Bug 1574865 - Wasm: Update encoding of nullref to match proposal. r=lth

This commit updates the encoding of nullref to match the one given in
the reference types proposal.

Spec: WebAssembly/reference-types#66

Differential Revision: https://phabricator.services.mozilla.com/D58882

js/src/jit-test/lib/wasm-binary.js

@@ -41,7 +41,7 @@ const F32Code          = 0x7d;
 const F64Code          = 0x7c;
 const AnyFuncCode      = 0x70;
 const AnyrefCode       = 0x6f;
-const RefCode          = 0x6e;
+const RefCode          = 0x6d;
 const FuncCode         = 0x60;
 const VoidCode         = 0x40;
 

js/src/wasm/WasmConstants.h

@@ -62,10 +62,13 @@ enum class TypeCode {
   FuncRef = 0x70,  // SLEB128(-0x10)
 
   // A reference to any type.
-  AnyRef = 0x6f,
+  AnyRef = 0x6f,  // SLEB128(-0x11)
+
+  // A null reference.
+  NullRef = 0x6e,  // SLEB128(-0x12)
 
   // Type constructor for reference types.
-  Ref = 0x6e,
+  Ref = 0x6d,
 
   // Type constructor for function types
   Func = 0x60,  // SLEB128(-0x20)
@@ -76,9 +79,6 @@ enum class TypeCode {
   // The 'empty' case of blocktype.
   BlockVoid = 0x40,  // SLEB128(-0x40)
 
-  // Type designator for null - unofficial, will not appear in the binary format
-  NullRef = 0x39,
-
   Limit = 0x80
 };