lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp

   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 "WebAssemblyAsmPrinter.h"
  17 #include "WebAssemblyMachineFunctionInfo.h"
  18 #include "WebAssemblyRuntimeLibcallSignatures.h"
  19 #include "WebAssemblyUtilities.h"
  20 #include "llvm/CodeGen/AsmPrinter.h"
  21 #include "llvm/CodeGen/MachineFunction.h"
  22 #include "llvm/IR/Constants.h"
  23 #include "llvm/MC/MCAsmInfo.h"
  24 #include "llvm/MC/MCContext.h"
  25 #include "llvm/MC/MCExpr.h"
  26 #include "llvm/MC/MCInst.h"
  27 #include "llvm/MC/MCSymbolWasm.h"
  28 #include "llvm/Support/ErrorHandling.h"
  29 #include "llvm/Support/raw_ostream.h"
  30 using namespace llvm;
  31
  32 // Defines llvm::WebAssembly::getStackOpcode to convert register instructions to
  33 // stack instructions
  34 #define GET_INSTRMAP_INFO 1
  35 #include "WebAssemblyGenInstrInfo.inc"
  36
  37 // This disables the removal of registers when lowering into MC, as required
  38 // by some current tests.
  39 cl::opt<bool>
  40     WasmKeepRegisters("wasm-keep-registers", cl::Hidden,
  41                       cl::desc("WebAssembly: output stack registers in"
  42                                " instruction output for test purposes only."),
  43                       cl::init(false));
  44
  45 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI);
  46
  47 MCSymbol *
  48 WebAssemblyMCInstLower::GetGlobalAddressSymbol(const MachineOperand &MO) const {
  49   const GlobalValue *Global = MO.getGlobal();
  50   auto *WasmSym = cast<MCSymbolWasm>(Printer.getSymbol(Global));
  51
  52   if (const auto *FuncTy = dyn_cast<FunctionType>(Global->getValueType())) {
  53     const MachineFunction &MF = *MO.getParent()->getParent()->getParent();
  54     const TargetMachine &TM = MF.getTarget();
  55     const Function &CurrentFunc = MF.getFunction();
  56
  57     SmallVector<MVT, 1> ResultMVTs;
  58     SmallVector<MVT, 4> ParamMVTs;
  59     computeSignatureVTs(FuncTy, CurrentFunc, TM, ParamMVTs, ResultMVTs);
  60
  61     auto Signature = signatureFromMVTs(ResultMVTs, ParamMVTs);
  62     WasmSym->setSignature(Signature.get());
  63     Printer.addSignature(std::move(Signature));
  64     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
  65   }
  66
  67   return WasmSym;
  68 }
  69
  70 MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
  71     const MachineOperand &MO) const {
  72   const char *Name = MO.getSymbolName();
  73   auto *WasmSym = cast<MCSymbolWasm>(Printer.GetExternalSymbolSymbol(Name));
  74   const WebAssemblySubtarget &Subtarget = Printer.getSubtarget();
  75
  76   // Except for the two exceptions (__stack_pointer and __cpp_exception), all
  77   // other external symbols used by CodeGen are functions. It's OK to hardcode
  78   // knowledge of specific symbols here; this method is precisely there for
  79   // fetching the signatures of known Clang-provided symbols.
  80   if (strcmp(Name, "__stack_pointer") == 0) {
  81     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
  82     WasmSym->setGlobalType(wasm::WasmGlobalType{
  83         uint8_t(Subtarget.hasAddr64() ? wasm::WASM_TYPE_I64
  84                                       : wasm::WASM_TYPE_I32),
  85         true});
  86     return WasmSym;
  87   }
  88
  89   SmallVector<wasm::ValType, 4> Returns;
  90   SmallVector<wasm::ValType, 4> Params;
  91   if (strcmp(Name, "__cpp_exception") == 0) {
  92     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_EVENT);
  93     // We can't confirm its signature index for now because there can be
  94     // imported exceptions. Set it to be 0 for now.
  95     WasmSym->setEventType(
  96         {wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION, /* SigIndex */ 0});
  97     // We may have multiple C++ compilation units to be linked together, each of
  98     // which defines the exception symbol. To resolve them, we declare them as
  99     // weak.
 100     WasmSym->setWeak(true);
 101     WasmSym->setExternal(true);
 102
 103     // All C++ exceptions are assumed to have a single i32 (for wasm32) or i64
 104     // (for wasm64) param type and void return type. The reaon is, all C++
 105     // exception values are pointers, and to share the type section with
 106     // functions, exceptions are assumed to have void return type.
