Changeset 73433 in webkit for trunk/JavaScriptCore/runtime/JSString.h

Timestamp:

Dec 7, 2010, 3:11:08 AM (14 years ago)

Author:

Antti Koivisto

Message:

​https://bugs.webkit.org/show_bug.cgi?id=50412
​http://www.wunderground.com/US/CA/Hayward.html causes big memory spike during page loading

Reviewed by Gavin Barraclough.

Creating a substring caused the original string be flattened if it was in the rope form. This could use
significant amount of memory by reducing buffer sharing between strings.

Add a rope specific substring function that constructs the substring by reusing the rope fibers
instead of flattening the rope.

No change observed in SunSpider.

• runtime/JSString.cpp:

(JSC::JSString::substringFromRope):

• runtime/JSString.h:

(JSC::jsSubstring):

• runtime/StringPrototype.cpp:

(JSC::stringProtoFuncSubstr):
(JSC::stringProtoFuncSubstring):

File:

• trunk/JavaScriptCore/runtime/JSString.h (modified) (3 diffs)

trunk/JavaScriptCore/runtime/JSString.h

@@ -357 +357 @@
 
         void resolveRope(ExecState*) const;
+        JSString* substringFromRope(ExecState*, unsigned offset, unsigned length);
 
         void appendStringInConstruct(unsigned& index, const UString& string)
@@ -436 +437 @@
         friend JSValue jsString(ExecState* exec, JSValue thisValue);
         friend JSString* jsStringWithFinalizer(ExecState*, const UString&, JSStringFinalizerCallback callback, void* context);
+        friend JSString* jsSubstring(ExecState* exec, JSString* s, unsigned offset, unsigned length);
     };
 
@@ -519 +521 @@
         JSGlobalData* globalData = &exec->globalData();
         return fixupVPtr(globalData, new (globalData) JSString(globalData, s, callback, context));
+    }
+    
+    inline JSString* jsSubstring(ExecState* exec, JSString* s, unsigned offset, unsigned length)
+    {
+        ASSERT(offset <= static_cast<unsigned>(s->length()));
+        ASSERT(length <= static_cast<unsigned>(s->length()));
+        ASSERT(offset + length <= static_cast<unsigned>(s->length()));
+        JSGlobalData* globalData = &exec->globalData();
+        if (!length)
+            return globalData->smallStrings.emptyString(globalData);
+        if (s->isRope())
+            return s->substringFromRope(exec, offset, length);
+        return jsSubstring(globalData, s->m_value, offset, length);
     }