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 "InstPrinter/WebAssemblyInstPrinter.h"
18 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
19 #include "MCTargetDesc/WebAssemblyTargetStreamer.h"
20 #include "WebAssembly.h"
21 #include "WebAssemblyMCInstLower.h"
22 #include "WebAssemblyMachineFunctionInfo.h"
23 #include "WebAssemblyRegisterInfo.h"
24 #include "WebAssemblySubtarget.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/IR/DataLayout.h"
31 #include "llvm/MC/MCContext.h"
32 #include "llvm/MC/MCStreamer.h"
33 #include "llvm/MC/MCSymbol.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/TargetRegistry.h"
36 #include "llvm/Support/raw_ostream.h"
37 using namespace llvm;
38 
39 #define DEBUG_TYPE "asm-printer"
40 
41 namespace {
42 
43 class WebAssemblyAsmPrinter final : public AsmPrinter {
44   const MachineRegisterInfo *MRI;
45   WebAssemblyFunctionInfo *MFI;
46 
47 public:
48   WebAssemblyAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
49       : AsmPrinter(TM, std::move(Streamer)), MRI(nullptr), MFI(nullptr) {}
50 
51 private:
52   StringRef getPassName() const override {
53     return "WebAssembly Assembly Printer";
54   }
55 
56   //===------------------------------------------------------------------===//
57   // MachineFunctionPass Implementation.
58   //===------------------------------------------------------------------===//
59 
60   bool runOnMachineFunction(MachineFunction &MF) override {
61     MRI = &MF.getRegInfo();
62     MFI = MF.getInfo<WebAssemblyFunctionInfo>();
63     return AsmPrinter::runOnMachineFunction(MF);
64   }
65 
66   //===------------------------------------------------------------------===//
67   // AsmPrinter Implementation.
68   //===------------------------------------------------------------------===//
69 
70   void EmitEndOfAsmFile(Module &M) override;
71   void EmitJumpTableInfo() override;
72   void EmitConstantPool() override;
73   void EmitFunctionBodyStart() override;
74   void EmitFunctionBodyEnd() override;
75   void EmitInstruction(const MachineInstr *MI) override;
76   const MCExpr *lowerConstant(const Constant *CV) override;
77   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
78                        unsigned AsmVariant, const char *ExtraCode,
79                        raw_ostream &OS) override;
80   bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
81                              unsigned AsmVariant, const char *ExtraCode,
82                              raw_ostream &OS) override;
83 
84   MVT getRegType(unsigned RegNo) const;
85   std::string regToString(const MachineOperand &MO);
86   WebAssemblyTargetStreamer *getTargetStreamer();
87 };
88 
89 } // end anonymous namespace
90 
91 //===----------------------------------------------------------------------===//
92 // Helpers.
93 //===----------------------------------------------------------------------===//
94 
95 MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
96   const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
97   for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
98                 MVT::v4i32, MVT::v4f32})
99     if (TRC->hasType(T))
100       return T;
101   DEBUG(errs() << "Unknown type for register number: " << RegNo);
102   llvm_unreachable("Unknown register type");
103   return MVT::Other;
104 }
105 
106 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
107   unsigned RegNo = MO.getReg();
108   assert(TargetRegisterInfo::isVirtualRegister(RegNo) &&
109          "Unlowered physical register encountered during assembly printing");
110   assert(!MFI->isVRegStackified(RegNo));
111   unsigned WAReg = MFI->getWAReg(RegNo);
112   assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
113   return '$' + utostr(WAReg);
114 }
115 
116 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
117   MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
118   return static_cast<WebAssemblyTargetStreamer *>(TS);
119 }
120 
121 //===----------------------------------------------------------------------===//
122 // WebAssemblyAsmPrinter Implementation.
123 //===----------------------------------------------------------------------===//
124 
125 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
126   for (const auto &F : M) {
127     // Emit function type info for all undefined functions
128     if (F.isDeclarationForLinker() && !F.isIntrinsic()) {
129       SmallVector<MVT, 4> Results;
130       SmallVector<MVT, 4> Params;
131       ComputeSignatureVTs(F, TM, Params, Results);
132       getTargetStreamer()->emitIndirectFunctionType(F.getName(), Params,
133                                                     Results);
134     }
135   }
136 }
137 
138 void WebAssemblyAsmPrinter::EmitConstantPool() {
139   assert(MF->getConstantPool()->getConstants().empty() &&
140          "WebAssembly disables constant pools");
141 }
142 
143 void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
144   // Nothing to do; jump tables are incorporated into the instruction stream.
145 }
146 
147 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
148   if (!MFI->getParams().empty())
149     getTargetStreamer()->emitParam(MFI->getParams());
150 
151   SmallVector<MVT, 4> ResultVTs;
152   const Function &F(*MF->getFunction());
153 
154   // Emit the function index.
155   if (MDNode *Idx = F.getMetadata("wasm.index")) {
156     assert(Idx->getNumOperands() == 1);
157 
158     getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
159         cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
160   }
161 
162   ComputeLegalValueVTs(F, TM, F.getReturnType(), ResultVTs);
163 
164   // If the return type needs to be legalized it will get converted into
165   // passing a pointer.
166   if (ResultVTs.size() == 1)
167     getTargetStreamer()->emitResult(ResultVTs);
168 
169   // FIXME: When ExplicitLocals is enabled by default, we won't need
170   // to define the locals here (and MFI can go back to being pointer-to-const).
