Cleanups: Remove Steele barrier code

Remove the code related to the Steele write barrier and incremental
garbage collection.

This is in preparation for a fully concurrent GC, that will not have
and incremental mode and will use a Yuasa write barrier.

Change-Id: I155a85211c5be61e792e056321fbceaee47c0d87
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

8 files changed, 13 insertions, 131 deletions

diff --git a/src/qml/compiler/qv4compileddata.cpp b/src/qml/compiler/qv4compileddata.cpp
index 7940e5715e..adc36ff1dd 100644
--- a/src/qml/compiler/qv4compileddata.cpp
+++ b/src/qml/compiler/qv4compileddata.cpp
@@ -125,10 +125,8 @@ QV4::Function *CompilationUnit::linkToEngine(ExecutionEngine *engine)
     runtimeStrings = (QV4::Heap::String **)malloc(data->stringTableSize * sizeof(QV4::Heap::String*));
     // memset the strings to 0 in case a GC run happens while we're within the loop below
     memset(runtimeStrings, 0, data->stringTableSize * sizeof(QV4::Heap::String*));
-    for (uint i = 0; i < data->stringTableSize; ++i) {
+    for (uint i = 0; i < data->stringTableSize; ++i)
         runtimeStrings[i] = engine->newIdentifier(data->stringAt(i));
-        runtimeStrings[i]->setMarkBit();
-    }
 
     runtimeRegularExpressions = new QV4::Value[data->regexpTableSize];
     // memset the regexps to 0 in case a GC run happens while we're within the loop below
@@ -144,12 +142,6 @@ QV4::Function *CompilationUnit::linkToEngine(ExecutionEngine *engine)
             flags |= IR::RegExp::RegExp_Multiline;
         QV4::Heap::RegExpObject *ro = engine->newRegExpObject(data->stringAt(re->stringIndex), flags);
         runtimeRegularExpressions[i] = ro;
-#if WRITEBARRIER(steele)
-        if (engine->memoryManager->nextGCIsIncremental) {
-            ro->setMarkBit();
-            ro->setGrayBit();
-        }
-#endif
     }
 
     if (data->lookupTableSize) {
diff --git a/src/qml/jit/qv4assembler_p.h b/src/qml/jit/qv4assembler_p.h
index d4a18ae886..8aa9d81ba2 100644
--- a/src/qml/jit/qv4assembler_p.h
+++ b/src/qml/jit/qv4assembler_p.h
@@ -189,18 +189,7 @@ struct RegisterSizeDependentAssembler<JITAssembler, MacroAssembler, TargetPlatfo
         as->pop(TargetPlatform::EngineRegister);
     }
 
-#if WRITEBARRIER(steele)
-    static void emitWriteBarrier(JITAssembler *as, Address addr)
-    {
-//        RegisterID test = addr.base == TargetPlatform::ReturnValueRegister ? TargetPlatform::ScratchRegister : TargetPlatform::ReturnValueRegister;
-        // if (engine->writeBarrier)
-//        as->load8(Address(TargetPlatform::EngineRegister, offsetof(EngineBase, writeBarrierActive)), test);
-//        typename JITAssembler::Jump jump = as->branch32(JITAssembler::Equal, test, TrustedImm32(0));
-        // ### emit fence
-        emitSetGrayBit(as, addr.base);
-//        jump.link(as);
-    }
-#elif WRITEBARRIER(none)
+#if WRITEBARRIER(none)
     static Q_ALWAYS_INLINE void emitWriteBarrier(JITAssembler *, Address) {}
 #endif
 
@@ -487,18 +476,7 @@ struct RegisterSizeDependentAssembler<JITAssembler, MacroAssembler, TargetPlatfo
         as->pop(TargetPlatform::EngineRegister);
     }
 
-#if WRITEBARRIER(steele)
-    static void emitWriteBarrier(JITAssembler *as, Address addr)
-    {
-//        RegisterID test = addr.base == TargetPlatform::ReturnValueRegister ? TargetPlatform::ScratchRegister : TargetPlatform::ReturnValueRegister;
-        // if (engine->writeBarrier)
-//        as->load8(Address(TargetPlatform::EngineRegister, offsetof(EngineBase, writeBarrierActive)), test);
-//        typename JITAssembler::Jump jump = as->branch32(JITAssembler::Equal, test, TrustedImm32(0));
-        // ### emit fence
-        emitSetGrayBit(as, addr.base);
-//        jump.link(as);
-    }
-#elif WRITEBARRIER(none)
+#if WRITEBARRIER(none)
     static Q_ALWAYS_INLINE void emitWriteBarrier(JITAssembler *, Address) {}
 #endif
 
diff --git a/src/qml/jsapi/qjsengine.cpp b/src/qml/jsapi/qjsengine.cpp
index b52c859ecb..e4c150057a 100644
--- a/src/qml/jsapi/qjsengine.cpp
+++ b/src/qml/jsapi/qjsengine.cpp
@@ -333,7 +333,7 @@ QJSEngine::~QJSEngine()
 */
 void QJSEngine::collectGarbage()
 {
-    d->m_v4Engine->memoryManager->runGC(/* forceFullCollection = */ true);
+    d->m_v4Engine->memoryManager->runGC();
 }
 
