[clang][WebAssembly] Implement support for table types and builtins

This commit implements support for WebAssembly table types and
respective builtins. Table tables are WebAssembly objects to store
reference types. They have a large amount of semantic restrictions
including, but not limited to, only being allowed to be declared
at the top-level as static arrays of zero-length. Not being arguments
or result of functions, not being stored ot memory, etc.

This commit introduces the __attribute__((wasm_table)) to attach to
arrays of WebAssembly reference types. And the following builtins to
manage tables:

* ref   __builtin_wasm_table_get(table, idx)
* void  __builtin_wasm_table_set(table, idx, ref)
* uint  __builtin_wasm_table_size(table)
* uint  __builtin_wasm_table_grow(table, ref, uint)
* void  __builtin_wasm_table_fill(table, idx, ref, uint)
* void  __builtin_wasm_table_copy(table, table, uint, uint, uint)

This commit also enables reference-types feature at bleeding-edge.

This is joint work with Alex Bradbury (@asb).

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D139010

1 files changed, 6 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index a5a57c3..9b7ff5f 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -172,6 +172,12 @@ bool Sema::CheckSpecifiedExceptionType(QualType &T, SourceRange Range) {
       RequireCompleteType(Range.getBegin(), PointeeT, DiagID, Kind, Range))
     return ReturnValueOnError;
 
+  // WebAssembly reference types can't be used in exception specifications.
+  if (PointeeT.isWebAssemblyReferenceType()) {
+    Diag(Range.getBegin(), diag::err_wasm_reftype_exception_spec);
+    return true;
+  }
+
   // The MSVC compatibility mode doesn't extend to sizeless types,
   // so diagnose them separately.
   if (PointeeT->isSizelessType() && Kind != 1) {