Add a mechanism to override the detected cpu features.

Add a mechanism to override the detected cpu features.

BUG=
R=svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=16772

[Sven Panne, 2013-09-16 13:48:05]

Before we land this, I'd like to see where and why we will need this change.

https://codereview.chromium.org/23523060/diff/1/src/ia32/assembler-ia32.h
File src/ia32/assembler-ia32.h (right):

https://codereview.chromium.org/23523060/diff/1/src/ia32/assembler-ia32.h#new...
src/ia32/assembler-ia32.h:538: if ((force_feature_ & (static_cast<uint64_t>(1)
<< f)) != 0) return true;
Lift out

   static_cast<uint64_t>(1) << f

into a private helper now that it's all over the place.

https://codereview.chromium.org/23523060/diff/1/src/ia32/assembler-ia32.h#new...
src/ia32/assembler-ia32.h:558: static void ForceFeature(CpuFeature f) {
I am not sure about the future use cases, perhaps some scoped form might be more
appropriate.

[oliv, 2013-09-17 11:30:16]

On 2013/09/16 13:48:05, Sven Panne wrote:
>
https://codereview.chromium.org/23523060/diff/1/src/ia32/assembler-ia32.h#new...
> src/ia32/assembler-ia32.h:558: static void ForceFeature(CpuFeature f) {
> I am not sure about the future use cases, perhaps some scoped form might be
more
> appropriate.

alright, looks much cleaner now.

[Sven Panne, 2013-09-17 12:37:34]

LGTM with a nit.

https://codereview.chromium.org/23523060/diff/6001/src/assembler.cc
File src/assembler.cc (right):

https://codereview.chromium.org/23523060/diff/6001/src/assembler.cc#newcode218
src/assembler.cc:218: CpuFeatures::found_by_runtime_probing_only_ |= mask;
Huh? "... &= ~mask" seems to be more straightforward. In any case, CpuFeatures
should really use EnumSet instead of this bit-fiddling, but that's something for
the future.

[oliv, 2013-09-17 13:01:04]

On 2013/09/17 12:37:34, Sven Panne wrote:
> LGTM with a nit.
> 
> https://codereview.chromium.org/23523060/diff/6001/src/assembler.cc
> File src/assembler.cc (right):
> 
> https://codereview.chromium.org/23523060/diff/6001/src/assembler.cc#newcode218
> src/assembler.cc:218: CpuFeatures::found_by_runtime_probing_only_ |= mask;
> Huh? "... &= ~mask" seems to be more straightforward. In any case, CpuFeatures
> should really use EnumSet instead of this bit-fiddling, but that's something
for
> the future.

omg, we discovered bit-not :/

[oliv, 2013-09-17 13:02:35]

Committed patchset #3 manually as r16772 (presubmit successful).