De-duplicate consecutive locals of same type in wasm_section_code()

asm.js

@@ -1278,24 +1278,20 @@ export class Assembler {
             const local_types = Object.values(locals);
             const local_count = local_types.length;
             if (local_count == 0) {
-                return [
-                    body.length + 2,
-                    0,
-                    ...body,
-                    opcodes["end"]
-                ]
+                const full_body = [ 0, body, opcodes.end ].flat()
+                return [ full_body.length, full_body ].flat();
             } else {
-                return [
-                    body.length + local_count + 3,
-                    local_count,
-                    local_count,
-                    ...local_types,
-                    ...body,
-                    opcodes["end"]
-                ];
+                const groups = this.group(local_types);
+                const full_body = [
+                    groups.length,
+					...groups.flat(),
+                    body,
+                    opcodes.end,
+                ].flat();
+                return [ full_body.length, full_body ].flat();
             }
         });
-        return [ contents.length ].concat(...contents);
+        return [ contents.length, contents ].flat(Infinity);
     }
 
     wasm_section_data() {
@@ -1369,4 +1365,15 @@ export class Assembler {
         for (const func of Object.values(this.funcs))
             func.type = this.ensure_type(this.func_type(func));
     }
+
+    group(array) {
+        return array.reduce((acc, val) => {
+			const last = acc.at(-1);
+			if (last != undefined && last[1] == val)
+				++last[0]
+			else
+				acc.push([1, val]);
+			return acc;
+		}, []);
+    }
 }