 #if QT_DEPRECATED_SINCE(5, 6)
diff --git a/src/qml/jsruntime/qv4identifiertable.cpp b/src/qml/jsruntime/qv4identifiertable.cpp
index d3ef238716..3def6defbf 100644
--- a/src/qml/jsruntime/qv4identifiertable.cpp
+++ b/src/qml/jsruntime/qv4identifiertable.cpp
@@ -81,7 +81,6 @@ void IdentifierTable::addEntry(Heap::String *str)
     str->identifier = new Identifier;
     str->identifier->string = str->toQString();
     str->identifier->hashValue = hash;
-    str->setMarkBit();
 
     bool grow = (alloc <= size*2);
 
diff --git a/src/qml/memory/qv4mm.cpp b/src/qml/memory/qv4mm.cpp
index aebbc07826..7c57b93d9b 100644
--- a/src/qml/memory/qv4mm.cpp
+++ b/src/qml/memory/qv4mm.cpp
@@ -931,8 +931,7 @@ void MarkStack::drain()
 
 void MemoryManager::collectRoots(MarkStack *markStack)
 {
-    if (!nextGCIsIncremental)
-        engine->markObjects(markStack);
+    engine->markObjects(markStack);
 
 //    qDebug() << "   mark stack after engine->mark" << (engine->jsStackTop - markBase);
 
@@ -982,23 +981,11 @@ void MemoryManager::mark()
     MarkStack markStack(engine);
     collectRoots(&markStack);
 
-    if (nextGCIsIncremental) {
-        // need to collect all gray items and push them onto the mark stack
-        blockAllocator.collectGrayItems(&markStack);
-        hugeItemAllocator.collectGrayItems(&markStack);
-    }
-
     markStack.drain();
 }
 
 void MemoryManager::sweep(bool lastSweep)
 {
-    if (lastSweep && nextGCIsIncremental) {
-        // ensure we properly clean up on destruction even if the GC is in incremental mode
-        blockAllocator.resetBlackBits();
-        hugeItemAllocator.resetBlackBits();
-    }
-
     for (PersistentValueStorage::Iterator it = m_weakValues->begin(); it != m_weakValues->end(); ++it) {
         Managed *m = (*it).managed();
         if (!m || m->markBit())
@@ -1077,20 +1064,13 @@ size_t dumpBins(BlockAllocator *b, bool printOutput = true)
     return totalSlotMem*Chunk::SlotSize;
 }
 
-void MemoryManager::runGC(bool forceFullCollection)
+void MemoryManager::runGC()
 {
     if (gcBlocked) {
 //        qDebug() << "Not running GC.";
         return;
     }
 
-    if (forceFullCollection) {
-        // do a full GC
-        blockAllocator.resetBlackBits();
-        hugeItemAllocator.resetBlackBits();
-        nextGCIsIncremental = false;
-    }
-
     QScopedValueRollback<bool> gcBlocker(gcBlocked, true);
 //    qDebug() << "runGC";
 
@@ -1112,7 +1092,6 @@ void MemoryManager::runGC(bool forceFullCollection)
         qDebug() << "    Allocations since last GC" << allocationCount;
         allocationCount = 0;
 #endif
-        qDebug() << "Incremental:" << nextGCIsIncremental;
         qDebug() << "Allocated" << totalMem << "bytes in" << blockAllocator.chunks.size() << "chunks";
         qDebug() << "Fragmented memory before GC" << (totalMem - usedBefore);
         dumpBins(&blockAllocator);
@@ -1138,10 +1117,6 @@ void MemoryManager::runGC(bool forceFullCollection)
             qDebug() << "   unmanaged heap limit:" << unmanagedHeapSizeGCLimit;
         }
         size_t memInBins = dumpBins(&blockAllocator);
-#ifdef MM_STATS
-        if (nextGCIsIncremental)
-            qDebug() << "  number of gray items:" << nGrayItems;
-#endif
         qDebug() << "Marked object in" << markTime << "us.";
         qDebug() << "   " << markStackSize << "objects marked";
         qDebug() << "Sweeped object in" << sweepTime << "us.";
@@ -1164,36 +1139,11 @@ void MemoryManager::runGC(bool forceFullCollection)
         Q_ASSERT(blockAllocator.allocatedMem() == getUsedMem() + dumpBins(&blockAllocator, false));
     }
 
