Implement better side effect tracking for load-to-load forwarding.

Implement better side effect tracking for load-to-load forwarding.

Any field store can interfere only with stores to the same offset.

Indexed store can only interfere with indexed load.

This tracking is not yet used by LICM.

R=fschneider@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=15518

[Florian Schneider, 2012-11-29 13:42:48]

LGTM.

Please add a test for both cases  (field and indexed loads).

https://codereview.chromium.org/11280232/diff/1/runtime/vm/flow_graph_optimiz...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/11280232/diff/1/runtime/vm/flow_graph_optimiz...
runtime/vm/flow_graph_optimizer.cc:2997: }
Maybe continue already here since IsInterferingStore implies 
IsLoadEliminatationCandidate(instr).

ASSERT(!IsLoadEliminationCandidate(instr))
continue;