Implement graph trimming in ControlReducer.

Implement graph trimming in ControlReducer.

Trimming the graph consists of breaking links from nodes that are not reachable from end to nodes that are reachable from end. Such dead nodes show up in the use lists of the live nodes and though mostly harmless, just clutter up the graph. They also can limit instruction selection opportunities, so it is good to get rid of them.

This CL is one half of the ControlReducer functionality, the other half
being branch folding.

R=bmeurer@chromium.org
BUG=

Committed: https://code.google.com/p/v8/source/detail?r=24694

[Benedikt Meurer, 2014-10-17 09:46:44]

https://codereview.chromium.org/661923002/diff/20001/src/compiler/control-red...
File src/compiler/control-reducer.cc (right):

https://codereview.chromium.org/661923002/diff/20001/src/compiler/control-red...
src/compiler/control-reducer.cc:37: NodeVector stack_;
Nit: Use deque here, or even better std::stack with std::deque as backing store?

https://codereview.chromium.org/661923002/diff/20001/src/compiler/control-red...
src/compiler/control-reducer.cc:38: NodeVector revisit_;
Nit: Use deque here.

[Benedikt Meurer, 2014-10-17 09:46:56]

LGTM if nits are addressed.

[titzer, 2014-10-17 11:15:51]

https://codereview.chromium.org/661923002/diff/20001/src/compiler/control-red...
File src/compiler/control-reducer.cc (right):

https://codereview.chromium.org/661923002/diff/20001/src/compiler/control-red...
src/compiler/control-reducer.cc:37: NodeVector stack_;
On 2014/10/17 09:46:44, Benedikt Meurer wrote:
> Nit: Use deque here, or even better std::stack with std::deque as backing
store?

Done.

https://codereview.chromium.org/661923002/diff/20001/src/compiler/control-red...
src/compiler/control-reducer.cc:38: NodeVector revisit_;
On 2014/10/17 09:46:44, Benedikt Meurer wrote:
> Nit: Use deque here.

Done.

[titzer, 2014-10-17 11:52:16]

Committed patchset #3 manually as 24694 (presubmit successful).