Group lexical context variables for faster look up.

Group lexical context variables for faster look up.

Currently, looking up a lexical context variable requires looking up
the variable name and then checking its mode. This can be a bottleneck
in Runtime_DeclareGlobals, even when no lexical context variables are
declared.

R=rossberg@chromium.org
BUG=crbug:517778
LOG=N

Committed: https://crrev.com/a45ed17bb6aca02e940f13bbf456d660cccc86ae
Cr-Commit-Position: refs/heads/master@{#30075}

[rossberg, 2015-08-07 13:37:08]

LGTM, I'm fine with landing this as a temporary hack, but can we have a couple
of comments (and perhaps TODOs) clarifying why it was introduced?

CC'ing Benedikt.

https://codereview.chromium.org/1281883002/diff/1/src/scopeinfo.cc
File src/scopeinfo.cc (right):

https://codereview.chromium.org/1281883002/diff/1/src/scopeinfo.cc#newcode591
src/scopeinfo.cc:591: int total_count = scope_info->ContextLocalCount();
So, this means that lexical variable lookup does not use the cache anymore? That
is going to make it worse in some cases. At least add a TODO.

[Yang, 2015-08-07 21:43:12]

On 2015/08/07 13:37:08, rossberg wrote:
> LGTM, I'm fine with landing this as a temporary hack, but can we have a couple
> of comments (and perhaps TODOs) clarifying why it was introduced?
> 
> CC'ing Benedikt.
> 
> https://codereview.chromium.org/1281883002/diff/1/src/scopeinfo.cc
> File src/scopeinfo.cc (right):
> 
> https://codereview.chromium.org/1281883002/diff/1/src/scopeinfo.cc#newcode591
> src/scopeinfo.cc:591: int total_count = scope_info->ContextLocalCount();
> So, this means that lexical variable lookup does not use the cache anymore?
That
> is going to make it worse in some cases. At least add a TODO.

Done. Added comments and TODOs. I'll explore using the context slot cache in a
follow-up.

[Yang, 2015-08-07 21:45:04]

The CQ bit was checked by yangguo@chromium.org

[Yang, 2015-08-07 21:45:05]

The patchset sent to the CQ was uploaded after l-g-t-m from
rossberg@chromium.org
Link to the patchset: https://codereview.chromium.org/1281883002/#ps20001
(title: "added comments and TODOs")

[commit-bot: I haz the power, 2015-08-07 21:45:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1281883002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1281883002/20001

[commit-bot: I haz the power, 2015-08-07 22:22:41]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-08-07 22:23:58]

Patchset 2 (id:??) landed as
https://crrev.com/a45ed17bb6aca02e940f13bbf456d660cccc86ae
Cr-Commit-Position: refs/heads/master@{#30075}

[Yang, 2015-08-13 06:55:52]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/1290053002/ by yangguo@chromium.org.

The reason for reverting is: This performance hack is no longer necessary..