1 // WebAssemblyMCInstLower.cpp - Convert WebAssembly MachineInstr to an MCInst //
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 code to lower WebAssembly MachineInstrs to their
12 /// corresponding MCInst records.
13 ///
14 //===----------------------------------------------------------------------===//
15 
16 #include "WebAssemblyMCInstLower.h"
17 #include "WebAssemblyAsmPrinter.h"
18 #include "WebAssemblyMachineFunctionInfo.h"
19 #include "WebAssemblyRuntimeLibcallSignatures.h"
20 #include "WebAssemblyUtilities.h"
21 #include "llvm/CodeGen/AsmPrinter.h"
22 #include "llvm/CodeGen/MachineFunction.h"
23 #include "llvm/IR/Constants.h"
24 #include "llvm/MC/MCAsmInfo.h"
25 #include "llvm/MC/MCContext.h"
26 #include "llvm/MC/MCExpr.h"
27 #include "llvm/MC/MCInst.h"
28 #include "llvm/MC/MCSymbolELF.h"
29 #include "llvm/MC/MCSymbolWasm.h"
30 #include "llvm/Support/ErrorHandling.h"
31 #include "llvm/Support/raw_ostream.h"
32 using namespace llvm;
33 
34 MCSymbol *
35 WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const {
36   const GlobalValue *Global = MO.getGlobal();
37   MCSymbol *Sym = Printer.getSymbol(Global);
38   if (isa<MCSymbolELF>(Sym))
39     return Sym;
40 
41   MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Sym);
42 
43   if (const auto *FuncTy = dyn_cast<FunctionType>(Global->getValueType())) {
44     const MachineFunction &MF = *MO.getParent()->getParent()->getParent();
45     const TargetMachine &TM = MF.getTarget();
46     const Function &CurrentFunc = *MF.getFunction();
47 
48     SmallVector<wasm::ValType, 4> Returns;
49     SmallVector<wasm::ValType, 4> Params;
50 
51     wasm::ValType iPTR =
52         MF.getSubtarget<WebAssemblySubtarget>().hasAddr64() ?
53         wasm::ValType::I64 :
54         wasm::ValType::I32;
55 
56     SmallVector<MVT, 4> ResultMVTs;
57     ComputeLegalValueVTs(CurrentFunc, TM, FuncTy->getReturnType(), ResultMVTs);
58     // WebAssembly can't currently handle returning tuples.
59     if (ResultMVTs.size() <= 1)
60       for (MVT ResultMVT : ResultMVTs)
61         Returns.push_back(WebAssembly::toValType(ResultMVT));
62     else
63       Params.push_back(iPTR);
64 
65     for (Type *Ty : FuncTy->params()) {
66       SmallVector<MVT, 4> ParamMVTs;
67       ComputeLegalValueVTs(CurrentFunc, TM, Ty, ParamMVTs);
68       for (MVT ParamMVT : ParamMVTs)
69         Params.push_back(WebAssembly::toValType(ParamMVT));
70     }
71 
72     if (FuncTy->isVarArg())
73       Params.push_back(iPTR);
74 
75     WasmSym->setReturns(std::move(Returns));
76     WasmSym->setParams(std::move(Params));
77     WasmSym->setIsFunction(true);
78   }
79 
80   return WasmSym;
81 }
82 
83 MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
84     const MachineOperand &MO) const {
85   const char *Name = MO.getSymbolName();
86   MCSymbol *Sym = Printer.GetExternalSymbolSymbol(Name);
87   if (isa<MCSymbolELF>(Sym))
88     return Sym;
89 
90   MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Sym);
91   const WebAssemblySubtarget &Subtarget = Printer.getSubtarget();
92 
93   // __stack_pointer is a global variable; all other external symbols used by
94   // CodeGen are functions.
95   if (strcmp(Name, "__stack_pointer") == 0)
96     return WasmSym;
97 
98   SmallVector<wasm::ValType, 4> Returns;
99   SmallVector<wasm::ValType, 4> Params;
100   GetSignature(Subtarget, Name, Returns, Params);
101 
102   WasmSym->setReturns(std::move(Returns));
103   WasmSym->setParams(std::move(Params));
104   WasmSym->setIsFunction(true);
105 
106   return WasmSym;
107 }
108 
109 MCOperand WebAssemblyMCInstLower::LowerSymbolOperand(MCSymbol *Sym,
110                                                      int64_t Offset,
111                                                      bool IsFunc) const {
112   MCSymbolRefExpr::VariantKind VK =
113       IsFunc ? MCSymbolRefExpr::VK_WebAssembly_FUNCTION
114              : MCSymbolRefExpr::VK_None;
115   if (!isa<MCSymbolELF>(Sym))
116     cast<MCSymbolWasm>(Sym)->setIsFunction(IsFunc);
117 
118   const MCExpr *Expr = MCSymbolRefExpr::create(Sym, VK, Ctx);
119 
120   if (Offset != 0) {
121     if (IsFunc)
122       report_fatal_error("Function addresses with offsets not supported");
123     Expr =
124         MCBinaryExpr::createAdd(Expr, MCConstantExpr::create(Offset, Ctx), Ctx);
125   }
126 
127   return MCOperand::createExpr(Expr);
128 }
129 
130 // Return the WebAssembly type associated with the given register class.
