Changeset 197485 in webkit for trunk/Source/JavaScriptCore/runtime/JSString.h

Timestamp:

Mar 2, 2016, 6:06:18 PM (9 years ago)

Author:

[email protected]

Message:

RegExpPrototype should check for exceptions after calling toString and doing so should not be expensive
​https://bugs.webkit.org/show_bug.cgi?id=154927

Reviewed by Saam Barati.

While working on regexp optimizations, I found that RegExpPrototype calls toString(), an
effectful operation that could do anything, without then checking for hadException().

So I added a call to hadException().

But that regressed Octane/regexp by 5%! That's a lot! It turns out that
exec->hadException() is soooper slow. So, I made it cheaper to check for exceptions from
toString(): there is now a variant called toStringFast() that returns null iff it throws an
exception.

This allowed me to add the exception check without regressing perf.

Note that toString() must retain its old behavior of returning an empty string on exception.
There is just too much code that relies on that behavior.

• runtime/JSCJSValue.cpp:

(JSC::JSValue::isValidCallee):
(JSC::JSValue::toStringSlowCase):
(JSC::JSValue::toWTFStringSlowCase):

• runtime/JSCJSValue.h:

(JSC::JSValue::asValue):

• runtime/JSString.h:

(JSC::JSValue::toString):
(JSC::JSValue::toStringFast):
(JSC::JSValue::toWTFString):

• runtime/RegExpPrototype.cpp:

(JSC::regExpProtoFuncTest):
(JSC::regExpProtoFuncExec):
(JSC::regExpProtoFuncCompile):

File:

• trunk/Source/JavaScriptCore/runtime/JSString.h (modified) (1 diff)

trunk/Source/JavaScriptCore/runtime/JSString.h

@@ -734 +734 @@
     if (isString())
         return jsCast<JSString*>(asCell());
-    return toStringSlowCase(exec);
+    bool returnEmptyStringOnError = true;
+    return toStringSlowCase(exec, returnEmptyStringOnError);
+}
+
+inline JSString* JSValue::toStringOrNull(ExecState* exec) const
+{
+    if (isString())
+        return jsCast<JSString*>(asCell());
+    bool returnEmptyStringOnError = false;
+    return toStringSlowCase(exec, returnEmptyStringOnError);
 }