Bug 1316098 - Optimize out result object allocation for await/return in async function.

Tag #1287

js/src/doc/Debugger/Conventions.md

@@ -110,8 +110,8 @@ resumption value has one of the following forms:
     the `new` expression returns the frame's `this` value. Similarly, if
     the function is the constructor for a subclass, then a non-object
     value may result in a TypeError.
-    If the frame is a generator or async function, then <i>value</i> must
+    If the frame is a generator function, then <i>value</i> must conform to the
-    conform to the iterator protocol: it must be a non-proxy object of the form
+    iterator protocol: it must be a non-proxy object of the form
     <code>{ done: <i>boolean</i>, value: <i>v</i> }</code>, where
     both `done` and `value` are ordinary properties.
 

js/src/frontend/BytecodeEmitter.cpp

@@ -8552,7 +8552,7 @@ bool
 BytecodeEmitter::emitYield(ParseNode* pn)
 {
     MOZ_ASSERT(sc->isFunctionBox());
-    MOZ_ASSERT(pn->getOp() == JSOP_YIELD || pn->getOp() == JSOP_AWAIT);
+    MOZ_ASSERT(pn->getOp() == JSOP_YIELD);
 
     bool needsIteratorResult = sc->asFunctionBox()->needsIteratorResult();
     if (needsIteratorResult) {
@@ -8574,12 +8574,27 @@ BytecodeEmitter::emitYield(ParseNode* pn)
     if (!emitGetDotGenerator())
         return false;
 
-    if (!emitYieldOp(pn->getOp()))
+    if (!emitYieldOp(JSOP_YIELD))
         return false;
 
     return true;
 }
 
+bool
+BytecodeEmitter::emitAwait(ParseNode* pn)
+{
+    MOZ_ASSERT(sc->isFunctionBox());
+    MOZ_ASSERT(pn->getOp() == JSOP_AWAIT);
+
+    if (!emitTree(pn->pn_kid))
+        return false;
+    if (!emitGetDotGenerator())
+        return false;
+    if (!emitYieldOp(JSOP_AWAIT))
+        return false;
+    return true;
+}
+
 bool
 BytecodeEmitter::emitYieldStar(ParseNode* iter)
 {
@@ -10631,11 +10646,15 @@ BytecodeEmitter::emitTree(ParseNode* pn, ValueUsage valueUsage /* = ValueUsage::
         break;
 
       case PNK_YIELD:
-      case PNK_AWAIT:
         if (!emitYield(pn))
             return false;
         break;
 
+      case PNK_AWAIT:
+        if (!emitAwait(pn))
+            return false;
+        break;
+
       case PNK_STATEMENTLIST:
         if (!emitStatementList(pn))
             return false;

js/src/frontend/BytecodeEmitter.h

@@ -613,6 +613,7 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     MOZ_MUST_USE bool emitYield(ParseNode* pn);
     MOZ_MUST_USE bool emitYieldOp(JSOp op);
     MOZ_MUST_USE bool emitYieldStar(ParseNode* iter);
+    MOZ_MUST_USE bool emitAwait(ParseNode* pn);
 
     MOZ_MUST_USE bool emitPropLHS(ParseNode* pn);
     MOZ_MUST_USE bool emitPropOp(ParseNode* pn, JSOp op);

js/src/frontend/SharedContext.h

@@ -553,7 +553,7 @@ class FunctionBox : public ObjectBox, public SharedContext
     }
 
     bool needsIteratorResult() const {
-        return isStarGenerator() || isAsync();
+        return isStarGenerator();
     }
 
     bool isAsync() const { return asyncKind() == AsyncFunction; }

js/src/jit-test/tests/debug/onExceptionUnwind-resumption-async.js

@@ -9,28 +9,6 @@ async function f() {
 }
 `);
 
