[clang][WebAssembly] Implement support for table types and appropriate semantic restrictions

[asb]

Summary

This patch isn't yet ready for merging, but I think is ready for high-level review. Note that it assumes something like this has been merged into D122215.

Todo:

• funcref support and test coverage

WebAssembly tables are modeled at the IR level as arrays in address space 1. As the instructions accessing tables take the table index as an immediate, use of tables is very restricted (i.e. it isn't possible to pass as an argument etc). This patch models tables in C as arrays of reference types and adds various semantic restrictions to avoid illegal uses. Some of these restrictions overlap with those for sizeless types, while of course the limitations on passing in parameters and so on go above and beyond that.

I'd really appreciate any high-level feedback / questions / concerns about this approach at this point.

[asb]

Addresses some potential null pointer dereferences.

[asb]

Update to latest version and update summary. As I say there, it would be really helpful to get some feedback at this point.

[rjmccall]

Sounds like you need an RFC thread on the forums describing the underlying WebAssembly feature and your proposed language design for exposing it in C.

[tlively]

clang/test/CodeGen/WebAssembly/table.c

6

Why must tables be declared with 0 size? I would expect declaring any concrete size to work, since the underlying module can declare tables of any size. Also, how will all this work with table growth? Is there some danger of static analysis thinking that a table has an out-of-bound access when in fact it has been grown beyond its original size? Would declaring a sizeless table help there?

clang/test/Sema/wasm-refs-and-tables.c

15

This error message is confusing because it's not really the element type that is the problem, but rather the lack of size declaration on the array itself. Also, as a matter of UX, it would be nice if we could avoid printing __attribute__((address_space(1))) as part of the externref type.

16

Is this a temporary restriction? The underlying Wasm format supports initializers.

17

Why is this?

44–45

Are we going to be able to work around this to provide a builtin for table.grow?

89

Does this need a separate error message since it isn't a binary expression?

[asb]

Update to address review comments.

@rjmccall: That makes sense - I'll write up an RFC for this. Thanks for taking a look.

clang/test/CodeGen/WebAssembly/table.c

6

That's a limitation in this initial support for tables but needn't be a limitation going forward. We don't currently support generating table initialisers, but I think tables can still be useful without that (so that functionality can be split out to some future patch).

Regarding static analysis: potentially a static analyser will complain until it's taught to ignore tables. Using something other than an array type (either just a pointer or new sizeless type) is definitely an alternative, but in the case of a pointer there's not good story for adding syntax to support initialisation. Introducing a new sizeless type would need a story on indicating the type of the table's contents. Modelling as an array at least gives us those things (and array-like syntax for getting/setting elements, though I'm not sure that's a big factor one way or another). Which all to say I'm totally open to alternatives, but when I started on this I'd understood that arrays were the current preferred approach and when I considered those other options, it didn't feel like the others were clearly better (just different trade-offs!).

clang/test/Sema/wasm-refs-and-tables.c

15

This error message is inherited from the code to support sizeless types. But it's easy enough to cover this case alongside the one for non-zero size, so I've done that. That also covers the initialisation case for the time being.

16

Yes that's right, I've changed the message now to be clearer this is a current restriction rather than a fundamental one.

17

I understood that's what had been agreed as the initial way to expose them, and going beyond that, I don't think there's a clear story on sharing tables between compilation units. So I'd again put this down to the "MVP"-ness of the patch.

44–45

Yep, D124162 provides the builtins that don't use element segments. Using custom type-checking for those builtins neatly sidesteps this being an issue.

89

Good point, that would be more precise. I've added one now.

[asb]

Re-add full context.

[tlively]

Nice! code looks good to me, but we'll need community signoff on an RFC as @rjmccall mentioned and it would be nice to have a clang maintainer sign off as well.

clang/test/CodeGen/WebAssembly/table.c

6

By "sizeless table" I meant using an array type without a size (not sure if there's a more precise term for that), so something like static __externref_t table[]. I wonder if that would help avoid false positives from static analyzers because they wouldn't be able to reason about sizes.

But starting out with many restrictions and incrementally relaxing them as necessary sounds good 👍

clang/test/Sema/wasm-refs-and-tables.c

17

Sounds good for the MVP. I expect that it will be useful to share tables across compilation units in the future, and I think we might even have support for the necessary table relocations in the backend and linker thanks to @pmatos's work.

[asb]

Rebase, and fix+test missed error case (taking the address of table).

[asb]

In D123510#3465123, @rjmccall wrote:

Sounds like you need an RFC thread on the forums describing the underlying WebAssembly feature and your proposed language design for exposing it in C.

Now posted as https://discourse.llvm.org/t/rfc-webassembly-tables-in-clang/62049

[asb]

Added semantic restrictions for C++ specific constructs.

It would likely make sense to introduce a isWebAssemblyTable method and refacctor to use that.

[asb]

Add a isWebAssemblyTable helper and refactor to use it.

[asb]

Rebase (partial - rebases my patch stack on top of latest LLVM, but still needs a rebase on to Paulo's patch introducing funcref support).

[asb]

Rebase on top of D128440

[asb]

Rebase again.

[pmatos]

@asb This can _also_ be closed since table support landed.

[asb]

Abandoning, as this was ultimately merged into D139010 which has now landed.

clang/include/clang/AST/Type.h

public:
   /// or layout.
   bool isSizelessType() const;
   bool isSizelessBuiltinType() const;
 
   /// Check if this is a WebAssembly Reference Type.
   bool isWebAssemblyReferenceType() const;
   bool isWebAssemblyExternrefType() const;
 
+  /// Returns true if this is a WebAssembly table type: either an array of
+  /// reference types, or a pointer to a reference type (which can only be
+  /// created by array to pointer decay).
+  bool isWebAssemblyTableType() const;
+
   /// Determines if this is a sizeless type supported by the
   /// 'arm_sve_vector_bits' type attribute, which can be applied to a single
   /// SVE vector or predicate, excluding tuple types such as svint32x4_t.
   bool isVLSTBuiltinType() const;
 
   /// Returns the representative type for the element of an SVE builtin type.
   /// This is used to represent fixed-length SVE vectors created with the
   /// 'arm_sve_vector_bits' type attribute as VectorType.

clang/include/clang/Basic/DiagnosticSemaKinds.td

 
 // WebAssembly reference type and table diagnostics
 def err_wasm_reference_pointer : Error<
   "pointers to WebAssembly reference types are illegal">;
 def err_wasm_reference_reference : Error<
   "references to WebAssembly reference types are illegal">;
 def err_wasm_capture_reference : Error<
   "cannot capture WebAssembly reference">;
+def err_wasm_table_pointer : Error<
+  "pointers to WebAssembly tables are illegal">;
+def err_wasm_table_reference : Error<
+  "references to WebAssembly tables are illegal">;
 def err_wasm_addrof_reference : Error<
   "cannot take address of WebAssembly reference">;
+def err_wasm_addrof_table : Error<
+  "cannot take address of WebAssembly table">;
+def err_typecheck_wasm_table_must_have_zero_length : Error<
+  "only zero-length WebAssembly tables are currently supported">;
+def err_wasm_table_in_function : Error<
+  "WebAssembly table cannot be declared within a function">;
+def err_wasm_table_as_function_argument : Error<
+  "cannot use WebAssembly table as a function argument">;
+def err_wasm_table_invalid_uett_operand : Error<
+  "invalid application of '%0' to WebAssembly table">;
+def err_wasm_cast_table : Error<
+  "cannot cast WebAssembly table">;
+def err_wasm_table_conditional_expression : Error<
+  "cannot use WebAssembly tables as the 2nd or 3rd operands of a conditional expression">;
+def err_wasm_table_assignment : Error<
+  "cannot assign WebAssembly table to a variable">;
+def err_wasm_table_return : Error<
+  "cannot return a WebAssembly table">;
+def err_wasm_table_throw : Error<
+  "cannot throw a WebAssembly table">;
+def err_wasm_table_catch : Error<
+  "cannot catch WebAssembly table">;
+def err_wasm_table_exception_spec : Error<
+  "WebAssembly table not allowed in exception sepcification">;
+def err_wasm_table_must_be_static : Error<
+  "WebAssembly table must be static">;
+def err_wasm_multidimensional_ref_array : Error<
+  "multi-dimensional arrays of WebAssembly references are illegal">;
 } // end of sema component.