171   for (unsigned Idx = 0, IdxE = MRI->getNumVirtRegs(); Idx != IdxE; ++Idx) {
172     unsigned VReg = TargetRegisterInfo::index2VirtReg(Idx);
173     unsigned WAReg = MFI->getWAReg(VReg);
174     // Don't declare unused registers.
175     if (WAReg == WebAssemblyFunctionInfo::UnusedReg)
176       continue;
177     // Don't redeclare parameters.
178     if (WAReg < MFI->getParams().size())
179       continue;
180     // Don't declare stackified registers.
181     if (int(WAReg) < 0)
182       continue;
183     MFI->addLocal(getRegType(VReg));
184   }
185 
186   getTargetStreamer()->emitLocal(MFI->getLocals());
187 
188   AsmPrinter::EmitFunctionBodyStart();
189 }
190 
191 void WebAssemblyAsmPrinter::EmitFunctionBodyEnd() {
192   getTargetStreamer()->emitEndFunc();
193 }
194 
195 void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
196   DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
197 
198   switch (MI->getOpcode()) {
199   case WebAssembly::ARGUMENT_I32:
200   case WebAssembly::ARGUMENT_I64:
201   case WebAssembly::ARGUMENT_F32:
202   case WebAssembly::ARGUMENT_F64:
203   case WebAssembly::ARGUMENT_v16i8:
204   case WebAssembly::ARGUMENT_v8i16:
205   case WebAssembly::ARGUMENT_v4i32:
206   case WebAssembly::ARGUMENT_v4f32:
207     // These represent values which are live into the function entry, so there's
208     // no instruction to emit.
209     break;
210   case WebAssembly::FALLTHROUGH_RETURN_I32:
211   case WebAssembly::FALLTHROUGH_RETURN_I64:
212   case WebAssembly::FALLTHROUGH_RETURN_F32:
213   case WebAssembly::FALLTHROUGH_RETURN_F64:
214   case WebAssembly::FALLTHROUGH_RETURN_v16i8:
215   case WebAssembly::FALLTHROUGH_RETURN_v8i16:
216   case WebAssembly::FALLTHROUGH_RETURN_v4i32:
217   case WebAssembly::FALLTHROUGH_RETURN_v4f32: {
218     // These instructions represent the implicit return at the end of a
219     // function body. The operand is always a pop.
220     assert(MFI->isVRegStackified(MI->getOperand(0).getReg()));
221 
222     if (isVerbose()) {
223       OutStreamer->AddComment("fallthrough-return: $pop" +
224                               utostr(MFI->getWARegStackId(
225                                   MFI->getWAReg(MI->getOperand(0).getReg()))));
226       OutStreamer->AddBlankLine();
227     }
228     break;
229   }
230   case WebAssembly::FALLTHROUGH_RETURN_VOID:
231     // This instruction represents the implicit return at the end of a
232     // function body with no return value.
233     if (isVerbose()) {
234       OutStreamer->AddComment("fallthrough-return");
235       OutStreamer->AddBlankLine();
236     }
237     break;
238   default: {
239     WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
240     MCInst TmpInst;
241     MCInstLowering.Lower(MI, TmpInst);
242     EmitToStreamer(*OutStreamer, TmpInst);
243     break;
244   }
245   }
246 }
247 
248 const MCExpr *WebAssemblyAsmPrinter::lowerConstant(const Constant *CV) {
249   if (const GlobalValue *GV = dyn_cast<GlobalValue>(CV))
250     if (GV->getValueType()->isFunctionTy())
251       return MCSymbolRefExpr::create(
252           getSymbol(GV), MCSymbolRefExpr::VK_WebAssembly_FUNCTION, OutContext);
253   return AsmPrinter::lowerConstant(CV);
254 }
255 
256 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
257                                             unsigned OpNo, unsigned AsmVariant,
258                                             const char *ExtraCode,
259                                             raw_ostream &OS) {
260   if (AsmVariant != 0)
261     report_fatal_error("There are no defined alternate asm variants");
262 
263   // First try the generic code, which knows about modifiers like 'c' and 'n'.
264   if (!AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, OS))
265     return false;
266 
267   if (!ExtraCode) {
268     const MachineOperand &MO = MI->getOperand(OpNo);
269     switch (MO.getType()) {
270     case MachineOperand::MO_Immediate:
271       OS << MO.getImm();
272       return false;
273     case MachineOperand::MO_Register:
274       OS << regToString(MO);
275       return false;
276     case MachineOperand::MO_GlobalAddress:
277       getSymbol(MO.getGlobal())->print(OS, MAI);
278       printOffset(MO.getOffset(), OS);
279       return false;
280     case MachineOperand::MO_ExternalSymbol:
281       GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
282       printOffset(MO.getOffset(), OS);
283       return false;
284     case MachineOperand::MO_MachineBasicBlock:
285       MO.getMBB()->getSymbol()->print(OS, MAI);
286       return false;
287     default:
288       break;
289     }
290   }
291 
292   return true;
293 }
294 
295 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
296                                                   unsigned OpNo,
297                                                   unsigned AsmVariant,
298                                                   const char *ExtraCode,
299                                                   raw_ostream &OS) {
300   if (AsmVariant != 0)
301     report_fatal_error("There are no defined alternate asm variants");
302 
303   if (!ExtraCode) {
304     // TODO: For now, we just hard-code 0 as the constant offset; teach
305     // SelectInlineAsmMemoryOperand how to do address mode matching.
306     OS << "0(" + regToString(MI->getOperand(OpNo)) + ')';
307     return false;
308   }
309 
310   return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, AsmVariant, ExtraCode, OS);
311 }
312 
313 // Force static initialization.
314 extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
315   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
316   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
317 }
318