Expand the class id to 32 bits and size field to 16 bits on 64-bit platforms.

runtime/vm/intermediate_language_arm.cc

Index: runtime/vm/intermediate_language_arm.cc
diff --git a/runtime/vm/intermediate_language_arm.cc b/runtime/vm/intermediate_language_arm.cc
index 2914a50475bf88c3b7ac34ba52cdf66ff5dad681..7643408673a6ff4e040e945716749a2872b9325a 100644
--- a/runtime/vm/intermediate_language_arm.cc
+++ b/runtime/vm/intermediate_language_arm.cc
@@ -1571,6 +1571,8 @@ LocationSummary* GuardFieldClassInstr::MakeLocationSummary(Zone* zone,
 
 
 void GuardFieldClassInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  ASSERT(sizeof(classid_t) == kInt16Size);
+
   const intptr_t value_cid = value()->Type()->ToCid();
   const intptr_t field_cid = field().guarded_cid();
   const intptr_t nullability = field().is_nullable() ? kNullCid : kIllegalCid;
@@ -2034,6 +2036,8 @@ static void EnsureMutableBox(FlowGraphCompiler* compiler,
 
 
 void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  ASSERT(sizeof(classid_t) == kInt16Size);
+
   Label skip_store;
 
   const Register instance_reg = locs()->in(0).reg();
@@ -2427,6 +2431,8 @@ LocationSummary* LoadFieldInstr::MakeLocationSummary(Zone* zone,
 
 
 void LoadFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  ASSERT(sizeof(classid_t) == kInt16Size);
+
   const Register instance_reg = locs()->in(0).reg();
   if (IsUnboxedLoad() && compiler->is_optimizing()) {
     const DRegister result = EvenDRegisterOf(locs()->out(0).fpu_reg());