clang/lib/AST/Type.cpp

 
 bool Type::isWebAssemblyExternrefType() const {
   const BuiltinType *BT = getAs<BuiltinType>();
   if (BT && BT->getKind() == BuiltinType::WasmExternRef)
     return true;
   return false;
 }
 
+bool Type::isWebAssemblyTableType() const {
+  return ((isArrayType() &&
+           getArrayElementTypeNoTypeQual()->isWebAssemblyReferenceType()) ||
+          (isPointerType() && getPointeeType()->isWebAssemblyReferenceType()));
+}
+
 bool Type::isSizelessType() const { return isSizelessBuiltinType(); }
 
 bool Type::isVLSTBuiltinType() const {
   if (const BuiltinType *BT = getAs<BuiltinType>()) {
     switch (BT->getKind()) {
     case BuiltinType::SveInt8:
     case BuiltinType::SveInt16:
     case BuiltinType::SveInt32:

clang/lib/Sema/SemaCast.cpp

else
       return;
     assert(SrcExpr.isUsable());
   }
   SrcExpr = Self.DefaultFunctionArrayLvalueConversion(SrcExpr.get());
   if (SrcExpr.isInvalid())
     return;
   QualType SrcType = SrcExpr.get()->getType();
 
+  if (SrcType->isWebAssemblyTableType()) {
+    Self.Diag(OpRange.getBegin(), diag::err_wasm_cast_table)
+        << SrcExpr.get()->getSourceRange();
+    SrcExpr = ExprError();
+    return;
+  }
+
   assert(!SrcType->isPlaceholderType());
 
   checkAddressSpaceCast(SrcType, DestType);
   if (SrcExpr.isInvalid())
     return;
 
   if (Self.RequireCompleteType(OpRange.getBegin(), DestType,
                                diag::err_typecheck_cast_to_incomplete)) {

clang/lib/Sema/SemaChecking.cpp

if (Op == OO_New || Op == OO_Array_New) {
         = FD->getType()->castAs<FunctionProtoType>();
       if (!Proto->isNothrow(/*ResultIfDependent*/true) &&
           CheckNonNullExpr(*this, RetValExp))
         Diag(ReturnLoc, diag::warn_operator_new_returns_null)
           << FD << getLangOpts().CPlusPlus11;
     }
   }
 
+  if (RetValExp && RetValExp->getType()->isWebAssemblyTableType()) {
+    Diag(ReturnLoc, diag::err_wasm_table_return);
+  }
+
   // PPC MMA non-pointer types are not allowed as return type. Checking the type
   // here prevent the user from using a PPC MMA type as trailing return type.
   if (Context.getTargetInfo().getTriple().isPPC64())
     CheckPPCMMAType(RetValExp->getType(), ReturnLoc);
 }
 
 /// Check for comparisons of floating-point values using == and !=. Issue a
 /// warning if the comparison is not likely to do what the programmer intended.
if (LangOpts.CPlusPlus && !Param->isInvalidDecl()) {
       // want to see if this function's declaration context is a record.
       DeclContext *DC = Param->getDeclContext();
       if (DC && DC->isFunctionOrMethod()) {
         if (auto *RD = dyn_cast<CXXRecordDecl>(DC->getParent()))
           CheckShadowInheritedFields(Param->getLocation(), Param->getDeclName(),
                                      RD, /*DeclIsField*/ false);
       }
     }
+
+    if (!Param->isInvalidDecl() &&
+        Param->getOriginalType()->isWebAssemblyTableType()) {
+      Param->setInvalidDecl();
+      HasInvalidParm = true;
+      Diag(Param->getLocation(), diag::err_wasm_table_as_function_argument);
+    }
   }
 
   return HasInvalidParm;
 }
 
 Optional<std::pair<CharUnits, CharUnits>>
 static getBaseAlignmentAndOffsetFromPtr(const Expr *E, ASTContext &Ctx);
 

clang/lib/Sema/SemaDecl.cpp

if (TSC != TSCS_unspecified) {
       Diag(D.getDeclSpec().getThreadStorageClassSpecLoc(),
            diag::err_opencl_unknown_type_specifier)
           << getLangOpts().getOpenCLVersionString()
           << DeclSpec::getSpecifierName(TSC) << 1;
       NewVD->setInvalidDecl();
     }
   }
 
+  // WebAssembly tables are always in address space 1 (wasm_var). Don't apply
+  // address space if the table has local storage (semantic checks elsewhere
+  // will produce an error anyway).
+  if (const Type *ElTy = NewVD->getType()->getArrayElementTypeNoTypeQual()) {
+    if (ElTy && ElTy->isWebAssemblyReferenceType() &&
+        !NewVD->hasLocalStorage()) {
+      QualType Type = Context.getAddrSpaceQualType(
+          NewVD->getType(), Context.getLangASForBuiltinAddressSpace(1));
+      NewVD->setType(Type);
+    }
+  }
+
   // Handle attributes prior to checking for duplicates in MergeVarDecl
   ProcessDeclAttributes(S, NewVD, D);
 
   // FIXME: This is probably the wrong location to be doing this and we should
   // probably be doing this for more attributes (especially for function
   // pointer attributes such as format, warn_unused_result, etc.). Ideally
   // the code to copy attributes would be generated by TableGen.
   if (R->isFunctionPointerType())
if (NewVD->hasLocalStorage() && T.isObjCGCWeak()
     if (getLangOpts().getGC() != LangOptions::NonGC)
       Diag(NewVD->getLocation(), diag::warn_gc_attribute_weak_on_local);
     else {
       assert(!getLangOpts().ObjCAutoRefCount);
       Diag(NewVD->getLocation(), diag::warn_attribute_weak_on_local);
     }
   }
 
+  // WebAssembly tables must be static with a zero length and can't be
+  // declared within functions.
+  if (T->isWebAssemblyTableType()) {
+    if (getCurScope()->isFunctionScope()) {
+      Diag(NewVD->getLocation(), diag::err_wasm_table_in_function);
+      NewVD->setInvalidDecl();
+      return;
+    }
+    if (NewVD->getStorageClass() != SC_Static) {
+      Diag(NewVD->getLocation(), diag::err_wasm_table_must_be_static);
+      NewVD->setInvalidDecl();
+      return;
+    }
+    const auto *ATy = dyn_cast<ConstantArrayType>(T.getTypePtr());
+    if (!ATy || ATy->getSize().getSExtValue() != 0) {
+      Diag(NewVD->getLocation(),
+           diag::err_typecheck_wasm_table_must_have_zero_length);
+      NewVD->setInvalidDecl();
+      return;
+    }
+  }
+
   bool isVM = T->isVariablyModifiedType();
   if (isVM || NewVD->hasAttr<CleanupAttr>() ||
       NewVD->hasAttr<BlocksAttr>())
     setFunctionHasBranchProtectedScope();
 
   if ((isVM && NewVD->hasLinkage()) ||
       (T->isVariableArrayType() && NewVD->hasGlobalStorage())) {
     bool SizeIsNegative;
if (getLangOpts().getOpenCLCompatibleVersion() >= 200) {
       if(const PipeType *PipeTy = PT->getAs<PipeType>()) {
         QualType ElemTy = PipeTy->getElementType();
           if (ElemTy->isReferenceType() || ElemTy->isPointerType()) {
             Diag(Param->getTypeSpecStartLoc(), diag::err_reference_pipe_type );
             D.setInvalidType();
           }
       }
     }
+    // WebAssembly tables can't be used as function parameters.
+    if (Context.getTargetInfo().getTriple().isWasm()) {
+      if (PT->isWebAssemblyTableType()) {
+        Diag(Param->getTypeSpecStartLoc(),
+             diag::err_wasm_table_as_function_argument);
+        D.setInvalidType();
+      }
+      }
   }
 
