[WebAssembly] Add except_ref as a first-class type

[aheejin]

Summary

Add except_ref as a first-class type, according to the Level 1 exception handling proposal.

[aheejin]

rebase

[aheejin]

• Opcode for except_ref has changed to -0x18

[dschuff]

include/llvm/CodeGen/MachineValueType.h

751

This seems fishy. What would a caller actually do with a 0-size type? Do we expect this to ever be called? Should it be an unreachable instead?

[aheejin]

rebase + change -0x18 to 0x68 to use uint8_t

[aheejin]

• deleted , at the end to match the previous code

[aheejin]

include/llvm/CodeGen/MachineValueType.h

751

Yes, it is called here, while tablegen generates tables. We need this line, because if it's an unreachable, it will crash the LLVM build while running tablegen.

Also we have one more 0 in this CL in this line in lib/Target/WebAssembly/WebAssemblyRegisterInfo.td:

def EXCEPT_REF : WebAssemblyRegClass<[ExceptRef], 0, (add EXCEPT_REF_0)>;

These two pieces of information is used by tablegen to generate this array in $(LLVM_ROOT)/build/lib/Target/WebAssembly/WebAssemblyGenRegisterInfo.inc:

static const TargetRegisterInfo::RegClassInfo RegClassInfos[] = {
  // Mode = 0 (Default)
  { 0, 0, 0, VTLists+13 },    // EXCEPT_REF
  { 32, 32, 32, VTLists+0 },    // I32
  { 32, 32, 32, VTLists+4 },    // F32
  { 64, 64, 64, VTLists+2 },    // I64
  { 64, 64, 64, VTLists+6 },    // F64
  { 128, 128, 128, VTLists+8 },    // V128
};

There is a line for each register class in this array. There are three zeros in the first line for EXCEPT_REF register class. First two zeros come from case ExceptRef: return 0; here and the third zero is from that def EXCEPT_REF : ... line from lib/Target/WebAssembly/WebAssemblyRegisterInfo.td. Each line makes up an instance of [[ https://github.com/llvm-mirror/llvm/blob/587a2e31eca58dbc0a7535c70aa3bbbb5cfe733c/include/llvm/CodeGen/TargetRegisterInfo.h#L224-L227 | TargetRegisterInfo::RegClassInfo ]].

So these 0s become RegSize, SpillSize, and SpillAlignment member variables in [[ https://github.com/llvm-mirror/llvm/blob/587a2e31eca58dbc0a7535c70aa3bbbb5cfe733c/include/llvm/CodeGen/TargetRegisterInfo.h#L224-L227 | TargetRegisterInfo::RegClassInfo ]] class. But in wasm we don't use this kind of size information anywhere because we don't use physical registers or run register allocation pass.

[aheejin]

• rebase

[dschuff]

Everything else seems pretty straightforward.

include/llvm/CodeGen/MachineValueType.h

751

Hm yeah I guess that makes sense and we are already weird when it comes to spilling (we don't). It seems like the other common case it's used for is getting sub/super registers (which we also don't need, but there's target-independent code) and debug info. Hopefully that won't be an issue since they can't be written to memory. Seems like 0 should be ok for now since it's more likely to expose any issues quickly compared to picking a number. But regardless of what we pick here we'll probably be revisiting this issue again.

include/llvm/BinaryFormat/Wasm.h

 
 // Type immediate encodings used in various contexts.
 enum : unsigned {
   WASM_TYPE_I32 = 0x7F,
   WASM_TYPE_I64 = 0x7E,
   WASM_TYPE_F32 = 0x7D,
   WASM_TYPE_F64 = 0x7C,
   WASM_TYPE_ANYFUNC = 0x70,
+  WASM_TYPE_EXCEPT_REF = 0x68,
   WASM_TYPE_FUNC = 0x60,
   WASM_TYPE_NORESULT = 0x40, // for blocks with no result values
 };
 
 // Kinds of externals (for imports and exports).
 enum : unsigned {
   WASM_EXTERNAL_FUNCTION = 0x0,
   WASM_EXTERNAL_TABLE = 0x1,

