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 "TargetInfo/WebAssemblyTargetInfo.h"
17 #include "Utils/WebAssemblyTypeUtilities.h"
18 #include "Utils/WebAssemblyUtilities.h"
19 #include "WebAssemblyAsmPrinter.h"
20 #include "WebAssemblyISelLowering.h"
21 #include "WebAssemblyMachineFunctionInfo.h"
22 #include "llvm/CodeGen/AsmPrinter.h"
23 #include "llvm/CodeGen/MachineFunction.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/MC/MCAsmInfo.h"
26 #include "llvm/MC/MCContext.h"
27 #include "llvm/MC/MCExpr.h"
28 #include "llvm/MC/MCInst.h"
29 #include "llvm/MC/MCSymbolWasm.h"
30 #include "llvm/Support/ErrorHandling.h"
31 #include "llvm/Support/raw_ostream.h"
32 
33 using namespace llvm;
34 
35 // This disables the removal of registers when lowering into MC, as required
36 // by some current tests.
37 cl::opt<bool>
38     WasmKeepRegisters("wasm-keep-registers", cl::Hidden,
39                       cl::desc("WebAssembly: output stack registers in"
40                                " instruction output for test purposes only."),
41                       cl::init(false));
42 
43 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI);
44 
45 MCSymbol *
46 WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const {
47   const GlobalValue *Global = MO.getGlobal();
48   if (!isa<Function>(Global)) {
49     auto *WasmSym = cast<MCSymbolWasm>(Printer.getSymbol(Global));
50     // If the symbol doesn't have an explicit WasmSymbolType yet and the
51     // GlobalValue is actually a WebAssembly global, then ensure the symbol is a
52     // WASM_SYMBOL_TYPE_GLOBAL.
53     if (WebAssembly::isWasmVarAddressSpace(Global->getAddressSpace()) &&
54         !WasmSym->getType()) {
55       const MachineFunction &MF = *MO.getParent()->getParent()->getParent();
56       const TargetMachine &TM = MF.getTarget();
57       const Function &CurrentFunc = MF.getFunction();
58       Type *GlobalVT = Global->getValueType();
59       SmallVector<MVT, 1> VTs;
60       computeLegalValueVTs(CurrentFunc, TM, GlobalVT, VTs);
61 
62       WebAssembly::wasmSymbolSetType(WasmSym, GlobalVT, VTs);
63     }
64     return WasmSym;
65   }
66 
67   const auto *FuncTy = cast<FunctionType>(Global->getValueType());
68   const MachineFunction &MF = *MO.getParent()->getParent()->getParent();
69   const TargetMachine &TM = MF.getTarget();
70   const Function &CurrentFunc = MF.getFunction();
71 
72   SmallVector<MVT, 1> ResultMVTs;
73   SmallVector<MVT, 4> ParamMVTs;
74   const auto *const F = dyn_cast<Function>(Global);
75   computeSignatureVTs(FuncTy, F, CurrentFunc, TM, ParamMVTs, ResultMVTs);
76   auto Signature = signatureFromMVTs(ResultMVTs, ParamMVTs);
77 
78   bool InvokeDetected = false;
79   auto *WasmSym = Printer.getMCSymbolForFunction(
80       F, WebAssembly::WasmEnableEmEH || WebAssembly::WasmEnableEmSjLj,
81       Signature.get(), InvokeDetected);
82   WasmSym->setSignature(Signature.get());
83   Printer.addSignature(std::move(Signature));
84   WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
85   return WasmSym;
86 }
87 
88 MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
89     const MachineOperand &MO) const {
90   return Printer.getOrCreateWasmSymbol(MO.getSymbolName());
91 }
92 
93 MCOperand WebAssemblyMCInstLower::lowerSymbolOperand(const MachineOperand &MO,
94                                                      MCSymbol *Sym) const {
95   MCSymbolRefExpr::VariantKind Kind = MCSymbolRefExpr::VK_None;
96   unsigned TargetFlags = MO.getTargetFlags();
97 
98   switch (TargetFlags) {
99     case WebAssemblyII::MO_NO_FLAG:
100       break;
101     case WebAssemblyII::MO_GOT_TLS:
102       Kind = MCSymbolRefExpr::VK_WASM_GOT_TLS;
103       break;
104     case WebAssemblyII::MO_GOT:
105       Kind = MCSymbolRefExpr::VK_GOT;
106       break;
107     case WebAssemblyII::MO_MEMORY_BASE_REL:
108       Kind = MCSymbolRefExpr::VK_WASM_MBREL;
109       break;
110     case WebAssemblyII::MO_TLS_BASE_REL:
111       Kind = MCSymbolRefExpr::VK_WASM_TLSREL;
112       break;
113     case WebAssemblyII::MO_TABLE_BASE_REL:
114       Kind = MCSymbolRefExpr::VK_WASM_TBREL;
115       break;
116     default:
117       llvm_unreachable("Unknown target flag on GV operand");
118   }
119 
