[turbofan] Don't mix element accesses with incompatible representations.

[turbofan] Don't mix element accesses with incompatible representations.

Due to speculative optimizations, the compiler can run into situations
where it's asked perform impossible operations, like loading a tagged
element as a float64 instead. All of this is guaranteed to be in dead
code (unless there's a bug), but leads to confusion and violates
assumptions in the compiler (that make perfect sense for code that is
not dead). So teach LoadElimination not to mix up element accesses with
incompatible representations.

BUG=chromium:719479
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2866233002
Cr-Commit-Position: refs/heads/master@{#45185}
Committed: https://chromium.googlesource.com/v8/v8/+/d412cade2a889f6b208c7c7c078209ea81538013

[Benedikt Meurer, 2017-05-09 08:46:59]

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

[commit-bot: I haz the power, 2017-05-09 08:47:02]

Dry run: CQ is trying da patch.

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

[Jarin, 2017-05-09 08:50:00]

lgtm. Should not we have the same thing for fields?

[Benedikt Meurer, 2017-05-09 08:55:52]

Fields cannot contain float64 hole, so they don't violate any invariant, even if
they are mixed.

[Benedikt Meurer, 2017-05-09 08:55:56]

The CQ bit was unchecked by bmeurer@chromium.org

[Benedikt Meurer, 2017-05-09 08:56:01]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2017-05-09 08:56:12]

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, 2017-05-09 10:16:14]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1494320161877630, "parent_rev":
"4aa5241fe984b705a605e1f33eb643319beed6dc", "commit_rev":
"d412cade2a889f6b208c7c7c078209ea81538013"}

[commit-bot: I haz the power, 2017-05-09 10:16:19]

Description was changed from

==========
[turbofan] Don't mix element accesses with incompatible representations.

Due to speculative optimizations, the compiler can run into situations
where it's asked perform impossible operations, like loading a tagged
element as a float64 instead. All of this is guaranteed to be in dead
code (unless there's a bug), but leads to confusion and violates
assumptions in the compiler (that make perfect sense for code that is
not dead). So teach LoadElimination not to mix up element accesses with
incompatible representations.

BUG=chromium:719479
R=jarin@chromium.org
==========

to

==========
[turbofan] Don't mix element accesses with incompatible representations.

Due to speculative optimizations, the compiler can run into situations
where it's asked perform impossible operations, like loading a tagged
element as a float64 instead. All of this is guaranteed to be in dead
code (unless there's a bug), but leads to confusion and violates
assumptions in the compiler (that make perfect sense for code that is
not dead). So teach LoadElimination not to mix up element accesses with
incompatible representations.

BUG=chromium:719479
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2866233002
Cr-Commit-Position: refs/heads/master@{#45185}
Committed:
https://chromium.googlesource.com/v8/v8/+/d412cade2a889f6b208c7c7c078209ea815...
==========

[commit-bot: I haz the power, 2017-05-09 10:16:20]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/v8/v8/+/d412cade2a889f6b208c7c7c078209ea815...