Changeset 262402 in webkit for trunk/Source/JavaScriptCore/assembler/AssemblerBuffer.h

Timestamp:

Jun 1, 2020, 5:51:53 PM (5 years ago)

Author:

[email protected]

Message:

Correct misunderstandings on how ThreadSpecific work
​https://bugs.webkit.org/show_bug.cgi?id=212616

Reviewed by Michael Saboff.

There were two misunderstandings I had when writing code using ThreadSpecific
when doing LLInt bytecode buffer caching in Wasm.

1. For ThreadSpecific<Vector>, I was calling Vector's constructor twice

unnecessarily, and incorrectly, since we ended up constructing over an
already constructed Vector for the second call. When doing operator* or
operator-> on a ThreadSpecific<T>, T() is called if it has not been
initialized yet. So there is no need to do manually call the constructor
the second time.

2. There is no need to try to destroy entries for ThreadSpecific manually

since we already run destructors when the thread goes away.

This patch removes code for (1) and (2) both from the Wasm bytecode
buffer and from AssemblerData.

• assembler/AssemblerBuffer.cpp:

(JSC::clearAssembleDataThreadSpecificCache): Deleted.

• assembler/AssemblerBuffer.h:

(JSC::AssemblerBuffer::AssemblerBuffer):
(JSC::AssemblerBuffer::~AssemblerBuffer):
(JSC::AssemblerBuffer::getThreadSpecificAssemblerData): Deleted.

• dfg/DFGWorklist.cpp:
• jit/JITWorklist.cpp:
• wasm/WasmLLIntGenerator.cpp:

(JSC::Wasm::LLIntGenerator::LLIntGenerator):
(JSC::Wasm::clearLLIntThreadSpecificCache): Deleted.

• wasm/WasmLLIntGenerator.h:
• wasm/WasmWorklist.cpp:

File:

• trunk/Source/JavaScriptCore/assembler/AssemblerBuffer.h (modified) (4 diffs)

trunk/Source/JavaScriptCore/assembler/AssemblerBuffer.h

@@ -47 +47 @@
 
     JS_EXPORT_PRIVATE ThreadSpecificAssemblerData& threadSpecificAssemblerData();
-    void clearAssembleDataThreadSpecificCache();
 
     class LinkBuffer;
@@ -211 +210 @@
             , m_index(0)
         {
-            auto& threadSpecific = getThreadSpecificAssemblerData();
+            auto& threadSpecific = threadSpecificAssemblerData();
             m_storage.takeBufferIfLarger(WTFMove(*threadSpecific));
         }
@@ -217 +216 @@
         ~AssemblerBuffer()
         {
-            auto& threadSpecific = getThreadSpecificAssemblerData();
+            auto& threadSpecific = threadSpecificAssemblerData();
             threadSpecific->takeBufferIfLarger(WTFMove(m_storage));
         }
@@ -335 +334 @@
 
     protected:
-        ThreadSpecificAssemblerData& getThreadSpecificAssemblerData()
-        {
-            auto& threadSpecific = threadSpecificAssemblerData();
-
-            if (!threadSpecific.isSet()) {
-                void* ptr = static_cast<AssemblerData*>(threadSpecific);
-                new (ptr) AssemblerData();
-            }
-
-            return threadSpecific;
-        }
-        
         template<typename IntegralType>
         void putIntegral(IntegralType value)