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

runtime/vm/locations.h

Index: runtime/vm/locations.h
diff --git a/runtime/vm/locations.h b/runtime/vm/locations.h
index d57b2fd0fdde1ef51190dd19e1de3ebf3de2348f..a2e8be3875e31beb0e7e2ce29af6b2381d6843e6 100644
--- a/runtime/vm/locations.h
+++ b/runtime/vm/locations.h
@@ -459,6 +459,8 @@ class SmallSet {
 
   void Remove(T value) { data_ &= ~ToMask(value); }
 
+  bool IsEmpty() const { return data_ != 0; }
+
   intptr_t data() const { return data_; }
 
  private:
@@ -535,6 +537,10 @@ class RegisterSet : public ValueObject {
     untagged_cpu_registers_.Add(loc.reg());
   }
 
+  bool HasUntaggedValues() const {
+    return !untagged_cpu_registers_.IsEmpty() || !fpu_registers_.IsEmpty();
+  }
+
   bool IsTagged(Register reg) const {
     return !untagged_cpu_registers_.Contains(reg);
   }