Make SNaN verification universal for all arches.

Make SNaN verification universal for all arches.

The mips HW prior to revision 5 has opposite encoding for NaNs.

TEST=mjsunit/regress/*, regress-1167, regress-undefined-nan2
BUG=

Committed: https://crrev.com/85ed0097d5c6efad770bf562a50992e6a204b815
Cr-Commit-Position: refs/heads/master@{#26568}

[dusmil.imgtec, 2015-02-10 17:54:01]

dusan.milosavljevic@imgtec.com changed reviewers:
+ akos.palfi@imgtec.com, balazs.kilvady@imgtec.com, bmeurer@chromium.org,
danno@chromium.org, jkummerow@chromium.org, paul.lind@imgtec.com

[paul.l..., 2015-02-10 17:56:46]

LGTM, but this one needs v8 team review.

[Benedikt Meurer, 2015-02-10 18:41:37]

Hm, I'm not sure I fully understand the idea... doesn't that mean that
kHoleNanInt64 is wrong as well?

[dusmil.imgtec, 2015-02-10 19:52:54]

Yes, the kHoleNanInt64 is quiet Nan on MIPS, but everything is working well
regarding hole nan checks because kHoleNanInt64 has distinctive bit pattern
0xfff7ffff ffffffff, the FPU on MIPS HW always generate 7ff7ffff fffffffff for
qNaN.
Hole nan checks compares exact bit-pattern of upper 32 bit, so even hole nan is
qnan on MIPS
it is correctly recognized. We only had problems with verification of fixed
double arrays
in debug mode on HW which this CL addresses.

The best part is that if kHoleNanInt64 is passed through the MIPS fpu it gets
converted to
7ff7ffff .... so we can do similar fast canonicalization optimization in
upcoming CL
as it is done for ia32 or arm. All that thanks to the chosen bit patter for
kHoleNanInt64.

[Benedikt Meurer, 2015-02-11 08:37:59]

I'm worried that this will break at some point... so I'd strongly encourage you
to change the hole nan to be signaling even on MIPS.

[Benedikt Meurer, 2015-02-11 08:38:03]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-02-11 08:38:03]

lgtm

[commit-bot: I haz the power, 2015-02-11 08:38:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/912833003/20001

[commit-bot: I haz the power, 2015-02-11 09:05:21]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-11 09:05:36]

Patchset 2 (id:??) landed as
https://crrev.com/85ed0097d5c6efad770bf562a50992e6a204b815
Cr-Commit-Position: refs/heads/master@{#26568}