[parser/ast] Reduce memory consumption for AstConsString.

[parser/ast] Reduce memory consumption for AstConsString.

The past re-factoring inadvertently increased memory consumption for
AstConsString. This implements a micro-optimization to revert and slightly
improve beyond the original state.

Example, Zone size for parsing closure.js:
  - 20,999,848 B (before refactoring)
  - 21,651,056 B (after refactoring patch; 3.1% regression)
  - 20,641,320 B (after this CL; 1.7% improvement over original)

(Reason: ZoneLinkedList requires 4 pointers to support
the std::list functionality (Zone*, head/tail ptr, payload ptr).
But since we only append and iterate in order and have the Zone*
available in the context, a super simple linked list (value + next ptr)
saves a bit of memory, especially for the common case of having 0 or 1
string segments.)


BUG=v8:6902, chromium:706935
Review-Url: https://codereview.chromium.org/2792353002
Cr-Commit-Position: refs/heads/master@{#44385}
Committed: https://chromium.googlesource.com/v8/v8/+/1769c7034ba4203c6301d5db5e3081b47585af0d

[vogelheim, 2017-04-04 12:43:23]

The CQ bit was checked by vogelheim@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-04-04 12:43:31]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[vogelheim, 2017-04-04 12:46:23]

vogelheim@chromium.org changed reviewers:
+ marja@chromium.org

[commit-bot: I haz the power, 2017-04-04 13:01:17]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-04-04 13:01:18]

Dry run: Try jobs failed on following builders:
  v8_linux_arm_rel_ng on master.tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_linux_arm_rel_ng/builds/...)
  v8_linux_arm_rel_ng_triggered on master.tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_linux_arm_rel_ng_trigger...)

[vogelheim, 2017-04-04 13:11:25]

The CQ bit was checked by vogelheim@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-04-04 13:11:31]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[vogelheim, 2017-04-04 13:32:43]

ptal (original version was broken; should be fixed now)

[commit-bot: I haz the power, 2017-04-04 13:33:52]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-04-04 13:33:52]

Dry run: This issue passed the CQ dry run.

[marja, 2017-04-04 13:44:54]

lgtm

(Offline discussion: ThreadedList, you can decide whether to use it or not. I'd
slightly prefer it but I'm not insisting...)

[vogelheim, 2017-04-04 14:44:33]

On 2017/04/04 13:44:54, marja wrote:
> lgtm
> 
> (Offline discussion: ThreadedList, you can decide whether to use it or not.
I'd
> slightly prefer it but I'm not insisting...)

The ThreadedList version is a bit shorter (-14 lines), but uses ~130KB more
memory (for the closure.js example). That is, it eliminates ca. half of the 1.7%
savings. The reason is that ThreadedList maintains a head + tail pointer, so for
each AstConsString with a single AstRawString it uses uses 4*sizeof(void*) vs 3*
for my version.

Unless you care strongly, I'd commit the current (non-ThreadedList) version...

[marja, 2017-04-04 14:47:28]

Ok, totally makes sense to use your version if it's slimmer!

[vogelheim, 2017-04-04 14:56:40]

The CQ bit was checked by vogelheim@chromium.org

[commit-bot: I haz the power, 2017-04-04 14:56:48]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-04-04 15:38:18]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1491317800768480,
"parent_rev": "2db1f598c56fb6e43c5c6f02062bc6793843a34f", "commit_rev":
"1769c7034ba4203c6301d5db5e3081b47585af0d"}

[commit-bot: I haz the power, 2017-04-04 15:38:25]

Description was changed from

==========
[parser/ast] Reduce memory consumption for AstConsString.

The past re-factoring inadvertently increased memory consumption for
AstConsString. This implements a micro-optimization to revert and slightly
improve beyond the original state.

Example, Zone size for parsing closure.js:
  - 20,999,848 B (before refactoring)
  - 21,651,056 B (after refactoring patch; 3.1% regression)
  - 20,641,320 B (after this CL; 1.7% improvement over original)

(Reason: ZoneLinkedList requires 4 pointers to support
the std::list functionality (Zone*, head/tail ptr, payload ptr).
But since we only append and iterate in order and have the Zone*
available in the context, a super simple linked list (value + next ptr)
saves a bit of memory, especially for the common case of having 0 or 1
string segments.)


BUG=v8:6902, chromium:706935
==========

to

==========
[parser/ast] Reduce memory consumption for AstConsString.

The past re-factoring inadvertently increased memory consumption for
AstConsString. This implements a micro-optimization to revert and slightly
improve beyond the original state.

Example, Zone size for parsing closure.js:
  - 20,999,848 B (before refactoring)
  - 21,651,056 B (after refactoring patch; 3.1% regression)
  - 20,641,320 B (after this CL; 1.7% improvement over original)

(Reason: ZoneLinkedList requires 4 pointers to support
the std::list functionality (Zone*, head/tail ptr, payload ptr).
But since we only append and iterate in order and have the Zone*
available in the context, a super simple linked list (value + next ptr)
saves a bit of memory, especially for the common case of having 0 or 1
string segments.)


BUG=v8:6902, chromium:706935

Review-Url: https://codereview.chromium.org/2792353002
Cr-Commit-Position: refs/heads/master@{#44385}
Committed:
https://chromium.googlesource.com/v8/v8/+/1769c7034ba4203c6301d5db5e3081b4758...
==========

[commit-bot: I haz the power, 2017-04-04 15:38:26]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/v8/v8/+/1769c7034ba4203c6301d5db5e3081b4758...