Ensure that BoxInt32 input is correctly preserved on the slow-path.

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 1996 matching lines @@
 
     return;
   }
 
   if (IsPotentialUnboxedStore()) {
     const Register value_reg = locs()->in(1).reg();
     const Register temp = locs()->temp(0).reg();
     const Register temp2 = locs()->temp(1).reg();
     const DRegister fpu_temp = EvenDRegisterOf(locs()->temp(2).fpu_reg());
 
+    if (ShouldEmitStoreBarrier()) {
+      // Value input is a writable register and should be manually preserved
+      // across allocation slow-path.
+      locs()->live_registers()->Add(locs()->in(1), kTagged);
+    }
+
     Label store_pointer;
     Label store_double;
     Label store_float32x4;
     Label store_float64x2;
 
     __ LoadObject(temp, Field::ZoneHandle(field().raw()));
 
     __ ldr(temp2, FieldAddress(temp, Field::is_nullable_offset()));
     __ CompareImmediate(temp2, kNullCid);
     __ b(&store_pointer, EQ);
@@ skipping 5188 matching lines @@
   compiler->GenerateCall(token_pos(), &label, stub_kind_, locs());
 #if defined(DEBUG)
   __ LoadImmediate(R4, kInvalidObjectPointer);
   __ LoadImmediate(R5, kInvalidObjectPointer);
 #endif
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM