Changeset 36317 in webkit for trunk/JavaScriptCore/VM/CodeGenerator.cpp

Timestamp:

Sep 10, 2008, 2:23:35 AM (17 years ago)

Author:

[email protected]

Message:

Add optimised access to known properties on the global object.

Reviewed by Maciej Stachowiak

Improve cross scope access to the global object by emitting
code to access it directly rather than by walking the scope chain.

This is a 0.8% win in SunSpider and a 1.7% win in the v8 benchmarks.

File:

• trunk/JavaScriptCore/VM/CodeGenerator.cpp (modified) (6 diffs)

trunk/JavaScriptCore/VM/CodeGenerator.cpp

@@ -678 +678 @@
 }
 
-bool CodeGenerator::findScopedProperty(const Identifier& property, int& index, size_t& stackDepth, bool forWriting)
+bool CodeGenerator::findScopedProperty(const Identifier& property, int& index, size_t& stackDepth, bool forWriting, JSValue*& globalObject)
 {
     // Cases where we cannot optimise the lookup
@@ -703 +703 @@
                 stackDepth = 0;
                 index = missingSymbolMarker();
+                if (++iter == end)
+                    globalObject = currentVariableObject;
                 return false;
             }
             stackDepth = depth;
             index = entry.getIndex();
+            if (++iter == end)
+                globalObject = currentVariableObject;
             return true;
         }
@@ -716 +720 @@
     stackDepth = depth;
     index = missingSymbolMarker();
+    JSObject* scope = *iter;
+    if (++iter == end)
+        globalObject = scope;
     return true;
 }
@@ -723 +730 @@
     size_t depth = 0;
     int index = 0;
-    if (!findScopedProperty(property, index, depth, false)) {
+    JSValue* globalObject = 0;
+    if (!findScopedProperty(property, index, depth, false, globalObject)) {
         // We can't optimise at all :-(
         emitOpcode(op_resolve);
@@ -742 +750 @@
 
     // Directly index the property lookup across multiple scopes.  Yay!
-    return emitGetScopedVar(dst, depth, index);
-}
-
-RegisterID* CodeGenerator::emitGetScopedVar(RegisterID* dst, size_t depth, int index)
-{
+    return emitGetScopedVar(dst, depth, index, globalObject);
+}
+
+RegisterID* CodeGenerator::emitGetScopedVar(RegisterID* dst, size_t depth, int index, JSValue* globalObject)
+{
+    if (globalObject) {
+        emitOpcode(op_get_global_var);
+        instructions().append(dst->index());
+        instructions().append(static_cast<JSCell*>(globalObject));
+        instructions().append(index);
+        return dst;
+    }
+
     emitOpcode(op_get_scoped_var);
     instructions().append(dst->index());
@@ -754 +770 @@
 }
 
-RegisterID* CodeGenerator::emitPutScopedVar(size_t depth, int index, RegisterID* value)
-{
+RegisterID* CodeGenerator::emitPutScopedVar(size_t depth, int index, RegisterID* value, JSValue* globalObject)
+{
+    if (globalObject) {
+        emitOpcode(op_put_global_var);
+        instructions().append(static_cast<JSCell*>(globalObject));
+        instructions().append(index);
+        instructions().append(value->index());
+        return value;
+    }
     emitOpcode(op_put_scoped_var);
     instructions().append(index);