[turbofan] Non-dictionary prototype maps are always stable.

[turbofan] Non-dictionary prototype maps are always stable.

We don't need to have an (untested) fallback for the case that a
prototype map is not stable when specializing a named property,
because prototype maps are always stable (which is now guarded
by a DCHECK in CompilationDependencies).  Less (dead) code is
better code.

R=verwaest@chromium.org
BUG=v8:4470
LOG=n

Committed: https://crrev.com/daf76e6d14b08c3949c8c80dfa2d1b1787947764
Cr-Commit-Position: refs/heads/master@{#31524}

[Benedikt Meurer, 2015-10-23 11:57:56]

Hey Toon,

As discussed offline. This also reduces code duplication (at least a little bit,
the rest is still on TODO).
Please take a look.

Thanks,
Benedikt

[Jarin, 2015-10-23 13:09:34]

jarin@chromium.org changed reviewers:
+ jarin@chromium.org

[Jarin, 2015-10-23 13:09:35]

lgtm

https://codereview.chromium.org/1417973006/diff/1/src/compiler/js-native-cont...
File src/compiler/js-native-context-specialization.cc (right):

https://codereview.chromium.org/1417973006/diff/1/src/compiler/js-native-cont...
src/compiler/js-native-context-specialization.cc:899: for (PrototypeIterator
j(map);; j.Advance()) {
Does not it make sense to dcheck that we are not at end here?

[Toon Verwaest, 2015-10-23 13:45:40]

https://codereview.chromium.org/1417973006/diff/1/src/compiler/js-native-cont...
File src/compiler/js-native-context-specialization.cc (right):

https://codereview.chromium.org/1417973006/diff/1/src/compiler/js-native-cont...
src/compiler/js-native-context-specialization.cc:757: 
What Object.prototype.x? Object.prototype has a null prototype, there won't be a
holder, but we also don't load a property from the map.

[Benedikt Meurer, 2015-10-23 13:56:26]

https://codereview.chromium.org/1417973006/diff/1/src/compiler/js-native-cont...
File src/compiler/js-native-context-specialization.cc (right):

https://codereview.chromium.org/1417973006/diff/1/src/compiler/js-native-cont...
src/compiler/js-native-context-specialization.cc:757: 
NotFound case is not implemented.

[Benedikt Meurer, 2015-10-23 13:56:30]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-10-23 13:56:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1417973006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1417973006/1

[Toon Verwaest, 2015-10-23 13:56:44]

lgtm

[commit-bot: I haz the power, 2015-10-23 13:57:59]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-23 13:58:32]

Patchset 1 (id:??) landed as
https://crrev.com/daf76e6d14b08c3949c8c80dfa2d1b1787947764
Cr-Commit-Position: refs/heads/master@{#31524}