[turbofan] Don't propagate truncations if output is tagged.

[turbofan] Don't propagate truncations if output is tagged.

Disable the propagation of truncations through Phi, Select or TypeGuard
if the output representation is tagged, because when the truncations are
taken we don't necessarily reflect this in the types and therefore we
might end up in a situation where we produce a word32 value, the type
says Number, and now we need to change that to tagged, which is not
possible since we don't know how to interpret the bits, i.e. whether the
value is Signed32 or Unsigned32.

BUG=chromium:644048
Committed: https://crrev.com/8af781ea8220f5fa70bef616e5779cee21064543
Cr-Commit-Position: refs/heads/master@{#39186}

[mvstanton, 2016-09-05 13:36:20]

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

[commit-bot: I haz the power, 2016-09-05 13:36:28]

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

[mvstanton, 2016-09-05 13:36:48]

mvstanton@chromium.org changed reviewers:
+ bmeurer@chromium.org

[mvstanton, 2016-09-05 13:36:49]

Hi Benedikt,
Here is the straightforward fix (back-mergable).
--Mike

[commit-bot: I haz the power, 2016-09-05 14:04:12]

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

[commit-bot: I haz the power, 2016-09-05 14:04:14]

Dry run: This issue passed the CQ dry run.

[Benedikt Meurer, 2016-09-05 16:41:57]

Description was changed from

==========
[turbofan] Disable simplified lowering word32->tagged changes

BUG=chromium:644048
==========

to

==========
[turbofan] Don't propagate truncations if output is tagged.

Disable the propagation of truncations through Phi, Select or TypeGuard
if the output representation is tagged, because when the truncations are
taken we don't necessarily reflect this in the types and therefore we 
might end up in a situation where we produce a word32 value, the type
says Number, and now we need to change that to tagged, which is not
possible since we don't know how to interpret the bits, i.e. whether the
value is Signed32 or Unsigned32.

BUG=chromium:644048
==========

[Benedikt Meurer, 2016-09-05 16:42:22]

Thanks, LGTM. I tweaked the description a bit.

[mvstanton, 2016-09-05 20:52:26]

The CQ bit was checked by mvstanton@chromium.org

[commit-bot: I haz the power, 2016-09-05 20:52:31]

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, 2016-09-05 20:54:32]

Description was changed from

==========
[turbofan] Don't propagate truncations if output is tagged.

Disable the propagation of truncations through Phi, Select or TypeGuard
if the output representation is tagged, because when the truncations are
taken we don't necessarily reflect this in the types and therefore we 
might end up in a situation where we produce a word32 value, the type
says Number, and now we need to change that to tagged, which is not
possible since we don't know how to interpret the bits, i.e. whether the
value is Signed32 or Unsigned32.

BUG=chromium:644048
==========

to

==========
[turbofan] Don't propagate truncations if output is tagged.

Disable the propagation of truncations through Phi, Select or TypeGuard
if the output representation is tagged, because when the truncations are
taken we don't necessarily reflect this in the types and therefore we 
might end up in a situation where we produce a word32 value, the type
says Number, and now we need to change that to tagged, which is not
possible since we don't know how to interpret the bits, i.e. whether the
value is Signed32 or Unsigned32.

BUG=chromium:644048
==========

[commit-bot: I haz the power, 2016-09-05 20:54:33]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-09-05 20:55:02]

Description was changed from

==========
[turbofan] Don't propagate truncations if output is tagged.

Disable the propagation of truncations through Phi, Select or TypeGuard
if the output representation is tagged, because when the truncations are
taken we don't necessarily reflect this in the types and therefore we 
might end up in a situation where we produce a word32 value, the type
says Number, and now we need to change that to tagged, which is not
possible since we don't know how to interpret the bits, i.e. whether the
value is Signed32 or Unsigned32.

BUG=chromium:644048
==========

to

==========
[turbofan] Don't propagate truncations if output is tagged.

Disable the propagation of truncations through Phi, Select or TypeGuard
if the output representation is tagged, because when the truncations are
taken we don't necessarily reflect this in the types and therefore we
might end up in a situation where we produce a word32 value, the type
says Number, and now we need to change that to tagged, which is not
possible since we don't know how to interpret the bits, i.e. whether the
value is Signed32 or Unsigned32.

BUG=chromium:644048

Committed: https://crrev.com/8af781ea8220f5fa70bef616e5779cee21064543
Cr-Commit-Position: refs/heads/master@{#39186}
==========

[commit-bot: I haz the power, 2016-09-05 20:55:02]

Patchset 1 (id:??) landed as
https://crrev.com/8af781ea8220f5fa70bef616e5779cee21064543
Cr-Commit-Position: refs/heads/master@{#39186}