Bug 1473213 (Part 1) - Track the number of tenured cells r=jonco

--HG--
extra : rebase_source : 96739a13fe0d44bcb00819cf7422ef97bc97f812
extra : intermediate-source : 8a10fc261acb99c7e8bb4fcb4ee0975c5166990d
extra : source : 445b672aa024fdfca38a2e819f54bcbf28e922dd

js/src/gc/Marking.cpp

@@ -3002,6 +3002,7 @@ js::TenuringTracer::moveToTenuredSlow(JSObject* src)
     }
 
     tenuredSize += dstSize;
+    tenuredCells++;
 
     // Copy the Cell contents.
     MOZ_ASSERT(OffsetToChunkEnd(src) >= ptrdiff_t(srcSize));
@@ -3050,6 +3051,7 @@ js::TenuringTracer::movePlainObjectToTenured(PlainObject* src)
 
     size_t srcSize = Arena::thingSize(dstKind);
     tenuredSize += srcSize;
+    tenuredCells++;
 
     // Copy the Cell contents.
     MOZ_ASSERT(OffsetToChunkEnd(src) >= ptrdiff_t(srcSize));
@@ -3166,6 +3168,7 @@ js::TenuringTracer::moveToTenured(JSString* src)
 
     JSString* dst = allocTenured<JSString>(zone, dstKind);
     tenuredSize += moveStringToTenured(dst, src, dstKind);
+    tenuredCells++;
 
     RelocationOverlay* overlay = RelocationOverlay::fromCell(src);
     overlay->forwardTo(dst);

js/src/gc/Nursery.cpp

@@ -540,6 +540,7 @@ js::TenuringTracer::TenuringTracer(JSRuntime* rt, Nursery* nursery)
   : JSTracer(rt, JSTracer::TracerKindTag::Tenuring, TraceWeakMapKeysValues)
   , nursery_(*nursery)
   , tenuredSize(0)
+  , tenuredCells(0)
   , objHead(nullptr)
   , objTail(&objHead)
   , stringHead(nullptr)
@@ -599,6 +600,7 @@ js::Nursery::renderProfileJSON(JSONPrinter& json) const
 
     json.property("reason", JS::gcreason::ExplainReason(previousGC.reason));
     json.property("bytes_tenured", previousGC.tenuredBytes);
+    json.property("cells_tenured", previousGC.tenuredCells);
     json.property("bytes_used", previousGC.nurseryUsedBytes);
     json.property("cur_capacity", previousGC.nurseryCapacity);
     const size_t newCapacity = spaceToEnd(maxChunkCount());
@@ -741,6 +743,7 @@ js::Nursery::collect(JS::gcreason::Reason reason)
         previousGC.nurseryCapacity = spaceToEnd(maxChunkCount());
         previousGC.nurseryLazyCapacity = spaceToEnd(allocatedChunkCount());
         previousGC.tenuredBytes = 0;
+        previousGC.tenuredCells = 0;
     }
 
     // Resize the nursery.
@@ -954,6 +957,7 @@ js::Nursery::doCollection(JS::gcreason::Reason reason, TenureCountCache& tenureC
     previousGC.nurseryLazyCapacity = spaceToEnd(allocatedChunkCount());
     previousGC.nurseryUsedBytes = initialNurseryUsedBytes;
     previousGC.tenuredBytes = mover.tenuredSize;
+    previousGC.tenuredCells = mover.tenuredCells;
 }
 
 void

js/src/gc/Nursery.h

@@ -76,6 +76,8 @@ class TenuringTracer : public JSTracer
 
     // Amount of data moved to the tenured generation during collection.
     size_t tenuredSize;
+    // Number of cells moved to the tenured generation.
+    size_t tenuredCells;
 
     // These lists are threaded through the Nursery using the space from
     // already moved things. The lists are used to fix up the moved things and
@@ -438,6 +440,7 @@ class Nursery
         size_t nurseryLazyCapacity = 0;
         size_t nurseryUsedBytes = 0;
         size_t tenuredBytes = 0;
+        size_t tenuredCells = 0;
     } previousGC;
 
     /*