Move type check elimination from backend to graph builder in new compiler.

Move type check elimination from backend to graph builder in new compiler.
Committed: https://code.google.com/p/dart/source/detail?r=6713

[srdjan, 2012-04-18 21:33:15]

LGTM

https://chromiumcodereview.appspot.com/10021070/diff/1/runtime/vm/flow_graph_...
File runtime/vm/flow_graph_builder.cc (right):

https://chromiumcodereview.appspot.com/10021070/diff/1/runtime/vm/flow_graph_...
runtime/vm/flow_graph_builder.cc:300: (literal_value.raw() ==
Object::transition_sentinel()));
Why is this assert needed?

[regis, 2012-04-18 21:58:30]

Thanks!

https://chromiumcodereview.appspot.com/10021070/diff/1/runtime/vm/flow_graph_...
File runtime/vm/flow_graph_builder.cc (right):

https://chromiumcodereview.appspot.com/10021070/diff/1/runtime/vm/flow_graph_...
runtime/vm/flow_graph_builder.cc:300: (literal_value.raw() ==
Object::transition_sentinel()));
On 2012/04/18 21:33:16, srdjan wrote:
> Why is this assert needed?

The assert is only to document the fact that we eliminate type checks with
sentinels as well, not just null. I have added this comment:

      // There are only three instances that can be of Class Null:
      // Object::null(), Object::sentinel(), and Object::transition_sentinel().
      // The inline code and run time code performing the type check will never
      // encounter the 2 sentinel values. The type check of a sentinel value
      // will always be eliminated here, because these sentinel values can only
      // be encountered as constants, never as actual value of an heap object
      // being type checked.