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   bool hasAddr64;
44   const WebAssemblyInstrInfo *TII;
45 
46 public:
47   WebAssemblyAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
48       : AsmPrinter(TM, std::move(Streamer)), TII(nullptr) {}
49 
50 private:
51   const char *getPassName() const override {
52     return "WebAssembly Assembly Printer";
53   }
54 
55   //===------------------------------------------------------------------===//
56   // MachineFunctionPass Implementation.
57   //===------------------------------------------------------------------===//
58 
59   void getAnalysisUsage(AnalysisUsage &AU) const override {
60     AsmPrinter::getAnalysisUsage(AU);
61   }
62 
63   bool runOnMachineFunction(MachineFunction &MF) override {
64     const auto &Subtarget = MF.getSubtarget<WebAssemblySubtarget>();
65     hasAddr64 = Subtarget.hasAddr64();
66     TII = Subtarget.getInstrInfo();
67     return AsmPrinter::runOnMachineFunction(MF);
68   }
69 
70   //===------------------------------------------------------------------===//
71   // AsmPrinter Implementation.
72   //===------------------------------------------------------------------===//
73 
74   void EmitGlobalVariable(const GlobalVariable *GV) override;
75 
76   void EmitConstantPool() override;
77   void EmitFunctionEntryLabel() override;
78   void EmitFunctionBodyStart() override;
79   void EmitFunctionBodyEnd() override;
80 
81   void EmitInstruction(const MachineInstr *MI) override;
82 };
83 
84 } // end anonymous namespace
85 
86 //===----------------------------------------------------------------------===//
87 // Helpers.
88 //===----------------------------------------------------------------------===//
89 
90 // Untyped, lower-case version of the opcode's name matching the names
91 // WebAssembly opcodes are expected to have. The tablegen names are uppercase
92 // and suffixed with their type (after an underscore).
93 static SmallString<32> OpcodeName(const WebAssemblyInstrInfo *TII,
94                                   const MachineInstr *MI) {
95   std::string N(StringRef(TII->getName(MI->getOpcode())).lower());
96   std::string::size_type End = N.rfind('_');
97   End = std::string::npos == End ? N.length() : End;
98   return SmallString<32>(&N[0], &N[End]);
99 }
100 
101 static std::string toSymbol(StringRef S) { return ("$" + S).str(); }
102 
103 static std::string toString(const APFloat &FP) {
104   static const size_t BufBytes = 128;
105   char buf[BufBytes];
106   if (FP.isNaN())
107     assert((FP.bitwiseIsEqual(APFloat::getQNaN(FP.getSemantics())) ||
108             FP.bitwiseIsEqual(
109                 APFloat::getQNaN(FP.getSemantics(), /*Negative=*/true))) &&
110            "convertToHexString handles neither SNaN nor NaN payloads");
111   // Use C99's hexadecimal floating-point representation.
112   auto Written = FP.convertToHexString(
113       buf, /*hexDigits=*/0, /*upperCase=*/false, APFloat::rmNearestTiesToEven);
114   (void)Written;
115   assert(Written != 0);
116   assert(Written < BufBytes);
117   return buf;
118 }
119 
120 static const char *toString(const Type *Ty, bool hasAddr64) {
121   switch (Ty->getTypeID()) {
122   default: break;
123   // Treat all pointers as the underlying integer into linear memory.
124   case Type::PointerTyID: return hasAddr64 ? "i64" : "i32";
125   case Type::FloatTyID:  return "f32";
126   case Type::DoubleTyID: return "f64";
127   case Type::IntegerTyID:
128     switch (Ty->getIntegerBitWidth()) {
129     case 8: return "i8";
130     case 16: return "i16";
131     case 32: return "i32";
132     case 64: return "i64";
133     default: break;
134     }
135   }
136   DEBUG(dbgs() << "Invalid type "; Ty->print(dbgs()); dbgs() << '\n');
137   llvm_unreachable("invalid type");
138   return "<invalid>";
139 }
140 
141 
142 //===----------------------------------------------------------------------===//
143 // WebAssemblyAsmPrinter Implementation.
144 //===----------------------------------------------------------------------===//
145 
146 void WebAssemblyAsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
147   SmallString<128> Str;
148   raw_svector_ostream OS(Str);
149   StringRef Name = GV->getName();
150   DEBUG(dbgs() << "Global " << Name << '\n');
151 
152   if (!GV->hasInitializer()) {
153     DEBUG(dbgs() << "  Skipping declaration.\n");
154     return;
155   }
156 
157   // Check to see if this is a special global used by LLVM.
158   static const char *Ignored[] = {"llvm.used", "llvm.metadata"};
159   for (const char *I : Ignored)
160     if (Name == I)
161       return;
162   // FIXME: Handle the following globals.
163   static const char *Unhandled[] = {"llvm.global_ctors", "llvm.global_dtors"};
164   for (const char *U : Unhandled)
165     if (Name == U)
166       report_fatal_error("Unhandled global");
167   if (Name.startswith("llvm."))
