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 *
34 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 
78 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 
109 MCOperand WebAssemblyMCInstLower::LowerSymbolOperand(MCSymbol *Sym,
110                                                      int64_t Offset,
111                                                      bool IsFunc,
112                                                      bool IsGlob) const {
113   MCSymbolRefExpr::VariantKind VK =
114       IsFunc ? MCSymbolRefExpr::VK_WebAssembly_FUNCTION :
115       IsGlob ? MCSymbolRefExpr::VK_WebAssembly_GLOBAL
116              : MCSymbolRefExpr::VK_None;
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     if (IsGlob)
124       report_fatal_error("Global indexes with offsets not supported");
125     Expr =
126         MCBinaryExpr::createAdd(Expr, MCConstantExpr::create(Offset, Ctx), Ctx);
127   }
128 
129   return MCOperand::createExpr(Expr);
130 }
131 
132 // Return the WebAssembly type associated with the given register class.
133 static wasm::ValType getType(const TargetRegisterClass *RC) {
134   if (RC == &WebAssembly::I32RegClass)
135     return wasm::ValType::I32;
136   if (RC == &WebAssembly::I64RegClass)
137     return wasm::ValType::I64;
138   if (RC == &WebAssembly::F32RegClass)
139     return wasm::ValType::F32;
140   if (RC == &WebAssembly::F64RegClass)
141     return wasm::ValType::F64;
142   llvm_unreachable("Unexpected register class");
143 }
144 
145 void WebAssemblyMCInstLower::Lower(const MachineInstr *MI,
146                                    MCInst &OutMI) const {
147   OutMI.setOpcode(MI->getOpcode());
148 
149   const MCInstrDesc &Desc = MI->getDesc();
150   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
151     const MachineOperand &MO = MI->getOperand(i);
152 
153     MCOperand MCOp;
154     switch (MO.getType()) {
155     default:
156       MI->print(errs());
157       llvm_unreachable("unknown operand type");
158     case MachineOperand::MO_MachineBasicBlock:
159       MI->print(errs());
160       llvm_unreachable("MachineBasicBlock operand should have been rewritten");
161     case MachineOperand::MO_Register: {
162       // Ignore all implicit register operands.
163       if (MO.isImplicit())
164         continue;
165       const WebAssemblyFunctionInfo &MFI =
166           *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>();
167       unsigned WAReg = MFI.getWAReg(MO.getReg());
168       MCOp = MCOperand::createReg(WAReg);
169       break;
170     }
171     case MachineOperand::MO_Immediate:
172       if (i < Desc.NumOperands) {
173         const MCOperandInfo &Info = Desc.OpInfo[i];
174         if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
175           MCSymbol *Sym = Printer.createTempSymbol("typeindex");
176 
177           SmallVector<wasm::ValType, 4> Returns;
178           SmallVector<wasm::ValType, 4> Params;
179 
180           const MachineRegisterInfo &MRI =
181               MI->getParent()->getParent()->getRegInfo();
182           for (const MachineOperand &MO : MI->defs())
183             Returns.push_back(getType(MRI.getRegClass(MO.getReg())));
184           for (const MachineOperand &MO : MI->explicit_uses())
185             if (MO.isReg())
186               Params.push_back(getType(MRI.getRegClass(MO.getReg())));
187 
188           // call_indirect instructions have a callee operand at the end which
189           // doesn't count as a param.
190           if (WebAssembly::isCallIndirect(*MI))
191             Params.pop_back();
192 
193           MCSymbolWasm *WasmSym = cast<MCSymbolWasm>(Sym);
194           WasmSym->setReturns(std::move(Returns));
195           WasmSym->setParams(std::move(Params));
196           WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
197 
198           const MCExpr *Expr = MCSymbolRefExpr::create(
199               WasmSym, MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX, Ctx);
200           MCOp = MCOperand::createExpr(Expr);
201           break;
202         }
203       }
204       MCOp = MCOperand::createImm(MO.getImm());
205       break;
206     case MachineOperand::MO_FPImmediate: {
207       // TODO: MC converts all floating point immediate operands to double.
208       // This is fine for numeric values, but may cause NaNs to change bits.
209       const ConstantFP *Imm = MO.getFPImm();
210       if (Imm->getType()->isFloatTy())
211         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat());
212       else if (Imm->getType()->isDoubleTy())
213         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble());
214       else
215         llvm_unreachable("unknown floating point immediate type");
216       break;
217     }
218     case MachineOperand::MO_GlobalAddress:
219       assert(MO.getTargetFlags() == WebAssemblyII::MO_NO_FLAG &&
220              "WebAssembly does not use target flags on GlobalAddresses");
221       MCOp = LowerSymbolOperand(GetGlobalAddressSymbol(MO), MO.getOffset(),
222                                 MO.getGlobal()->getValueType()->isFunctionTy(),
223                                 false);
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() & ~WebAssemblyII::MO_SYMBOL_MASK) == 0 &&
229              "WebAssembly uses only symbol flags on ExternalSymbols");
230       MCOp = LowerSymbolOperand(GetExternalSymbolSymbol(MO), /*Offset=*/0,
231           (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_FUNCTION) != 0,
232           (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_GLOBAL) != 0);
233       break;
234     }
235 
236     OutMI.addOperand(MCOp);
237   }
238 }
239