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