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