 107     Params.push_back(Subtarget.hasAddr64() ? wasm::ValType::I64
 108                                            : wasm::ValType::I32);
 109   } else { // Function symbols
 110     WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
 111     getLibcallSignature(Subtarget, Name, Returns, Params);
 112   }
 113   auto Signature =
 114       make_unique<wasm::WasmSignature>(std::move(Returns), std::move(Params));
 115   WasmSym->setSignature(Signature.get());
 116   Printer.addSignature(std::move(Signature));
 117
 118   return WasmSym;
 119 }
 120
 121 MCOperand WebAssemblyMCInstLower::lowerSymbolOperand(MCSymbol *Sym,
 122                                                      int64_t Offset,
 123                                                      bool IsFunc, bool IsGlob,
 124                                                      bool IsEvent) const {
 125   MCSymbolRefExpr::VariantKind VK =
 126       IsFunc ? MCSymbolRefExpr::VK_WebAssembly_FUNCTION
 127              : IsGlob ? MCSymbolRefExpr::VK_WebAssembly_GLOBAL
 128                       : IsEvent ? MCSymbolRefExpr::VK_WebAssembly_EVENT
 129                                 : MCSymbolRefExpr::VK_None;
 130
 131   const MCExpr *Expr = MCSymbolRefExpr::create(Sym, VK, Ctx);
 132
 133   if (Offset != 0) {
 134     if (IsFunc)
 135       report_fatal_error("Function addresses with offsets not supported");
 136     if (IsGlob)
 137       report_fatal_error("Global indexes with offsets not supported");
 138     if (IsEvent)
 139       report_fatal_error("Event indexes with offsets not supported");
 140     Expr =
 141         MCBinaryExpr::createAdd(Expr, MCConstantExpr::create(Offset, Ctx), Ctx);
 142   }
 143
 144   return MCOperand::createExpr(Expr);
 145 }
 146
 147 // Return the WebAssembly type associated with the given register class.
 148 static wasm::ValType getType(const TargetRegisterClass *RC) {
 149   if (RC == &WebAssembly::I32RegClass)
 150     return wasm::ValType::I32;
 151   if (RC == &WebAssembly::I64RegClass)
 152     return wasm::ValType::I64;
 153   if (RC == &WebAssembly::F32RegClass)
 154     return wasm::ValType::F32;
 155   if (RC == &WebAssembly::F64RegClass)
 156     return wasm::ValType::F64;
 157   if (RC == &WebAssembly::V128RegClass)
 158     return wasm::ValType::V128;
 159   llvm_unreachable("Unexpected register class");
 160 }
 161
 162 void WebAssemblyMCInstLower::lower(const MachineInstr *MI,
 163                                    MCInst &OutMI) const {
 164   OutMI.setOpcode(MI->getOpcode());
 165
 166   const MCInstrDesc &Desc = MI->getDesc();
 167   for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
 168     const MachineOperand &MO = MI->getOperand(I);
 169
 170     MCOperand MCOp;
 171     switch (MO.getType()) {
 172     default:
 173       MI->print(errs());
 174       llvm_unreachable("unknown operand type");
 175     case MachineOperand::MO_MachineBasicBlock:
 176       MI->print(errs());
 177       llvm_unreachable("MachineBasicBlock operand should have been rewritten");
 178     case MachineOperand::MO_Register: {
 179       // Ignore all implicit register operands.
 180       if (MO.isImplicit())
 181         continue;
 182       const WebAssemblyFunctionInfo &MFI =
 183           *MI->getParent()->getParent()->getInfo<WebAssemblyFunctionInfo>();
 184       unsigned WAReg = MFI.getWAReg(MO.getReg());
 185       MCOp = MCOperand::createReg(WAReg);
 186       break;
 187     }
 188     case MachineOperand::MO_Immediate:
 189       if (I < Desc.NumOperands) {
 190         const MCOperandInfo &Info = Desc.OpInfo[I];
 191         if (Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
 192           MCSymbol *Sym = Printer.createTempSymbol("typeindex");
 193
 194           SmallVector<wasm::ValType, 4> Returns;
 195           SmallVector<wasm::ValType, 4> Params;
 196
 197           const MachineRegisterInfo &MRI =
 198               MI->getParent()->getParent()->getRegInfo();
 199           for (const MachineOperand &MO : MI->defs())
 200             Returns.push_back(getType(MRI.getRegClass(MO.getReg())));
 201           for (const MachineOperand &MO : MI->explicit_uses())
 202             if (MO.isReg())
 203               Params.push_back(getType(MRI.getRegClass(MO.getReg())));
 204
 205           // call_indirect instructions have a callee operand at the end which
 206           // doesn't count as a param.