120   const MCExpr *Expr = MCSymbolRefExpr::create(Sym, Kind, Ctx);
121 
122   if (MO.getOffset() != 0) {
123     const auto *WasmSym = cast<MCSymbolWasm>(Sym);
124     if (TargetFlags == WebAssemblyII::MO_GOT)
125       report_fatal_error("GOT symbol references do not support offsets");
126     if (WasmSym->isFunction())
127       report_fatal_error("Function addresses with offsets not supported");
128     if (WasmSym->isGlobal())
129       report_fatal_error("Global indexes with offsets not supported");
130     if (WasmSym->isTag())
131       report_fatal_error("Tag indexes with offsets not supported");
132     if (WasmSym->isTable())
133       report_fatal_error("Table indexes with offsets not supported");
134 
135     Expr = MCBinaryExpr::createAdd(
136         Expr, MCConstantExpr::create(MO.getOffset(), Ctx), Ctx);
137   }
138 
139   return MCOperand::createExpr(Expr);
140 }
141 
142 MCOperand WebAssemblyMCInstLower::lowerTypeIndexOperand(
143     SmallVector<wasm::ValType, 1> &&Returns,
144     SmallVector<wasm::ValType, 4> &&Params) const {
145   auto Signature = std::make_unique<wasm::WasmSignature>(std::move(Returns),
146                                                          std::move(Params));
147   MCSymbol *Sym = Printer.createTempSymbol("typeindex");
148   auto *WasmSym = cast<MCSymbolWasm>(Sym);
149   WasmSym->setSignature(Signature.get());
150   Printer.addSignature(std::move(Signature));
151   WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
152   const MCExpr *Expr =
153       MCSymbolRefExpr::create(WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, Ctx);
154   return MCOperand::createExpr(Expr);
155 }
156 
157 static void getFunctionReturns(const MachineInstr *MI,
158                                SmallVectorImpl<wasm::ValType> &Returns) {
159   const Function &F = MI->getMF()->getFunction();
160   const TargetMachine &TM = MI->getMF()->getTarget();
161   Type *RetTy = F.getReturnType();
162   SmallVector<MVT, 4> CallerRetTys;
163   computeLegalValueVTs(F, TM, RetTy, CallerRetTys);
164   valTypesFromMVTs(CallerRetTys, Returns);
165 }
166 
167 void WebAssemblyMCInstLower::lower(const MachineInstr *MI,
168                                    MCInst &OutMI) const {
169   OutMI.setOpcode(MI->getOpcode());
170 
171   const MCInstrDesc &Desc = MI->getDesc();
172   unsigned NumVariadicDefs = MI->getNumExplicitDefs() - Desc.getNumDefs();
173   for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
174     const MachineOperand &MO = MI->getOperand(I);
175 
176     MCOperand MCOp;
177     switch (MO.getType()) {
178     default:
179       MI->print(errs());
180       llvm_unreachable("unknown operand type");
181     case MachineOperand::MO_MachineBasicBlock:
182       MI->print(errs());
183       llvm_unreachable("MachineBasicBlock operand should have been rewritten");
184     case MachineOperand::MO_Register: {
185       // Ignore all implicit register operands.
186       if (MO.isImplicit())
187         continue;
188       const WebAssemblyFunctionInfo &MFI =
189           *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>();
190       unsigned WAReg = MFI.getWAReg(MO.getReg());
191       MCOp = MCOperand::createReg(WAReg);
192       break;
193     }
194     case MachineOperand::MO_Immediate: {
195       unsigned DescIndex = I - NumVariadicDefs;
196       if (DescIndex < Desc.NumOperands) {
197         const MCOperandInfo &Info = Desc.operands()[DescIndex];
198         if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
199           SmallVector<wasm::ValType, 4> Returns;
200           SmallVector<wasm::ValType, 4> Params;
201 
202           const MachineRegisterInfo &MRI =
203               MI->getParent()->getParent()->getRegInfo();
204           for (const MachineOperand &MO : MI->defs())
205             Returns.push_back(
206                 WebAssembly::regClassToValType(MRI.getRegClass(MO.getReg())));
207           for (const MachineOperand &MO : MI->explicit_uses())
208             if (MO.isReg())
209               Params.push_back(
210                   WebAssembly::regClassToValType(MRI.getRegClass(MO.getReg())));
211 
212           // call_indirect instructions have a callee operand at the end which
213           // doesn't count as a param.
