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/MCSymbolELF.h"
38 #include "llvm/MC/MCSymbolWasm.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/TargetRegistry.h"
41 #include "llvm/Support/raw_ostream.h"
42 using namespace llvm;
43 
44 #define DEBUG_TYPE "asm-printer"
45 
46 //===----------------------------------------------------------------------===//
47 // Helpers.
48 //===----------------------------------------------------------------------===//
49 
50 MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
51   const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
52   const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
53   for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
54                 MVT::v4i32, MVT::v4f32})
55     if (TRI->isTypeLegalForClass(*TRC, T))
56       return T;
57   LLVM_DEBUG(errs() << "Unknown type for register number: " << RegNo);
58   llvm_unreachable("Unknown register type");
59   return MVT::Other;
60 }
61 
62 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
63   unsigned RegNo = MO.getReg();
64   assert(TargetRegisterInfo::isVirtualRegister(RegNo) &&
65          "Unlowered physical register encountered during assembly printing");
66   assert(!MFI->isVRegStackified(RegNo));
67   unsigned WAReg = MFI->getWAReg(RegNo);
68   assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
69   return '$' + utostr(WAReg);
70 }
71 
72 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
73   MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
74   return static_cast<WebAssemblyTargetStreamer *>(TS);
75 }
76 
77 //===----------------------------------------------------------------------===//
78 // WebAssemblyAsmPrinter Implementation.
79 //===----------------------------------------------------------------------===//
80 
81 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
82   for (const auto &F : M) {
83     // Emit function type info for all undefined functions
84     if (F.isDeclarationForLinker() && !F.isIntrinsic()) {
85       SmallVector<MVT, 4> Results;
86       SmallVector<MVT, 4> Params;
87       ComputeSignatureVTs(F, TM, Params, Results);
88       MCSymbol *Sym = getSymbol(&F);
89       getTargetStreamer()->emitIndirectFunctionType(Sym, Params, Results);
90 
91       if (TM.getTargetTriple().isOSBinFormatWasm() &&
92           F.hasFnAttribute("wasm-import-module")) {
93         MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Sym);
94         StringRef Name = F.getFnAttribute("wasm-import-module")
95                              .getValueAsString();
96         getTargetStreamer()->emitImportModule(WasmSym, Name);
97       }
98     }
99   }
100   for (const auto &G : M.globals()) {
101     if (!G.hasInitializer() && G.hasExternalLinkage()) {
102       if (G.getValueType()->isSized()) {
103         uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
104         if (TM.getTargetTriple().isOSBinFormatELF())
105           getTargetStreamer()->emitGlobalImport(G.getGlobalIdentifier());
106         OutStreamer->emitELFSize(getSymbol(&G),
107                                  MCConstantExpr::create(Size, OutContext));
108       }
109     }
110   }
111 
112   if (const NamedMDNode *Named = M.getNamedMetadata("wasm.custom_sections")) {
113     for (const Metadata *MD : Named->operands()) {
114       const MDTuple *Tuple = dyn_cast<MDTuple>(MD);
115       if (!Tuple || Tuple->getNumOperands() != 2)
116         continue;
117       const MDString *Name = dyn_cast<MDString>(Tuple->getOperand(0));
118       const MDString *Contents = dyn_cast<MDString>(Tuple->getOperand(1));
119       if (!Name || !Contents)
120         continue;
121 
122       OutStreamer->PushSection();
123       std::string SectionName = (".custom_section." + Name->getString()).str();
124       MCSectionWasm *mySection =
125           OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
126       OutStreamer->SwitchSection(mySection);
127       OutStreamer->EmitBytes(Contents->getString());
128       OutStreamer->PopSection();
129     }
130   }
131 }
132 
133 void WebAssemblyAsmPrinter::EmitConstantPool() {
134   assert(MF->getConstantPool()->getConstants().empty() &&
135          "WebAssembly disables constant pools");
136 }
137 
138 void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
139   // Nothing to do; jump tables are incorporated into the instruction stream.
140 }
141 
142 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
143   getTargetStreamer()->emitParam(CurrentFnSym, MFI->getParams());
144 
145   SmallVector<MVT, 4> ResultVTs;
146   const Function &F = MF->getFunction();
147 
148   // Emit the function index.
149   if (MDNode *Idx = F.getMetadata("wasm.index")) {
150     assert(Idx->getNumOperands() == 1);
151 
152     getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
153         cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
154   }
155 
156   ComputeLegalValueVTs(F, TM, F.getReturnType(), ResultVTs);
157 
158   // If the return type needs to be legalized it will get converted into
159   // passing a pointer.
160   if (ResultVTs.size() == 1)
161     getTargetStreamer()->emitResult(CurrentFnSym, ResultVTs);
162   else
163     getTargetStreamer()->emitResult(CurrentFnSym, ArrayRef<MVT>());
164 
165   if (TM.getTargetTriple().isOSBinFormatELF()) {
166     assert(MFI->getLocals().empty());
167     for (unsigned Idx = 0, IdxE = MRI->getNumVirtRegs(); Idx != IdxE; ++Idx) {
168       unsigned VReg = TargetRegisterInfo::index2VirtReg(Idx);
169       unsigned WAReg = MFI->getWAReg(VReg);
170       // Don't declare unused registers.
171       if (WAReg == WebAssemblyFunctionInfo::UnusedReg)
172         continue;
173       // Don't redeclare parameters.