131 static wasm::ValType getType(const TargetRegisterClass *RC) {
132   if (RC == &WebAssembly::I32RegClass)
133     return wasm::ValType::I32;
134   if (RC == &WebAssembly::I64RegClass)
135     return wasm::ValType::I64;
136   if (RC == &WebAssembly::F32RegClass)
137     return wasm::ValType::F32;
138   if (RC == &WebAssembly::F64RegClass)
139     return wasm::ValType::F64;
140   llvm_unreachable("Unexpected register class");
141 }
142 
143 void WebAssemblyMCInstLower::Lower(const MachineInstr *MI,
144                                    MCInst &OutMI) const {
145   OutMI.setOpcode(MI->getOpcode());
146 
147   const MCInstrDesc &Desc = MI->getDesc();
148   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
149     const MachineOperand &MO = MI->getOperand(i);
150 
151     MCOperand MCOp;
152     switch (MO.getType()) {
153     default:
154       MI->print(errs());
155       llvm_unreachable("unknown operand type");
156     case MachineOperand::MO_MachineBasicBlock:
157       MI->print(errs());
158       llvm_unreachable("MachineBasicBlock operand should have been rewritten");
159     case MachineOperand::MO_Register: {
160       // Ignore all implicit register operands.
161       if (MO.isImplicit())
162         continue;
163       const WebAssemblyFunctionInfo &MFI =
164           *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>();
165       unsigned WAReg = MFI.getWAReg(MO.getReg());
166       MCOp = MCOperand::createReg(WAReg);
167       break;
168     }
169     case MachineOperand::MO_Immediate:
170       if (i < Desc.NumOperands) {
171         const MCOperandInfo &Info = Desc.OpInfo[i];
172         if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
173           MCSymbol *Sym = Printer.createTempSymbol("typeindex");
174           if (!isa<MCSymbolELF>(Sym)) {
175             SmallVector<wasm::ValType, 4> Returns;
176             SmallVector<wasm::ValType, 4> Params;
177 
178             const MachineRegisterInfo &MRI =
179                 MI->getParent()->getParent()->getRegInfo();
180             for (const MachineOperand &MO : MI->defs())
181               Returns.push_back(getType(MRI.getRegClass(MO.getReg())));
182             for (const MachineOperand &MO : MI->explicit_uses())
183               if (MO.isReg())
184                 Params.push_back(getType(MRI.getRegClass(MO.getReg())));
185 
186             // call_indirect instructions have a callee operand at the end which
187             // doesn't count as a param.
188             if (WebAssembly::isCallIndirect(*MI))
189               Params.pop_back();
190 
191             MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Sym);
192             WasmSym->setReturns(std::move(Returns));
193             WasmSym->setParams(std::move(Params));
194             WasmSym->setIsFunction(true);
195 
196             const MCExpr *Expr =
197                 MCSymbolRefExpr::create(WasmSym,
198                                         MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX,
199                                         Ctx);
200             MCOp = MCOperand::createExpr(Expr);
201             break;
202           }
203         }
204       }
205       MCOp = MCOperand::createImm(MO.getImm());
206       break;
207     case MachineOperand::MO_FPImmediate: {
208       // TODO: MC converts all floating point immediate operands to double.
209       // This is fine for numeric values, but may cause NaNs to change bits.
210       const ConstantFP *Imm = MO.getFPImm();
211       if (Imm->getType()->isFloatTy())
212         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat());
213       else if (Imm->getType()->isDoubleTy())
214         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble());
215       else
216         llvm_unreachable("unknown floating point immediate type");
217       break;
218     }
219     case MachineOperand::MO_GlobalAddress:
220       assert(MO.getTargetFlags() == 0 &&
221              "WebAssembly does not use target flags on GlobalAddresses");
222       MCOp = LowerSymbolOperand(GetGlobalAddressSymbol(MO), MO.getOffset(),
223                                 MO.getGlobal()->getValueType()->isFunctionTy());
224       break;
225     case MachineOperand::MO_ExternalSymbol:
226       // The target flag indicates whether this is a symbol for a
227       // variable or a function.
228       assert((MO.getTargetFlags() & -2) == 0 &&
229              "WebAssembly uses only one target flag bit on ExternalSymbols");
230       MCOp = LowerSymbolOperand(GetExternalSymbolSymbol(MO), /*Offset=*/0,
231                                 MO.getTargetFlags() & 1);
232       break;
233     }
234 
235     OutMI.addOperand(MCOp);
236   }
237 }
238