Bug 1290034 - Ensure nursery allocations are correctly aligned r=terrence

js/src/gc/Nursery.cpp

@@ -253,6 +253,8 @@ js::Nursery::allocate(size_t size)
     MOZ_ASSERT(isEnabled());
     MOZ_ASSERT(!runtime()->isHeapBusy());
     MOZ_ASSERT(position() >= currentStart_);
+    MOZ_ASSERT(position() % gc::CellSize == 0);
+    MOZ_ASSERT(size % gc::CellSize == 0);
 
 #ifdef JS_GC_ZEAL
     static const size_t CanarySize = (sizeof(Nursery::Canary) + CellSize - 1) & ~CellMask;

js/src/jit/MacroAssembler.cpp

@@ -781,6 +781,7 @@ MacroAssembler::nurseryAllocate(Register result, Register temp, gc::AllocKind al
     const Nursery& nursery = GetJitContext()->runtime->gcNursery();
     int thingSize = int(gc::Arena::thingSize(allocKind));
     int totalSize = thingSize + nDynamicSlots * sizeof(HeapSlot);
+    MOZ_ASSERT(totalSize % gc::CellSize == 0);
     loadPtr(AbsoluteAddress(nursery.addressOfPosition()), result);
     computeEffectiveAddress(Address(result, totalSize), temp);
     branchPtr(Assembler::Below, AbsoluteAddress(nursery.addressOfCurrentEnd()), temp, fail);