Emit stackmaps even in unoptimized code if slow path pushes untagged values.

runtime/vm/object.cc

 // Copyright (c) 2012, 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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 12644 matching lines @@
   // frame slots which are marked as having objects.
   *maps = stackmaps();
   *map = Stackmap::null();
   for (intptr_t i = 0; i < maps->Length(); i++) {
     *map ^= maps->At(i);
     ASSERT(!map->IsNull());
     if (map->PcOffset() == pc_offset) {
       return map->raw();  // We found a stack map for this frame.
     }
   }
-  // If the code has stackmaps, it must have them for all safepoints.
-  UNREACHABLE();
+  ASSERT(!is_optimized());
   return Stackmap::null();
 }
 
 
 intptr_t Code::GetCallerId(intptr_t inlined_id) const {
   if (inlined_id < 0) return -1;
   const Array& intervals = Array::Handle(inlined_intervals());
   Smi& temp_smi = Smi::Handle();
   for (intptr_t i = 0; i < intervals.Length() - Code::kInlIntNumEntries;
        i += Code::kInlIntNumEntries) {
@@ skipping 8017 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart