[x64] Generate test reg,reg instead of cmp reg,0.

[x64] Generate test reg,reg instead of cmp reg,0.

The instruction sequence is shorter and saves decoding bandwidth.

R=svenpanne@chromium.org

Committed: https://crrev.com/a7fb5ed400701b22c455d0ad410bc98b211e5730
Cr-Commit-Position: refs/heads/master@{#26734}

[Benedikt Meurer, 2015-02-18 13:09:44]

PTAL

[Sven Panne, 2015-02-18 13:21:34]

The CQ bit was checked by svenpanne@chromium.org

[Sven Panne, 2015-02-18 13:21:34]

lgtm

[commit-bot: I haz the power, 2015-02-18 13:22:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/916543004/1

[commit-bot: I haz the power, 2015-02-18 13:32:46]

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

[commit-bot: I haz the power, 2015-02-18 13:32:47]

Try jobs failed on following builders:
  v8_win_rel on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_win_rel/builds/3184)

[Benedikt Meurer, 2015-02-19 06:29:10]

New patchsets have been uploaded after l-g-t-m from svenpanne@chromium.org

[Benedikt Meurer, 2015-02-19 07:34:30]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-02-19 07:34:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/916543004/20001

[Benedikt Meurer, 2015-02-19 07:45:24]

The CQ bit was unchecked by bmeurer@chromium.org

[Benedikt Meurer, 2015-02-19 07:45:59]

Committed patchset #2 (id:20001) manually as
a7fb5ed400701b22c455d0ad410bc98b211e5730 (presubmit successful).

[commit-bot: I haz the power, 2015-02-19 07:46:01]

Patchset 2 (id:??) landed as
https://crrev.com/a7fb5ed400701b22c455d0ad410bc98b211e5730
Cr-Commit-Position: refs/heads/master@{#26734}

[Benedikt Meurer, 2015-02-19 10:37:29]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/939923003/ by bmeurer@chromium.org.

The reason for reverting is: Tanks some benchmarks (for no obvious reason).