If we can't rehash the backing store for weak sets & maps, do a last resort GC

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 9f7524ccefb7a4dc85ae9ee1677840b14e8d1bad..351862d78d144fe9619079c9bec7cd76aab48d39 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -17747,6 +17747,20 @@ Handle<ObjectHashTable> ObjectHashTable::Put(Handle<ObjectHashTable> table,
   if ((table->NumberOfDeletedElements() << 1) > table->NumberOfElements()) {
     table->Rehash(isolate->factory()->undefined_value());
   }
+  // If we're out of luck, we didn't get a GC recently, and so rehashing
+  // isn't enough to avoid a crash.
+  int nof = table->NumberOfElements() + 1;
+  if (!table->HasSufficientCapacity(nof)) {
+    int capacity = ObjectHashTable::ComputeCapacity(nof * 2);
+    if (capacity > ObjectHashTable::kMaxCapacity) {
+      for (size_t i = 0; i < 2; ++i) {
+        isolate->heap()->CollectAllGarbage(
+            Heap::kFinalizeIncrementalMarkingMask,
+            "last resort gc (object hash table)");

[Hannes Payer (out of office), 2016/07/07 15:22:00]

let's not call this last resort gc, to not confuse it with the actual emergency
gc. just call it "full object hash table"

+      }
+      table->Rehash(isolate->factory()->undefined_value());
+    }
+  }
 
   // Check whether the hash table should be extended.
   table = EnsureCapacity(table, 1, key);