Changeset 28923 in webkit for trunk/JavaScriptCore/kjs/Parser.h

Timestamp:

Dec 20, 2007, 6:18:11 PM (17 years ago)

Author:

[email protected]

Message:

Reviewed by Oliver Hunt.

AST optimization: Avoid NULL-checking ForNode's child nodes.

0.6% speedup on SunSpider.

This is a proof of concept patch that demonstrates how to optimize
grammar productions with optional components, like

for (optional; optional; optional) {

...

}

The parser emits NULL for an optional component that is not present.

Instead of checking for a NULL child at execution time, a node that
expects an optional component to be present more often than not checks
for a NULL child at construction time, and substitutes a viable
alternative node in its place.

(We'd like the parser to start emitting NULL a lot more once we teach
it to emit NULL for certain no-op productions like EmptyStatement and
VariableStatement, so, as a foundation, it's important for nodes with
NULL optional components to be fast.)

• kjs/Parser.cpp: (KJS::Parser::didFinishParsing): Check for NULL SourceElements. Also, moved didFinishParsing into the .cpp file because adding a branch while it was in the header file caused a substantial and inexplicable performance regression. (Did I mention that GCC is crazy?)

• kjs/grammar.y:

• kjs/nodes.cpp: (KJS::BlockNode::BlockNode): Check for NULL SourceElements. (KJS::ForNode::optimizeVariableAccess): No need to check for NULL here. (KJS::ForNode::execute): No need to check for NULL here.
• kjs/nodes.h: (KJS::ForNode::): Check for NULL SourceElements. Substitute a TrueNode because it's semantically harmless, and it evaluates to boolean in an efficient manner.

File:

• trunk/JavaScriptCore/kjs/Parser.h (modified) (1 diff)

trunk/JavaScriptCore/kjs/Parser.h

@@ -54 +54 @@
         int sourceId() const { return m_sourceId; }
 
-        void didFinishParsing(SourceElements* sourceElements, ParserRefCountedData<DeclarationStacks::VarStack>* varStack, 
-                              ParserRefCountedData<DeclarationStacks::FunctionStack>* funcStack, int lastLine)
-        {
-            m_sourceElements.set(sourceElements);
-            m_varDeclarations = varStack;
-            m_funcDeclarations = funcStack;
-            m_lastLine = lastLine;
-        }
+        void didFinishParsing(SourceElements*, ParserRefCountedData<DeclarationStacks::VarStack>*, 
+                              ParserRefCountedData<DeclarationStacks::FunctionStack>*, int lastLine);
 
     private: