Add support for reference types proposal (#2451)

This adds support for the reference type proposal. This includes support
for all reference types (`anyref`, `funcref`(=`anyfunc`), and `nullref`)
and four new instructions: `ref.null`, `ref.is_null`, `ref.func`, and
new typed `select`. This also adds subtype relationship support between
reference types.

This does not include table instructions yet. This also does not include
wasm2js support.

Fixes #2444 and fixes #2447.

1 files changed, 23 insertions, 1 deletions

diff --git a/src/wasm-type.h b/src/wasm-type.h
index 53ef39ef8..668ac3e4d 100644
--- a/src/wasm-type.h
+++ b/src/wasm-type.h
@@ -36,7 +36,9 @@ public:
     f32,
     f64,
     v128,
+    funcref,
     anyref,
+    nullref,
     exnref,
     _last_value_type,
   };
@@ -64,7 +66,8 @@ public:
   bool isInteger() const { return id == i32 || id == i64; }
   bool isFloat() const { return id == f32 || id == f64; }
   bool isVector() const { return id == v128; };
-  bool isRef() const { return id == anyref || id == exnref; }
+  bool isNumber() const { return id >= i32 && id <= v128; }
+  bool isRef() const { return id >= funcref && id <= exnref; }
 
   // (In)equality must be defined for both Type and ValueType because it is
   // otherwise ambiguous whether to convert both this and other to int or
@@ -94,6 +97,23 @@ public:
   // type.
   static Type get(unsigned byteSize, bool float_);
 
+  // Returns true if left is a subtype of right. Subtype includes itself.
+  static bool isSubType(Type left, Type right);
+
+  // Computes the least upper bound from the type lattice.
+  // If one of the type is unreachable, the other type becomes the result. If
+  // the common supertype does not exist, returns none, a poison value.
+  static Type getLeastUpperBound(Type a, Type b);
+
+  // Computes the least upper bound for all types in the given list.
+  template<typename T> static Type mergeTypes(const T& types) {
+    Type type = Type::unreachable;
+    for (auto other : types) {
+      type = Type::getLeastUpperBound(type, other);
+    }
+    return type;
+  }
+
   std::string toString() const;
 };
 
@@ -134,7 +154,9 @@ constexpr Type i64 = Type::i64;
 constexpr Type f32 = Type::f32;
 constexpr Type f64 = Type::f64;
 constexpr Type v128 = Type::v128;
+constexpr Type funcref = Type::funcref;
 constexpr Type anyref = Type::anyref;
+constexpr Type nullref = Type::nullref;
 constexpr Type exnref = Type::exnref;
 constexpr Type unreachable = Type::unreachable;