   // Here we have an function template explicit specialization at class scope.
   // The actual specialization will be postponed to template instatiation
   // time via the ClassScopeFunctionSpecializationDecl node.
   if (isDependentClassScopeExplicitSpecialization) {
     ClassScopeFunctionSpecializationDecl *NewSpec =
                          ClassScopeFunctionSpecializationDecl::Create(
void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
   VarDecl *VDecl = dyn_cast<VarDecl>(RealDecl);
   if (!VDecl) {
     assert(!isa<FieldDecl>(RealDecl) && "field init shouldn't get here");
     Diag(RealDecl->getLocation(), diag::err_illegal_initializer);
     RealDecl->setInvalidDecl();
     return;
   }
 
+  // WebAssembly tables can't be used to initialise a variable.
+  if (Init && !Init->getType().isNull() &&
+      Init->getType()->isWebAssemblyTableType()) {
+    Diag(Init->getExprLoc(), diag::err_wasm_table_assignment);
+    VDecl->setInvalidDecl();
+    return;
+  }
+
   // C++11 [decl.spec.auto]p6. Deduce the type which 'auto' stands in for.
   if (VDecl->getType()->isUndeducedType()) {
     // Attempt typo correction early so that the type of the init expression can
     // be deduced based on the chosen correction if the original init contains a
     // TypoExpr.
     ExprResult Res = CorrectDelayedTyposInExpr(Init, VDecl);
     if (!Res.isUsable()) {
       // There are unresolved typos in Init, just drop them.

clang/lib/Sema/SemaDeclCXX.cpp

if (!Invalid && (Mode == 0 || !BaseType->isVoidType()) &&
       !BaseType->isDependentType() && RequireCompleteType(Loc, BaseType, DK))
     Invalid = true;
 
   if (!Invalid && Mode != 1 && BaseType->isSizelessType()) {
     Diag(Loc, diag::err_catch_sizeless) << (Mode == 2 ? 1 : 0) << BaseType;
     Invalid = true;
   }
 
+  if (!Invalid && BaseType->isWebAssemblyReferenceType()) {
+    Diag(Loc, diag::err_wasm_table_catch);
+    Invalid = true;
+  }
+
   if (!Invalid && !ExDeclType->isDependentType() &&
       RequireNonAbstractType(Loc, ExDeclType,
                              diag::err_abstract_type_in_decl,
                              AbstractVariableType))
     Invalid = true;
 
   // Only the non-fragile NeXT runtime currently supports C++ catches
   // of ObjC types, and no runtime supports catching ObjC types by value.

clang/lib/Sema/SemaExceptionSpec.cpp

 
 /// CheckSpecifiedExceptionType - Check if the given type is valid in an
 /// exception specification. Incomplete types, or pointers to incomplete types
 /// other than void are not allowed.
 ///
 /// \param[in,out] T  The exception type. This will be decayed to a pointer type
 ///                   when the input is an array or a function type.
 bool Sema::CheckSpecifiedExceptionType(QualType &T, SourceRange Range) {
+
   // C++11 [except.spec]p2:
   //   A type cv T, "array of T", or "function returning T" denoted
   //   in an exception-specification is adjusted to type T, "pointer to T", or
   //   "pointer to function returning T", respectively.
   //
   // We also apply this rule in C++98.
   if (T->isArrayType())
     T = Context.getArrayDecayedType(T);
bool Sema::CheckSpecifiedExceptionType(QualType &T, SourceRange Range) {
   // The MSVC compatibility mode doesn't extend to sizeless types,
   // so diagnose them separately.
   if (PointeeT->isSizelessType() && Kind != 1) {
     Diag(Range.getBegin(), diag::err_sizeless_in_exception_spec)
         << (Kind == 2 ? 1 : 0) << PointeeT << Range;
     return true;
   }
 
+  // WebAssembly tables can't be used in exception specifications.
+  if (PointeeT->isWebAssemblyReferenceType()) {
+    Diag(Range.getBegin(), diag::err_wasm_table_exception_spec);
+    return true;
+  }
+
   return false;
 }
 
 /// CheckDistantExceptionSpec - Check if the given type is a pointer or pointer
 /// to member to a function with an exception specification. This means that
 /// it is invalid to add another level of indirection.
 bool Sema::CheckDistantExceptionSpec(QualType T) {
   // C++17 removes this rule in favor of putting exception specifications into

clang/lib/Sema/SemaExpr.cpp

if (ExprKind == UETT_VecStep)
     return CheckVecStepTraitOperandType(*this, ExprTy, E->getExprLoc(),
                                         E->getSourceRange());
 
   // Explicitly list some types as extensions.
   if (!CheckExtensionTraitOperandType(*this, ExprTy, E->getExprLoc(),
                                       E->getSourceRange(), ExprKind))
     return false;
 
+  // WebAssembly tables are always illegal operands to unary expressions and
+  // type traits.
+  if (Context.getTargetInfo().getTriple().isWasm() &&
+      E->getType()->isWebAssemblyTableType()) {
+    Diag(E->getExprLoc(), diag::err_wasm_table_invalid_uett_operand)
+        << getTraitSpelling(ExprKind);
+    return true;
+  }
+
   // 'alignof' applied to an expression only requires the base element type of
   // the expression to be complete. 'sizeof' requires the expression's type to
   // be complete (and will attempt to complete it if it's an array of unknown
   // bound).
   if (ExprKind == UETT_AlignOf || ExprKind == UETT_PreferredAlignOf) {
     if (RequireCompleteSizedType(
             E->getExprLoc(), Context.getBaseElementType(E->getType()),
             diag::err_sizeof_alignof_incomplete_or_sizeless_type,
if (RequireCompleteSizedType(
     return true;
 
   if (ExprType->isFunctionType()) {
     Diag(OpLoc, diag::err_sizeof_alignof_function_type)
         << getTraitSpelling(ExprKind) << ExprRange;
     return true;
   }
 
+  // WebAssembly tables are always illegal operands to unary expressions and
+  // type traits.
+  if (Context.getTargetInfo().getTriple().isWasm() &&
+      ExprType->isWebAssemblyTableType()) {
+    Diag(OpLoc, diag::err_wasm_table_invalid_uett_operand)
+        << getTraitSpelling(ExprKind);
+    return true;
+  }
+
   if (CheckObjCTraitOperandConstraints(*this, ExprType, OpLoc, ExprRange,
                                        ExprKind))
     return true;
 
   return false;
 }
 
 static bool CheckAlignOfExpr(Sema &S, Expr *E, UnaryExprOrTypeTrait ExprKind) {
if (ResultType->isVoidType() && !getLangOpts().CPlusPlus) {
     Diag(LLoc, diag::ext_gnu_subscript_void_type)
       << BaseExpr->getSourceRange();
 