 };
 
 // Subset of types that a value can have
 enum class ValType {
   I32 = WASM_TYPE_I32,
   I64 = WASM_TYPE_I64,
   F32 = WASM_TYPE_F32,
   F64 = WASM_TYPE_F64,
+  EXCEPT_REF = WASM_TYPE_EXCEPT_REF,
 };
 
 // Kind codes used in the custom "name" section
 enum : unsigned {
   WASM_NAMES_FUNCTION = 0x1,
   WASM_NAMES_LOCAL    = 0x2,
 };
 

include/llvm/CodeGen/MachineValueType.h

enum SimpleValueType : uint8_t {
       Glue           =  110,   // This glues nodes together during pre-RA sched
 
       isVoid         =  111,   // This has no value
 
       Untyped        =  112,   // This value takes a register, but has
                                // unspecified type.  The register class
                                // will be determined by the opcode.
 
+      ExceptRef      = 113,    // WebAssembly's except_ref type
+
       FIRST_VALUETYPE = 1,     // This is always the beginning of the list.
-      LAST_VALUETYPE =  113,   // This always remains at the end of the list.
+      LAST_VALUETYPE =  114,   // This always remains at the end of the list.
 
       // This is the current maximum for LAST_VALUETYPE.
       // MVT::MAX_ALLOWED_VALUETYPE is used for asserts and to size bit vectors
       // This value must be a multiple of 32.
       MAX_ALLOWED_VALUETYPE = 128,
 
       // A value of type llvm::TokenTy
       token          = 248,
unsigned getSizeInBits() const {
       case v16i64:
       case nxv32i32:
       case nxv16i64: return 1024;
       case v256i8:
       case v128i16:
       case v64i32:
       case v32i64:
       case nxv32i64: return 2048;
+      case ExceptRef: return 0; // opaque type
       }
     }
 
     unsigned getScalarSizeInBits() const {
       return getScalarType().getSizeInBits();
     }
 
     /// Return the number of bytes overwritten by a store of the specified value

include/llvm/CodeGen/ValueTypes.td

 def nxv2f64  : ValueType<128, 106>; // n x  2 x f64 vector value
 def nxv4f64  : ValueType<256, 107>; // n x  4 x f64 vector value
 def nxv8f64  : ValueType<512, 108>; // n x  8 x f64 vector value
 
 def x86mmx : ValueType<64 , 109>;   // X86 MMX value
 def FlagVT : ValueType<0  , 110>;   // Pre-RA sched glue
 def isVoid : ValueType<0  , 111>;   // Produces no value
 def untyped: ValueType<8  , 112>;   // Produces an untyped value
+def ExceptRef: ValueType<0, 113>;   // WebAssembly's except_ref type
 def token  : ValueType<0  , 248>;   // TokenTy
 def MetadataVT: ValueType<0, 249>;  // Metadata
 
 // Pseudo valuetype mapped to the current pointer size to any address space.
 // Should only be used in TableGen.
 def iPTRAny   : ValueType<0, 250>;
 
 // Pseudo valuetype to represent "vector of any size"

lib/Target/WebAssembly/InstPrinter/WebAssemblyInstPrinter.cpp

WebAssemblyInstPrinter::printWebAssemblySignatureOperand(const MCInst *MI,
   case WebAssembly::ExprType::F64: O << "f64"; break;
   case WebAssembly::ExprType::I8x16: O << "i8x16"; break;
   case WebAssembly::ExprType::I16x8: O << "i16x8"; break;
   case WebAssembly::ExprType::I32x4: O << "i32x4"; break;
   case WebAssembly::ExprType::F32x4: O << "f32x4"; break;
   case WebAssembly::ExprType::B8x16: O << "b8x16"; break;
   case WebAssembly::ExprType::B16x8: O << "b16x8"; break;
   case WebAssembly::ExprType::B32x4: O << "b32x4"; break;
+  case WebAssembly::ExprType::ExceptRef: O << "except_ref"; break;
   }
 }
 
