[JSC] CodeBlock aging: no clock reads on the compile/sweep paths

Source/JavaScriptCore/bytecode/CodeBlock.cpp

@@ -905,7 +905,7 @@ CodeBlock::~CodeBlock()
 
 #if ENABLE(JIT) && USE(BUN_JSC_ADDITIONS)
     if (jitType() == JITType::BaselineJIT)
-        static_cast<BaselineJITCode*>(m_jitCode.get())->m_ownerWentAwayAt = ApproximateTime::now();
+        static_cast<BaselineJITCode*>(m_jitCode.get())->m_ownerWentAwayAt = vm.heap.lastGCBoundaryTime();
 #endif
 
     if (JITCode::isBaselineCode(jitType())) {

Source/JavaScriptCore/heap/Heap.cpp

@@ -1244,7 +1244,7 @@ void Heap::releaseUnusedSharedBaselineCode()
 #if ENABLE(JIT) && USE(BUN_JSC_ADDITIONS)
     if (!Options::useBaselineJITCodeSharing() || !Options::useExecutionCountForCodeBlockAging())
         return;
-    ApproximateTime cutoff = ApproximateTime::now() - CodeBlock::timeToLive(JITType::BaselineJIT) * Options::codeBlockAgingLeaseMultiplier();
+    MonotonicTime cutoff = m_currentGCStartTime - CodeBlock::timeToLive(JITType::BaselineJIT) * Options::codeBlockAgingLeaseMultiplier();
     // End phase: the world is stopped and allocation already is, so no HeapIterationScope.
     auto visit = [&] (HeapCell* cell, HeapCell::Kind) {
         auto& code = static_cast<UnlinkedCodeBlock*>(cell)->m_unlinkedBaselineCode;

Source/JavaScriptCore/heap/Heap.h

@@ -393,6 +393,10 @@ class Heap {
     MutatorState mutatorState() const { return m_mutatorState; }
     std::optional<CollectionScope> collectionScope() const { return m_collectionScope; }
     std::optional<CollectionScope> lastCollectionScope() const { return m_lastCollectionScope; }
+#if USE(BUN_JSC_ADDITIONS)
+    // The most recent collection boundary: the end of the last one, or the start of the one in progress.
+    MonotonicTime lastGCBoundaryTime() const { return std::max(m_lastGCEndTime, m_currentGCStartTime); }
+#endif
     bool hasHeapAccess() const { return m_worldState.load() & hasAccessBit; }
     bool worldIsStopped() const { return m_worldIsStopped; }
     bool worldIsRunning() const { return !worldIsStopped(); }

Source/JavaScriptCore/jit/BaselineJITCode.h

@@ -27,7 +27,7 @@
 
 #include "CallLinkInfo.h"
 #include "JITCode.h"
-#include <wtf/ApproximateTime.h>
+#include <wtf/MonotonicTime.h>
 #include "JITCodeMap.h"
 #include "PropertyInlineCache.h"
 #include <wtf/ButterflyArray.h>
@@ -107,9 +107,11 @@ class BaselineJITCode : public DirectJITCode, public MathICHolder {
     JITCodeMap m_jitCodeMap;
     JITConstantPool m_constantPool;
     std::unique_ptr<PCToCodeOriginMap> m_pcToCodeOriginMap;
-    // When a CodeBlock running this code last went away; UnlinkedCodeBlock's cached copy is released once no CodeBlock
-    // has used it for a while (Heap::releaseUnusedSharedBaselineCode).
-    ApproximateTime m_ownerWentAwayAt { ApproximateTime::now() };
+#if USE(BUN_JSC_ADDITIONS)
+    // The collection in which a CodeBlock running this code last died (Heap::lastGCBoundaryTime); UnlinkedCodeBlock's
+    // cached copy is released once no CodeBlock has used it for a while (Heap::releaseUnusedSharedBaselineCode).
+    MonotonicTime m_ownerWentAwayAt;
+#endif
 private:
     // The percentage of ValueProfiles that had some profiling data in them.
     double m_livenessRate { 0 };