     // C forbids expressions of unqualified void type from being l-values.
     // See IsCForbiddenLValueType.
     if (!ResultType.hasQualifiers())
       VK = VK_PRValue;
   } else if (!ResultType->isDependentType() &&
+             !ResultType->isWebAssemblyReferenceType() &&
              RequireCompleteSizedType(
                  LLoc, ResultType,
                  diag::err_subscript_incomplete_or_sizeless_type, BaseExpr))
     return ExprError();
 
   assert(VK == VK_PRValue || LangOpts.CPlusPlus ||
          !ResultType.isCForbiddenLValueType());
 
ExprResult Sema::BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl,
   if (CheckCallReturnType(FuncT->getReturnType(), Fn->getBeginLoc(), TheCall,
                           FDecl))
     return ExprError();
 
   // We know the result type of the call, set it.
   TheCall->setType(FuncT->getCallResultType(Context));
   TheCall->setValueKind(Expr::getValueKindForType(FuncT->getReturnType()));
 
+  // WebAssembly tables can't be used as arguments.
+  if (Context.getTargetInfo().getTriple().isWasm()) {
+    for (const Expr *Arg : Args) {
+      if (Arg && Arg->getType()->isWebAssemblyTableType()) {
+        return ExprError(
+            Diag(Arg->getExprLoc(), diag::err_wasm_table_as_function_argument));
+      }
+    }
+  }
+
   if (Proto) {
     if (ConvertArgumentsForCall(TheCall, Fn, FDecl, Proto, Args, RParenLoc,
                                 IsExecConfig))
       return ExprError();
   } else {
     assert(isa<FunctionNoProtoType>(FuncT) && "Unknown FunctionType!");
 
     if (FDecl) {
QualType Sema::CheckConditionalOperands(ExprResult &Cond, ExprResult &LHS,
 
   QualType ResTy =
       UsualArithmeticConversions(LHS, RHS, QuestionLoc, ACK_Conditional);
   if (LHS.isInvalid() || RHS.isInvalid())
     return QualType();
 
   QualType LHSTy = LHS.get()->getType();
   QualType RHSTy = RHS.get()->getType();
+  if (LHSTy->isWebAssemblyTableType() || RHSTy->isWebAssemblyTableType()) {
+    Diag(QuestionLoc, diag::err_wasm_table_conditional_expression)
+        << LHS.get()->getSourceRange() << RHS.get()->getSourceRange();
+    return QualType();
+  }
 
   // Diagnose attempts to convert between __ibm128, __float128 and long double
   // where such conversions currently can't be handled.
   if (unsupportedTypeConversion(*this, LHSTy, RHSTy)) {
     Diag(QuestionLoc,
          diag::err_typecheck_cond_incompatible_operands) << LHSTy << RHSTy
       << LHS.get()->getSourceRange() << RHS.get()->getSourceRange();
     return QualType();
QualType Sema::CheckCompareOperands(ExprResult &LHS, ExprResult &RHS,
   diagnoseTautologicalComparison(*this, Loc, LHS.get(), RHS.get(), Opc);
 
   QualType LHSType = LHS.get()->getType();
   QualType RHSType = RHS.get()->getType();
   if ((LHSType->isArithmeticType() || LHSType->isEnumeralType()) &&
       (RHSType->isArithmeticType() || RHSType->isEnumeralType()))
     return checkArithmeticOrEnumeralCompare(*this, LHS, RHS, Loc, Opc);
 
+  if ((LHSType->isPointerType() &&
+       LHSType->getPointeeType()->isWebAssemblyReferenceType()) ||
+      (RHSType->isPointerType() &&
+       RHSType->getPointeeType()->isWebAssemblyReferenceType()))
+    return InvalidOperands(Loc, LHS, RHS);
+
   const Expr::NullPointerConstantKind LHSNullKind =
       LHS.get()->isNullPointerConstant(Context, Expr::NPC_ValueDependentIsNull);
   const Expr::NullPointerConstantKind RHSNullKind =
       RHS.get()->isNullPointerConstant(Context, Expr::NPC_ValueDependentIsNull);
   bool LHSIsNull = LHSNullKind != Expr::NPCK_NotNull;
   bool RHSIsNull = RHSNullKind != Expr::NPCK_NotNull;
 
   auto computeResultTy = [&]() {
if (const auto *DREHS = dyn_cast<DeclRefExpr>(HS.get())) {
       if (ECDHS && ECDHS->getInitVal() != 0 && ECDHS->getInitVal() != 1)
         EnumConstantInBoolContext = true;
     }
   }
 
   if (EnumConstantInBoolContext)
     Diag(Loc, diag::warn_enum_constant_in_bool_context);
 
+  // WebAssembly tables can't be used with logical operators.
+  QualType LHSTy = LHS.get()->getType();
+  QualType RHSTy = RHS.get()->getType();
+  if ((LHSTy->isArrayType() &&
+       LHSTy->getArrayElementTypeNoTypeQual()->isWebAssemblyReferenceType()) ||
+      (RHSTy->isArrayType() &&
+       RHSTy->getArrayElementTypeNoTypeQual()->isWebAssemblyReferenceType())) {
+    return InvalidOperands(Loc, LHS, RHS);
+  }
+
   // Diagnose cases where the user write a logical and/or but probably meant a
   // bitwise one.  We do this when the LHS is a non-bool integer and the RHS
   // is a constant.
   if (!EnumConstantInBoolContext && LHS.get()->getType()->isIntegerType() &&
       !LHS.get()->getType()->isBooleanType() &&
       RHS.get()->getType()->isIntegerType() && !RHS.get()->isValueDependent() &&
       // Don't warn in macros or template instantiations.
       !Loc.isMacroID() && !inTemplateInstantiation()) {
QualType Sema::CheckAssignmentOperands(Expr *LHSExpr, ExprResult &RHS,
   if (getLangOpts().OpenCL &&
       !getOpenCLOptions().isAvailableOption("cl_khr_fp16", getLangOpts()) &&
       LHSType->isHalfType()) {
     Diag(Loc, diag::err_opencl_half_load_store) << 1
         << LHSType.getUnqualifiedType();
     return QualType();
   }
 
+  // WebAssembly tables can't be used on RHS of an assignment expression.
+  if (RHSType->isWebAssemblyTableType()) {
+    Diag(Loc, diag::err_wasm_table_assignment);
+    return QualType();
+  }
+
   AssignConvertType ConvTy;
   if (CompoundType.isNull()) {
     Expr *RHSCheck = RHS.get();
 
     CheckIdentityFieldAssignment(LHSExpr, RHSCheck, Loc, *this);
 
     QualType LHSTy(LHSType);
     ConvTy = CheckSingleAssignmentConstraints(LHSTy, RHS);
if (lval == Expr::LV_IncompleteVoidType) {
     // Example: "extern void x; void* y = &x;".
     Diag(OpLoc, diag::ext_typecheck_addrof_void) << op->getSourceRange();
   }
 
   // If the operand has type "type", the result has type "pointer to type".
   if (op->getType()->isObjCObjectType())
     return Context.getObjCObjectPointerType(op->getType());
 
-  if (Context.getTargetInfo().getTriple().isWasm() &&
-      op->getType()->isWebAssemblyReferenceType()) {
+  // Cannot take the address of WebAssembly references or tables.
+  if (Context.getTargetInfo().getTriple().isWasm()) {
+    QualType OpTy = op->getType();
+    if (OpTy->isWebAssemblyReferenceType()) {
       Diag(OpLoc, diag::err_wasm_addrof_reference)
           << OrigOp.get()->getSourceRange();
       return QualType();
     }
+    if (OpTy->isWebAssemblyTableType()) {
+      Diag(OpLoc, diag::err_wasm_addrof_table)
+          << OrigOp.get()->getSourceRange();
+      return QualType();
+    }
+  }
 