174       if (WAReg < MFI->getParams().size())
175         continue;
176       // Don't declare stackified registers.
177       if (int(WAReg) < 0)
178         continue;
179       MFI->addLocal(getRegType(VReg));
180     }
181   }
182 
183   getTargetStreamer()->emitLocal(MFI->getLocals());
184 
185   AsmPrinter::EmitFunctionBodyStart();
186 }
187 
188 void WebAssemblyAsmPrinter::EmitFunctionBodyEnd() {
189   if (TM.getTargetTriple().isOSBinFormatELF())
190     getTargetStreamer()->emitEndFunc();
191 }
192 
193 void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
194   LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
195 
196   switch (MI->getOpcode()) {
197   case WebAssembly::ARGUMENT_I32:
198   case WebAssembly::ARGUMENT_I64:
199   case WebAssembly::ARGUMENT_F32:
200   case WebAssembly::ARGUMENT_F64:
201   case WebAssembly::ARGUMENT_v16i8:
202   case WebAssembly::ARGUMENT_v8i16:
203   case WebAssembly::ARGUMENT_v4i32:
204   case WebAssembly::ARGUMENT_v4f32:
205     // These represent values which are live into the function entry, so there's
206     // no instruction to emit.
207     break;
208   case WebAssembly::FALLTHROUGH_RETURN_I32:
209   case WebAssembly::FALLTHROUGH_RETURN_I64:
210   case WebAssembly::FALLTHROUGH_RETURN_F32:
211   case WebAssembly::FALLTHROUGH_RETURN_F64:
212   case WebAssembly::FALLTHROUGH_RETURN_v16i8:
213   case WebAssembly::FALLTHROUGH_RETURN_v8i16:
214   case WebAssembly::FALLTHROUGH_RETURN_v4i32:
215   case WebAssembly::FALLTHROUGH_RETURN_v4f32: {
216     // These instructions represent the implicit return at the end of a
217     // function body. The operand is always a pop.
218     assert(MFI->isVRegStackified(MI->getOperand(0).getReg()));
219 
220     if (isVerbose()) {
221       OutStreamer->AddComment("fallthrough-return: $pop" +
222                               Twine(MFI->getWARegStackId(
223                                   MFI->getWAReg(MI->getOperand(0).getReg()))));
224       OutStreamer->AddBlankLine();
225     }
226     break;
227   }
228   case WebAssembly::FALLTHROUGH_RETURN_VOID:
229     // This instruction represents the implicit return at the end of a
230     // function body with no return value.
231     if (isVerbose()) {
232       OutStreamer->AddComment("fallthrough-return");
233       OutStreamer->AddBlankLine();
234     }
235     break;
236   default: {
237     WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
238     MCInst TmpInst;
239     MCInstLowering.Lower(MI, TmpInst);
240     EmitToStreamer(*OutStreamer, TmpInst);
241     break;
242   }
243   }
244 }
245 
246 const MCExpr *WebAssemblyAsmPrinter::lowerConstant(const Constant *CV) {
247   if (const GlobalValue *GV = dyn_cast<GlobalValue>(CV))
248     if (GV->getValueType()->isFunctionTy()) {
249       return MCSymbolRefExpr::create(
250           getSymbol(GV), MCSymbolRefExpr::VK_WebAssembly_FUNCTION, OutContext);
251     }
252   return AsmPrinter::lowerConstant(CV);
253 }
254 
255 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
256                                             unsigned OpNo, unsigned AsmVariant,
257                                             const char *ExtraCode,
258                                             raw_ostream &OS) {
259   if (AsmVariant != 0)
260     report_fatal_error("There are no defined alternate asm variants");
261 
262   // First try the generic code, which knows about modifiers like 'c' and 'n'.
263   if (!AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, OS))
264     return false;
265 
266   if (!ExtraCode) {
267     const MachineOperand &MO = MI->getOperand(OpNo);
268     switch (MO.getType()) {
269     case MachineOperand::MO_Immediate:
270       OS << MO.getImm();
271       return false;
272     case MachineOperand::MO_Register:
273       OS << regToString(MO);
274       return false;
275     case MachineOperand::MO_GlobalAddress:
276       getSymbol(MO.getGlobal())->print(OS, MAI);
277       printOffset(MO.getOffset(), OS);
278       return false;
279     case MachineOperand::MO_ExternalSymbol:
280       GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
281       printOffset(MO.getOffset(), OS);
282       return false;
283     case MachineOperand::MO_MachineBasicBlock:
284       MO.getMBB()->getSymbol()->print(OS, MAI);
285       return false;
286     default:
287       break;
288     }
289   }
290 
291   return true;
292 }
293 
294 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
295                                                   unsigned OpNo,
296                                                   unsigned AsmVariant,
297                                                   const char *ExtraCode,
298                                                   raw_ostream &OS) {
299   if (AsmVariant != 0)
300     report_fatal_error("There are no defined alternate asm variants");
301 
302   // The current approach to inline asm is that "r" constraints are expressed
303   // as local indices, rather than values on the operand stack. This simplifies
304   // using "r" as it eliminates the need to push and pop the values in a
305   // particular order, however it also makes it impossible to have an "m"
306   // constraint. So we don't support it.
307 
308   return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, AsmVariant, ExtraCode, OS);
309 }
310 
311 // Force static initialization.
312 extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
313   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
314   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
315 }
316