Register allocation tweaks:

Register allocation tweaks:

- Improve heuristic detecting interference on the back-edge. Any value live_in for the loop header can introduce interfering moves at the back edge due to control flow resolution connecting split siblings. Apply adjustments based on this heuristic at the latest point when allocating a free register;

- Don't allocate a register for constants that have no constrained uses.

R=fschneider@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=20374

[Florian Schneider, 2013-03-21 13:17:06]

LGTM.

https://codereview.chromium.org/12946004/diff/1/runtime/vm/flow_graph_allocat...
File runtime/vm/flow_graph_allocator.cc (right):

https://codereview.chromium.org/12946004/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:860: // TODO(vegorov) improve allocation when
we have enough registers to keep
insert : after the TODO(vegorov).

[Vyacheslav Egorov (Google), 2013-03-22 11:30:35]

Thanks! Landing.

https://codereview.chromium.org/12946004/diff/1/runtime/vm/flow_graph_allocat...
File runtime/vm/flow_graph_allocator.cc (right):

https://codereview.chromium.org/12946004/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:860: // TODO(vegorov) improve allocation when
we have enough registers to keep
On 2013/03/21 13:17:06, Florian Schneider wrote:
> insert : after the TODO(vegorov).

Done.

[Vyacheslav Egorov (Google), 2013-03-22 11:44:48]

Committed patchset #2 manually as r20374 (presubmit successful).