Store current cell in SlotAcceptor

Differential Revision: D64713261
facebook · Nov 7, 2024 · e7c2aa4 · e7c2aa4
1 parent a973b3e
commit e7c2aa4
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Showing 3 changed files with 19 additions and 0 deletions.
diff --git a/include/hermes/VM/SlotAcceptor.h b/include/hermes/VM/SlotAcceptor.h
@@ -31,11 +31,21 @@ class GCCell;
 /// pointer.  For example, if the pointer is in compressed form.)
 /// This is used by a visitor, see \c SlotVisitor.
 struct SlotAcceptor {
+  /// The cell that contains the slot being visited.
+  const GCCell *currentCell;
+
   virtual ~SlotAcceptor() = default;
   virtual void accept(GCPointerBase &ptr) = 0;
   virtual void accept(GCHermesValue &hv) = 0;
   virtual void accept(GCSmallHermesValue &hv) = 0;
   virtual void accept(const GCSymbolID &sym) = 0;
+
+  void startCell(const GCCell *cell) {
+    this->currentCell = cell;
+  }
+  void finishCell() {
+    this->currentCell = nullptr;
+  }
 };
 
 struct RootSectionAcceptor {

diff --git a/include/hermes/VM/SlotVisitor.h b/include/hermes/VM/SlotVisitor.h
@@ -154,6 +154,7 @@ void visit(
     Acceptor &acceptor,
     GCCell *cell,
     const Metadata::SlotOffsets &offsets) {
+  acceptor.startCell(cell);
   auto *base = reinterpret_cast<char *>(cell);
 
   size_t i = 0;
@@ -166,6 +167,7 @@ void visit(
   if (offsets.array)
     detail::visitArray<Acceptor, /* WithNames */ false>(
         acceptor, base, *offsets.array);
+  acceptor.finishCell();
 }
 
 /// Like \c visit, but only invokes the acceptor on slots that begin within
@@ -177,6 +179,7 @@ void visitWithinRange(
     const Metadata::SlotOffsets &offsets,
     const char *begin,
     const char *end) {
+  acceptor.startCell(cell);
   auto *base = reinterpret_cast<char *>(cell);
 
   size_t i = 0;
@@ -196,6 +199,7 @@ void visitWithinRange(
 
   if (offsets.array)
     detail::visitArrayWithinRange(acceptor, base, *offsets.array, begin, end);
+  acceptor.finishCell();
 }
 
 /// Like \c visit, but invokes the acceptor with names.
@@ -205,6 +209,7 @@ void visitWithNames(
     GCCell *cell,
     const Metadata::SlotOffsets &offsets,
     const Metadata::SlotNames &names) {
+  acceptor.startCell(cell);
   auto *base = reinterpret_cast<char *>(cell);
 
   // Ignore sizes for special fields, since these are known types with known
@@ -220,6 +225,7 @@ void visitWithNames(
   if (offsets.array)
     detail::visitArray<Acceptor, /* WithNames */ true>(
         acceptor, base, *offsets.array);
+  acceptor.finishCell();
 }
 
 } // namespace SlotVisitor

diff --git a/lib/VM/gcs/HadesGC.cpp b/lib/VM/gcs/HadesGC.cpp
@@ -406,6 +406,7 @@ class HadesGC::EvacAcceptor final : public RootAndSlotAcceptor,
   }
 
   LLVM_NODISCARD GCCell *acceptHeap(GCCell *ptr, void *heapLoc) {
+    assert(currentCell && "There must be a cell being visited");
     if (shouldForward(ptr)) {
       assert(
           AlignedHeapSegmentBase::getCellMarkBit(ptr) &&
@@ -423,6 +424,7 @@ class HadesGC::EvacAcceptor final : public RootAndSlotAcceptor,
 
   LLVM_NODISCARD CompressedPointer
   acceptHeap(CompressedPointer cptr, void *heapLoc) {
+    assert(currentCell && "There must be a cell being visited");
     if (shouldForward(cptr)) {
       GCCell *ptr = cptr.getNonNull(pointerBase_);
       assert(
@@ -643,6 +645,7 @@ class HadesGC::MarkAcceptor final : public RootAndSlotAcceptor {
   void acceptHeap(GCCell *cell, const void *heapLoc) {
     assert(cell && "Cannot pass null pointer to acceptHeap");
     assert(!gc.inYoungGen(heapLoc) && "YG slot found in OG marking");
+    assert(currentCell && "There must be a cell being visited");
     if (gc.compactee_.contains(cell) && !gc.compactee_.contains(heapLoc)) {
       // This is a pointer in the heap pointing into the compactee, dirty the
       // corresponding card.