Replace start_env with initial_definitions in GraphEntryInstr.

Replace start_env with initial_definitions in GraphEntryInstr.

The initial definitions do not have any deoptimization information and can be
represented as just a list of definitions. For easy access, the constant_null
getter remains but assumes that index 0 contains the constant.

R=kmillikin@google.com

Committed: https://code.google.com/p/dart/source/detail?r=12555

[zerny-google, 2012-09-19 11:36:34]

Please have a look.

[Kevin Millikin (Google), 2012-09-19 11:49:29]

LGTM with comments.

https://codereview.chromium.org/10939031/diff/1/runtime/vm/flow_graph_allocat...
File runtime/vm/flow_graph_allocator.cc (right):

https://codereview.chromium.org/10939031/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:547: }
} else {
  UNREACHABLE();
}

https://codereview.chromium.org/10939031/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:554: // All incoming parameters are tagged.
This comment is wrong so remove it or say something like: "Parameters and the
constant null are tagged, so allocated to CPU [general purpose?] registers."

https://codereview.chromium.org/10939031/diff/1/runtime/vm/flow_graph_inliner.cc
File runtime/vm/flow_graph_inliner.cc (right):

https://codereview.chromium.org/10939031/diff/1/runtime/vm/flow_graph_inliner...
runtime/vm/flow_graph_inliner.cc:133: intptr_t j = 0;
j ==> arg_index or arg_idx or the like.

https://codereview.chromium.org/10939031/diff/3001/runtime/vm/intermediate_la...
File runtime/vm/intermediate_language.h (right):

https://codereview.chromium.org/10939031/diff/3001/runtime/vm/intermediate_la...
runtime/vm/intermediate_language.h:806: GrowableArray<Definition*>&
initial_definitions() {
We normally make this return GrowableArray<Definition*>*, i.e.,
&initial_definitions_.

[zerny-google, 2012-09-19 12:15:05]

Done.

https://codereview.chromium.org/10939031/diff/1/runtime/vm/flow_graph_allocat...
File runtime/vm/flow_graph_allocator.cc (right):

https://codereview.chromium.org/10939031/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:547: }
On 2012/09/19 11:49:29, kmillikin wrote:
> } else {
>   UNREACHABLE();
> }

Done.

https://codereview.chromium.org/10939031/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:554: // All incoming parameters are tagged.
On 2012/09/19 11:49:29, kmillikin wrote:
> This comment is wrong so remove it or say something like: "Parameters and the
> constant null are tagged, so allocated to CPU [general purpose?] registers."

Done.