Stub Cache: speed up load callback accessor by allocating data handle on stack.

src/arm/stub-cache-arm.cc

Index: src/arm/stub-cache-arm.cc
diff --git a/src/arm/stub-cache-arm.cc b/src/arm/stub-cache-arm.cc
index d6650c9862572a9a8a1a9014324b0491e39daa29..cfb75b2609d5c4fe36fb130b5d79bd873501426b 100644
--- a/src/arm/stub-cache-arm.cc
+++ b/src/arm/stub-cache-arm.cc
@@ -467,15 +467,17 @@ void StubCompiler::GenerateLoadCallback(JSObject* object,
 
   // Push the arguments on the JS stack of the caller.
   __ push(receiver);  // receiver
+  __ push(reg);  // holder
   __ mov(ip, Operand(Handle<AccessorInfo>(callback)));  // callback data
   __ push(ip);
+  __ ldr(reg, FieldMemOperand(ip, AccessorInfo::kDataOffset));

[antonm, 2009/07/23 21:12:58]

why not push data immediately if data() belongs to new space?

[iposva, 2009/07/24 00:30:07]

Maybe because on ARM loading an Object constant is also a load instruction from
the constant pool? No difference and you save on code/constant pool space.

[antonm, 2009/07/24 02:43:21]

Sorry, didn't know that and was under induction of compiling getter_adder into
the stub.  In this case you don't load callback and thus loading data stores you
one operation.

[Vitaly Repeshko, 2009/07/24 13:45:38]

I didn't measure performance here, but based on what Ivan said and my
measurements for x86 I decided to leave simpler code here as well.

+  __ push(reg);
   __ push(name_reg);  // name
-  __ push(reg);  // holder
 
   // Do tail-call to the runtime system.
   ExternalReference load_callback_property =
       ExternalReference(IC_Utility(IC::kLoadCallbackProperty));
-  __ TailCallRuntime(load_callback_property, 4);
+  __ TailCallRuntime(load_callback_property, 5);
 }