 const char *llvm::WebAssembly::TypeToString(MVT Ty) {
   switch (Ty.SimpleTy) {
   case MVT::i32:
     return "i32";
   case MVT::i64:
     return "i64";
   case MVT::f32:
     return "f32";
   case MVT::f64:
     return "f64";
   case MVT::v16i8:
   case MVT::v8i16:
   case MVT::v4i32:
   case MVT::v4f32:
     return "v128";
+  case MVT::ExceptRef:
+    return "except_ref";
   default:
     llvm_unreachable("unsupported type");
   }
 }
 
 const char *llvm::WebAssembly::TypeToString(wasm::ValType Type) {
   switch (Type) {
   case wasm::ValType::I32:
     return "i32";
   case wasm::ValType::I64:
     return "i64";
   case wasm::ValType::F32:
     return "f32";
   case wasm::ValType::F64:
     return "f64";
+  case wasm::ValType::EXCEPT_REF:
+    return "except_ref";
   }
   llvm_unreachable("unsupported type");
 }

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h

 static const unsigned StoreAddressOperandNo = 2;
 
 /// The operand number of the load or store p2align in load/store instructions.
 static const unsigned LoadP2AlignOperandNo = 1;
 static const unsigned StoreP2AlignOperandNo = 0;
 
 /// This is used to indicate block signatures.
 enum class ExprType : unsigned {
-  Void    = 0x40,
-  I32     = 0x7F,
-  I64     = 0x7E,
-  F32     = 0x7D,
-  F64     = 0x7C,
-  I8x16   = 0x7B,
-  I16x8   = 0x7A,
-  I32x4   = 0x79,
-  F32x4   = 0x78,
-  B8x16   = 0x77,
-  B16x8   = 0x76,
-  B32x4   = 0x75
+  Void      = 0x40,
+  I32       = 0x7F,
+  I64       = 0x7E,
+  F32       = 0x7D,
+  F64       = 0x7C,
+  I8x16     = 0x7B,
+  I16x8     = 0x7A,
+  I32x4     = 0x79,
+  F32x4     = 0x78,
+  B8x16     = 0x77,
+  B16x8     = 0x76,
+  B32x4     = 0x75,
+  ExceptRef = 0x68
 };
 
 /// Instruction opcodes emitted via means other than CodeGen.
 static const unsigned Nop = 0x01;
 static const unsigned End = 0x0b;
 
 wasm::ValType toValType(const MVT &Ty);
 
 } // end namespace WebAssembly
 } // end namespace llvm
 
 #endif

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.cpp

 }
 
 wasm::ValType WebAssembly::toValType(const MVT &Ty) {
   switch (Ty.SimpleTy) {
   case MVT::i32: return wasm::ValType::I32;
   case MVT::i64: return wasm::ValType::I64;
   case MVT::f32: return wasm::ValType::F32;
   case MVT::f64: return wasm::ValType::F64;
+  case MVT::ExceptRef: return wasm::ValType::EXCEPT_REF;
   default: llvm_unreachable("unexpected type");
   }
 }

lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp

static void FixEndsAtEndOfFunction(
   case MVT::i32: retType = WebAssembly::ExprType::I32; break;
   case MVT::i64: retType = WebAssembly::ExprType::I64; break;
   case MVT::f32: retType = WebAssembly::ExprType::F32; break;
   case MVT::f64: retType = WebAssembly::ExprType::F64; break;
   case MVT::v16i8: retType = WebAssembly::ExprType::I8x16; break;
   case MVT::v8i16: retType = WebAssembly::ExprType::I16x8; break;
   case MVT::v4i32: retType = WebAssembly::ExprType::I32x4; break;
   case MVT::v4f32: retType = WebAssembly::ExprType::F32x4; break;
+  case MVT::ExceptRef: retType = WebAssembly::ExprType::ExceptRef; break;
   default: llvm_unreachable("unexpected return type");
   }
 
