DBC: Support large offsets in optimized field access.

runtime/vm/constants_dbc.h

Index: runtime/vm/constants_dbc.h
diff --git a/runtime/vm/constants_dbc.h b/runtime/vm/constants_dbc.h
index 44398aaa22d704c49b29cc7f5ae4c06a2ef6f07a..d3d6b9fc1d3bf9bf7003cae0fad30a96c1a44cd3 100644
--- a/runtime/vm/constants_dbc.h
+++ b/runtime/vm/constants_dbc.h
@@ -396,6 +396,12 @@ namespace dart {
 //
 //    Store value FP[rC] into object FP[rA] at offset (in words) B.
 //
+//  - StoreFieldExt rA, rD
+//
+//    Store value FP[rD] into object FP[rA] at offset (in words)
+//    stored in the following Nop instruction. Used to access fields with
+//    large offsets.
+//
 //  - StoreFieldTOS D
 //
 //    Store value SP[0] into object SP[-1] at offset (in words) D.
@@ -404,6 +410,12 @@ namespace dart {
 //
 //    Load value at offset (in words) C from object FP[rB] into FP[rA].
 //
+//  - LoadFieldExt rA, rD
+//
+//    Load value from object FP[rD] at offset (in words) stored in the
+//    following Nop instruction into FP[rA]. Used to access fields with
+//    large offsets.
+//
 //  - LoadUntagged rA, rB, C
 //
 //    Like LoadField, but assumes that FP[rB] is untagged.
@@ -758,8 +770,10 @@ namespace dart {
   V(LoadIndexedOneByteString,    A_B_C, reg, reg, reg) \
   V(LoadIndexedTwoByteString,    A_B_C, reg, reg, reg) \
   V(StoreField,                  A_B_C, reg, num, reg) \
+  V(StoreFieldExt,                 A_D, reg, reg, ___) \
   V(StoreFieldTOS,                   D, num, ___, ___) \
   V(LoadField,                   A_B_C, reg, reg, num) \
+  V(LoadFieldExt,                  A_D, reg, reg, ___) \
   V(LoadUntagged,                A_B_C, reg, reg, num) \
   V(LoadFieldTOS,                    D, num, ___, ___) \
   V(BooleanNegateTOS,                0, ___, ___, ___) \