[arm] Optimize vcmp when lhs operand is #0.0

[arm] Optimize vcmp when lhs operand is #0.0

This patch checks the type of the lhs operand of a floating point
comparison for ARM, and commutes the operands if it is #0.0.  It allows
us to optimize a comparison with zero, as the vcmp instruction
accepts #0.0 as rhs operand.

Code before for "0.0 < 0.123":
------------------------------
movw ip, #29360
movt ip, #37224
movw r9, #31981
movt r9, #16319
vmov d0, ip, r9
mov ip, #0
vmov d1, ip, ip
vcmp.f64 d1, d0
vmrs APSR, FPSCR
bcc +12

Code after:
-----------
movw ip, #29360
movt ip, #37224
movw r9, #31981
movt r9, #16319
vmov d0, ip, r9
vcmp.f64 d0, #0.0
vmrs APSR, FPSCR
bgt +12

BUG=

Committed: https://crrev.com/d1472d65dd25b79a65103d6a62af857517aef9cb
Cr-Commit-Position: refs/heads/master@{#30911}

[Pierre Langlois, 2015-09-24 10:25:42]

pierre.langlois@arm.com changed reviewers:
+ bmeurer@chromium.org, jacob.bramley@arm.com

[Benedikt Meurer, 2015-09-24 11:10:06]

lgtm

[Pierre Langlois, 2015-09-24 11:41:26]

The CQ bit was checked by pierre.langlois@arm.com

[commit-bot: I haz the power, 2015-09-24 11:41:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1361913003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1361913003/1

[commit-bot: I haz the power, 2015-09-24 12:04:04]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-24 12:04:21]

Patchset 1 (id:??) landed as
https://crrev.com/d1472d65dd25b79a65103d6a62af857517aef9cb
Cr-Commit-Position: refs/heads/master@{#30911}