   for (MachineBasicBlock &MBB : reverse(MF)) {
     for (MachineInstr &MI : reverse(MBB)) {
       if (MI.isPosition() || MI.isDebugValue())
         continue;
       if (MI.getOpcode() == WebAssembly::END_BLOCK) {

lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp

static unsigned getDropOpcode(const TargetRegisterClass *RC) {
   if (RC == &WebAssembly::I64RegClass)
     return WebAssembly::DROP_I64;
   if (RC == &WebAssembly::F32RegClass)
     return WebAssembly::DROP_F32;
   if (RC == &WebAssembly::F64RegClass)
     return WebAssembly::DROP_F64;
   if (RC == &WebAssembly::V128RegClass)
     return WebAssembly::DROP_V128;
+  if (RC == &WebAssembly::EXCEPT_REFRegClass)
+    return WebAssembly::DROP_EXCEPT_REF;
   llvm_unreachable("Unexpected register class");
 }
 
 /// Get the appropriate get_local opcode for the given register class.
 static unsigned getGetLocalOpcode(const TargetRegisterClass *RC) {
   if (RC == &WebAssembly::I32RegClass)
     return WebAssembly::GET_LOCAL_I32;
   if (RC == &WebAssembly::I64RegClass)
     return WebAssembly::GET_LOCAL_I64;
   if (RC == &WebAssembly::F32RegClass)
     return WebAssembly::GET_LOCAL_F32;
   if (RC == &WebAssembly::F64RegClass)
     return WebAssembly::GET_LOCAL_F64;
   if (RC == &WebAssembly::V128RegClass)
     return WebAssembly::GET_LOCAL_V128;
+  if (RC == &WebAssembly::EXCEPT_REFRegClass)
+    return WebAssembly::GET_LOCAL_EXCEPT_REF;
   llvm_unreachable("Unexpected register class");
 }
 
 /// Get the appropriate set_local opcode for the given register class.
 static unsigned getSetLocalOpcode(const TargetRegisterClass *RC) {
   if (RC == &WebAssembly::I32RegClass)
     return WebAssembly::SET_LOCAL_I32;
   if (RC == &WebAssembly::I64RegClass)
     return WebAssembly::SET_LOCAL_I64;
   if (RC == &WebAssembly::F32RegClass)
     return WebAssembly::SET_LOCAL_F32;
   if (RC == &WebAssembly::F64RegClass)
     return WebAssembly::SET_LOCAL_F64;
   if (RC == &WebAssembly::V128RegClass)
     return WebAssembly::SET_LOCAL_V128;
+  if (RC == &WebAssembly::EXCEPT_REFRegClass)
+    return WebAssembly::SET_LOCAL_EXCEPT_REF;
   llvm_unreachable("Unexpected register class");
 }
 
 /// Get the appropriate tee_local opcode for the given register class.
 static unsigned getTeeLocalOpcode(const TargetRegisterClass *RC) {
   if (RC == &WebAssembly::I32RegClass)
     return WebAssembly::TEE_LOCAL_I32;
   if (RC == &WebAssembly::I64RegClass)
     return WebAssembly::TEE_LOCAL_I64;
   if (RC == &WebAssembly::F32RegClass)
     return WebAssembly::TEE_LOCAL_F32;
   if (RC == &WebAssembly::F64RegClass)
     return WebAssembly::TEE_LOCAL_F64;
   if (RC == &WebAssembly::V128RegClass)
     return WebAssembly::TEE_LOCAL_V128;
+  if (RC == &WebAssembly::EXCEPT_REFRegClass)
+    return WebAssembly::TEE_LOCAL_EXCEPT_REF;
   llvm_unreachable("Unexpected register class");
 }
 
 /// Get the type associated with the given register class.
 static MVT typeForRegClass(const TargetRegisterClass *RC) {
   if (RC == &WebAssembly::I32RegClass)
     return MVT::i32;
   if (RC == &WebAssembly::I64RegClass)
     return MVT::i64;
   if (RC == &WebAssembly::F32RegClass)
     return MVT::f32;
   if (RC == &WebAssembly::F64RegClass)
     return MVT::f64;
+  if (RC == &WebAssembly::EXCEPT_REFRegClass)
+    return MVT::ExceptRef;
   llvm_unreachable("unrecognized register class");
 }
 
