More compact string representation on 64 bit.

runtime/vm/simulator_dbc.cc

Index: runtime/vm/simulator_dbc.cc
diff --git a/runtime/vm/simulator_dbc.cc b/runtime/vm/simulator_dbc.cc
index 26419a784003eec6043add9027b2fd3eb71f3235..75b94dd9236a77ce62d06c7b8c67fdcb81cbf762 100644
--- a/runtime/vm/simulator_dbc.cc
+++ b/runtime/vm/simulator_dbc.cc
@@ -2957,9 +2957,11 @@ RawObject* Simulator::Call(const Code& code,
     BYTECODE(CreateArrayOpt, A_B_C);
     const intptr_t length = Smi::Value(RAW_CAST(Smi, FP[rB]));
     if (LIKELY(static_cast<uintptr_t>(length) <= Array::kMaxElements)) {
-      const intptr_t fixed_size = sizeof(RawArray) + kObjectAlignment - 1;
+      const intptr_t fixed_size_plus_alignment_padding =
+          sizeof(RawArray) + kObjectAlignment - 1;
       const intptr_t instance_size =
-          (fixed_size + length * kWordSize) & ~(kObjectAlignment - 1);
+          (fixed_size_plus_alignment_padding + length * kWordSize) &
+          ~(kObjectAlignment - 1);
       const uword start =
           thread->heap()->new_space()->TryAllocate(instance_size);
       if (LIKELY(start != 0)) {