[turbofan] Better narrow the derived type for the right shift operation.

[turbofan] Better narrow the derived type for the right shift operation.

Currently the derived type of a right shift does not narrow the input
type based on the actual shift amount - well it does some narrowing
but more can be down. For patterns such as u32[i>>2], which is very
common is asm.js code, this limits the ability to later prove that an
index bounds check is unnecessary which can have a significant
performance impact.

Committed: https://crrev.com/531f7ab1d2ae78fba35cbfac94cae98cf306f8ac
Cr-Commit-Position: refs/heads/master@{#26270}

[dougc, 2015-01-26 04:01:59]

dtc-v8@scieneer.com changed reviewers:
+ jarin@chromium.org

[Benedikt Meurer, 2015-01-26 07:23:46]

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

[Benedikt Meurer, 2015-01-26 07:23:47]

Nice patch. Just two drive-by-nits from me.

https://codereview.chromium.org/873143002/diff/1/src/compiler/typer.cc
File src/compiler/typer.cc (right):

https://codereview.chromium.org/873143002/diff/1/src/compiler/typer.cc#newcod...
src/compiler/typer.cc:919: if (rhs->Min() > 0 && rhs->Max() <= 31)
Nit: please add { and }.

https://codereview.chromium.org/873143002/diff/1/src/compiler/typer.cc#newcod...
src/compiler/typer.cc:926: if (rhs->Min() > 0 && rhs->Max() <= 31)
Nit: please add { and }.

[dougc, 2015-01-26 13:21:18]

PTAL

[Jarin, 2015-01-26 13:36:43]

lgtm

[dougc, 2015-01-26 13:57:52]

The CQ bit was checked by dtc-v8@scieneer.com

[commit-bot: I haz the power, 2015-01-26 13:58:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/873143002/20001

[commit-bot: I haz the power, 2015-01-26 14:11:31]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-26 14:11:41]

Patchset 2 (id:??) landed as
https://crrev.com/531f7ab1d2ae78fba35cbfac94cae98cf306f8ac
Cr-Commit-Position: refs/heads/master@{#26270}