   CheckAddressOfPackedMember(op);
 
   return Context.getPointerType(op->getType());
 }
 
 static void RecordModifiableNonNullParam(Sema &S, const Expr *Exp) {
   const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Exp);
case UO_LNot: // logical negation
     resultType = Input.get()->getType();
 
     // Though we still have to promote half FP to float...
     if (resultType->isHalfType() && !Context.getLangOpts().NativeHalfType) {
       Input = ImpCastExprToType(Input.get(), Context.FloatTy, CK_FloatingCast).get();
       resultType = Context.FloatTy;
     }
 
+    // WebAsembly tables can't be used in unary expressions.
+    if (resultType->isPointerType() &&
+        resultType->getPointeeType()->isWebAssemblyReferenceType()) {
+      return ExprError(Diag(OpLoc, diag::err_typecheck_unary_expr)
+                       << resultType << Input.get()->getSourceRange());
+    }
+
     if (resultType->isDependentType())
       break;
     if (resultType->isScalarType() && !isScopedEnumerationType(resultType)) {
       // C99 6.5.3.3p1: ok, fallthrough;
       if (Context.getLangOpts().CPlusPlus) {
         // C++03 [expr.unary.op]p8, C++0x [expr.unary.op]p9:
         // operand contextually converted to bool.
         Input = ImpCastExprToType(Input.get(), Context.BoolTy,

clang/lib/Sema/SemaExprCXX.cpp

if (!isPointer && Ty->isSizelessType()) {
       return true;
     }
 
     if (RequireNonAbstractType(ThrowLoc, ExceptionObjectTy,
                                diag::err_throw_abstract_type, E))
       return true;
   }
 
+  // Cannot throw WebAssembly tables (throwing WebAssembly references is
+  // caught earlier in this function).
+  if (Ty->isWebAssemblyReferenceType()) {
+    Diag(ThrowLoc, diag::err_wasm_table_throw) << E->getSourceRange();
+    return true;
+  }
+
   // If the exception has class type, we need additional handling.
   CXXRecordDecl *RD = Ty->getAsCXXRecordDecl();
   if (!RD)
     return false;
 
   // If we are throwing a polymorphic class type or pointer thereof,
   // exception handling will make use of the vtable.
   MarkVTableUsed(ThrowLoc, RD);

clang/lib/Sema/SemaStmt.cpp

if (MD->hasRelatedResultType() && MD->getClassInterface()) {
       // type used to type-check the validity of return statements within the
       // method body is a pointer to the type of the class being implemented.
       RelatedRetType = Context.getObjCInterfaceType(MD->getClassInterface());
       RelatedRetType = Context.getObjCObjectPointerType(RelatedRetType);
     }
   } else // If we don't have a function/method context, bail.
     return StmtError();
 
+  if (RetValExp) {
+    if (RetValExp->getType()->isArrayType() &&
+        RetValExp->getType()
+            ->getArrayElementTypeNoTypeQual()
+            ->isWebAssemblyReferenceType()) {
+      Diag(ReturnLoc, diag::err_wasm_table_return);
+      return StmtError();
+    }
+  }
+
   // C++1z: discarded return statements are not considered when deducing a
   // return type.
   if (ExprEvalContexts.back().isDiscardedStatementContext() &&
       FnRetType->getContainedAutoType()) {
     if (RetValExp) {
       ExprResult ER =
           ActOnFinishFullExpr(RetValExp, ReturnLoc, /*DiscardedValue*/ false);
       if (ER.isInvalid())

clang/lib/Sema/SemaType.cpp

QualType Sema::BuildPointerType(QualType T,
 
   // In ARC, it is forbidden to build pointers to unqualified pointers.
   if (getLangOpts().ObjCAutoRefCount)
     T = inferARCLifetimeForPointee(*this, T, Loc, /*reference*/ false);
 
   if (getLangOpts().OpenCL)
     T = deduceOpenCLPointeeAddrSpace(*this, T);
 
-  // In WebAssembly, pointers to reference types are illegal.
+  // In WebAssembly, pointers to reference types and pointers to tables are
+  // illegal.
   if (getASTContext().getTargetInfo().getTriple().isWasm()) {
     if (T->isWebAssemblyReferenceType()) {
       Diag(Loc, diag::err_wasm_reference_pointer);
       return QualType();
+    } else if (T->isWebAssemblyTableType()) {
+      Diag(Loc, diag::err_wasm_table_pointer);
+      return QualType();
     }
   }
 
   // Build the pointer type.
   return Context.getPointerType(T);
 }
 
 /// Build a reference type.
QualType Sema::BuildReferenceType(QualType T, bool SpelledAsLValue,
 
   // In ARC, it is forbidden to build references to unqualified pointers.
   if (getLangOpts().ObjCAutoRefCount)
     T = inferARCLifetimeForPointee(*this, T, Loc, /*reference*/ true);
 
   if (getLangOpts().OpenCL)
     T = deduceOpenCLPointeeAddrSpace(*this, T);
 
-  // In WebAssembly, references to reference types are illegal.
+  // In WebAssembly, references to reference types and tables are illegal.
   if (getASTContext().getTargetInfo().getTriple().isWasm()) {
     if (T->isWebAssemblyReferenceType()) {
       Diag(Loc, diag::err_wasm_reference_reference);
       return QualType();
+    } else if (T->isWebAssemblyTableType()) {
+      Diag(Loc, diag::err_wasm_table_reference);
+      return QualType();
     }
   }
 
   // Handle restrict on references.
   if (LValueRef)
     return Context.getLValueReferenceType(T, SpelledAsLValue);
   return Context.getRValueReferenceType(T);
 }
if (getLangOpts().CPlusPlus) {
     if (Context.getTargetInfo().getCXXABI().isMicrosoft())
       if (const MemberPointerType *MPTy = T->getAs<MemberPointerType>())
         if (!MPTy->getClass()->isDependentType())
           (void)isCompleteType(Loc, T);
 
   } else {
     // C99 6.7.5.2p1: If the element type is an incomplete or function type,
     // reject it (e.g. void ary[7], struct foo ary[7], void ary[7]())
-    if (RequireCompleteSizedType(Loc, T,
+    if (!T->isWebAssemblyReferenceType() &&
+        RequireCompleteSizedType(Loc, T,
                                  diag::err_array_incomplete_or_sizeless_type))
       return QualType();
   }
 
-  if (T->isSizelessType()) {
+  // Multi-dimensional arrays of WebAssembly references are not allowed.
+  if (Context.getTargetInfo().getTriple().isWasm() && T->isArrayType()) {
+    const Type *BaseTy = T->getBaseElementTypeUnsafe();
+    if (BaseTy->isWebAssemblyReferenceType()) {
+      Diag(Loc, diag::err_wasm_multidimensional_ref_array);
+      return QualType();
+    }
+  }
+
+  if (T->isSizelessType() && !T->isWebAssemblyReferenceType()) {
     Diag(Loc, diag::err_array_incomplete_or_sizeless_type) << 1 << T;
     return QualType();
   }
 
   if (T->isFunctionType()) {
     Diag(Loc, diag::err_illegal_decl_array_of_functions)
       << getPrintableNameForEntity(Entity) << T;
     return QualType();
for (unsigned Idx = 0, Cnt = ParamTypes.size(); Idx < Cnt; ++Idx) {
     if (ParamType->isVoidType()) {
       Diag(Loc, diag::err_param_with_void_type);
       Invalid = true;
     } else if (ParamType->isHalfType() && !getLangOpts().HalfArgsAndReturns) {
       // Disallow half FP arguments.
       Diag(Loc, diag::err_parameters_retval_cannot_have_fp16_type) << 0 <<
         FixItHint::CreateInsertion(Loc, "*");
       Invalid = true;
+    } else if (ParamType->isWebAssemblyTableType()) {
+      Diag(Loc, diag::err_wasm_table_as_function_argument);
+      Invalid = true;
     }
 
