << '(' << OpcodeName(TII, MI);
298     for (const MachineOperand &MO : MI->uses())
299       switch (MO.getType()) {
300       default:
301         llvm_unreachable("unexpected machine operand type");
302       case MachineOperand::MO_Register: {
303         if (MO.isImplicit())
304           continue;
305         unsigned Reg = MO.getReg();
306         OS << " @" << TargetRegisterInfo::virtReg2Index(Reg);
307       } break;
308       case MachineOperand::MO_Immediate: {
309         OS << ' ' << MO.getImm();
310       } break;
311       case MachineOperand::MO_FPImmediate: {
312         OS << ' ' << toString(MO.getFPImm()->getValueAPF());
313       } break;
314       case MachineOperand::MO_GlobalAddress: {
315         OS << ' ' << toSymbol(MO.getGlobal()->getName());
316       } break;
317       case MachineOperand::MO_MachineBasicBlock: {
318         OS << ' ' << toSymbol(MO.getMBB()->getSymbol()->getName());
319       } break;
320       }
321     OS << ')';
322   }
323 
324   if (NumDefs != 0)
325     OS << ')';
326 
327   OutStreamer->EmitRawText(OS.str());
328 }
329 
330 // Force static initialization.
331 extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
332   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(TheWebAssemblyTarget32);
333   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(TheWebAssemblyTarget64);
334 }
335