Changeset 184865 in webkit for trunk/Source/JavaScriptCore

Timestamp:

May 26, 2015, 11:54:01 AM (10 years ago)

Author:

[email protected]

Message:

String.prototype.charAt() should use StringView.
<​https://webkit.org/b/145352>

Reviewed by Darin Adler.

Remove the jsSingleCharacterSubstring() function since it's actually completely
counter-productive: it could create a single-character string that would retain
a much larger string for the duration of its lifetime.

This made sense before StringImpl learned to put its characters at the tail end
of its own allocation. Now that it does, it's far better to just create a new
single-character StringImpl.

With that out of the way, we can make String.prototype.charAt() use StringView
to avoid reifying substring JSStrings (and avoid some ref churn too.)

• runtime/JSString.cpp:

(JSC::JSRopeString::getIndexSlowCase):

• runtime/JSString.h:

(JSC::JSString::getIndex):
(JSC::jsSingleCharacterSubstring): Deleted.

• runtime/StringPrototype.cpp:

(JSC::stringProtoFuncCharAt):
(JSC::stringProtoFuncSplit):

Location:

trunk/Source/JavaScriptCore

Files:

• ChangeLog (modified) (1 diff)
• runtime/JSString.cpp (modified) (1 diff)
• runtime/JSString.h (modified) (3 diffs)
• runtime/StringPrototype.cpp (modified) (2 diffs)

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2015-05-26  Andreas Kling  <[email protected]>
+
+        String.prototype.charAt() should use StringView.
+        <https://webkit.org/b/145352>
+
+        Reviewed by Darin Adler.
+
+        Remove the jsSingleCharacterSubstring() function since it's actually completely
+        counter-productive: it could create a single-character string that would retain
+        a much larger string for the duration of its lifetime.
+
+        This made sense before StringImpl learned to put its characters at the tail end
+        of its own allocation. Now that it does, it's far better to just create a new
+        single-character StringImpl.
+
+        With that out of the way, we can make String.prototype.charAt() use StringView
+        to avoid reifying substring JSStrings (and avoid some ref churn too.)
+
+        * runtime/JSString.cpp:
+        (JSC::JSRopeString::getIndexSlowCase):
+        * runtime/JSString.h:
+        (JSC::JSString::getIndex):
+        (JSC::jsSingleCharacterSubstring): Deleted.
+        * runtime/StringPrototype.cpp:
+        (JSC::stringProtoFuncCharAt):
+        (JSC::stringProtoFuncSplit):
+
 2015-05-26  Yusuke Suzuki  <[email protected]>
 

trunk/Source/JavaScriptCore/runtime/JSString.cpp

@@ -375 +375 @@
     ASSERT(!isRope());
     RELEASE_ASSERT(i < m_value.length());
-    return jsSingleCharacterSubstring(exec, m_value, i);
+    return jsSingleCharacterString(exec, m_value[i]);
 }
 

trunk/Source/JavaScriptCore/runtime/JSString.h

@@ -46 +46 @@
 JSString* jsSingleCharacterString(VM*, UChar);
 JSString* jsSingleCharacterString(ExecState*, UChar);
-JSString* jsSingleCharacterSubstring(ExecState*, const String&, unsigned offset);
 JSString* jsSubstring(VM*, const String&, unsigned offset, unsigned length);
 JSString* jsSubstring(ExecState*, const String&, unsigned offset, unsigned length);
@@ -445 +444 @@
 }
 
-ALWAYS_INLINE JSString* jsSingleCharacterSubstring(ExecState* exec, const String& s, unsigned offset)
-{
-    VM* vm = &exec->vm();
-    ASSERT(offset < static_cast<unsigned>(s.length()));
-    UChar c = s.characterAt(offset);
-    if (c <= maxSingleCharacterString)
-        return vm->smallStrings.singleCharacterString(c);
-    return JSString::create(*vm, StringImpl::createSubstringSharingImpl(s.impl(), offset, 1));
-}
-
 inline JSString* jsNontrivialString(VM* vm, const String& s)
 {
@@ -508 +497 @@
         return static_cast<JSRopeString*>(this)->getIndexSlowCase(exec, i);
     ASSERT(i < m_value.length());
-    return jsSingleCharacterSubstring(exec, m_value, i);
+    return jsSingleCharacterString(exec, m_value[i]);
 }
 

trunk/Source/JavaScriptCore/runtime/StringPrototype.cpp

@@ -786 +786 @@
     if (!checkObjectCoercible(thisValue))
         return throwVMTypeError(exec);
-    String s = thisValue.toString(exec)->value(exec);
-    unsigned len = s.length();
+    StringView string = thisValue.toString(exec)->view(exec);
     JSValue a0 = exec->argument(0);
     if (a0.isUInt32()) {
         uint32_t i = a0.asUInt32();
-        if (i < len)
-            return JSValue::encode(jsSingleCharacterSubstring(exec, s, i));
+        if (i < string.length())
+            return JSValue::encode(jsSingleCharacterString(exec, string[i]));
         return JSValue::encode(jsEmptyString(exec));
     }
     double dpos = a0.toInteger(exec);
-    if (dpos >= 0 && dpos < len)
-        return JSValue::encode(jsSingleCharacterSubstring(exec, s, static_cast<unsigned>(dpos)));
+    if (dpos >= 0 && dpos < string.length())
+        return JSValue::encode(jsSingleCharacterString(exec, string[static_cast<unsigned>(dpos)]));
     return JSValue::encode(jsEmptyString(exec));
 }
@@ -1247 +1246 @@
 
             do {
-                result->putDirectIndex(exec, position, jsSingleCharacterSubstring(exec, input, position));
+                result->putDirectIndex(exec, position, jsSingleCharacterString(exec, input[position]));
             } while (++position < limit);