1 // WebAssemblyMCInstLower.cpp - Convert WebAssembly MachineInstr to an MCInst //
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 ///
9 /// \file
10 /// This file contains code to lower WebAssembly MachineInstrs to their
11 /// corresponding MCInst records.
12 ///
13 //===----------------------------------------------------------------------===//
14 
15 #include "WebAssemblyMCInstLower.h"
16 #include "WebAssemblyAsmPrinter.h"
17 #include "WebAssemblyMachineFunctionInfo.h"
18 #include "WebAssemblyRuntimeLibcallSignatures.h"
19 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
20 #include "llvm/CodeGen/AsmPrinter.h"
21 #include "llvm/CodeGen/MachineFunction.h"
22 #include "llvm/IR/Constants.h"
23 #include "llvm/MC/MCAsmInfo.h"
24 #include "llvm/MC/MCContext.h"
25 #include "llvm/MC/MCExpr.h"
26 #include "llvm/MC/MCInst.h"
27 #include "llvm/MC/MCSymbolWasm.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Support/raw_ostream.h"
30 using namespace llvm;
31 
32 // Defines llvm::WebAssembly::getStackOpcode to convert register instructions to
33 // stack instructions
34 #define GET_INSTRMAP_INFO 1
35 #include "WebAssemblyGenInstrInfo.inc"
36 
37 // This disables the removal of registers when lowering into MC, as required
38 // by some current tests.
39 cl::opt<bool>
40     WasmKeepRegisters("wasm-keep-registers", cl::Hidden,
41                       cl::desc("WebAssembly: output stack registers in"
42                                " instruction output for test purposes only."),
43                       cl::init(false));
44 
45 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI);
46 
47 MCSymbol *
48 WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const {
49   const GlobalValue *Global = MO.getGlobal();
50   auto *WasmSym = cast<MCSymbolWasm>(Printer.getSymbol(Global));
51 
52   if (const auto *FuncTy = dyn_cast<FunctionType>(Global->getValueType())) {
53     const MachineFunction &MF = *MO.getParent()->getParent()->getParent();
54     const TargetMachine &TM = MF.getTarget();
55     const Function &CurrentFunc = MF.getFunction();
56 
57     SmallVector<MVT, 1> ResultMVTs;
58     SmallVector<MVT, 4> ParamMVTs;
59     computeSignatureVTs(FuncTy, CurrentFunc, TM, ParamMVTs, ResultMVTs);
60 
61     auto Signature = signatureFromMVTs(ResultMVTs, ParamMVTs);
62     WasmSym->setSignature(Signature.get());
63     Printer.addSignature(std::move(Signature));
64     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
65   }
66 
67   return WasmSym;
68 }
69 
70 MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
71     const MachineOperand &MO) const {
72   const char *Name = MO.getSymbolName();
73   auto *WasmSym = cast<MCSymbolWasm>(Printer.GetExternalSymbolSymbol(Name));
74   const WebAssemblySubtarget &Subtarget = Printer.getSubtarget();
75 
76   // Except for certain known symbols, all symbols used by CodeGen are
77   // functions. It's OK to hardcode knowledge of specific symbols here; this
78   // method is precisely there for fetching the signatures of known
79   // Clang-provided symbols.
80   if (strcmp(Name, "__stack_pointer") == 0 || strcmp(Name, "__tls_base") == 0 ||
81       strcmp(Name, "__memory_base") == 0 || strcmp(Name, "__table_base") == 0 ||
82       strcmp(Name, "__tls_size") == 0 || strcmp(Name, "__tls_align") == 0) {
83     bool Mutable =
84         strcmp(Name, "__stack_pointer") == 0 || strcmp(Name, "__tls_base") == 0;
85     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
86     WasmSym->setGlobalType(wasm::WasmGlobalType{
87         uint8_t(Subtarget.hasAddr64() ? wasm::WASM_TYPE_I64
88                                       : wasm::WASM_TYPE_I32),
89         Mutable});
90     return WasmSym;
91   }
92 
93   SmallVector<wasm::ValType, 4> Returns;
94   SmallVector<wasm::ValType, 4> Params;
95   if (strcmp(Name, "__cpp_exception") == 0) {
96     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_EVENT);
97     // We can't confirm its signature index for now because there can be
98     // imported exceptions. Set it to be 0 for now.
99     WasmSym->setEventType(
100         {wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION, /* SigIndex */ 0});
101     // We may have multiple C++ compilation units to be linked together, each of
102     // which defines the exception symbol. To resolve them, we declare them as
103     // weak.
