[turbofan] Utilize the fact that empty string is canonicalized.

[turbofan] Utilize the fact that empty string is canonicalized.

Since the empty string is canonical HeapObject now, we can use
this fact to optimize

  - strict equality comparisons with the empty string to a
    simple ReferenceEqual operation, and
  - optimize ToBoolean to avoid instance type checks completely.

Drive-by-fix: Allow InternalizedString for Type::HeapConstant
in the type system. This is safe, since InternalizedStrings
can be compared to other heap constants by reference (except
for non-InternalizedStrings, which are excluded from the
HeapConstant type).

BUG=v8:5267
R=yangguo@chromium.org

Review-Url: https://codereview.chromium.org/2681273002
Cr-Commit-Position: refs/heads/master@{#43050}
Committed: https://chromium.googlesource.com/v8/v8/+/cd9724d4b48bce53dff968635f72252e3ec687d4

[Benedikt Meurer, 2017-02-09 06:37:29]

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

[commit-bot: I haz the power, 2017-02-09 06:37:35]

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

[Yang, 2017-02-09 06:41:34]

On 2017/02/09 06:37:28, Benedikt Meurer wrote:

lgtm.

[Yang, 2017-02-09 06:41:41]

https://codereview.chromium.org/2681273002/diff/1/src/compiler/js-typed-lower...
File src/compiler/js-typed-lowering.cc (right):

https://codereview.chromium.org/2681273002/diff/1/src/compiler/js-typed-lower...
src/compiler/js-typed-lowering.cc:542: graph()->zone())),
can we have a helper function that returns this monstrosity?

[Benedikt Meurer, 2017-02-09 06:56:55]

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

[commit-bot: I haz the power, 2017-02-09 06:57:05]

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

[Benedikt Meurer, 2017-02-09 06:58:10]

The CQ bit was unchecked by bmeurer@chromium.org

[Benedikt Meurer, 2017-02-09 06:58:13]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2017-02-09 06:58:14]

The patchset sent to the CQ was uploaded after l-g-t-m from yangguo@chromium.org
Link to the patchset: https://codereview.chromium.org/2681273002/#ps20001
(title: "Feedback. Cleanup.")

[commit-bot: I haz the power, 2017-02-09 06:58:15]

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

[Benedikt Meurer, 2017-02-09 06:58:24]

https://codereview.chromium.org/2681273002/diff/1/src/compiler/js-typed-lower...
File src/compiler/js-typed-lowering.cc (right):

https://codereview.chromium.org/2681273002/diff/1/src/compiler/js-typed-lower...
src/compiler/js-typed-lowering.cc:542: graph()->zone())),
On 2017/02/09 06:41:41, Yang wrote:
> can we have a helper function that returns this monstrosity?

Done.

[commit-bot: I haz the power, 2017-02-09 07:23:09]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1486623493919790,
"parent_rev": "1a989bdeefdc679745215ae547007773edb3d29e", "commit_rev":
"cd9724d4b48bce53dff968635f72252e3ec687d4"}

[commit-bot: I haz the power, 2017-02-09 07:23:12]

Description was changed from

==========
[turbofan] Utilize the fact that empty string is canonicalized.

Since the empty string is canonical HeapObject now, we can use
this fact to optimize

  - strict equality comparisons with the empty string to a
    simple ReferenceEqual operation, and
  - optimize ToBoolean to avoid instance type checks completely.

Drive-by-fix: Allow InternalizedString for Type::HeapConstant
in the type system. This is safe, since InternalizedStrings
can be compared to other heap constants by reference (except
for non-InternalizedStrings, which are excluded from the
HeapConstant type).

BUG=v8:5267
R=yangguo@chromium.org
==========

to

==========
[turbofan] Utilize the fact that empty string is canonicalized.

Since the empty string is canonical HeapObject now, we can use
this fact to optimize

  - strict equality comparisons with the empty string to a
    simple ReferenceEqual operation, and
  - optimize ToBoolean to avoid instance type checks completely.

Drive-by-fix: Allow InternalizedString for Type::HeapConstant
in the type system. This is safe, since InternalizedStrings
can be compared to other heap constants by reference (except
for non-InternalizedStrings, which are excluded from the
HeapConstant type).

BUG=v8:5267
R=yangguo@chromium.org

Review-Url: https://codereview.chromium.org/2681273002
Cr-Commit-Position: refs/heads/master@{#43050}
Committed:
https://chromium.googlesource.com/v8/v8/+/cd9724d4b48bce53dff968635f72252e3ec...
==========

[commit-bot: I haz the power, 2017-02-09 07:23:13]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/v8/v8/+/cd9724d4b48bce53dff968635f72252e3ec...