Changeset 127293 in webkit for trunk/Source/JavaScriptCore/runtime/JSVariableObject.h

Timestamp:

Aug 31, 2012, 11:22:01 AM (13 years ago)

Author:

[email protected]

Message:

Shrink activation objects by half
​https://bugs.webkit.org/show_bug.cgi?id=95591

Reviewed by Sam Weinig.

Removed the global object, global data, and global this pointers from
JSScope, and changed an int to a bitfield. This gets the JSActivation
class down to 64 bytes, which in practice cuts it in half by getting it
out of the 128 byte size class.

Now, it's one extra indirection to get these pointers. These pointers
aren't accessed by JIT code, so I thought there would be no cost to the
extra indirection. However, some C++-heavy SunSpider tests regressed a
bit in an early version of the patch, which added even more indirection.
This suggests that calls to exec->globalData() and/or exec->lexicalGlobalObject()
are common and probably duplicated in lots of places, and could stand
further optimization in C++.

• dfg/DFGAbstractState.cpp:

(JSC::DFG::AbstractState::execute): Test against the specific activation
for our global object, since there's no VM-shared activation structure
anymore. This is guaranteed to have the same success rate as the old test
because activation scope is fixed at compile time.

• heap/MarkedBlock.cpp:

(JSC::MarkedBlock::MarkedBlock):

• heap/MarkedBlock.h:

(JSC::MarkedBlock::globalData):

• heap/WeakSet.cpp:

(JSC::WeakSet::addAllocator):

• heap/WeakSet.h:

(WeakSet):
(JSC::WeakSet::WeakSet):
(JSC::WeakSet::globalData): Store a JSGlobalData* instead of a Heap*
because JSGlobalData->Heap is just a constant fold in the addressing
mode, while Heap->JSGlobalData is an extra pointer dereference. (These
objects should eventually just merge.)

• jit/JITOpcodes.cpp:

(JSC::JIT::emit_op_resolve_global_dynamic): See DFGAbstractState.cpp.

• llint/LowLevelInterpreter32_64.asm:
• llint/LowLevelInterpreter64.asm: Load the activation structure from

the code block instead of the global data because the structure is not
VM-shared anymore. (See DFGAbstractState.cpp.)

• runtime/JSActivation.cpp:

(JSC::JSActivation::JSActivation):

• runtime/JSActivation.h:

(JSActivation): This is the point of the patch: Remove the data.

• runtime/JSGlobalData.cpp:

(JSC::JSGlobalData::JSGlobalData):

• runtime/JSGlobalData.h:

(JSGlobalData): No longer VM-shared. (See DFGAbstractState.cpp.)

(JSC::WeakSet::heap): (See WeakSet.h.)

• runtime/JSGlobalObject.cpp:

(JSC::JSGlobalObject::JSGlobalObject):
(JSC::JSGlobalObject::setGlobalThis):
(JSC::JSGlobalObject::reset):
(JSC::JSGlobalObject::visitChildren):

• runtime/JSGlobalObject.h:

(JSGlobalObject):
(JSC::JSGlobalObject::withScopeStructure):
(JSC::JSGlobalObject::strictEvalActivationStructure):
(JSC::JSGlobalObject::activationStructure):
(JSC::JSGlobalObject::nameScopeStructure):
(JSC::JSScope::globalThis):
(JSC::JSGlobalObject::globalThis): Data that used to be in the JSScope
class goes here now, so it's not duplicated across all activations.

• runtime/JSNameScope.h:

(JSC::JSNameScope::JSNameScope):

• runtime/JSScope.cpp:

(JSC::JSScope::visitChildren): This is the point of the patch: Remove the data.

• runtime/JSScope.h:

(JSScope):
(JSC::JSScope::JSScope):
(JSC::JSScope::globalObject):
(JSC::JSScope::globalData):

• runtime/JSSegmentedVariableObject.h:

(JSC::JSSegmentedVariableObject::JSSegmentedVariableObject):

• runtime/JSSymbolTableObject.h:

(JSC::JSSymbolTableObject::JSSymbolTableObject):

• runtime/JSVariableObject.h:

(JSC::JSVariableObject::JSVariableObject):

• runtime/JSWithScope.h:

(JSC::JSWithScope::JSWithScope):

• runtime/StrictEvalActivation.cpp:

(JSC::StrictEvalActivation::StrictEvalActivation): Simplified now that
we don't need to pass so much data to JSScope.

File:

• trunk/Source/JavaScriptCore/runtime/JSVariableObject.h (modified) (1 diff)

trunk/Source/JavaScriptCore/runtime/JSVariableObject.h

@@ -61 +61 @@
             Structure* structure,
             Register* registers,
-            JSGlobalObject* globalObject,
-            JSObject* globalThis,
             JSScope* scope
         )
-            : Base(globalData, structure, globalObject, globalThis, scope)
+            : Base(globalData, structure, scope)
             , m_registers(reinterpret_cast<WriteBarrierBase<Unknown>*>(registers))
         {