Changeset 176035 in webkit for trunk/Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp

Timestamp:

Nov 12, 2014, 1:13:13 PM (11 years ago)

Author:

[email protected]

Message:

Generate get_by_id for bracket access with constant string subscript.
<​https://webkit.org/b/138663>

Reviewed by Michael Saboff.

Transform of into o.f when generating bytecode. This allows our JIT
to inline-cache those accesses instead of always dropping out to C++.

This is surprisingly common in real-web content, less so in benchmarks.
Interestingly, Speedometer does hit the optimization quite a bit.

• bytecompiler/NodesCodegen.cpp:

(JSC::BracketAccessorNode::emitBytecode):

File:

• trunk/Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp (modified) (1 diff)

trunk/Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp

@@ -390 +390 @@
     }
 
-    RefPtr<RegisterID> base = generator.emitNodeForLeftHandSide(m_base, m_subscriptHasAssignments, m_subscript->isPure(generator));
-    RegisterID* property = generator.emitNode(m_subscript);
+    RegisterID* ret;
+    RegisterID* finalDest = generator.finalDestination(dst);
+
+    if (m_subscript->isString()) {
+        RefPtr<RegisterID> base = generator.emitNode(m_base);
+        ret = generator.emitGetById(finalDest, base.get(), static_cast<StringNode*>(m_subscript)->value());
+    } else {
+        RefPtr<RegisterID> base = generator.emitNodeForLeftHandSide(m_base, m_subscriptHasAssignments, m_subscript->isPure(generator));
+        RegisterID* property = generator.emitNode(m_subscript);
+        ret = generator.emitGetByVal(finalDest, base.get(), property);
+    }
+
     generator.emitExpressionInfo(divot(), divotStart(), divotEnd());
-    RegisterID* finalDest = generator.finalDestination(dst);
-    RegisterID* ret = generator.emitGetByVal(finalDest, base.get(), property);
+
     if (generator.vm()->typeProfiler()) {
         generator.emitProfileType(finalDest, ProfileTypeBytecodeDoesNotHaveGlobalID, nullptr);