 /// Given a MachineOperand of a stackified vreg, return the instruction at the
 /// start of the expression tree.
 static MachineInstr *FindStartOfTree(MachineOperand &MO,
                                      MachineRegisterInfo &MRI,
                                      WebAssemblyFunctionInfo &MFI) {

lib/Target/WebAssembly/WebAssemblyFastISel.cpp

MVT::SimpleValueType getLegalType(MVT::SimpleValueType VT) {
     case MVT::i1:
     case MVT::i8:
     case MVT::i16:
       return MVT::i32;
     case MVT::i32:
     case MVT::i64:
     case MVT::f32:
     case MVT::f64:
+    case MVT::ExceptRef:
       return VT;
     case MVT::f16:
       return MVT::f32;
     case MVT::v16i8:
     case MVT::v8i16:
     case MVT::v4i32:
     case MVT::v4f32:
       if (Subtarget->hasSIMD128())
for (auto const &Arg : F->args()) {
     case MVT::v4i32:
       Opc = WebAssembly::ARGUMENT_v4i32;
       RC = &WebAssembly::V128RegClass;
       break;
     case MVT::v4f32:
       Opc = WebAssembly::ARGUMENT_v4f32;
       RC = &WebAssembly::V128RegClass;
       break;
+    case MVT::ExceptRef:
+      Opc = WebAssembly::ARGUMENT_EXCEPT_REF;
+      RC = &WebAssembly::EXCEPT_REFRegClass;
+      break;
     default:
       return false;
     }
     unsigned ResultReg = createResultReg(RC);
     BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(Opc), ResultReg)
       .addImm(i);
     updateValueMap(&Arg, ResultReg);
 
case MVT::v4i32:
           IsDirect ? WebAssembly::CALL_v4i32 : WebAssembly::PCALL_INDIRECT_v4i32;
       ResultReg = createResultReg(&WebAssembly::V128RegClass);
       break;
     case MVT::v4f32:
       Opc =
           IsDirect ? WebAssembly::CALL_v4f32 : WebAssembly::PCALL_INDIRECT_v4f32;
       ResultReg = createResultReg(&WebAssembly::V128RegClass);
       break;
+    case MVT::ExceptRef:
+      Opc = IsDirect ? WebAssembly::CALL_EXCEPT_REF
+                     : WebAssembly::PCALL_INDIRECT_EXCEPT_REF;
+      ResultReg = createResultReg(&WebAssembly::EXCEPT_REFRegClass);
+      break;
     default:
       return false;
     }
   }
 
   SmallVector<unsigned, 8> Args;
   for (unsigned i = 0, e = Call->getNumArgOperands(); i < e; ++i) {
     Value *V = Call->getArgOperand(i);
bool WebAssemblyFastISel::selectSelect(const Instruction *I) {
   case MVT::f32:
     Opc = WebAssembly::SELECT_F32;
     RC = &WebAssembly::F32RegClass;
     break;
   case MVT::f64:
     Opc = WebAssembly::SELECT_F64;
     RC = &WebAssembly::F64RegClass;
     break;
+  case MVT::ExceptRef:
+    Opc = WebAssembly::SELECT_EXCEPT_REF;
+    RC = &WebAssembly::EXCEPT_REFRegClass;
+    break;
   default:
     return false;
   }
 
   unsigned ResultReg = createResultReg(RC);
   BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(Opc), ResultReg)
     .addReg(TrueReg)
     .addReg(FalseReg)
case MVT::v8i16:
     Opc = WebAssembly::RETURN_v8i16;
     break;
   case MVT::v4i32:
     Opc = WebAssembly::RETURN_v4i32;
     break;
   case MVT::v4f32:
     Opc = WebAssembly::RETURN_v4f32;
     break;
+  case MVT::ExceptRef:
+    Opc = WebAssembly::RETURN_EXCEPT_REF;
+    break;
   default: return false;
   }
 