-// To continue testing after uncaught exception, remember the exception and
-// return normal completeion.
-var currentFrame;
-var uncaughtException;
-dbg.uncaughtExceptionHook = function(e) {
-    uncaughtException = e;
-    return {
-        return: currentFrame.eval("({ done: true, value: 'uncaught' })").return
-    };
-};
-function testUncaughtException() {
-    uncaughtException = undefined;
-    var val = g.eval(`
-var val;
-f().then(v => { val = v });
-drainJobQueue();
-val;
-`);
-    assertEq(val, "uncaught");
-    assertEq(uncaughtException instanceof TypeError, true);
-}
-
 // Just continue
 dbg.onExceptionUnwind = function(frame) {
     return undefined;
@@ -42,83 +20,10 @@ drainJobQueue();
 assertEq(exc instanceof ReferenceError, true);
 `);
 
-// Should return object.
+// Return with resumption value.
 dbg.onExceptionUnwind = function(frame) {
-    currentFrame = frame;
     return {
-        return: "foo"
+        return: 10
-    };
-};
-testUncaughtException();
-
-// The object should have `done` property and `value` property.
-dbg.onExceptionUnwind = function(frame) {
-    currentFrame = frame;
-    return {
-        return: frame.eval("({})").return
-    };
-};
-testUncaughtException();
-
-// The object should have `done` property.
-dbg.onExceptionUnwind = function(frame) {
-    currentFrame = frame;
-    return {
-        return: frame.eval("({ value: 10 })").return
-    };
-};
-testUncaughtException();
-
-// The object should have `value` property.
-dbg.onExceptionUnwind = function(frame) {
-    currentFrame = frame;
-    return {
-        return: frame.eval("({ done: true })").return
-    };
-};
-testUncaughtException();
-
-// `done` property should be a boolean value.
-dbg.onExceptionUnwind = function(frame) {
-    currentFrame = frame;
-    return {
-        return: frame.eval("({ done: 10, value: 10 })").return
-    };
-};
-testUncaughtException();
-
-// `done` property shouldn't be an accessor.
-dbg.onExceptionUnwind = function(frame) {
-    currentFrame = frame;
-    return {
-        return: frame.eval("({ get done() { return true; }, value: 10 })").return
-    };
-};
-testUncaughtException();
-
-// `value` property shouldn't be an accessor.
-dbg.onExceptionUnwind = function(frame) {
-    currentFrame = frame;
-    return {
-        return: frame.eval("({ done: true, get value() { return 10; } })").return
-    };
-};
-testUncaughtException();
-
-// The object shouldn't be a Proxy.
-dbg.onExceptionUnwind = function(frame) {
-    currentFrame = frame;
-    return {
-        return: frame.eval("new Proxy({ done: true, value: 10 }, {})").return
-    };
-};
-testUncaughtException();
-
-// Correct resumption value.
-dbg.onExceptionUnwind = function(frame) {
-    currentFrame = frame;
-    return {
-        return: frame.eval("({ done: true, value: 10 })").return
     };
 };
 var val = g.eval(`

js/src/js.msg

@@ -438,7 +438,6 @@ MSG_DEF(JSMSG_SC_SAB_DISABLED,         0, JSEXN_TYPEERR, "SharedArrayBuffer not
 
 // Debugger
 MSG_DEF(JSMSG_ASSIGN_FUNCTION_OR_NULL, 1, JSEXN_TYPEERR, "value assigned to {0} must be a function or null")
-MSG_DEF(JSMSG_DEBUG_BAD_AWAIT,         0, JSEXN_TYPEERR, "await expression received invalid value")
 MSG_DEF(JSMSG_DEBUG_BAD_LINE,          0, JSEXN_TYPEERR, "invalid line number")
 MSG_DEF(JSMSG_DEBUG_BAD_OFFSET,        0, JSEXN_TYPEERR, "invalid script offset")
 MSG_DEF(JSMSG_DEBUG_BAD_REFERENT,      2, JSEXN_TYPEERR, "{0} does not refer to {1}")

js/src/vm/AsyncFunction.cpp

@@ -171,22 +171,14 @@ AsyncFunctionResume(JSContext* cx, Handle<PromiseObject*> resultPromise, HandleV
                                  : cx->names().StarGeneratorThrow;
     FixedInvokeArgs<1> args(cx);
     args[0].set(valueOrReason);
-    RootedValue result(cx);
+    RootedValue value(cx);
-    if (!CallSelfHostedFunction(cx, funName, generatorVal, args, &result))
+    if (!CallSelfHostedFunction(cx, funName, generatorVal, args, &value))
         return AsyncFunctionThrown(cx, resultPromise);
 