     // C++2a [dcl.fct]p4:
     //   A parameter with volatile-qualified type is deprecated
     if (ParamType.isVolatileQualified() && getLangOpts().CPlusPlus20)
       Diag(Loc, diag::warn_deprecated_volatile_param) << ParamType;
 
     ParamTypes[Idx] = ParamType;

clang/test/CodeGen/WebAssembly/table.c

+// RUN: %clang_cc1 -triple wasm32 -target-feature +reference-types -o - -emit-llvm %s | FileCheck %s
+// REQUIRES: webassembly-registered-target
+
+// CHECK: @table = internal addrspace(1) global [0 x ptr addrspace(10)] zeroinitializer, align 1
+static __externref_t table[0];
+
+void use() {
+  // Ensure the table isn't discarded as unused.
+  table[0];
+}

clang/test/Sema/wasm-refs-and-tables.c

-// RUN: %clang_cc1 -fsyntax-only -verify -triple wasm32 -target-feature +reference-types %s
+// RUN: %clang_cc1 -fsyntax-only -verify -triple wasm32 -Wno-unused-value -target-feature +reference-types %s
 
 // Note: As WebAssembly references are sizeless types, we don't exhaustively
 // test for cases covered by sizeless-1.c and similar tests.
 
 // Unlike standard sizeless types, reftype globals are supported.
 __externref_t r1;
 extern __externref_t r2;
 static __externref_t r3;
 
 __externref_t *t1;               // expected-error {{pointers to WebAssembly reference types are illegal}}
 __externref_t **t2;              // expected-error {{pointers to WebAssembly reference types are illegal}}
 __externref_t ******t3;          // expected-error {{pointers to WebAssembly reference types are illegal}}
-static __externref_t t4[3];      // expected-error {{array has sizeless element type '__externref_t'}}
-static __externref_t t5[];       // expected-error {{array has sizeless element type '__externref_t'}}
-static __externref_t t6[] = {0}; // expected-error {{array has sizeless element type '__externref_t'}}
-__externref_t t7[0];             // expected-error {{array has sizeless element type '__externref_t'}}
-static __externref_t t8[0][0];   // expected-error {{array has sizeless element type '__externref_t'}}
+static __externref_t t4[3];      // expected-error {{only zero-length WebAssembly tables are currently supported}}
+static __externref_t t5[];       // expected-error {{only zero-length WebAssembly tables are currently supported}}
+static __externref_t t6[] = {0}; // expected-error {{only zero-length WebAssembly tables are currently supported}}
+__externref_t t7[0];             // expected-error {{WebAssembly table must be static}}
+static __externref_t t8[0][0];   // expected-error {{multi-dimensional arrays of WebAssembly references are illegal}}
+static __externref_t (*t9)[0];   // expected-error {{pointers to WebAssembly tables are illegal}}
 
-static __externref_t table[0]; // expected-error {{array has sizeless element type '__externref_t'}}
+static __externref_t table[0];
+static __externref_t other_table[0] = {};
 
 struct s {
   __externref_t f1;       // expected-error {{field has sizeless type '__externref_t'}}
-  __externref_t f2[0];    // expected-error {{array has sizeless element type '__externref_t'}}
-  __externref_t f3[];     // expected-error {{array has sizeless element type '__externref_t'}}
-  __externref_t f4[0][0]; // expected-error {{array has sizeless element type '__externref_t'}}
+  __externref_t f2[0];    // expected-error {{field has sizeless type '__externref_t'}}
+  __externref_t f3[];     // expected-error {{field has sizeless type '__externref_t'}}
+  __externref_t f4[0][0]; // expected-error {{multi-dimensional arrays of WebAssembly references are illegal}}
   __externref_t *f5;      // expected-error {{pointers to WebAssembly reference types are illegal}}
   __externref_t ****f6;   // expected-error {{pointers to WebAssembly reference types are illegal}}
+  __externref_t (*f7)[0]; // expected-error {{pointers to WebAssembly tables are illegal}}
 };
 
 union u {
   __externref_t f1;       // expected-error {{field has sizeless type '__externref_t'}}
-  __externref_t f2[0];    // expected-error {{array has sizeless element type '__externref_t'}}
-  __externref_t f3[];     // expected-error {{array has sizeless element type '__externref_t'}}
-  __externref_t f4[0][0]; // expected-error {{array has sizeless element type '__externref_t'}}
+  __externref_t f2[0];    // expected-error {{field has sizeless type '__externref_t'}}
+  __externref_t f3[];     // expected-error {{field has sizeless type '__externref_t'}}
+  __externref_t f4[0][0]; // expected-error {{multi-dimensional arrays of WebAssembly references are illegal}}
   __externref_t *f5;      // expected-error {{pointers to WebAssembly reference types are illegal}}
   __externref_t ****f6;   // expected-error {{pointers to WebAssembly reference types are illegal}}
+  __externref_t (*f7)[0]; // expected-error {{pointers to WebAssembly tables are illegal}}
 };
 
-void illegal_argument_1(__externref_t table[]);     // expected-error {{array has sizeless element type '__externref_t'}}
-void illegal_argument_2(__externref_t table[0][0]); // expected-error {{array has sizeless element type '__externref_t'}}
+void illegal_argument_1(__externref_t table[]);     // expected-error {{cannot use WebAssembly table as a function argument}}
+void illegal_argument_2(__externref_t table[0][0]); // expected-error {{multi-dimensional arrays of WebAssembly references are illegal}}
 void illegal_argument_3(__externref_t *table);      // expected-error {{pointers to WebAssembly reference types are illegal}}
 void illegal_argument_4(__externref_t ***table);    // expected-error {{pointers to WebAssembly reference types are illegal}}
+void illegal_argument_5(__externref_t (*table)[0]); // expected-error {{pointers to WebAssembly tables are illegal}}
 
 __externref_t *illegal_return_1();   // expected-error {{pointers to WebAssembly reference types are illegal}}
 __externref_t ***illegal_return_2(); // expected-error {{pointers to WebAssembly reference types are illegal}}
+__externref_t (*illegal_return_3())[0]; // expected-error {{pointers to WebAssembly tables are illegal}}
 
 void varargs(int, ...);
 
