Support using JSPI to load secondary wasm-split module. (#18519)

Passes all the needed arguments to the JSPI pass and the wasm-split run.
Changes the current `instantiateAsync` and friends to use arguments
instead of globals so they can be reused by the new
`emscripten_load_secondary_module` to asynchronously load the secondary
module.

Depends on WebAssembly/binaryen#5431

Author: brendandahl

emcc.py

@@ -104,7 +104,7 @@
   'emscripten_idb_store', 'emscripten_idb_delete', 'emscripten_idb_exists',
   'emscripten_idb_load_blob', 'emscripten_idb_store_blob', 'SDL_Delay',
   'emscripten_scan_registers', 'emscripten_lazy_load_code',
-  'emscripten_fiber_swap',
+  'emscripten_fiber_swap', '__load_secondary_module',
   'wasi_snapshot_preview1.fd_sync', '__wasi_fd_sync', '_emval_await',
   '_dlopen_js', '__asyncjs__*'
 ]
@@ -706,6 +706,9 @@ def check_human_readable_list(items):
     passes += ['--jspi']
     passes += ['--pass-arg=jspi-imports@%s' % ','.join(settings.ASYNCIFY_IMPORTS)]
     passes += ['--pass-arg=jspi-exports@%s' % ','.join(settings.ASYNCIFY_EXPORTS)]
+    if settings.SPLIT_MODULE:
+      passes += ['--pass-arg=jspi-split-module']
+
   if settings.BINARYEN_IGNORE_IMPLICIT_TRAPS:
     passes += ['--ignore-implicit-traps']
   # normally we can assume the memory, if imported, has not been modified
@@ -751,9 +754,12 @@ def make_js_executable(script):
     pass # can fail if e.g. writing the executable to /dev/null
 
 
-def do_split_module(wasm_file):
+def do_split_module(wasm_file, options):
   os.rename(wasm_file, wasm_file + '.orig')
   args = ['--instrument']
+  if options.requested_debug:
+    # Tell wasm-split to preserve function names.
+    args += ['-g']
   building.run_binaryen_command('wasm-split', wasm_file + '.orig', outfile=wasm_file, args=args)
 
 
@@ -2527,6 +2533,9 @@ def check_memory_setting(setting):
   if settings.LEGALIZE_JS_FFI:
     settings.REQUIRED_EXPORTS += ['__get_temp_ret', '__set_temp_ret']
 
+  if settings.SPLIT_MODULE and settings.ASYNCIFY == 2:
+    settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE += ['_load_secondary_module']
+
   # wasm side modules have suffix .wasm
   if settings.SIDE_MODULE and shared.suffix(target) == '.js':
     diagnostics.warning('emcc', 'output suffix .js requested, but wasm side modules are just wasm files; emitting only a .wasm, no .js')
@@ -3192,7 +3201,7 @@ def phase_final_emitting(options, state, target, wasm_target, memfile):
 
   if settings.SPLIT_MODULE:
     diagnostics.warning('experimental', 'The SPLIT_MODULE setting is experimental and subject to change')
-    do_split_module(wasm_target)
+    do_split_module(wasm_target, options)
 
   for f in generated_text_files_with_native_eols:
     tools.line_endings.convert_line_endings_in_file(f, os.linesep, options.output_eol)

emscripten.py

@@ -666,6 +666,11 @@ def add_standard_wasm_imports(send_items_map):
       'store_val_f64',
     ]
 
+  if settings.SPLIT_MODULE and settings.ASYNCIFY == 2:
+    # Calls to this function are generated by binaryen so it must be manually
+    # imported.
+    extra_sent_items.append('__load_secondary_module')
+
   for s in extra_sent_items:
     send_items_map[s] = s
 

src/library_async.js

@@ -533,6 +533,18 @@ mergeInto(LibraryManager.library, {
     });
   },
 
+  _load_secondary_module__sig: 'v',
+  _load_secondary_module: async function() {
+    // Mark the module as loading for the wasm module (so it doesn't try to load it again).
+    Module['asm']['load_secondary_module_status'].value = 1;
+    var imports = {'primary': Module['asm']};
+    // Replace '.wasm' suffix with '.deferred.wasm'.
+    var deferred = wasmBinaryFile.slice(0, -5) + '.deferred.wasm';
+    await new Promise((resolve) => {
+      instantiateAsync(null, deferred, imports, resolve);
+    });
+  },
+
   $Fibers__deps: ['$Asyncify'],
   $Fibers: {
     nextFiber: 0,