168     report_fatal_error("Unknown LLVM-internal global");
169 
170   if (GV->isThreadLocal())
171     report_fatal_error("TLS isn't yet supported by WebAssembly");
172 
173   const DataLayout &DL = getDataLayout();
174   const Constant *Init = GV->getInitializer();
175   if (isa<UndefValue>(Init))
176     Init = Constant::getNullValue(Init->getType());
177   unsigned Align = DL.getPrefTypeAlignment(Init->getType());
178 
179   switch (GV->getLinkage()) {
180   case GlobalValue::InternalLinkage:
181   case GlobalValue::PrivateLinkage:
182     break;
183   case GlobalValue::AppendingLinkage:
184   case GlobalValue::LinkOnceAnyLinkage:
185   case GlobalValue::LinkOnceODRLinkage:
186   case GlobalValue::WeakAnyLinkage:
187   case GlobalValue::WeakODRLinkage:
188   case GlobalValue::ExternalLinkage:
189   case GlobalValue::CommonLinkage:
190     report_fatal_error("Linkage types other than internal and private aren't "
191                        "supported by WebAssembly yet");
192   default:
193     llvm_unreachable("Unknown linkage type");
194     return;
195   }
196 
197   OS << "(global " << toSymbol(Name) << ' '
198      << toString(Init->getType(), hasAddr64) << ' ';
199   if (const auto *C = dyn_cast<ConstantInt>(Init)) {
200     assert(C->getBitWidth() <= 64 && "Printing wider types unimplemented");
201     OS << C->getZExtValue();
202   } else if (const auto *C = dyn_cast<ConstantFP>(Init)) {
203     OS << toString(C->getValueAPF());
204   } else {
205     assert(false && "Only integer and floating-point constants are supported");
206   }
207   OS << ") ;; align " << Align;
208   OutStreamer->EmitRawText(OS.str());
209 }
210 
211 void WebAssemblyAsmPrinter::EmitConstantPool() {
212   assert(MF->getConstantPool()->getConstants().empty() &&
213          "WebAssembly disables constant pools");
214 }
215 
216 void WebAssemblyAsmPrinter::EmitFunctionEntryLabel() {
217   SmallString<128> Str;
218   raw_svector_ostream OS(Str);
219 
220   CurrentFnSym->redefineIfPossible();
221 
222   // The function label could have already been emitted if two symbols end up
223   // conflicting due to asm renaming.  Detect this and emit an error.
224   if (CurrentFnSym->isVariable())
225     report_fatal_error("'" + Twine(CurrentFnSym->getName()) +
226                        "' is a protected alias");
227   if (CurrentFnSym->isDefined())
228     report_fatal_error("'" + Twine(CurrentFnSym->getName()) +
229                        "' label emitted multiple times to assembly file");
230 
231   OS << "(func " << toSymbol(CurrentFnSym->getName());
232   OutStreamer->EmitRawText(OS.str());
233 }
234 
235 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
236   SmallString<128> Str;
237   raw_svector_ostream OS(Str);
238   const Function *F = MF->getFunction();
239   const Type *Rt = F->getReturnType();
240   if (!Rt->isVoidTy() || !F->arg_empty()) {
241     for (const Argument &A : F->args())
242       OS << " (param " << toString(A.getType(), hasAddr64) << ')';
243     if (!Rt->isVoidTy())
244       OS << " (result " << toString(Rt, hasAddr64) << ')';
245     OutStreamer->EmitRawText(OS.str());
246   }
247 }
248 
249 void WebAssemblyAsmPrinter::EmitFunctionBodyEnd() {
250   SmallString<128> Str;
251   raw_svector_ostream OS(Str);
252   OS << ") ;; end func " << toSymbol(CurrentFnSym->getName());
253   OutStreamer->EmitRawText(OS.str());
254 }
255 
256 void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
257   DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
258   SmallString<128> Str;
259   raw_svector_ostream OS(Str);
260 
261   unsigned NumDefs = MI->getDesc().getNumDefs();
262   assert(NumDefs <= 1 &&
263          "Instructions with multiple result values not implemented");
264 
265   OS << '\t';
266 
267   if (NumDefs != 0) {
268     const MachineOperand &MO = MI->getOperand(0);
269     unsigned Reg = MO.getReg();
270     OS << "(setlocal @" << TargetRegisterInfo::virtReg2Index(Reg) << ' ';
271   }
272 
273   if (MI->getOpcode() == WebAssembly::COPY) {
274     OS << '@' << TargetRegisterInfo::virtReg2Index(MI->getOperand(1).getReg());
275   } else {
276     OS << '(' << OpcodeName(TII, MI);
277     for (const MachineOperand &MO : MI->uses())
278       switch (MO.getType()) {
279       default:
280         llvm_unreachable("unexpected machine operand type");
281       case MachineOperand::MO_Register: {
282         if (MO.isImplicit())
283           continue;
284         unsigned Reg = MO.getReg();
285         OS << " @" << TargetRegisterInfo::virtReg2Index(Reg);
286       } break;
287       case MachineOperand::MO_Immediate: {
288         OS << ' ' << MO.getImm();
289       } break;
290       case MachineOperand::MO_FPImmediate: {
291         OS << ' ' << toString(MO.getFPImm()->getValueAPF());
292       } break;
293       case MachineOperand::MO_GlobalAddress: {
294         OS << ' ' << toSymbol(MO.getGlobal()->getName());
295       } break;
296       }
297     OS << ')';
298   }
299 
300   if (NumDefs != 0)
301     OS << ')';
302 
303   OutStreamer->EmitRawText(OS.str());
304 }
305 
306 // Force static initialization.
307 extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
308   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(TheWebAssemblyTarget32);
309   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(TheWebAssemblyTarget64);
310 }
311