Try aligning unboxed double array backing store in allocation or scavenge promotion.

src/ia32/stub-cache-ia32.cc

Index: src/ia32/stub-cache-ia32.cc
diff --git a/src/ia32/stub-cache-ia32.cc b/src/ia32/stub-cache-ia32.cc
index d78341546f38a5b409022a6a8dc9c1417ca87256..f8fb72192f1026eb3409d2a1508df3851ce676a9 100644
--- a/src/ia32/stub-cache-ia32.cc
+++ b/src/ia32/stub-cache-ia32.cc
@@ -4030,6 +4030,7 @@ void KeyedStoreStubCompiler::GenerateStoreFastDoubleElement(
 
     int size = FixedDoubleArray::SizeFor(JSArray::kPreallocatedArrayElements);
     __ AllocateInNewSpace(size, edi, ebx, ecx, &prepare_slow, TAG_OBJECT);
+
     // Restore the key, which is known to be the array length.
     __ mov(ecx, Immediate(0));