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/MCSymbolWasm.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/raw_ostream.h"
31 using namespace llvm;
32 
33 MCSymbol *
GetGlobalAddressSymbol(const MachineOperand & MO) const34 WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const {
35   const GlobalValue *Global = MO.getGlobal();
36   MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Printer.getSymbol(Global));
37 
38   if (const auto *FuncTy = dyn_cast<FunctionType>(Global->getValueType())) {
39     const MachineFunction &MF = *MO.getParent()->getParent()->getParent();
40     const TargetMachine &TM = MF.getTarget();
41     const Function &CurrentFunc = MF.getFunction();
42 
43     SmallVector<wasm::ValType, 4> Returns;
44     SmallVector<wasm::ValType, 4> Params;
45 
46     wasm::ValType iPTR =
47         MF.getSubtarget<WebAssemblySubtarget>().hasAddr64() ?
48         wasm::ValType::I64 :
49         wasm::ValType::I32;
50 
51     SmallVector<MVT, 4> ResultMVTs;
52     ComputeLegalValueVTs(CurrentFunc, TM, FuncTy->getReturnType(), ResultMVTs);
53     // WebAssembly can't currently handle returning tuples.
54     if (ResultMVTs.size() <= 1)
55       for (MVT ResultMVT : ResultMVTs)
56         Returns.push_back(WebAssembly::toValType(ResultMVT));
57     else
58       Params.push_back(iPTR);
59 
60     for (Type *Ty : FuncTy->params()) {
61       SmallVector<MVT, 4> ParamMVTs;
62       ComputeLegalValueVTs(CurrentFunc, TM, Ty, ParamMVTs);
63       for (MVT ParamMVT : ParamMVTs)
64         Params.push_back(WebAssembly::toValType(ParamMVT));
65     }
66 
67     if (FuncTy->isVarArg())
68       Params.push_back(iPTR);
69 
70     WasmSym->setReturns(std::move(Returns));
71     WasmSym->setParams(std::move(Params));
72     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
73   }
74 
75   return WasmSym;
76 }
77 
GetExternalSymbolSymbol(const MachineOperand & MO) const78 MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
79     const MachineOperand &MO) const {
80   const char *Name = MO.getSymbolName();
81   MCSymbolWasm *WasmSym =
82       cast<MCSymbolWasm>(Printer.GetExternalSymbolSymbol(Name));
83   const WebAssemblySubtarget &Subtarget = Printer.getSubtarget();
84 
85   // __stack_pointer is a global variable; all other external symbols used by
86   // CodeGen are functions.  It's OK to hardcode knowledge of specific symbols
87   // here; this method is precisely there for fetching the signatures of known
88   // Clang-provided symbols.
89   if (strcmp(Name, "__stack_pointer") == 0) {
90     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
91     WasmSym->setGlobalType(wasm::WasmGlobalType{
92         uint8_t(Subtarget.hasAddr64() ? wasm::WASM_TYPE_I64
93                                       : wasm::WASM_TYPE_I32),
94         true});
95     return WasmSym;
96   }
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->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
105 
106   return WasmSym;
107 }
108 
LowerSymbolOperand(MCSymbol * Sym,int64_t Offset,bool IsFunc) const109 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 
116   const MCExpr *Expr = MCSymbolRefExpr::create(Sym, VK, Ctx);
117 
118   if (Offset != 0) {
119     if (IsFunc)
120       report_fatal_error("Function addresses with offsets not supported");
121     Expr =
122         MCBinaryExpr::createAdd(Expr, MCConstantExpr::create(Offset, Ctx), Ctx);
123   }
124 
125   return MCOperand::createExpr(Expr);
126 }
127 
128 // Return the WebAssembly type associated with the given register class.