104     WasmSym->setWeak(true);
105     WasmSym->setExternal(true);
106 
107     // All C++ exceptions are assumed to have a single i32 (for wasm32) or i64
108     // (for wasm64) param type and void return type. The reaon is, all C++
109     // exception values are pointers, and to share the type section with
110     // functions, exceptions are assumed to have void return type.
111     Params.push_back(Subtarget.hasAddr64() ? wasm::ValType::I64
112                                            : wasm::ValType::I32);
113   } else { // Function symbols
114     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
115     getLibcallSignature(Subtarget, Name, Returns, Params);
116   }
117   auto Signature =
118       make_unique<wasm::WasmSignature>(std::move(Returns), std::move(Params));
119   WasmSym->setSignature(Signature.get());
120   Printer.addSignature(std::move(Signature));
121 
122   return WasmSym;
123 }
124 
125 MCOperand WebAssemblyMCInstLower::lowerSymbolOperand(const MachineOperand &MO,
126                                                      MCSymbol *Sym) const {
127   MCSymbolRefExpr::VariantKind Kind = MCSymbolRefExpr::VK_None;
128   unsigned TargetFlags = MO.getTargetFlags();
129 
130   switch (TargetFlags) {
131     case WebAssemblyII::MO_NO_FLAG:
132       break;
133     case WebAssemblyII::MO_GOT:
134       Kind = MCSymbolRefExpr::VK_GOT;
135       break;
136     case WebAssemblyII::MO_MEMORY_BASE_REL:
137       Kind = MCSymbolRefExpr::VK_WASM_MBREL;
138       break;
139     case WebAssemblyII::MO_TABLE_BASE_REL:
140       Kind = MCSymbolRefExpr::VK_WASM_TBREL;
141       break;
142     default:
143       llvm_unreachable("Unknown target flag on GV operand");
144   }
145 
146   const MCExpr *Expr = MCSymbolRefExpr::create(Sym, Kind, Ctx);
147 
148   if (MO.getOffset() != 0) {
149     const auto *WasmSym = cast<MCSymbolWasm>(Sym);
150     if (TargetFlags == WebAssemblyII::MO_GOT)
151       report_fatal_error("GOT symbol references do not support offsets");
152     if (WasmSym->isFunction())
153       report_fatal_error("Function addresses with offsets not supported");
154     if (WasmSym->isGlobal())
155       report_fatal_error("Global indexes with offsets not supported");
156     if (WasmSym->isEvent())
157       report_fatal_error("Event indexes with offsets not supported");
158 
159     Expr = MCBinaryExpr::createAdd(
160         Expr, MCConstantExpr::create(MO.getOffset(), Ctx), Ctx);
161   }
162 
163   return MCOperand::createExpr(Expr);
164 }
165 
166 // Return the WebAssembly type associated with the given register class.
167 static wasm::ValType getType(const TargetRegisterClass *RC) {
168   if (RC == &WebAssembly::I32RegClass)
169     return wasm::ValType::I32;
170   if (RC == &WebAssembly::I64RegClass)
171     return wasm::ValType::I64;
172   if (RC == &WebAssembly::F32RegClass)
173     return wasm::ValType::F32;
174   if (RC == &WebAssembly::F64RegClass)
175     return wasm::ValType::F64;
176   if (RC == &WebAssembly::V128RegClass)
177     return wasm::ValType::V128;
178   llvm_unreachable("Unexpected register class");
179 }
180 
181 void WebAssemblyMCInstLower::lower(const MachineInstr *MI,
182                                    MCInst &OutMI) const {
183   OutMI.setOpcode(MI->getOpcode());
184 
185   const MCInstrDesc &Desc = MI->getDesc();
186   for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
187     const MachineOperand &MO = MI->getOperand(I);
188 
189     MCOperand MCOp;
190     switch (MO.getType()) {
191     default:
192       MI->print(errs());
193       llvm_unreachable("unknown operand type");
194     case MachineOperand::MO_MachineBasicBlock:
195       MI->print(errs());
196       llvm_unreachable("MachineBasicBlock operand should have been rewritten");
197     case MachineOperand::MO_Register: {
198       // Ignore all implicit register operands.
199       if (MO.isImplicit())
200         continue;
201       const WebAssemblyFunctionInfo &MFI =
202           *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>();
203       unsigned WAReg = MFI.getWAReg(MO.getReg());
204       MCOp = MCOperand::createReg(WAReg);
205       break;
206     }
207     case MachineOperand::MO_Immediate:
208       if (I < Desc.NumOperands) {
209         const MCOperandInfo &Info = Desc.OpInfo[I];
210         if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
211           MCSymbol *Sym = Printer.createTempSymbol("typeindex");
212 
213           SmallVector<wasm::ValType, 4> Returns;
214           SmallVector<wasm::ValType, 4> Params;
215 
216           const MachineRegisterInfo &MRI =
217               MI->getParent()->getParent()->getRegInfo();
218           for (const MachineOperand &MO : MI->defs())
219             Returns.push_back(getType(MRI.getRegClass(MO.getReg())));
220           for (const MachineOperand &MO : MI->explicit_uses())
221             if (MO.isReg())
222               Params.push_back(getType(MRI.getRegClass(MO.getReg())));
223 
224           // call_indirect instructions have a callee operand at the end which
225           // doesn't count as a param.
