Optimize JS function proxying (emscripten-core#9164)

src/jsifier.js

@@ -46,6 +46,16 @@ var NEED_ALL_ASM2WASM_IMPORTS = BINARYEN_TRAP_MODE == 'js';
 // the current compilation unit.
 var HAS_MAIN = ('_main' in IMPLEMENTED_FUNCTIONS) || MAIN_MODULE || SIDE_MODULE;
 
+// Mangles the given C/JS side function name to assembly level function name (adds an underscore)
+function mangleCSymbolName(f) {
+  return f[0] == '$' ? f.substr(1) : '_' + f;
+}
+
+// Reverses C/JS name mangling: _foo -> foo, and foo -> $foo.
+function demangleCSymbolName(f) {
+  return f[0] == '_' ? f.substr(1) : '$' + f;
+}
+
 // JSifier
 function JSify(data, functionsOnly) {
   var mainPass = !functionsOnly;
@@ -72,7 +82,7 @@ function JSify(data, functionsOnly) {
     }
     libFuncsToInclude.forEach(function(ident) {
       data.functionStubs.push({
-        ident: '_' + ident
+        ident: mangleCSymbolName(ident)
       });
     });
   }
@@ -129,12 +139,7 @@ function JSify(data, functionsOnly) {
         return '';
       }
 
-      // $ident's are special, we do not prefix them with a '_'.
-      if (ident[0] === '$') {
-        var finalName = ident.substr(1);
-      } else {
-        var finalName = '_' + ident;
-      }
+      var finalName = mangleCSymbolName(ident);
 
       // if the function was implemented in compiled code, we just need to export it so we can reach it from JS
       if (finalName in IMPLEMENTED_FUNCTIONS) {
@@ -175,7 +180,7 @@ function JSify(data, functionsOnly) {
             realIdent = realIdent.substr(2);
           }
 
-          var target = (SIDE_MODULE ? 'parent' : '') + "Module['_" + realIdent + "']";
+          var target = (SIDE_MODULE ? 'parent' : '') + "Module['" + mangleCSymbolName(realIdent) + "']";
           var assertion = '';
           if (ASSERTIONS) {
             var what = 'function';
@@ -211,18 +216,20 @@ function JSify(data, functionsOnly) {
       var isFunction = false;
 
       if (typeof snippet === 'string') {
-        var target = LibraryManager.library[snippet];
-        if (target) {
-          // Redirection for aliases. We include the parent, and at runtime make ourselves equal to it.
-          // This avoid having duplicate functions with identical content.
-          redirectedIdent = snippet;
-          deps.push(snippet);
-          snippet = '_' + snippet;
-        }
-        // In asm, we need to know about library functions. If there is a target, though, then no
-        // need to consider this a library function - we will call directly to it anyhow
-        if (!redirectedIdent && (typeof target == 'function' || /Math_\w+/.exec(snippet))) {
-          Functions.libraryFunctions[finalName] = 1;
+        if (snippet[0] != '=') {
+          var target = LibraryManager.library[snippet];
+          if (target) {
+            // Redirection for aliases. We include the parent, and at runtime make ourselves equal to it.
+            // This avoid having duplicate functions with identical content.
+            redirectedIdent = snippet;
+            deps.push(snippet);
+            snippet = mangleCSymbolName(snippet);
+          }
+          // In asm, we need to know about library functions. If there is a target, though, then no
+          // need to consider this a library function - we will call directly to it anyhow
+          if (!redirectedIdent && (typeof target == 'function' || /Math_\w+/.exec(snippet))) {
+            Functions.libraryFunctions[finalName] = 1;
+          }
         }
       } else if (typeof snippet === 'object') {
         snippet = stringifyWithFunctions(snippet);
@@ -282,9 +289,18 @@ function JSify(data, functionsOnly) {
           contentText = snippet; // Regular JS function that will be executed in the context of the calling thread.
         }
       } else if (typeof snippet === 'string' && snippet.indexOf(';') == 0) {
+        // In JS libraries
+        //   foo: ';[code here verbatim]'
+        //  emits
+        //   'var foo;[code here verbatim];'
         contentText = 'var ' + finalName + snippet;
         if (snippet[snippet.length-1] != ';' && snippet[snippet.length-1] != '}') contentText += ';';
       } else {
+        // In JS libraries
+        //   foo: '=[value]'
+        //  emits
+        //   'var foo = [value];'
+        if (typeof snippet === 'string' && snippet[0] == '=') snippet = snippet.substr(1);
         contentText = 'var ' + finalName + '=' + snippet + ';';
       }
       var sig = LibraryManager.library[ident + '__sig'];
@@ -307,15 +323,15 @@ function JSify(data, functionsOnly) {
         // We set EXPORTED_FUNCTIONS here to tell emscripten.py to do that.
         deps.forEach(function(dep) {
           if (LibraryManager.library[dep + '__asm']) {
-            EXPORTED_FUNCTIONS['_' + dep] = 0;
+            EXPORTED_FUNCTIONS[mangleCSymbolName(dep)] = 0;
           }
         });
       }
       return depsText + contentText;
     }
 
