Prevent compiling cpu_unittest on i386 (Take 2)....

Prevent compiling cpu_unittest on i386 (Take 2).
This change prevents compiling cpu_unittest on 32-bit GCC since some builders does not compile with SSE support.

TBR=jiesun
BUG=none
TEST=fix build.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=75872

[jiesun, 2011-02-24 17:22:58]

LGTM.
do you happened to know the reason why sse support is disabled on those
builders? posix 32 bits? does  that means on chromeos, all sse2 path is
disabled?...

[Hironori Bono, 2011-02-25 04:50:42]

Greetings,

Thank you for your review. To read "src/build/common.gypi" deeply, it seems SSE2
is disabled only when building Google Chrome on Linux i386 as listed in the
following snippet. So, I should have used GOOGLE_CHROME_BUILD instead of
__x86_64__. (I will create another change to replace it.)

  ['branding=="Chromium" and disable_sse2==0', {
    'cflags': [
      '-march=pentium4',
      '-msse2',
      '-mfpmath=sse',
      ],
    }],
  ...(snip)...
  ['chromeos==1 and disable_sse2==0', {
    'cflags': [
      '-msse2',
    ],
  }],

Regards,

Hironori Bono

[jiesun, 2011-02-25 19:02:50]

from gcc help : "For the i386 compiler, you need to use -march=cpu-type,
-msse or -msse2 switches to enable SSE extensions and make this option
effective.
               For the x86-64 compiler, these extensions are enabled by
default."
so for 64 bits, it could compile always.
for 32 bits, only when chromium or chromeos case, it could compile.
I think for window always accept intrinsics.
evannier@ suggest me to use #if defined __SSE2___ to detect if -msse2 is
passed. http://codereview.chromium.org/6334070/
I thought it maybe cleaner to use this rather than detect chromium and
chrome-os case... otherwise changing gypi file will need to change all the
other places in the code base.
but I had not tried myself.

On Thu, Feb 24, 2011 at 8:50 PM, <hbono@chromium.org> wrote:

> Greetings,
>
> Thank you for your review. To read "src/build/common.gypi" deeply, it seems
> SSE2
> is disabled only when building Google Chrome on Linux i386 as listed in the
> following snippet. So, I should have used GOOGLE_CHROME_BUILD instead of
> __x86_64__. (I will create another change to replace it.)
>
>  ['branding=="Chromium" and disable_sse2==0', {
>    'cflags': [
>      '-march=pentium4',
>      '-msse2',
>      '-mfpmath=sse',
>      ],
>    }],
>  ...(snip)...
>  ['chromeos==1 and disable_sse2==0', {
>    'cflags': [
>      '-msse2',
>    ],
>  }],
>
> Regards,
>
> Hironori Bono
>
>
> http://codereview.chromium.org/6581032/
>