226           if (WebAssembly::isCallIndirect(MI->getOpcode()))
227             Params.pop_back();
228 
229           // return_call_indirect instructions have the return type of the
230           // caller
231           if (MI->getOpcode() == WebAssembly::RET_CALL_INDIRECT) {
232             const Function &F = MI->getMF()->getFunction();
233             const TargetMachine &TM = MI->getMF()->getTarget();
234             Type *RetTy = F.getReturnType();
235             SmallVector<MVT, 4> CallerRetTys;
236             computeLegalValueVTs(F, TM, RetTy, CallerRetTys);
237             valTypesFromMVTs(CallerRetTys, Returns);
238           }
239 
240           auto *WasmSym = cast<MCSymbolWasm>(Sym);
241           auto Signature = make_unique<wasm::WasmSignature>(std::move(Returns),
242                                                             std::move(Params));
243           WasmSym->setSignature(Signature.get());
244           Printer.addSignature(std::move(Signature));
245           WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
246 
247           const MCExpr *Expr = MCSymbolRefExpr::create(
248               WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, Ctx);
249           MCOp = MCOperand::createExpr(Expr);
250           break;
251         }
252       }
253       MCOp = MCOperand::createImm(MO.getImm());
254       break;
255     case MachineOperand::MO_FPImmediate: {
256       // TODO: MC converts all floating point immediate operands to double.
257       // This is fine for numeric values, but may cause NaNs to change bits.
258       const ConstantFP *Imm = MO.getFPImm();
259       if (Imm->getType()->isFloatTy())
260         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat());
261       else if (Imm->getType()->isDoubleTy())
262         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble());
263       else
264         llvm_unreachable("unknown floating point immediate type");
265       break;
266     }
267     case MachineOperand::MO_GlobalAddress:
268       MCOp = lowerSymbolOperand(MO, GetGlobalAddressSymbol(MO));
269       break;
270     case MachineOperand::MO_ExternalSymbol:
271       // The target flag indicates whether this is a symbol for a
272       // variable or a function.
273       assert(MO.getTargetFlags() == 0 &&
274              "WebAssembly uses only symbol flags on ExternalSymbols");
275       MCOp = lowerSymbolOperand(MO, GetExternalSymbolSymbol(MO));
276       break;
277     case MachineOperand::MO_MCSymbol:
278       // This is currently used only for LSDA symbols (GCC_except_table),
279       // because global addresses or other external symbols are handled above.
280       assert(MO.getTargetFlags() == 0 &&
281              "WebAssembly does not use target flags on MCSymbol");
282       MCOp = lowerSymbolOperand(MO, MO.getMCSymbol());
283       break;
284     }
285 
286     OutMI.addOperand(MCOp);
287   }
288 
289   if (!WasmKeepRegisters)
290     removeRegisterOperands(MI, OutMI);
291 }
292 
293 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI) {
294   // Remove all uses of stackified registers to bring the instruction format
295   // into its final stack form used thruout MC, and transition opcodes to
296   // their _S variant.
297   // We do this seperate from the above code that still may need these
298   // registers for e.g. call_indirect signatures.
299   // See comments in lib/Target/WebAssembly/WebAssemblyInstrFormats.td for
300   // details.
301   // TODO: the code above creates new registers which are then removed here.
302   // That code could be slightly simplified by not doing that, though maybe
303   // it is simpler conceptually to keep the code above in "register mode"
304   // until this transition point.
305   // FIXME: we are not processing inline assembly, which contains register
306   // operands, because it is used by later target generic code.
307   if (MI->isDebugInstr() || MI->isLabel() || MI->isInlineAsm())
308     return;
309 
310   // Transform to _S instruction.
311   auto RegOpcode = OutMI.getOpcode();
312   auto StackOpcode = WebAssembly::getStackOpcode(RegOpcode);
313   assert(StackOpcode != -1 && "Failed to stackify instruction");
314   OutMI.setOpcode(StackOpcode);
315 
316   // Remove register operands.
317   for (auto I = OutMI.getNumOperands(); I; --I) {
318     auto &MO = OutMI.getOperand(I - 1);
319     if (MO.isReg()) {
320       OutMI.erase(&MO);
321     }
322   }
323 }
324