   unsigned Reg;
   if (FuncInfo.Fn->getAttributes().hasAttribute(0, Attribute::SExt))
     Reg = getRegForSignedValue(RV);
   else if (FuncInfo.Fn->getAttributes().hasAttribute(0, Attribute::ZExt))
     Reg = getRegForUnsignedValue(RV);

lib/Target/WebAssembly/WebAssemblyInstrCall.td

def CALL_INDIRECT_#vt : SIMD_I<(outs V128:$dst),
                                   0x11>;
 }
 
 let Uses = [SP32, SP64], isCall = 1 in {
   defm : CALL<I32, "i32.">;
   defm : CALL<I64, "i64.">;
   defm : CALL<F32, "f32.">;
   defm : CALL<F64, "f64.">;
+  defm : CALL<EXCEPT_REF, "except_ref.">;
   defm : SIMD_CALL<v16i8, "i8x16.">;
   defm : SIMD_CALL<v8i16, "i16x8.">;
   defm : SIMD_CALL<v4i32, "i32x4.">;
   defm : SIMD_CALL<v4f32, "f32x4.">;
 
   def CALL_VOID : I<(outs), (ins function32_op:$callee, variable_ops),
                     [(WebAssemblycall0 (i32 imm:$callee))],
                     "call    \t$callee", 0x10>;

 def : Pat<(v16i8 (WebAssemblycall1 (WebAssemblywrapper tglobaladdr:$callee))),
           (CALL_v16i8 tglobaladdr:$callee)>, Requires<[HasSIMD128]>;
 def : Pat<(v8i16 (WebAssemblycall1 (WebAssemblywrapper tglobaladdr:$callee))),
           (CALL_v8i16 tglobaladdr:$callee)>, Requires<[HasSIMD128]>;
 def : Pat<(v4i32 (WebAssemblycall1 (WebAssemblywrapper tglobaladdr:$callee))),
           (CALL_v4i32 tglobaladdr:$callee)>, Requires<[HasSIMD128]>;
 def : Pat<(v4f32 (WebAssemblycall1 (WebAssemblywrapper tglobaladdr:$callee))),
           (CALL_v4f32 tglobaladdr:$callee)>, Requires<[HasSIMD128]>;
+def : Pat<(ExceptRef
+           (WebAssemblycall1 (WebAssemblywrapper tglobaladdr:$callee))),
+          (CALL_EXCEPT_REF tglobaladdr:$callee)>;
 def : Pat<(WebAssemblycall0 (WebAssemblywrapper tglobaladdr:$callee)),
           (CALL_VOID tglobaladdr:$callee)>;
 
 // Patterns for matching a direct call to an external symbol.
 def : Pat<(i32 (WebAssemblycall1 (WebAssemblywrapper texternalsym:$callee))),
           (CALL_I32 texternalsym:$callee)>;
 def : Pat<(i64 (WebAssemblycall1 (WebAssemblywrapper texternalsym:$callee))),
           (CALL_I64 texternalsym:$callee)>;
 def : Pat<(f32 (WebAssemblycall1 (WebAssemblywrapper texternalsym:$callee))),
           (CALL_F32 texternalsym:$callee)>;
 def : Pat<(f64 (WebAssemblycall1 (WebAssemblywrapper texternalsym:$callee))),
           (CALL_F64 texternalsym:$callee)>;
 def : Pat<(v16i8 (WebAssemblycall1 (WebAssemblywrapper texternalsym:$callee))),
           (CALL_v16i8 texternalsym:$callee)>, Requires<[HasSIMD128]>;
 def : Pat<(v8i16 (WebAssemblycall1 (WebAssemblywrapper texternalsym:$callee))),
           (CALL_v8i16 texternalsym:$callee)>, Requires<[HasSIMD128]>;
 def : Pat<(v4i32 (WebAssemblycall1 (WebAssemblywrapper texternalsym:$callee))),
           (CALL_v4i32 texternalsym:$callee)>, Requires<[HasSIMD128]>;
 def : Pat<(v4f32 (WebAssemblycall1 (WebAssemblywrapper texternalsym:$callee))),
           (CALL_v4f32 texternalsym:$callee)>, Requires<[HasSIMD128]>;
+def : Pat<(ExceptRef
+           (WebAssemblycall1 (WebAssemblywrapper texternalsym:$callee))),
+          (CALL_EXCEPT_REF texternalsym:$callee)>;
 def : Pat<(WebAssemblycall0 (WebAssemblywrapper texternalsym:$callee)),
           (CALL_VOID texternalsym:$callee)>;