214           if (WebAssembly::isCallIndirect(MI->getOpcode()))
215             Params.pop_back();
216 
217           // return_call_indirect instructions have the return type of the
218           // caller
219           if (MI->getOpcode() == WebAssembly::RET_CALL_INDIRECT)
220             getFunctionReturns(MI, Returns);
221 
222           MCOp = lowerTypeIndexOperand(std::move(Returns), std::move(Params));
223           break;
224         } else if (Info.OperandType == WebAssembly::OPERAND_SIGNATURE) {
225           auto BT = static_cast<WebAssembly::BlockType>(MO.getImm());
226           assert(BT != WebAssembly::BlockType::Invalid);
227           if (BT == WebAssembly::BlockType::Multivalue) {
228             SmallVector<wasm::ValType, 1> Returns;
229             getFunctionReturns(MI, Returns);
230             MCOp = lowerTypeIndexOperand(std::move(Returns),
231                                          SmallVector<wasm::ValType, 4>());
232             break;
233           }
234         }
235       }
236       MCOp = MCOperand::createImm(MO.getImm());
237       break;
238     }
239     case MachineOperand::MO_FPImmediate: {
240       const ConstantFP *Imm = MO.getFPImm();
241       const uint64_t BitPattern =
242           Imm->getValueAPF().bitcastToAPInt().getZExtValue();
243       if (Imm->getType()->isFloatTy())
244         MCOp = MCOperand::createSFPImm(static_cast<uint32_t>(BitPattern));
245       else if (Imm->getType()->isDoubleTy())
246         MCOp = MCOperand::createDFPImm(BitPattern);
247       else
248         llvm_unreachable("unknown floating point immediate type");
249       break;
250     }
251     case MachineOperand::MO_GlobalAddress:
252       MCOp = lowerSymbolOperand(MO, GetGlobalAddressSymbol(MO));
253       break;
254     case MachineOperand::MO_ExternalSymbol:
255       MCOp = lowerSymbolOperand(MO, GetExternalSymbolSymbol(MO));
256       break;
257     case MachineOperand::MO_MCSymbol:
258       assert(MO.getTargetFlags() == 0 &&
259              "WebAssembly does not use target flags on MCSymbol");
260       MCOp = lowerSymbolOperand(MO, MO.getMCSymbol());
261       break;
262     }
263 
264     OutMI.addOperand(MCOp);
265   }
266 
267   if (!WasmKeepRegisters)
268     removeRegisterOperands(MI, OutMI);
269   else if (Desc.variadicOpsAreDefs())
270     OutMI.insert(OutMI.begin(), MCOperand::createImm(MI->getNumExplicitDefs()));
271 }
272 
273 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI) {
274   // Remove all uses of stackified registers to bring the instruction format
275   // into its final stack form used thruout MC, and transition opcodes to
276   // their _S variant.
277   // We do this separate from the above code that still may need these
278   // registers for e.g. call_indirect signatures.
279   // See comments in lib/Target/WebAssembly/WebAssemblyInstrFormats.td for
280   // details.
281   // TODO: the code above creates new registers which are then removed here.
282   // That code could be slightly simplified by not doing that, though maybe
283   // it is simpler conceptually to keep the code above in "register mode"
284   // until this transition point.
285   // FIXME: we are not processing inline assembly, which contains register
286   // operands, because it is used by later target generic code.
287   if (MI->isDebugInstr() || MI->isLabel() || MI->isInlineAsm())
288     return;
289 
290   // Transform to _S instruction.
291   auto RegOpcode = OutMI.getOpcode();
292   auto StackOpcode = WebAssembly::getStackOpcode(RegOpcode);
293   assert(StackOpcode != -1 && "Failed to stackify instruction");
294   OutMI.setOpcode(StackOpcode);
295 
296   // Remove register operands.
297   for (auto I = OutMI.getNumOperands(); I; --I) {
298     auto &MO = OutMI.getOperand(I - 1);
299     if (MO.isReg()) {
300       OutMI.erase(&MO);
301     }
302   }
303 }
304