DBC: Adds DecodeLoadObjectFromPoolOrThread, enables tests

runtime/vm/instructions_dbc.cc

Index: runtime/vm/instructions_dbc.cc
diff --git a/runtime/vm/instructions_dbc.cc b/runtime/vm/instructions_dbc.cc
index 38b69f41a04a97cc160b39e6704d3d6f0ccaf9c0..65143ac3a2dcf194d0b5dfcccf2db131eff8ce99 100644
--- a/runtime/vm/instructions_dbc.cc
+++ b/runtime/vm/instructions_dbc.cc
@@ -112,7 +112,17 @@ uword InstructionPattern::DecodeLoadWordFromPool(uword end,
 bool DecodeLoadObjectFromPoolOrThread(uword pc,
                                       const Code& code,
                                       Object* obj) {
-  UNIMPLEMENTED();
+  ASSERT(code.ContainsInstructionAt(pc));
+  Instr instr = Bytecode::At(pc);
+  if ((Bytecode::DecodeOpcode(instr) == Bytecode::kPushConstant) ||
+      (Bytecode::DecodeOpcode(instr) == Bytecode::kLoadConstant)) {

[Vyacheslav Egorov (Google), 2016/05/09 18:26:13]

There are more instructions that load stuff from pool:

StaticCall and InstanceCall* also load stuff from pool 

StoreStaticTOS, PushStatic load field from PP

Allocate D loads class from PP

InstantiateType, InstantiateTypeArgumentsTOS, AssertAssignable. 

I am not sure if this is important for the observatory use case or not. 

At least InstanceCall* might be important because they load ICData.

[zra, 2016/05/09 19:36:11]

Ah, yah, it looks like lots of these have potentially useful information, so
I've just included all of them.

+    uint16_t index = Bytecode::DecodeD(instr);
+    const ObjectPool& pool = ObjectPool::Handle(code.object_pool());
+    if (pool.InfoAt(index) == ObjectPool::kTaggedObject) {
+      *obj = pool.ObjectAt(index);
+      return true;
+    }
+  }
   return false;
 }