lib/Target/WebAssembly/WebAssemblyInstrControl.td

 
 let isTerminator = 1, hasCtrlDep = 1, isBarrier = 1 in {
 
 let isReturn = 1 in {
   defm : RETURN<I32>;
   defm : RETURN<I64>;
   defm : RETURN<F32>;
   defm : RETURN<F64>;
+  defm : RETURN<EXCEPT_REF>;
   defm : SIMD_RETURN<v16i8>;
   defm : SIMD_RETURN<v8i16>;
   defm : SIMD_RETURN<v4i32>;
   defm : SIMD_RETURN<v4f32>;
 
   def RETURN_VOID : I<(outs), (ins), [(WebAssemblyreturn)], "return", 0x0f>;
 
   // This is to RETURN_VOID what FALLTHROUGH_RETURN_#vt is to RETURN_#vt.

lib/Target/WebAssembly/WebAssemblyInstrExceptRef.td

+// WebAssemblyInstrExceptRef.td-WebAssembly except_ref codegen --*- tablegen -*-
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief WebAssembly except_ref operand code-gen constructs.
+///
+//===----------------------------------------------------------------------===//
+
+let Defs = [ARGUMENTS] in {
+
+def SELECT_EXCEPT_REF : I<(outs EXCEPT_REF:$dst),
+                          (ins EXCEPT_REF:$lhs, EXCEPT_REF:$rhs, I32:$cond),
+                          [(set EXCEPT_REF:$dst,
+                           (select I32:$cond, EXCEPT_REF:$lhs,
+                            EXCEPT_REF:$rhs))],
+                          "except_ref.select\t$dst, $lhs, $rhs, $cond", 0x1b>;
+
+} // Defs = [ARGUMENTS]
+
+def : Pat<(select (i32 (setne I32:$cond, 0)), EXCEPT_REF:$lhs, EXCEPT_REF:$rhs),
+          (SELECT_EXCEPT_REF EXCEPT_REF:$lhs, EXCEPT_REF:$rhs, I32:$cond)>;
+def : Pat<(select (i32 (seteq I32:$cond, 0)), EXCEPT_REF:$lhs, EXCEPT_REF:$rhs),
+          (SELECT_EXCEPT_REF EXCEPT_REF:$rhs, EXCEPT_REF:$lhs, I32:$cond)>;

lib/Target/WebAssembly/WebAssemblyInstrInfo.td

multiclass SIMD_ARGUMENT<ValueType vt> {
   def ARGUMENT_#vt : SIMD_I<(outs V128:$res), (ins i32imm:$argno),
                             [(set (vt V128:$res),
                                   (WebAssemblyargument timm:$argno))]>;
 }
 defm : ARGUMENT<I32>;
 defm : ARGUMENT<I64>;
 defm : ARGUMENT<F32>;
 defm : ARGUMENT<F64>;
+defm : ARGUMENT<EXCEPT_REF>;
 defm : SIMD_ARGUMENT<v16i8>;
 defm : SIMD_ARGUMENT<v8i16>;
 defm : SIMD_ARGUMENT<v4i32>;
 defm : SIMD_ARGUMENT<v4f32>;
 