 207           if (WebAssembly::isCallIndirect(*MI))
 208             Params.pop_back();
 209
 210           auto *WasmSym = cast<MCSymbolWasm>(Sym);
 211           auto Signature = make_unique<wasm::WasmSignature>(std::move(Returns),
 212                                                             std::move(Params));
 213           WasmSym->setSignature(Signature.get());
 214           Printer.addSignature(std::move(Signature));
 215           WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
 216
 217           const MCExpr *Expr = MCSymbolRefExpr::create(
 218               WasmSym, MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX, Ctx);
 219           MCOp = MCOperand::createExpr(Expr);
 220           break;
 221         }
 222       }
 223       MCOp = MCOperand::createImm(MO.getImm());
 224       break;
 225     case MachineOperand::MO_FPImmediate: {
 226       // TODO: MC converts all floating point immediate operands to double.
 227       // This is fine for numeric values, but may cause NaNs to change bits.
 228       const ConstantFP *Imm = MO.getFPImm();
 229       if (Imm->getType()->isFloatTy())
 230         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToFloat());
 231       else if (Imm->getType()->isDoubleTy())
 232         MCOp = MCOperand::createFPImm(Imm->getValueAPF().convertToDouble());
 233       else
 234         llvm_unreachable("unknown floating point immediate type");
 235       break;
 236     }
 237     case MachineOperand::MO_GlobalAddress:
 238       assert(MO.getTargetFlags() == WebAssemblyII::MO_NO_FLAG &&
 239              "WebAssembly does not use target flags on GlobalAddresses");
 240       MCOp = lowerSymbolOperand(GetGlobalAddressSymbol(MO), MO.getOffset(),
 241                                 MO.getGlobal()->getValueType()->isFunctionTy(),
 242                                 false, false);
 243       break;
 244     case MachineOperand::MO_ExternalSymbol:
 245       // The target flag indicates whether this is a symbol for a
 246       // variable or a function.
 247       assert((MO.getTargetFlags() & ~WebAssemblyII::MO_SYMBOL_MASK) == 0 &&
 248              "WebAssembly uses only symbol flags on ExternalSymbols");
 249       MCOp = lowerSymbolOperand(
 250           GetExternalSymbolSymbol(MO), /*Offset=*/0,
 251           (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_FUNCTION) != 0,
 252           (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_GLOBAL) != 0,
 253           (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_EVENT) != 0);
 254       break;
 255     case MachineOperand::MO_MCSymbol:
 256       // This is currently used only for LSDA symbols (GCC_except_table),
 257       // because global addresses or other external symbols are handled above.
 258       assert(MO.getTargetFlags() == 0 &&
 259              "WebAssembly does not use target flags on MCSymbol");
 260       MCOp = lowerSymbolOperand(MO.getMCSymbol(), /*Offset=*/0, false, false,
 261                                 false);
 262       break;
 263     }
 264
 265     OutMI.addOperand(MCOp);
 266   }
 267
 268   if (!WasmKeepRegisters)
 269     removeRegisterOperands(MI, OutMI);
 270 }
 271
 272 static void removeRegisterOperands(const MachineInstr *MI, MCInst &OutMI) {
 273   // Remove all uses of stackified registers to bring the instruction format
 274   // into its final stack form used thruout MC, and transition opcodes to
 275   // their _S variant.
 276   // We do this seperate from the above code that still may need these
 277   // registers for e.g. call_indirect signatures.
 278   // See comments in lib/Target/WebAssembly/WebAssemblyInstrFormats.td for
 279   // details.
 280   // TODO: the code above creates new registers which are then removed here.
 281   // That code could be slightly simplified by not doing that, though maybe
 282   // it is simpler conceptually to keep the code above in "register mode"
 283   // until this transition point.
 284   // FIXME: we are not processing inline assembly, which contains register
 285   // operands, because it is used by later target generic code.
 286   if (MI->isDebugInstr() || MI->isLabel() || MI->isInlineAsm())
 287     return;
 288
 289   // Transform to _S instruction.
 290   auto RegOpcode = OutMI.getOpcode();
 291   auto StackOpcode = WebAssembly::getStackOpcode(RegOpcode);
 292   assert(StackOpcode != -1 && "Failed to stackify instruction");
 293   OutMI.setOpcode(StackOpcode);
 294
 295   // Remove register operands.
 296   for (auto I = OutMI.getNumOperands(); I; --I) {
 297     auto &MO = OutMI.getOperand(I - 1);
 298     if (MO.isReg()) {
 299       OutMI.erase(&MO);
 300     }
 301   }
 302 }