-    RootedObject resultObj(cx, &result.toObject());
+    if (generatorVal.toObject().as<GeneratorObject>().isAfterAwait())
-    RootedValue doneVal(cx);
-    RootedValue value(cx);
-    if (!GetProperty(cx, resultObj, resultObj, cx->names().done, &doneVal))
-        return false;
-    if (!GetProperty(cx, resultObj, resultObj, cx->names().value, &value))
-        return false;
-
-    if (doneVal.toBoolean())
-        return AsyncFunctionReturned(cx, resultPromise, value);
-
         return AsyncFunctionAwait(cx, resultPromise, value);
+
+    return AsyncFunctionReturned(cx, resultPromise, value);
 }
 
 // Async Functions proposal 2.2 steps 3-8.
@@ -242,9 +234,3 @@ js::IsWrappedAsyncFunction(JSFunction* fun)
 {
     return fun->maybeNative() == WrappedAsyncFunction;
 }
-
-MOZ_MUST_USE bool
-js::CheckAsyncResumptionValue(JSContext* cx, HandleValue v)
-{
-    return CheckStarGeneratorResumptionValue(cx, v);
-}

js/src/vm/AsyncFunction.h

@@ -35,9 +35,6 @@ MOZ_MUST_USE bool
 AsyncFunctionAwaitedRejected(JSContext* cx, Handle<PromiseObject*> resultPromise,
                              HandleValue generatorVal, HandleValue reason);
 
-MOZ_MUST_USE bool
-CheckAsyncResumptionValue(JSContext* cx, HandleValue v);
-
 } // namespace js
 
 #endif /* vm_AsyncFunction_h */

js/src/vm/Debugger.cpp

@@ -32,7 +32,6 @@
 #include "js/Vector.h"
 #include "proxy/ScriptedProxyHandler.h"
 #include "vm/ArgumentsObject.h"
-#include "vm/AsyncFunction.h"
 #include "vm/DebuggerMemory.h"
 #include "vm/GeneratorObject.h"
 #include "vm/SPSProfiler.h"
@@ -1560,16 +1559,11 @@ CheckResumptionValue(JSContext* cx, AbstractFramePtr frame, const Maybe<HandleVa
                      JSTrapStatus status, MutableHandleValue vp)
 {
     if (status == JSTRAP_RETURN && frame && frame.isFunctionFrame()) {
-        // Don't let a { return: ... } resumption value make a generator or
+        // Don't let a { return: ... } resumption value make a generator
-        // async function violate the iterator protocol. The return value from
+        // function violate the iterator protocol. The return value from
         // such a frame must have the form { done: <bool>, value: <anything> }.
         RootedFunction callee(cx, frame.callee());
-        if (callee->isAsync()) {
+        if (callee->isStarGenerator()) {
-            if (!CheckAsyncResumptionValue(cx, vp)) {
-                JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_DEBUG_BAD_AWAIT);
-                return false;
-            }
-        } else if (callee->isStarGenerator() || callee->isAsync()) {
             if (!CheckStarGeneratorResumptionValue(cx, vp)) {
                 JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_DEBUG_BAD_YIELD);
                 return false;

js/src/vm/Opcodes.h

@@ -2130,12 +2130,12 @@
      */ \
     macro(JSOP_DEBUGAFTERYIELD,  208, "debugafteryield",  NULL,  1,  0,  0,  JOF_BYTE) \
     /*
-     * Pops the generator and the return value 'result', stops interpretation
+     * Pops the generator and the return value 'promise', stops interpretation
-     * and returns 'result'. Pushes resolved value onto the stack.
+     * and returns 'promise'. Pushes resolved value onto the stack.
      *   Category: Statements
      *   Type: Generator
      *   Operands: uint24_t yieldAndAwaitIndex
-     *   Stack: result, gen => resolved
+     *   Stack: promise, gen => resolved
      */ \
     macro(JSOP_AWAIT,         209, "await",        NULL,  4,  2,  1,  JOF_UINT24) \
     macro(JSOP_UNUSED210,     210, "unused210",    NULL,  1,  0,  0,  JOF_BYTE) \