 let Defs = [ARGUMENTS] in {
 
 // get_local and set_local are not generated by instruction selection; they

 
 } // hasSideEffects = 0
 }
 defm : LOCAL<I32>;
 defm : LOCAL<I64>;
 defm : LOCAL<F32>;
 defm : LOCAL<F64>;
 defm : LOCAL<V128>, Requires<[HasSIMD128]>;
+defm : LOCAL<EXCEPT_REF>, Requires<[HasExceptionHandling]>;
 
 let isMoveImm = 1, isAsCheapAsAMove = 1, isReMaterializable = 1 in {
 def CONST_I32 : I<(outs I32:$res), (ins i32imm_op:$imm),
                   [(set I32:$res, imm:$imm)],
                   "i32.const\t$res, $imm", 0x41>;
 def CONST_I64 : I<(outs I64:$res), (ins i64imm_op:$imm),
                   [(set I64:$res, imm:$imm)],
                   "i64.const\t$res, $imm", 0x42>;

 include "WebAssemblyInstrMemory.td"
 include "WebAssemblyInstrCall.td"
 include "WebAssemblyInstrControl.td"
 include "WebAssemblyInstrInteger.td"
 include "WebAssemblyInstrConv.td"
 include "WebAssemblyInstrFloat.td"
 include "WebAssemblyInstrAtomics.td"
 include "WebAssemblyInstrSIMD.td"
+include "WebAssemblyInstrExceptRef.td"

lib/Target/WebAssembly/WebAssemblyRegisterInfo.td

 def SP32 : WebAssemblyReg<"%SP32">;
 def SP64 : WebAssemblyReg<"%SP64">;
 
 // The register allocation framework requires register classes have at least
 // one register, so we define a few for the floating point register classes
 // since we otherwise don't need a physical register in those classes.
 def F32_0 : WebAssemblyReg<"%f32.0">;
 def F64_0 : WebAssemblyReg<"%f64.0">;
-
 def V128_0: WebAssemblyReg<"%v128">;
+def EXCEPT_REF_0 : WebAssemblyReg<"%except_ref.0">;
 
 // The value stack "register". This is an opaque entity which serves to order
 // uses and defs that must remain in LIFO order.
 def VALUE_STACK : WebAssemblyReg<"STACK">;
 
 // The incoming arguments "register". This is an opaque entity which serves to
 // order the ARGUMENT instructions that are emulating live-in registers and
 // must not be scheduled below other instructions.
 def ARGUMENTS : WebAssemblyReg<"ARGUMENTS">;
 
 //===----------------------------------------------------------------------===//
 //  Register classes
 //===----------------------------------------------------------------------===//
 
 def I32 : WebAssemblyRegClass<[i32], 32, (add FP32, SP32)>;
 def I64 : WebAssemblyRegClass<[i64], 64, (add FP64, SP64)>;
 def F32 : WebAssemblyRegClass<[f32], 32, (add F32_0)>;
 def F64 : WebAssemblyRegClass<[f64], 64, (add F64_0)>;
 def V128 : WebAssemblyRegClass<[v4f32, v4i32, v16i8, v8i16], 128, (add V128_0)>;
-
+def EXCEPT_REF : WebAssemblyRegClass<[ExceptRef], 0, (add EXCEPT_REF_0)>;

utils/TableGen/CodeGenTarget.cpp

StringRef llvm::getEnumName(MVT::SimpleValueType T) {
   case MVT::nxv2f64:  return "MVT::nxv2f64";
   case MVT::nxv4f64:  return "MVT::nxv4f64";
   case MVT::nxv8f64:  return "MVT::nxv8f64";
   case MVT::token:    return "MVT::token";
   case MVT::Metadata: return "MVT::Metadata";
   case MVT::iPTR:     return "MVT::iPTR";
   case MVT::iPTRAny:  return "MVT::iPTRAny";
   case MVT::Untyped:  return "MVT::Untyped";
+  case MVT::ExceptRef: return "MVT::ExceptRef";
   default: llvm_unreachable("ILLEGAL VALUE TYPE!");
   }
 }
 
 /// getQualifiedName - Return the name of the specified record, with a
 /// namespace qualifier if the record contains one.
 ///
 std::string llvm::getQualifiedName(const Record *R) {