getType(const TargetRegisterClass * RC)129 static wasm::ValType getType(const TargetRegisterClass *RC) {
130   if (RC == &WebAssembly::I32RegClass)
131     return wasm::ValType::I32;
132   if (RC == &WebAssembly::I64RegClass)
133     return wasm::ValType::I64;
134   if (RC == &WebAssembly::F32RegClass)
135     return wasm::ValType::F32;
136   if (RC == &WebAssembly::F64RegClass)
137     return wasm::ValType::F64;
138   llvm_unreachable("Unexpected register class");
139 }
140 
Lower(const MachineInstr * MI,MCInst & OutMI) const141 void WebAssemblyMCInstLower::Lower(const MachineInstr *MI,
142                                    MCInst &OutMI) const {
143   OutMI.setOpcode(MI->getOpcode());
144 
145   const MCInstrDesc &Desc = MI->getDesc();
146   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
147     const MachineOperand &MO = MI->getOperand(i);
148 
149     MCOperand MCOp;
150     switch (MO.getType()) {
151     default:
152       MI->print(errs());
153       llvm_unreachable("unknown operand type");
154     case MachineOperand::MO_MachineBasicBlock:
155       MI->print(errs());
156       llvm_unreachable("MachineBasicBlock operand should have been rewritten");
157     case MachineOperand::MO_Register: {
158       // Ignore all implicit register operands.
159       if (MO.isImplicit())
160         continue;
161       const WebAssemblyFunctionInfo &MFI =
162           *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>();
163       unsigned WAReg = MFI.getWAReg(MO.getReg());
164       MCOp = MCOperand::createReg(WAReg);
165       break;
166     }
167     case MachineOperand::MO_Immediate:
168       if (i < Desc.NumOperands) {
169         const MCOperandInfo &Info = Desc.OpInfo[i];
170         if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
171           MCSymbol *Sym = Printer.createTempSymbol("typeindex");
172 
173           SmallVector<wasm::ValType, 4> Returns;
174           SmallVector<wasm::ValType, 4> Params;
175 
176           const MachineRegisterInfo &MRI =
177               MI->getParent()->getParent()->getRegInfo();
178           for (const MachineOperand &MO : MI->defs())
179             Returns.push_back(getType(MRI.getRegClass(MO.getReg())));
180           for (const MachineOperand &MO : MI->explicit_uses())
181             if (MO.isReg())
182               Params.push_back(getType(MRI.getRegClass(MO.getReg())));
183 
184           // call_indirect instructions have a callee operand at the end which
185           // doesn't count as a param.
186           if (WebAssembly::isCallIndirect(*MI))
187             Params.pop_back();
188 
189           MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Sym);
190           WasmSym->setReturns(std::move(Returns));
191           WasmSym->setParams(std::move(Params));
192           WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
193 
194           const MCExpr *Expr = MCSymbolRefExpr::create(
195               WasmSym, MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX, Ctx);
196           MCOp = MCOperand::createExpr(Expr);
197           break;
198         }
199       }
200       MCOp = MCOperand::createImm(MO.getImm());
201       break;
202     case MachineOperand::MO_FPImmediate: {
203       // TODO: MC converts all floating point immediate operands to double.
204       // This is fine for numeric values, but may cause NaNs to change bits.
205       const ConstantFP *Imm = MO.getFPImm();
206       if (Imm->getType()->isFloatTy())
207         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat());
208       else if (Imm->getType()->isDoubleTy())
209         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble());
210       else
211         llvm_unreachable("unknown floating point immediate type");
212       break;
213     }
214     case MachineOperand::MO_GlobalAddress:
215       assert(MO.getTargetFlags() == 0 &&
216              "WebAssembly does not use target flags on GlobalAddresses");
217       MCOp = LowerSymbolOperand(GetGlobalAddressSymbol(MO), MO.getOffset(),
218                                 MO.getGlobal()->getValueType()->isFunctionTy());
219       break;
220     case MachineOperand::MO_ExternalSymbol:
221       // The target flag indicates whether this is a symbol for a
222       // variable or a function.
223       assert((MO.getTargetFlags() & -2) == 0 &&
224              "WebAssembly uses only one target flag bit on ExternalSymbols");
225       MCOp = LowerSymbolOperand(GetExternalSymbolSymbol(MO), /*Offset=*/0,
226                                 MO.getTargetFlags() & 1);
227       break;
228     }
229 
230     OutMI.addOperand(MCOp);
231   }
232 }
233