[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, 1 insertions, 0 deletions

diff --git a/clang/lib/Basic/Targets/WebAssembly.cpp b/clang/lib/Basic/Targets/WebAssembly.cpp
index 3a5e035..e9b77e0 100644
--- a/clang/lib/Basic/Targets/WebAssembly.cpp
+++ b/clang/lib/Basic/Targets/WebAssembly.cpp
@@ -151,6 +151,7 @@ bool WebAssemblyTargetInfo::initFeatureMap(
     Features["atomics"] = true;
     Features["mutable-globals"] = true;
     Features["tail-call"] = true;
+    Features["reference-types"] = true;
     setSIMDLevel(Features, SIMD128, true);
   } else if (CPU == "generic") {
     Features["sign-ext"] = true;