Fix WASM_WORKERS + MINIMAL_RUNTIME to transfer compiled module (#24865)

The current code was transferring `Module['wasm']` which, on them the
main thread is normally a byte array and not the compiled module. The
new code uses the same pattern that pthreads uses to stash the compiled
module and postMessage that instead, which should be more performant.

In the worker / pthread the global `Module['wasm']` is then set to the
received object so somewhat confusingly `Module['wasm']` is always a
compiled module in a worker / pthread (at least under
`MINIMAL_RUNTIME`).

Author: sbc100

src/lib/libwasm_worker.js

@@ -200,11 +200,7 @@ if (ENVIRONMENT_IS_WASM_WORKER
       // Signal with a non-zero value that this Worker will be a Wasm Worker,
       // and not the main browser thread.
       wwID: _wasmWorkersID,
-#if MINIMAL_RUNTIME
-      wasm: Module['wasm'],
-#else
       wasm: wasmModule,
-#endif
       wasmMemory,
       stackLowestAddress, // sb = stack bottom (lowest stack address, SP points at this when stack is full)
       stackSize,          // sz = stack size

src/postamble_minimal.js

@@ -88,11 +88,9 @@ Module['wasm'] = base64Decode('<<< WASM_BINARY_DATA >>>');
 var wasmExports;
 #endif
 
-#if PTHREADS
+#if PTHREADS || WASM_WORKERS
 var wasmModule;
-#endif
 
-#if PTHREADS || WASM_WORKERS
 function loadModule() {
   assignWasmImports();
 #endif
@@ -152,12 +150,14 @@ WebAssembly.instantiate(Module['wasm'], imports).then(/** @suppress {missingProp
   // output.module objects. But if Module['wasm'] is an already compiled
   // WebAssembly module, then output is the WebAssembly instance itself.
   // Depending on the build mode, Module['wasm'] can mean a different thing.
-#if PTHREADS
-  // In pthreads, Module['wasm'] is an already compiled WebAssembly.Module. In
-  // that case, 'output' is a WebAssembly.Instance.
+#if PTHREADS || WASM_WORKERS
+  // In pthreads and wasm workers, Module['wasm'] is a compiled
+  // WebAssembly.Module. In that case, 'output' is a WebAssembly.Instance.
   // In main thread, Module['wasm'] is either a typed array or a fetch stream.
   // In that case, 'output.instance' is the WebAssembly.Instance.
   wasmExports = (output.instance || output).exports;
+  // Stash the Wasm module for future worker creation.
+  wasmModule = output.module || Module['wasm'];
 #elif MINIMAL_RUNTIME_STREAMING_WASM_COMPILATION
   // In MINIMAL_RUNTIME_STREAMING_WASM_COMPILATION mode, Module['wasm'] is the
   // compiled module so we just get the instance back.
@@ -217,9 +217,8 @@ WebAssembly.instantiate(Module['wasm'], imports).then(/** @suppress {missingProp
   <<< ATPRERUNS >>>
 
   initRuntime(wasmExports);
+
 #if PTHREADS
-  // Export Wasm module for pthread creation to access.
-  wasmModule = output.module || Module['wasm'];
   PThread.loadWasmModuleToAllWorkers(ready);
 #else
   ready();

test/code_size/audio_worklet_wasm.js

@@ -220,7 +220,7 @@ function y() {
     WebAssembly.instantiate(l.wasm, {
         a: Z
     }).then((a => {
-        a = a.instance.exports;
+        a = (a.instance || a).exports;
         X = a.j;
         I = a.l;
         D = a.m;

test/code_size/hello_wasm_worker_wasm.js

@@ -1,74 +1,75 @@
-var b = Module, c = "em-ww" == globalThis.name, e, f, l, x, y, z;
+var c = Module, d = "em-ww" == globalThis.name, e, f, l, y, z, A, t;
 
-c && (onmessage = a => {
+d && (onmessage = a => {
     onmessage = null;
     e = a = a.data;
     f = a.o;
     g();
-    b ||= {};
-    b.wasm = a.j;
+    c ||= {};
+    c.wasm = a.j;
     h();
     a.j = a.s = 0;
 });
 
 function g() {}
 
-c || (f = b.mem || new WebAssembly.Memory({
+d || (f = c.mem || new WebAssembly.Memory({
     initial: 256,
     maximum: 256,
     shared: !0
 }), g());
 
 var k = [], n = a => {
     a = a.data;
-    let d = a._wsc;
-    d && l.get(d)(...a.x);
+    let b = a._wsc;
+    b && l.get(b)(...a.x);
 }, p = a => {
     k.push(a);
-}, q = {}, r = 1, t = (a, d) => {
-    let m = q[r] = new Worker(b.js, {
+}, q = {}, r = 1, u = (a, b) => {
+    let m = q[r] = new Worker(c.js, {
         name: "em-ww"
     });
     m.postMessage({
         u: r,
-        j: b.wasm,
+        j: t,
         o: f,
         l: a,
-        m: d
+        m: b
     });
     m.onmessage = n;
     return r++;
-}, u = () => !1, v = (a, d) => {
+}, v = () => !1, w = (a, b) => {
     q[a].postMessage({
-        _wsc: d,
+        _wsc: b,
         x: []
     });
 };
 
-c && (q[0] = globalThis, addEventListener("message", p));
+d && (q[0] = globalThis, addEventListener("message", p));
 
-function w() {
+function x() {
     console.log("Hello from wasm worker!");
 }
 
 function h() {
-    z = {
-        b: t,
-        c: u,
-        d: v,
-        e: w,
+    A = {
+        b: u,
+        c: v,
+        d: w,
+        e: x,
         a: f
     };
-    WebAssembly.instantiate(b.wasm, {
-        a: z
+    WebAssembly.instantiate(c.wasm, {
+        a: A
     }).then((a => {
-        a = a.instance.exports;
-        x = a.g;
-        y = a.i;
-        l = a.h;
-        c ? (y(e.l, e.m), removeEventListener("message", p), k = k.forEach(n), addEventListener("message", n)) : a.f();
-        c || x();
+        var b = (a.instance || a).exports;
+        t = a.module || c.wasm;
+        y = b.g;
+        z = b.i;
+        l = b.h;
+        d ? (z(e.l, e.m), removeEventListener("message", p), k = k.forEach(n), addEventListener("message", n)) : b.f();
+        d || y();
     }));
 }
 
-c || h();
+d || h();

test/code_size/test_minimal_runtime_code_size_audio_worklet.json

@@ -1,10 +1,10 @@
 {
   "a.html": 519,
   "a.html.gz": 357,
-  "a.js": 3871,
-  "a.js.gz": 2036,
+  "a.js": 3876,
+  "a.js.gz": 2042,
   "a.wasm": 1288,
   "a.wasm.gz": 860,
-  "total": 5678,
-  "total_gz": 3253
+  "total": 5683,
+  "total_gz": 3259
 }

test/code_size/test_minimal_runtime_code_size_hello_wasm_worker.json

@@ -1,10 +1,10 @@
 {
   "a.html": 519,
   "a.html.gz": 357,
-  "a.js": 830,
-  "a.js.gz": 525,
+  "a.js": 855,
+  "a.js.gz": 543,
   "a.wasm": 1885,
   "a.wasm.gz": 1072,
-  "total": 3234,
-  "total_gz": 1954
+  "total": 3259,
+  "total_gz": 1972
 }