 __externref_t func(__externref_t ref) {
   &ref; // expected-error {{cannot take address of WebAssembly reference}}
   int foo = 40;
   (__externref_t *)(&foo);     // expected-error {{pointers to WebAssembly reference types are illegal}}
   (__externref_t ****)(&foo);  // expected-error {{pointers to WebAssembly reference types are illegal}}
   sizeof(ref);                 // expected-error {{invalid application of 'sizeof' to sizeless type '__externref_t'}}
   sizeof(__externref_t);       // expected-error {{invalid application of 'sizeof' to sizeless type '__externref_t'}}
-  sizeof(__externref_t[0]);    // expected-error {{array has sizeless element type '__externref_t'}}
-  sizeof(__externref_t[0][0]); // expected-error {{array has sizeless element type '__externref_t'}}
+  sizeof(__externref_t[0]);    // expected-error {{invalid application of 'sizeof' to WebAssembly table}}
+  sizeof(table);               // expected-error {{invalid application of 'sizeof' to WebAssembly table}}
+  sizeof(__externref_t[0][0]); // expected-error {{multi-dimensional arrays of WebAssembly references are illegal}}
   sizeof(__externref_t *);     // expected-error {{pointers to WebAssembly reference types are illegal}}
   sizeof(__externref_t ***);   // expected-error {{pointers to WebAssembly reference types are illegal}};
   // expected-warning@+1 {{'_Alignof' applied to an expression is a GNU extension}}
   _Alignof(ref);                 // expected-error {{invalid application of 'alignof' to sizeless type '__externref_t'}}
   _Alignof(__externref_t);       // expected-error {{invalid application of 'alignof' to sizeless type '__externref_t'}}
-  _Alignof(__externref_t[]);     // expected-error {{array has sizeless element type '__externref_t'}}
-  _Alignof(__externref_t[0][0]); // expected-error {{array has sizeless element type '__externref_t'}}
+  _Alignof(__externref_t[]);     // expected-error {{invalid application of 'alignof' to sizeless type '__externref_t'}}
+  _Alignof(__externref_t[0]);    // expected-error {{invalid application of 'alignof' to sizeless type '__externref_t'}}
+  _Alignof(table);               // expected-warning {{'_Alignof' applied to an expression is a GNU extension}} expected-error {{invalid application of 'alignof' to WebAssembly table}}
+  _Alignof(__externref_t[0][0]); // expected-error {{multi-dimensional arrays of WebAssembly references are illegal}}
   _Alignof(__externref_t *);     // expected-error {{pointers to WebAssembly reference types are illegal}}
   _Alignof(__externref_t ***);   // expected-error {{pointers to WebAssembly reference types are illegal}};
   varargs(1, ref);               // expected-error {{cannot pass expression of type '__externref_t' to variadic function}}
 
+  __externref_t lt1[0];           // expected-error {{WebAssembly table cannot be declared within a function}}
+  static __externref_t lt2[0];    // expected-error {{WebAssembly table cannot be declared within a function}}
+  static __externref_t lt3[0][0]; // expected-error {{multi-dimensional arrays of WebAssembly references are illegal}}
+  static __externref_t(*lt4)[0];  // expected-error {{pointers to WebAssembly tables are illegal}}
+  illegal_argument_1(table);      // expected-error {{cannot use WebAssembly table as a function argument}}
+  varargs(1, table);              // expected-error {{cannot use WebAssembly table as a function argument}}
+  table == 1;                     // expected-error {{invalid operands to binary expression ('__attribute__((address_space(1))) __externref_t[0]' and 'int')}}
+  1 >= table;                     // expected-error {{invalid operands to binary expression ('int' and '__attribute__((address_space(1))) __externref_t[0]')}}
+  !table;                         // expected-error {{invalid argument type '__attribute__((address_space(1))) __externref_t *' to unary expression}}
+  1 && table;                     // expected-error {{invalid operands to binary expression ('int' and '__attribute__((address_space(1))) __externref_t[0]')}}
+  table || 1;                     // expected-error {{invalid operands to binary expression ('__attribute__((address_space(1))) __externref_t[0]' and 'int')}}
+  1 ? table : table;              // expected-error {{cannot use WebAssembly tables as the 2nd or 3rd operands of a conditional expression}}
+  (void *)table;                  // expected-error {{cannot cast WebAssembly table}}
+  void *u;
+  u = table;       // expected-error {{cannot assign WebAssembly table to a variable}}
+  void *v = table; // expected-error {{cannot assign WebAssembly table to a variable}}
+  &table;          // expected-error {{cannot take address of WebAssembly table}}
+
+  table[0];
+  table[0] = ref;
   return ref;
 }
+
+void *ret_void_ptr() {
+  return table; // expected-error {{cannot return a WebAssembly table}}
+}

clang/test/SemaCXX/wasm-refs-and-tables.cpp

 // RUN: %clang_cc1 -fcxx-exceptions -fsyntax-only -verify -std=gnu++11 -triple wasm32 -Wno-unused-value -target-feature +reference-types %s
 
 // This file tests C++ specific constructs with WebAssembly references and
 // tables. See wasm-refs-and-tables.c for C constructs.
 
 __externref_t ref;
 __externref_t &ref_ref1 = ref; // expected-error {{references to WebAssembly reference types are illegal}}
 __externref_t &ref_ref2(ref);  // expected-error {{references to WebAssembly reference types are illegal}}
 
-static __externref_t table[0];                    // expected-error {{array has sizeless element type '__externref_t'}}
-static __externref_t (&ref_to_table1)[0] = table; // expected-error {{array has sizeless element type '__externref_t'}}
-static __externref_t (&ref_to_table2)[0](table);  // expected-error {{array has sizeless element type '__externref_t'}}
+static __externref_t table[0];                    // expected-note 2 {{'table' declared here}}
+static __externref_t (&ref_to_table1)[0] = table; // expected-error {{references to WebAssembly tables are illegal}}
+static __externref_t (&ref_to_table2)[0](table);  // expected-error {{references to WebAssembly tables are illegal}}
 
 void illegal_argument_1(__externref_t &r); // expected-error {{references to WebAssembly reference types are illegal}}
-void illegal_argument_2(__externref_t (&t)[0]); // expected-error {{array has sizeless element type '__externref_t'}}
+void illegal_argument_2(__externref_t (&t)[0]); // expected-error {{references to WebAssembly tables are illegal}}
 
 __externref_t &illegal_return_1(); // expected-error {{references to WebAssembly reference types are illegal}}
-__externref_t (&illegal_return_2())[0]; // expected-error {{array has sizeless element type '__externref_t'}}
+__externref_t (&illegal_return_2())[0]; // expected-error {{references to WebAssembly tables are illegal}}
 
 void illegal_throw1() throw(__externref_t);   // expected-error {{sizeless type '__externref_t' is not allowed in exception specification}}
 void illegal_throw2() throw(__externref_t *); // expected-error {{pointers to WebAssembly reference types are illegal}}
 void illegal_throw3() throw(__externref_t &); // expected-error {{references to WebAssembly reference types are illegal}}
-void illegal_throw4() throw(__externref_t[0]); // expected-error {{array has sizeless element type '__externref_t'}}
+void illegal_throw4() throw(__externref_t[0]); // expected-error {{WebAssembly table not allowed in exception sepcification}}
 
 class RefClass {
   __externref_t f1;       // expected-error {{field has sizeless type '__externref_t'}}
-  __externref_t f2[0];    // expected-error {{array has sizeless element type '__externref_t'}}
-  __externref_t f3[];     // expected-error {{array has sizeless element type '__externref_t'}}
-  __externref_t f4[0][0]; // expected-error {{array has sizeless element type '__externref_t'}}
+  __externref_t f2[0];    // expected-error {{field has sizeless type '__externref_t'}}
+  __externref_t f3[];     // expected-error {{field has sizeless type '__externref_t'}}
+  __externref_t f4[0][0]; // expected-error {{multi-dimensional arrays of WebAssembly references are illegal}}
   __externref_t *f5;      // expected-error {{pointers to WebAssembly reference types are illegal}}
   __externref_t ****f6;   // expected-error {{pointers to WebAssembly reference types are illegal}}
-  __externref_t (*f7)[0]; // expected-error {{array has sizeless element type '__externref_t'}}
+  __externref_t (*f7)[0]; // expected-error {{pointers to WebAssembly tables are illegal}}
 };
 
 struct AStruct {};
 
