Changeset 293710 in webkit for trunk/Source/JavaScriptCore/runtime/Structure.h

Timestamp:

May 2, 2022, 8:02:04 PM (3 years ago)

Author:

[email protected]

Message:

[JSC] Introduce shifting Structure encoding
​https://bugs.webkit.org/show_bug.cgi?id=239957

Reviewed by Mark Lam.

For platforms which have limited amount of virtual address space (<= 36 bits), this patch introduces
shifting Structure encoding. We align Structure on a 32-bytes boundary instead of 16 bytes so that
we can ensure that lower 5 bits are zero. Then, we can use 1 bit for nuke, and shifting 4 bits to
convert 36 bit address to 32 bit StructureID. By using this mechanism, we do not need to allocate
large virtual address space for these platforms. If we an address can have more than 36 bits, then
we should just reserve a larger address region since we have enough address space. Current Structure
size is 112 bytes, which is 3.5 atoms at 32 bytes / atom. Hence, this alignment costs us 16 bytes per
Structure.
Relanding with debug build failure & crash on static atomSize assumption in IsoSubspace.

• ftl/FTLLowerDFGToB3.cpp:

(JSC::FTL::DFG::LowerDFGToB3::compileCompareStrictEq):

• heap/Heap.cpp:
• heap/IsoSubspace.h:

(JSC::GCClient::IsoSubspace::allocatorFor):

• heap/IsoSubspaceInlines.h:

(JSC::GCClient::IsoSubspace::allocate):

• heap/StructureAlignedMemoryAllocator.cpp:

(JSC::StructureMemoryManager::StructureMemoryManager):

• jit/AssemblyHelpers.cpp:

(JSC::AssemblyHelpers::emitNonNullDecodeStructureID):

• llint/LLIntOfflineAsmConfig.h:
• llint/LowLevelInterpreter64.asm:
• runtime/JSCell.h:
• runtime/JSCellInlines.h:

(JSC::JSCell::JSCell):

• runtime/Structure.cpp:

(JSC::Structure::Structure):

• runtime/Structure.h:
• runtime/StructureID.h:

(JSC::StructureID::decode const):
(JSC::StructureID::tryDecode const):
(JSC::StructureID::encode):

• tools/IntegrityInlines.h:

(JSC::Integrity::auditStructureID):

File:

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

trunk/Source/JavaScriptCore/runtime/Structure.h

@@ -175 +175 @@
     static constexpr unsigned StructureFlags = Base::StructureFlags | StructureIsImmortal;
     static constexpr uint8_t numberOfLowerTierCells = 0;
-    
+
+#if ENABLE(STRUCTURE_ID_WITH_SHIFT)
+    static constexpr size_t atomSize = 32;
+#endif
+    static_assert(JSCell::atomSize >= MarkedBlock::atomSize);
+
     enum PolyProtoTag { PolyProto };
     static Structure* create(VM&, JSGlobalObject*, JSValue prototype, const TypeInfo&, const ClassInfo*, IndexingType = NonArray, unsigned inlineCapacity = 0);