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   const 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   const char *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   const char *toString(MVT VT) const;
86   std::string regToString(const MachineOperand &MO);
87   WebAssemblyTargetStreamer *getTargetStreamer();
88 };
89 
90 } // end anonymous namespace
91 
92 //===----------------------------------------------------------------------===//
93 // Helpers.
94 //===----------------------------------------------------------------------===//
95 
96 MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
97   const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
98   for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
99                 MVT::v4i32, MVT::v4f32})
100     if (TRC->hasType(T))
101       return T;
102   DEBUG(errs() << "Unknown type for register number: " << RegNo);
103   llvm_unreachable("Unknown register type");
104   return MVT::Other;
105 }
106 
107 const char *WebAssemblyAsmPrinter::toString(MVT VT) const {
108   return WebAssembly::TypeToString(VT);
109 }
110 
111 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
112   unsigned RegNo = MO.getReg();
113   assert(TargetRegisterInfo::isVirtualRegister(RegNo) &&
114          "Unlowered physical register encountered during assembly printing");
115   assert(!MFI->isVRegStackified(RegNo));
116   unsigned WAReg = MFI->getWAReg(RegNo);
117   assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
118   return '$' + utostr(WAReg);
119 }
120 
121 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
122   MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
123   return static_cast<WebAssemblyTargetStreamer *>(TS);
124 }
125 
126 //===----------------------------------------------------------------------===//
127 // WebAssemblyAsmPrinter Implementation.
128 //===----------------------------------------------------------------------===//
129 static void ComputeLegalValueVTs(const Function &F, const TargetMachine &TM,
130                                  Type *Ty, SmallVectorImpl<MVT> &ValueVTs) {
131   const DataLayout &DL(F.getParent()->getDataLayout());
132   const WebAssemblyTargetLowering &TLI =
133       *TM.getSubtarget<WebAssemblySubtarget>(F).getTargetLowering();
134   SmallVector<EVT, 4> VTs;
135   ComputeValueVTs(TLI, DL, Ty, VTs);
136 
137   for (EVT VT : VTs) {
138     unsigned NumRegs = TLI.getNumRegisters(F.getContext(), VT);
139     MVT RegisterVT = TLI.getRegisterType(F.getContext(), VT);
140     for (unsigned i = 0; i != NumRegs; ++i)
141       ValueVTs.push_back(RegisterVT);
142   }
143 }
144 
145 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
146   for (const auto &F : M) {
147     // Emit function type info for all undefined functions
148     if (F.isDeclarationForLinker() && !F.isIntrinsic()) {
149       SmallVector<MVT, 4> SignatureVTs;
150       ComputeLegalValueVTs(F, TM, F.getReturnType(), SignatureVTs);
151       size_t NumResults = SignatureVTs.size();
152       if (SignatureVTs.size() > 1) {
153         // WebAssembly currently can't lower returns of multiple values without
154         // demoting to sret (see WebAssemblyTargetLowering::CanLowerReturn). So
155         // replace multiple return values with a pointer parameter.
156         SignatureVTs.clear();
157         SignatureVTs.push_back(
158             MVT::getIntegerVT(M.getDataLayout().getPointerSizeInBits()));
159         NumResults = 0;
160       }
161 
162       for (auto &Arg : F.args()) {
163         ComputeLegalValueVTs(F, TM, Arg.getType(), SignatureVTs);
164       }
165 
166       getTargetStreamer()->emitIndirectFunctionType(F.getName(), SignatureVTs,
167                                                     NumResults);
168     }
169   }
170 }
171 
172 void WebAssemblyAsmPrinter::EmitConstantPool() {
173   assert(MF->getConstantPool()->getConstants().empty() &&
174          "WebAssembly disables constant pools");
175 }
176 
177 void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
178   // Nothing to do; jump tables are incorporated into the instruction stream.
179 }
180 
181 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
182   if (!MFI->getParams().empty())
183     getTargetStreamer()->emitParam(MFI->getParams());
184 
185   SmallVector<MVT, 4> ResultVTs;
186   const Function &F(*MF->getFunction());
187 
188   // Emit the function index.
189   if (MDNode *Idx = F.getMetadata("wasm.index")) {
190     assert(Idx->getNumOperands() == 1);
191 
192     getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
193         cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
194   }
195 
196   ComputeLegalValueVTs(F, TM, F.getReturnType(), ResultVTs);
197 
198   // If the return type needs to be legalized it will get converted into
199   // passing a pointer.
200   if (ResultVTs.size() == 1)
201     getTargetStreamer()->emitResult(ResultVTs);
202 
203   bool AnyWARegs = false;
204   SmallVector<MVT, 16> LocalTypes;
205   for (unsigned Idx = 0, IdxE = MRI->getNumVirtRegs(); Idx != IdxE; ++Idx) {
206     unsigned VReg = TargetRegisterInfo::index2VirtReg(Idx);
207     unsigned WAReg = MFI->getWAReg(VReg);
208     // Don't declare unused registers.
209     if (WAReg == WebAssemblyFunctionInfo::UnusedReg)
210       continue;
211     // Don't redeclare parameters.
212     if (WAReg < MFI->getParams().size())
213       continue;
214     // Don't declare stackified registers.