     itemsDict.functionStub.push(item);
-    var shortident = item.ident.substr(1);
+    var shortident = demangleCSymbolName(item.ident);
     // If this is not linkable, anything not in the library is definitely missing
     if (item.ident in DEAD_FUNCTIONS) {
       if (LibraryManager.library[shortident + '__asm']) {

src/library_pthread.js

@@ -1157,40 +1157,38 @@ var LibraryPThread = {
     // all the args here.
     // We also pass 'sync' to C separately, since C needs to look at it.
     var numCallArgs = arguments.length - 2;
+#if ASSERTIONS
+    if (numCallArgs > {{{ cDefine('EM_QUEUED_JS_CALL_MAX_ARGS') }}}-1) throw 'emscripten_proxy_to_main_thread_js: Too many arguments ' + numCallArgs + ' to proxied function idx=' + index + ', maximum supported is ' + ({{{ cDefine('EM_QUEUED_JS_CALL_MAX_ARGS') }}}-1) + '!';
+#endif
     // Allocate a buffer, which will be copied by the C code.
     var stack = stackSave();
-    var buffer = stackAlloc(numCallArgs * 8);
+    // First passed parameter specifies the number of arguments to the function.
+    var args = stackAlloc(numCallArgs * 8);
+    var b = args >> 3;
     for (var i = 0; i < numCallArgs; i++) {
-      HEAPF64[(buffer >> 3) + i] = arguments[2 + i];
+      HEAPF64[b + i] = arguments[2 + i];
     }
-    var ret = _emscripten_run_in_main_runtime_thread_js(index, numCallArgs, buffer, sync);
+    var ret = _emscripten_run_in_main_runtime_thread_js(index, numCallArgs, args, sync);
     stackRestore(stack);
     return ret;
   },
 
-  emscripten_receive_on_main_thread_js__deps: ['emscripten_proxy_to_main_thread_js'],
-  emscripten_receive_on_main_thread_js: function(index, numCallArgs, buffer) {
-    // Avoid garbage by reusing a single JS array for call arguments.
-    if (!_emscripten_receive_on_main_thread_js.callArgs) {
-      _emscripten_receive_on_main_thread_js.callArgs = [];
-    }
-    var callArgs = _emscripten_receive_on_main_thread_js.callArgs;
-    callArgs.length = numCallArgs;
+  emscripten_receive_on_main_thread_js_callArgs: '=[]',
+
+  emscripten_receive_on_main_thread_js__deps: ['emscripten_proxy_to_main_thread_js', 'emscripten_receive_on_main_thread_js_callArgs'],
+  emscripten_receive_on_main_thread_js: function(index, numCallArgs, args) {
+    _emscripten_receive_on_main_thread_js_callArgs.length = numCallArgs;
+    var b = args >> 3;
     for (var i = 0; i < numCallArgs; i++) {
-      callArgs[i] = HEAPF64[(buffer >> 3) + i];
+      _emscripten_receive_on_main_thread_js_callArgs[i] = HEAPF64[b + i];
     }
     // Proxied JS library funcs are encoded as positive values, and
     // EM_ASMs as negative values (see include_asm_consts)
-    var func;
-    if (index > 0) {
-      func = proxiedFunctionTable[index];
-    } else {
-      func = ASM_CONSTS[-index - 1];
-    }
+    var func = index > 0 ? proxiedFunctionTable[index] : ASM_CONSTS[-index - 1];
 #if ASSERTIONS
     assert(func.length == numCallArgs);
 #endif
-    return func.apply(null, callArgs);
+    return func.apply(null, _emscripten_receive_on_main_thread_js_callArgs);
   },
 