-    if (!nextGCIsIncremental)
-        usedSlotsAfterLastFullSweep = blockAllocator.usedSlotsAfterLastSweep;
+    usedSlotsAfterLastFullSweep = blockAllocator.usedSlotsAfterLastSweep;
 
-#if WRITEBARRIER(steele)
-    static int count = 0;
-    ++count;
-    if (aggressiveGC) {
-        nextGCIsIncremental = (count % 256);
-    } else {
-        size_t total = blockAllocator.totalSlots();
-        size_t usedSlots = blockAllocator.usedSlotsAfterLastSweep;
-        if (!nextGCIsIncremental) {
-            // always try an incremental GC after a full one, unless there is anyway lots of memory pressure
-            nextGCIsIncremental = usedSlots * 4 < total * 3;
-            count = 0;
-        } else {
-            if (count > 16)
-                nextGCIsIncremental = false;
-            else
-                nextGCIsIncremental = usedSlots * 4 < total * 3; // less than 75% full
-        }
-    }
-#else
-    nextGCIsIncremental = false;
-#endif
-    if (!nextGCIsIncremental) {
-        // do a full GC
-        blockAllocator.resetBlackBits();
-        hugeItemAllocator.resetBlackBits();
-    }
+    // reset all black bits
+    blockAllocator.resetBlackBits();
+    hugeItemAllocator.resetBlackBits();
 }
 
 size_t MemoryManager::getUsedMem() const
diff --git a/src/qml/memory/qv4mm_p.h b/src/qml/memory/qv4mm_p.h
index 1335ea59b6..76ffec42de 100644
--- a/src/qml/memory/qv4mm_p.h
+++ b/src/qml/memory/qv4mm_p.h
@@ -422,7 +422,7 @@ public:
         return t->d();
     }
 
-    void runGC(bool forceFullCollection = false);
+    void runGC();
 
     void dumpStats() const;
 
@@ -467,7 +467,6 @@ public:
     bool gcBlocked = false;
     bool aggressiveGC = false;
     bool gcStats = false;
-    bool nextGCIsIncremental = false;
 };
 
 }
diff --git a/src/qml/memory/qv4writebarrier_p.h b/src/qml/memory/qv4writebarrier_p.h
index a2f85822ca..e36ea0749a 100644
--- a/src/qml/memory/qv4writebarrier_p.h
+++ b/src/qml/memory/qv4writebarrier_p.h
@@ -55,7 +55,6 @@
 
 QT_BEGIN_NAMESPACE
 
-#define WRITEBARRIER_steele -1
 #define WRITEBARRIER_none 1
 
 #define WRITEBARRIER(x) (1/WRITEBARRIER_##x == 1)
@@ -78,42 +77,7 @@ enum NewValueType {
 // ### this needs to be filled with a real memory fence once marking is concurrent
 Q_ALWAYS_INLINE void fence() {}
 
-#if WRITEBARRIER(steele)
-
-template <NewValueType type>
-static Q_CONSTEXPR inline bool isRequired() {
-    return type != Primitive;
-}
-
-inline void write(EngineBase *engine, Heap::Base *base, Value *slot, Value value)
-{
-    Q_UNUSED(engine);
-    *slot = value;
-    if (isRequired<Unknown>()) {
-        fence();
-        base->setGrayBit();
-    }
-}
-
-inline void write(EngineBase *engine, Heap::Base *base, Value *slot, Heap::Base *value)
-{
-    Q_UNUSED(engine);
-    *slot = value;
-    if (isRequired<Object>()) {
-        fence();
-        base->setGrayBit();
-    }
-}
-
-inline void write(EngineBase *engine, Heap::Base *base, Heap::Base **slot, Heap::Base *value)
-{
-    Q_UNUSED(engine);
-    *slot = value;
-    fence();
-    base->setGrayBit();
-}
-
-#elif WRITEBARRIER(none)
+#if WRITEBARRIER(none)
 
 template <NewValueType type>
 static Q_CONSTEXPR inline bool isRequired() {
diff --git a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
index 68a64a28f0..8cc0b32168 100644
--- a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
+++ b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
@@ -2019,7 +2019,7 @@ void GlobalExtensions::method_qsTrIdNoOp(const BuiltinFunction *, Scope &scope,
 
 void GlobalExtensions::method_gc(const BuiltinFunction *, Scope &scope, CallData *)
 {
-    scope.engine->memoryManager->runGC(/* forceFullCollection = */ true);
+    scope.engine->memoryManager->runGC();
 
     scope.result = QV4::Encode::undefined();
 }