 template <typename T>
 struct TemplatedStruct {
-  T f; // expected-error {{field has sizeless type '__externref_t'}}
-  void foo(T);
-  T bar(void);
-  T arr[0]; // expected-error {{array has sizeless element type '__externref_t'}}
-  T *ptr;   // expected-error {{pointers to WebAssembly reference types are illegal}}
+  T f;         // expected-error 2 {{field has sizeless type '__externref_t'}}
+  void foo(T); // expected-error {{cannot use WebAssembly table as a function argument}}
+  T bar(void); // expected-error {{function cannot return array type '__externref_t[0]'}}
+  T arr[0];    // expected-error {{field has sizeless type '__externref_t'}} expected-error {{multi-dimensional arrays of WebAssembly references are illegal}}
+  T *ptr;      // expected-error {{pointers to WebAssembly reference types are illegal}} expected-error {{pointers to WebAssembly tables are illegal}}
 };
 
 void func() {
   int foo = 40;
   static_cast<__externref_t>(foo);      // expected-error {{static_cast from 'int' to '__externref_t' is not allowed}}
   static_cast<__externref_t *>(&foo);   // expected-error {{pointers to WebAssembly reference types are illegal}}
   static_cast<int>(ref);                // expected-error {{static_cast from '__externref_t' to 'int' is not allowed}}
   __externref_t(10);                    // expected-error {{functional-style cast from 'int' to '__externref_t' is not allowed}}
   int i(ref);                           // expected-error {{cannot initialize a variable of type 'int' with an lvalue of type '__externref_t'}}
-  const_cast<__externref_t[0]>(table);  // expected-error {{array has sizeless element type '__externref_t'}}
+  int j(table);                         // expected-error {{cannot initialize a variable of type 'int' with an lvalue of type '__attribute__((address_space(1))) __externref_t[0]'}}
+  const_cast<__externref_t[0]>(table);  // expected-error {{const_cast to '__externref_t[0]', which is not a reference, pointer-to-object, or pointer-to-data-member}}
   const_cast<__externref_t *>(table);   // expected-error {{pointers to WebAssembly reference types are illegal}}
   reinterpret_cast<__externref_t>(foo); // expected-error {{reinterpret_cast from 'int' to '__externref_t' is not allowed}}
   reinterpret_cast<int>(ref);           // expected-error {{reinterpret_cast from '__externref_t' to 'int' is not allowed}}
+  reinterpret_cast<int *>(table);       // expected-error {{reinterpret_cast from '__attribute__((address_space(1))) __externref_t *' to 'int *' is not allowed}}
   int iarr[0];
-  reinterpret_cast<__externref_t[0]>(iarr); // expected-error {{array has sizeless element type '__externref_t'}}
+  reinterpret_cast<__externref_t[0]>(iarr); // expected-error {{reinterpret_cast from 'int *' to '__externref_t[0]' is not allowed}}
   reinterpret_cast<__externref_t *>(iarr);  // expected-error {{pointers to WebAssembly reference types are illegal}}
   dynamic_cast<__externref_t>(foo);         // expected-error {{invalid target type '__externref_t' for dynamic_cast; target type must be a reference or pointer type to a defined class}}
   dynamic_cast<__externref_t *>(&foo);      // expected-error {{pointers to WebAssembly reference types are illegal}}
+  dynamic_cast<AStruct *>(table);           // expected-error {{'__externref_t' is not a class type}}
+
+  for (auto x : table) { // expected-error {{cannot assign WebAssembly table to a variable}}
+  }
 
   TemplatedStruct<__externref_t> ts1;    // expected-note {{in instantiation}}
   TemplatedStruct<__externref_t *> ts2;  // expected-error {{pointers to WebAssembly reference types are illegal}}
   TemplatedStruct<__externref_t &> ts3;  // expected-error {{references to WebAssembly reference types are illegal}}
-  TemplatedStruct<__externref_t[0]> ts4; // expected-error {{array has sizeless element type '__externref_t'}}
+  TemplatedStruct<__externref_t[0]> ts4; // expected-note {{in instantiation}}
 
+  auto auto_table = table; // expected-error {{cannot assign WebAssembly table to a variable}}
   auto auto_ref = ref;
 
   auto fn1 = [](__externref_t x) { return x; };
   auto fn2 = [](__externref_t *x) { return x; };   // expected-error {{pointers to WebAssembly reference types are illegal}}
   auto fn3 = [](__externref_t &x) { return x; };   // expected-error {{references to WebAssembly reference types are illegal}}
-  auto fn4 = [](__externref_t x[0]) { return x; }; // expected-error {{array has sizeless element type '__externref_t'}}
-  auto fn5 = [&auto_ref](void) { return true; };   // expected-error {{cannot capture WebAssembly reference}}
-  auto fn6 = [auto_ref](void) { return true; };    // expected-error {{cannot capture WebAssembly reference}}
-  auto fn7 = [&](void) { auto_ref; return true; };                        // expected-error {{cannot capture WebAssembly reference}}
-  auto fn8 = [=](void) { auto_ref; return true; };                        // expected-error {{cannot capture WebAssembly reference}}
+  auto fn4 = [](__externref_t x[0]) { return x; }; // expected-error {{cannot use WebAssembly table as a function argument}}
+  auto fn5 = [](void) { return table; };           // expected-error {{cannot return a WebAssembly table}}
+  auto fn6 = [&auto_ref](void) { return true; };   // expected-error {{cannot capture WebAssembly reference}}
+  auto fn7 = [auto_ref](void) { return true; };    // expected-error {{cannot capture WebAssembly reference}}
+  auto fn8 = [&](void) { auto_ref; return true; };                        // expected-error {{cannot capture WebAssembly reference}}
+  auto fn9 = [=](void) { auto_ref; return true; };                        // expected-error {{cannot capture WebAssembly reference}}
+  auto fn10 = [table](void) { return true; };      // expected-error {{'table' cannot be captured because it does not have automatic storage duration}}
+  auto fn11 = [&table](void) { return true; };     // expected-error {{'table' cannot be captured because it does not have automatic storage duration}}
 
   alignof(__externref_t);    // expected-error {{invalid application of 'alignof' to sizeless type '__externref_t'}}
   alignof(ref);              // expected-warning {{'alignof' applied to an expression is a GNU extension}} expected-error {{invalid application of 'alignof' to sizeless type '__externref_t'}}
-  alignof(__externref_t[0]); // expected-error {{array has sizeless element type '__externref_t'}}
+  alignof(__externref_t[0]); // expected-error {{invalid application of 'alignof' to sizeless type '__externref_t'}}
+  alignof(table);            // expected-warning {{'alignof' applied to an expression is a GNU extension}} expected-error {{invalid application of 'alignof' to WebAssembly table}}
 
   throw ref;  // expected-error {{cannot throw object of sizeless type '__externref_t'}}
   throw &ref; // expected-error {{cannot take address of WebAssembly reference}}
+  throw table;  // expected-error {{cannot throw a WebAssembly table}}
+  throw &table; // expected-error {{cannot take address of WebAssembly table}}
 
   try {
   } catch (__externref_t) { // expected-error {{cannot catch sizeless type '__externref_t'}}
   }
   try {
   } catch (__externref_t *) { // expected-error {{pointers to WebAssembly reference types are illegal}}
   }
   try {
   } catch (__externref_t &) { // expected-error {{references to WebAssembly reference types are illegal}}
   }
   try {
-  } catch (__externref_t[0]) { // expected-error {{array has sizeless element type '__externref_t'}}
+  } catch (__externref_t[0]) { // expected-error {{cannot catch WebAssembly table}}
   }
 
   new __externref_t;    // expected-error {{allocation of sizeless type '__externref_t'}}
   new __externref_t[0]; // expected-error {{allocation of sizeless type '__externref_t'}}
 
   delete ref;     // expected-error {{cannot delete expression of type '__externref_t'}}
+  delete[] table; // expected-error {{annot delete expression of type '__attribute__((address_space(1))) __externref_t[0]'}}
 }