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

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
diff --git a/runtime/vm/intermediate_language_ia32.cc b/runtime/vm/intermediate_language_ia32.cc
index b5f8482caa8cc58f1b3a0e5f17c479e5dde2397a..2ebfc4e10536fbe71884e5573c5bee017aec0c19 100644
--- a/runtime/vm/intermediate_language_ia32.cc
+++ b/runtime/vm/intermediate_language_ia32.cc
@@ -1419,6 +1419,7 @@ 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;
@@ -1766,6 +1767,7 @@ static void EnsureMutableBox(FlowGraphCompiler* compiler,
 
 
 void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  ASSERT(sizeof(classid_t) == kInt16Size);
   Label skip_store;
 
   Register instance_reg = locs()->in(0).reg();
@@ -2168,6 +2170,8 @@ LocationSummary* LoadFieldInstr::MakeLocationSummary(Zone* zone,
 
 
 void LoadFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  ASSERT(sizeof(classid_t) == kInt16Size);
+
   Register instance_reg = locs()->in(0).reg();
   if (IsUnboxedLoad() && compiler->is_optimizing()) {
     XmmRegister result = locs()->out(0).fpu_reg();