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 /// 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->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
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.  It's OK to hardcode knowledge of specific symbols
95   // here; this method is precisely there for fetching the signatures of known
96   // Clang-provided symbols.
97   if (strcmp(Name, "__stack_pointer") == 0) {
98     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
99     WasmSym->setGlobalType(wasm::WasmGlobalType{
100         uint8_t(Subtarget.hasAddr64() ? wasm::WASM_TYPE_I64
101                                       : wasm::WASM_TYPE_I32),
102         true});
103     return WasmSym;
104   }
105 
106   SmallVector<wasm::ValType, 4> Returns;
107   SmallVector<wasm::ValType, 4> Params;
108   GetSignature(Subtarget, Name, Returns, Params);
109 
110   WasmSym->setReturns(std::move(Returns));
111   WasmSym->setParams(std::move(Params));
112   WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
113 
114   return WasmSym;
115 }
116 
117 MCOperand WebAssemblyMCInstLower::LowerSymbolOperand(MCSymbol *Sym,
118                                                      int64_t Offset,
119                                                      bool IsFunc) const {
120   MCSymbolRefExpr::VariantKind VK =
121       IsFunc ? MCSymbolRefExpr::VK_WebAssembly_FUNCTION
122              : MCSymbolRefExpr::VK_None;
123 
124   const MCExpr *Expr = MCSymbolRefExpr::create(Sym, VK, Ctx);
125 
126   if (Offset != 0) {
127     if (IsFunc)
128       report_fatal_error("Function addresses with offsets not supported");
129     Expr =
130         MCBinaryExpr::createAdd(Expr, MCConstantExpr::create(Offset, Ctx), Ctx);
131   }
132 
133   return MCOperand::createExpr(Expr);
134 }
135 
136 // Return the WebAssembly type associated with the given register class.
137 static wasm::ValType getType(const TargetRegisterClass *RC) {
138   if (RC == &WebAssembly::I32RegClass)
139     return wasm::ValType::I32;
140   if (RC == &WebAssembly::I64RegClass)
141     return wasm::ValType::I64;
142   if (RC == &WebAssembly::F32RegClass)
143     return wasm::ValType::F32;
144   if (RC == &WebAssembly::F64RegClass)
145     return wasm::ValType::F64;
146   llvm_unreachable("Unexpected register class");
147 }
148 
149 void WebAssemblyMCInstLower::Lower(const MachineInstr *MI,
150                                    MCInst &OutMI) const {
151   OutMI.setOpcode(MI->getOpcode());
152 
153   const MCInstrDesc &Desc = MI->getDesc();
154   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
155     const MachineOperand &MO = MI->getOperand(i);
156 
157     MCOperand MCOp;
158     switch (MO.getType()) {
159     default:
160       MI->print(errs());
161       llvm_unreachable("unknown operand type");
162     case MachineOperand::MO_MachineBasicBlock:
163       MI->print(errs());
164       llvm_unreachable("MachineBasicBlock operand should have been rewritten");
165     case MachineOperand::MO_Register: {
166       // Ignore all implicit register operands.
167       if (MO.isImplicit())
168         continue;
169       const WebAssemblyFunctionInfo &MFI =
170           *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>();
171       unsigned WAReg = MFI.getWAReg(MO.getReg());
172       MCOp = MCOperand::createReg(WAReg);
173       break;
174     }
175     case MachineOperand::MO_Immediate:
176       if (i < Desc.NumOperands) {
177         const MCOperandInfo &Info = Desc.OpInfo[i];
178         if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
179           MCSymbol *Sym = Printer.createTempSymbol("typeindex");
180           if (!isa<MCSymbolELF>(Sym)) {
181             SmallVector<wasm::ValType, 4> Returns;
182             SmallVector<wasm::ValType, 4> Params;
183 
184             const MachineRegisterInfo &MRI =
185                 MI->getParent()->getParent()->getRegInfo();
186             for (const MachineOperand &MO : MI->defs())
187               Returns.push_back(getType(MRI.getRegClass(MO.getReg())));
188             for (const MachineOperand &MO : MI->explicit_uses())
189               if (MO.isReg())
190                 Params.push_back(getType(MRI.getRegClass(MO.getReg())));
191 
192             // call_indirect instructions have a callee operand at the end which
193             // doesn't count as a param.
194             if (WebAssembly::isCallIndirect(*MI))
195               Params.pop_back();
196 
197             MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Sym);
198             WasmSym->setReturns(std::move(Returns));
199             WasmSym->setParams(std::move(Params));
200             WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
201 
202             const MCExpr *Expr =
203                 MCSymbolRefExpr::create(WasmSym,
204                                         MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX,
205                                         Ctx);
206             MCOp = MCOperand::createExpr(Expr);
207             break;
208           }
209         }
210       }
211       MCOp = MCOperand::createImm(MO.getImm());
212       break;
213     case MachineOperand::MO_FPImmediate: {
214       // TODO: MC converts all floating point immediate operands to double.
215       // This is fine for numeric values, but may cause NaNs to change bits.
216       const ConstantFP *Imm = MO.getFPImm();
217       if (Imm->getType()->isFloatTy())
218         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat());
219       else if (Imm->getType()->isDoubleTy())
220         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble());
221       else
222         llvm_unreachable("unknown floating point immediate type");
223       break;
224     }
225     case MachineOperand::MO_GlobalAddress:
226       assert(MO.getTargetFlags() == 0 &&
227              "WebAssembly does not use target flags on GlobalAddresses");
228       MCOp = LowerSymbolOperand(GetGlobalAddressSymbol(MO), MO.getOffset(),
229                                 MO.getGlobal()->getValueType()->isFunctionTy());
230       break;
231     case MachineOperand::MO_ExternalSymbol:
232       // The target flag indicates whether this is a symbol for a
233       // variable or a function.
234       assert((MO.getTargetFlags() & -2) == 0 &&
235              "WebAssembly uses only one target flag bit on ExternalSymbols");
236       MCOp = LowerSymbolOperand(GetExternalSymbolSymbol(MO), /*Offset=*/0,
237                                 MO.getTargetFlags() & 1);
238       break;
239     }
240 
241     OutMI.addOperand(MCOp);
242   }
243 }
244