Improve LoadOptimizer::ReplacePhiWith.

Improve LoadOptimizer::ReplacePhiWith.

Previously we were only looking for congruent phis. But we can also include all operations that allow CSE and have no dependencies (e.g. arithmetic) into the congruency check.

This allows in the code like

var idx = 0;
for (var el in src) dst[idx++] = el;

see the congruency between Phi introduced for idx and Phi that LoadOptimizer emits for iterator's _index field. As the result we are able to optimize this code to use a single iteration variable instead of two.

R=fschneider@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=39864

[Vyacheslav Egorov (Google), 2014-09-04 11:57:31]

PTAL

[Florian Schneider, 2014-09-04 12:30:49]

lgtm

https://codereview.chromium.org/537963002/diff/1/runtime/vm/flow_graph_optimi...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/537963002/diff/1/runtime/vm/flow_graph_optimi...
runtime/vm/flow_graph_optimizer.cc:6934: // During the comparison worklist
contains pairs of definintions to be
s/definintions/definitions/

https://codereview.chromium.org/537963002/diff/1/runtime/vm/flow_graph_optimi...
runtime/vm/flow_graph_optimizer.cc:7072: 
2dd

[Vyacheslav Egorov (Google), 2014-09-04 12:56:13]

https://codereview.chromium.org/537963002/diff/1/runtime/vm/flow_graph_optimi...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/537963002/diff/1/runtime/vm/flow_graph_optimi...
runtime/vm/flow_graph_optimizer.cc:6934: // During the comparison worklist
contains pairs of definintions to be
On 2014/09/04 12:30:48, Florian Schneider wrote:
> s/definintions/definitions/

Done.

https://codereview.chromium.org/537963002/diff/1/runtime/vm/flow_graph_optimi...
runtime/vm/flow_graph_optimizer.cc:7072: 
On 2014/09/04 12:30:48, Florian Schneider wrote:
> 2dd

Done.

[Vyacheslav Egorov (Google), 2014-09-04 12:56:24]

Committed patchset #1 (id:1) manually as 39864 (presubmit successful).