[turbofan] Ensure that NTLs are always properly connected to the end.

[turbofan] Ensure that NTLs are always properly connected to the end.

Up until now we used a special Terminate node to artifically connect non
terminating loops to the End node, but this was kind of adhoc and didn't
work for the CFG. So without all kinds of weird hacks, the end block in
the CFG will not be connected to NTLs, which makes it impossible to
compute post dominance / control dependence in the current setting.

So instead of Terminate, we add a special Branch to NTLs, whose
condition is the special Always node, which corresponds to True, except
that it cannot be folded away. This way we don't need any special
machinery in the scheduler, since it's just a regular Branch.

R=titzer@chromium.org

Committed: https://crrev.com/59a02ebdbeb6594a596cd61a380841e3c4bc9851
Cr-Commit-Position: refs/heads/master@{#26294}

[Benedikt Meurer, 2015-01-27 13:33:07]

bmeurer@chromium.org changed reviewers:
+ mstarzinger@chromium.org

[Benedikt Meurer, 2015-01-27 13:33:07]

PTAL

[titzer, 2015-01-27 13:54:23]

lgtm

[Benedikt Meurer, 2015-01-27 13:55:06]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-01-27 13:56:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/875263004/1

[commit-bot: I haz the power, 2015-01-27 14:02:28]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-27 14:02:43]

Patchset 1 (id:??) landed as
https://crrev.com/59a02ebdbeb6594a596cd61a380841e3c4bc9851
Cr-Commit-Position: refs/heads/master@{#26294}