Eliminate phis that do not reach any non-environment uses.

Eliminate phis that do not reach any non-environment uses.

This takes care of phis for temporary variables like :expr_temp, lia, lix, igr, casc, alloc, sca that currently create unnecessary pressure on the back-edge of loops.

R=srdjan@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=10377

[Vyacheslav Egorov (Google), 2012-08-08 10:21:56]

routing to Kevin for review.

[Kevin Millikin (Google), 2012-08-08 11:07:43]

Hacky.  We should try to get rid of these local variables.

LGTM.

http://codereview.chromium.org/10832180/diff/1/runtime/vm/flow_graph_allocato...
File runtime/vm/flow_graph_allocator.cc (right):

http://codereview.chromium.org/10832180/diff/1/runtime/vm/flow_graph_allocato...
runtime/vm/flow_graph_allocator.cc:160: if ((phi == NULL) || !phi->is_alive())
continue;
It doesn't work to set (*join->phis())[j] = NULL when !phi->is_alive()?  That
seems better than leaving them in and skipping them everywhere.

[Vyacheslav Egorov (Google), 2012-08-08 11:49:35]

PTAL

[Kevin Millikin (Google), 2012-08-08 12:09:59]

Changes LGTM.