215     if (int(WAReg) < 0)
216       continue;
217     LocalTypes.push_back(getRegType(VReg));
218     AnyWARegs = true;
219   }
220   if (AnyWARegs)
221     getTargetStreamer()->emitLocal(LocalTypes);
222 
223   AsmPrinter::EmitFunctionBodyStart();
224 }
225 
226 void WebAssemblyAsmPrinter::EmitFunctionBodyEnd() {
227   getTargetStreamer()->emitEndFunc();
228 }
229 
230 void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
231   DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
232 
233   switch (MI->getOpcode()) {
234   case WebAssembly::ARGUMENT_I32:
235   case WebAssembly::ARGUMENT_I64:
236   case WebAssembly::ARGUMENT_F32:
237   case WebAssembly::ARGUMENT_F64:
238   case WebAssembly::ARGUMENT_v16i8:
239   case WebAssembly::ARGUMENT_v8i16:
240   case WebAssembly::ARGUMENT_v4i32:
241   case WebAssembly::ARGUMENT_v4f32:
242     // These represent values which are live into the function entry, so there's
243     // no instruction to emit.
244     break;
245   case WebAssembly::FALLTHROUGH_RETURN_I32:
246   case WebAssembly::FALLTHROUGH_RETURN_I64:
247   case WebAssembly::FALLTHROUGH_RETURN_F32:
248   case WebAssembly::FALLTHROUGH_RETURN_F64:
249   case WebAssembly::FALLTHROUGH_RETURN_v16i8:
250   case WebAssembly::FALLTHROUGH_RETURN_v8i16:
251   case WebAssembly::FALLTHROUGH_RETURN_v4i32:
252   case WebAssembly::FALLTHROUGH_RETURN_v4f32: {
253     // These instructions represent the implicit return at the end of a
254     // function body. The operand is always a pop.
255     assert(MFI->isVRegStackified(MI->getOperand(0).getReg()));
256 
257     if (isVerbose()) {
258       OutStreamer->AddComment("fallthrough-return: $pop" +
259                               utostr(MFI->getWARegStackId(
260                                   MFI->getWAReg(MI->getOperand(0).getReg()))));
261       OutStreamer->AddBlankLine();
262     }
263     break;
264   }
265   case WebAssembly::FALLTHROUGH_RETURN_VOID:
266     // This instruction represents the implicit return at the end of a
267     // function body with no return value.
268     if (isVerbose()) {
269       OutStreamer->AddComment("fallthrough-return");
270       OutStreamer->AddBlankLine();
271     }
272     break;
273   default: {
274     WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
275     MCInst TmpInst;
276     MCInstLowering.Lower(MI, TmpInst);
277     EmitToStreamer(*OutStreamer, TmpInst);
278     break;
279   }
280   }
281 }
282 
283 const MCExpr *WebAssemblyAsmPrinter::lowerConstant(const Constant *CV) {
284   if (const GlobalValue *GV = dyn_cast<GlobalValue>(CV))
285     if (GV->getValueType()->isFunctionTy())
286       return MCSymbolRefExpr::create(
287           getSymbol(GV), MCSymbolRefExpr::VK_WebAssembly_FUNCTION, OutContext);
288   return AsmPrinter::lowerConstant(CV);
289 }
290 
291 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
292                                             unsigned OpNo, unsigned AsmVariant,
293                                             const char *ExtraCode,
294                                             raw_ostream &OS) {
295   if (AsmVariant != 0)
296     report_fatal_error("There are no defined alternate asm variants");
297 
298   // First try the generic code, which knows about modifiers like 'c' and 'n'.
299   if (!AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, OS))
300     return false;
301 
302   if (!ExtraCode) {
303     const MachineOperand &MO = MI->getOperand(OpNo);
304     switch (MO.getType()) {
305     case MachineOperand::MO_Immediate:
306       OS << MO.getImm();
307       return false;
308     case MachineOperand::MO_Register:
309       OS << regToString(MO);
310       return false;
311     case MachineOperand::MO_GlobalAddress:
312       getSymbol(MO.getGlobal())->print(OS, MAI);
313       printOffset(MO.getOffset(), OS);
314       return false;
315     case MachineOperand::MO_ExternalSymbol:
316       GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
317       printOffset(MO.getOffset(), OS);
318       return false;
319     case MachineOperand::MO_MachineBasicBlock:
320       MO.getMBB()->getSymbol()->print(OS, MAI);
321       return false;
322     default:
323       break;
324     }
325   }
326 
327   return true;
328 }
329 
330 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
331                                                   unsigned OpNo,
332                                                   unsigned AsmVariant,
333                                                   const char *ExtraCode,
334                                                   raw_ostream &OS) {
335   if (AsmVariant != 0)
336     report_fatal_error("There are no defined alternate asm variants");
337 
338   if (!ExtraCode) {
339     // TODO: For now, we just hard-code 0 as the constant offset; teach
340     // SelectInlineAsmMemoryOperand how to do address mode matching.
341     OS << "0(" + regToString(MI->getOperand(OpNo)) + ')';
342     return false;
343   }
344 
345   return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, AsmVariant, ExtraCode, OS);
346 }
347 
348 // Force static initialization.
349 extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
350   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(TheWebAssemblyTarget32);
351   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(TheWebAssemblyTarget64);
352 }
353