 #if MODULARIZE

src/modules.js

@@ -207,8 +207,8 @@ var LibraryManager = {
       if (typeof lib[x] === 'string') {
         var target = x;
         while (typeof lib[target] === 'string') {
-          // ignore code, aliases are just simple names
-          if (lib[target].search(/[({; ]/) >= 0) continue libloop;
+          // ignore code and variable assignments, aliases are just simple names
+          if (lib[target].search(/[=({; ]/) >= 0) continue libloop;
           // ignore trivial pass-throughs to Math.*
           if (lib[target].indexOf('Math_') == 0) continue libloop;
           target = lib[target];

src/struct_info.json

@@ -1512,6 +1512,9 @@
             "EM_PROXIED_SYSCALL",
             "EM_PROXIED_CREATE_CONTEXT",
             "EM_PROXIED_RESIZE_OFFSCREENCANVAS",
+            "EM_PROXIED_JS_FUNCTION",
+            "EM_QUEUED_CALL_MAX_ARGS",
+            "EM_QUEUED_JS_CALL_MAX_ARGS",
             "EM_THREAD_STATUS_NOTSTARTED",
             "EM_THREAD_STATUS_RUNNING",
             "EM_THREAD_STATUS_SLEEPING",

system/include/emscripten/threading.h

@@ -102,16 +102,17 @@ typedef union em_variant_val
   char *cp;
 } em_variant_val;
 
+// Proxied C/C++ functions support at most this many arguments. Dispatch is static/strongly typed by signature.
 #define EM_QUEUED_CALL_MAX_ARGS 11
+// Proxied JS function can support a few more arguments than proxied C/C++ functions, because the dispatch
+// is variadic and signature independent.
+#define EM_QUEUED_JS_CALL_MAX_ARGS 20
 typedef struct em_queued_call
 {
   int functionEnum;
   void *functionPtr;
   int operationDone;
-  // If set, this is a JS call: number of arguments are in functionEnum, the index in functionPtr,
-  // and args in args.
-  int js;
-  em_variant_val args[EM_QUEUED_CALL_MAX_ARGS];
+  em_variant_val args[EM_QUEUED_JS_CALL_MAX_ARGS];
   em_variant_val returnValue;
 
   // An optional pointer to a secondary data block that should be free()d when this queued call is freed.
@@ -254,6 +255,7 @@ typedef int (*em_func_iiiiiiiiii)(int, int, int, int, int, int, int, int, int);
 #define EM_PROXIED_SYSCALL (EM_PROXIED_FUNC_SPECIAL(1) | EM_FUNC_SIG_III)
 #define EM_PROXIED_CREATE_CONTEXT (EM_PROXIED_FUNC_SPECIAL(2) | EM_FUNC_SIG_III)
 #define EM_PROXIED_RESIZE_OFFSCREENCANVAS (EM_PROXIED_FUNC_SPECIAL(3) | EM_FUNC_SIG_IIII)
+#define EM_PROXIED_JS_FUNCTION (EM_PROXIED_FUNC_SPECIAL(4) | EM_FUNC_SIG_D)
 
 // Runs the given function synchronously on the main Emscripten runtime thread.
 // If this thread is the main thread, the operation is immediately performed, and the result is returned.