2 files changed, 11 insertions, 9 deletions
diff --git a/js/src/vm/TypeInference.cpp b/js/src/vm/TypeInference.cpp
index 3d09c7464..c86345d9c 100644
--- a/js/src/vm/TypeInference.cpp
+++ b/js/src/vm/TypeInference.cpp
@@ -12,6 +12,8 @@
 #include "mozilla/SizePrintfMacros.h"
 #include "mozilla/Sprintf.h"
 
+#include <new>
+
 #include "jsapi.h"
 #include "jscntxt.h"
 #include "jsgc.h"
@@ -859,10 +861,8 @@ TypeSet::IsTypeAboutToBeFinalized(TypeSet::Type* v)
 }
 
 bool
-TypeSet::clone(LifoAlloc* alloc, TemporaryTypeSet* result) const
+TypeSet::cloneIntoUninitialized(LifoAlloc* alloc, TemporaryTypeSet* result) const
 {
-    MOZ_ASSERT(result->empty());
-
     unsigned objectCount = baseObjectCount();
     unsigned capacity = (objectCount >= 2) ? TypeHashSet::Capacity(objectCount) : 0;
 
@@ -874,15 +874,15 @@ TypeSet::clone(LifoAlloc* alloc, TemporaryTypeSet* result) const
         PodCopy(newSet, objectSet, capacity);
     }
 
-    new(result) TemporaryTypeSet(flags, capacity ? newSet : objectSet);
+    new (result) TemporaryTypeSet(flags, capacity ? newSet : objectSet);
     return true;
 }
 
 TemporaryTypeSet*
 TypeSet::clone(LifoAlloc* alloc) const
 {
-    TemporaryTypeSet* res = alloc->new_<TemporaryTypeSet>();
-    if (!res || !clone(alloc, res))
+    TemporaryTypeSet* res = alloc->pod_malloc<TemporaryTypeSet>();
+    if (!res || !cloneIntoUninitialized(alloc, res))
         return nullptr;
     return res;
 }
@@ -1150,10 +1150,9 @@ TypeScript::FreezeTypeSets(CompilerConstraintList* constraints, JSScript* script
     TemporaryTypeSet* types = alloc->newArrayUninitialized<TemporaryTypeSet>(count);
     if (!types)
         return false;
-    PodZero(types, count);
 
     for (size_t i = 0; i < count; i++) {
-        if (!existing[i].clone(alloc, &types[i]))
+        if (!existing[i].cloneIntoUninitialized(alloc, &types[i]))
             return false;
     }
 
diff --git a/js/src/vm/TypeInference.h b/js/src/vm/TypeInference.h
index 0e737bad7..0f1cd4936 100644
--- a/js/src/vm/TypeInference.h
+++ b/js/src/vm/TypeInference.h
@@ -498,7 +498,10 @@ class TypeSet
 
     // Clone a type set into an arbitrary allocator.
     TemporaryTypeSet* clone(LifoAlloc* alloc) const;
-    bool clone(LifoAlloc* alloc, TemporaryTypeSet* result) const;
+
+    // |*result| is not even partly initialized when this function is called:
+    // this function placement-new's its contents into existence.
+    bool cloneIntoUninitialized(LifoAlloc* alloc, TemporaryTypeSet* result) const;
 
     // Create a new TemporaryTypeSet where undefined and/or null has been filtered out.
     TemporaryTypeSet* filter(LifoAlloc* alloc, bool filterUndefined, bool filterNull) const;