For nullable/double typed fields compare with null for deoptimization, else assume double.

runtime/vm/intermediate_language_arm.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_ARM.
 #if defined(TARGET_ARCH_ARM)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/cpu.h"
@@ skipping 3293 matching lines @@
   summary->set_in(0, needs_writable_input
                      ? Location::WritableRegister()
                      : Location::RequiresRegister());
   if (needs_temp) summary->set_temp(0, Location::RequiresRegister());
   summary->set_out(0, Location::RequiresFpuRegister());
   return summary;
 }
 
 
 void UnboxDoubleInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
-  const intptr_t value_cid = value()->Type()->ToCid();
+  CompileType* value_type = value()->Type();
+  const intptr_t value_cid = value_type->ToCid();
   const Register value = locs()->in(0).reg();
   const DRegister result = EvenDRegisterOf(locs()->out(0).fpu_reg());
 
   if (value_cid == kDoubleCid) {
     __ LoadDFromOffset(result, value, Double::value_offset() - kHeapObjectTag);
   } else if (value_cid == kSmiCid) {
     __ SmiUntag(value);  // Untag input before conversion.
     __ vmovsr(STMP, value);
     __ vcvtdi(result, STMP);
   } else {
     Label* deopt = compiler->AddDeoptStub(deopt_id_,
                                           ICData::kDeoptBinaryDoubleOp);
     Register temp = locs()->temp(0).reg();
-    Label is_smi, done;
-    __ tst(value, ShifterOperand(kSmiTagMask));
-    __ b(&is_smi, EQ);
-    __ CompareClassId(value, kDoubleCid, temp);
-    __ b(deopt, NE);
-    __ LoadDFromOffset(result, value, Double::value_offset() - kHeapObjectTag);
-    __ b(&done);
-    __ Bind(&is_smi);
-    // TODO(regis): Why do we preserve value here but not above?
-    __ mov(IP, ShifterOperand(value, ASR, 1));  // Copy and untag.
-    __ vmovsr(STMP, IP);
-    __ vcvtdi(result, STMP);
-    __ Bind(&done);
+    if (value_type->is_nullable() &&
+        (value_type->ToNullableCid() == kDoubleCid)) {
+      __ CompareImmediate(value, reinterpret_cast<intptr_t>(Object::null()));
+      __ b(deopt, EQ);
+      // It must be double now.
+      __ LoadDFromOffset(result, value,
+          Double::value_offset() - kHeapObjectTag);
+    } else {
+      Label is_smi, done;
+      __ tst(value, ShifterOperand(kSmiTagMask));
+      __ b(&is_smi, EQ);
+      __ CompareClassId(value, kDoubleCid, temp);
+      __ b(deopt, NE);
+      __ LoadDFromOffset(result, value,
+          Double::value_offset() - kHeapObjectTag);
+      __ b(&done);
+      __ Bind(&is_smi);
+      // TODO(regis): Why do we preserve value here but not above?
+      __ mov(IP, ShifterOperand(value, ASR, 1));  // Copy and untag.
+      __ vmovsr(STMP, IP);
+      __ vcvtdi(result, STMP);
+      __ Bind(&done);
+    }
   }
 }
 
 
 LocationSummary* BoxFloat32x4Instr::MakeLocationSummary(bool opt) const {
   const intptr_t kNumInputs = 1;
   const intptr_t kNumTemps = 1;
   LocationSummary* summary =
       new LocationSummary(kNumInputs,
                           kNumTemps,
@@ skipping 2715 matching lines @@
   compiler->GenerateCall(token_pos(),
                          &label,
                          PcDescriptors::kOther,
                          locs());
   __ Drop(ArgumentCount());  // Discard arguments.
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM