Changeset 50254 in webkit for trunk/JavaScriptCore/bytecompiler

Timestamp:

Oct 28, 2009, 6:25:02 PM (16 years ago)

Author:

[email protected]

Message:

Improve for..in enumeration performance
​https://bugs.webkit.org/show_bug.cgi?id=30887

Reviewed by Geoff Garen.

Improve indexing of an object with a for..in iterator by
identifying cases where get_by_val is being used with a iterator
as the subscript and replace it with a new get_by_pname
bytecode. get_by_pname then optimizes lookups that directly access
the base object.

Location:

trunk/JavaScriptCore/bytecompiler

Files:

• BytecodeGenerator.cpp (modified) (1 diff)
• BytecodeGenerator.h (modified) (3 diffs)

trunk/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp

@@ -1282 +1282 @@
 RegisterID* BytecodeGenerator::emitGetByVal(RegisterID* dst, RegisterID* base, RegisterID* property)
 {
+    for (size_t i = m_forInContextStack.size(); i > 0; i--) {
+        ForInContext& context = m_forInContextStack[i - 1];
+        if (context.propertyRegister == property) {
+            emitOpcode(op_get_by_pname);
+            instructions().append(dst->index());
+            instructions().append(base->index());
+            instructions().append(property->index());
+            instructions().append(context.expectedSubscriptRegister->index());
+            instructions().append(context.iterRegister->index());
+            instructions().append(context.indexRegister->index());
+            return dst;
+        }
+    }
     emitOpcode(op_get_by_val);
     instructions().append(dst->index());

trunk/JavaScriptCore/bytecompiler/BytecodeGenerator.h

@@ -62 +62 @@
     };
 
+    struct ForInContext {
+        RefPtr<RegisterID> expectedSubscriptRegister;
+        RefPtr<RegisterID> iterRegister;
+        RefPtr<RegisterID> indexRegister;
+        RefPtr<RegisterID> propertyRegister;
+    };
+
     class BytecodeGenerator : public FastAllocBase {
     public:
@@ -332 +339 @@
         void popFinallyContext();
 
+        void pushOptimisedForIn(RegisterID* expectedBase, RegisterID* iter, RegisterID* index, RegisterID* propertyRegister)
+        {
+            ForInContext context = { expectedBase, iter, index, propertyRegister };
+            m_forInContextStack.append(context);
+        }
+
+        void popOptimisedForIn()
+        {
+            m_forInContextStack.removeLast();
+        }
+
         LabelScope* breakTarget(const Identifier&);
         LabelScope* continueTarget(const Identifier&);
@@ -468 +486 @@
         Vector<ControlFlowContext> m_scopeContextStack;
         Vector<SwitchInfo> m_switchContextStack;
+        Vector<ForInContext> m_forInContextStack;
 
         int m_nextGlobalIndex;