[turbofan] Add support for overflow add/sub to the MachineOperatorReducer.

[turbofan] Add support for overflow add/sub to the MachineOperatorReducer.

TEST=base-unittests,compiler-unittests,cctest
R=svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=23809

[Benedikt Meurer, 2014-09-09 13:03:03]

PTAL

[Sven Panne, 2014-09-09 13:10:49]

LGTM with a nit

https://codereview.chromium.org/555833002/diff/20001/src/base/bits.h
File src/base/bits.h (right):

https://codereview.chromium.org/555833002/diff/20001/src/base/bits.h#newcode128
src/base/bits.h:128: return (((res ^ lhs) & (res ^ rhs)) >> 31) & 1;
I think that

   return (((res ^ lhs) & (res ^ rhs) & (1U << 31)) != 0;

is a bit clearer and involves no implicit conversion, similar below.

[Benedikt Meurer, 2014-09-09 14:15:23]

https://codereview.chromium.org/555833002/diff/20001/src/base/bits.h
File src/base/bits.h (right):

https://codereview.chromium.org/555833002/diff/20001/src/base/bits.h#newcode128
src/base/bits.h:128: return (((res ^ lhs) & (res ^ rhs)) >> 31) & 1;
On 2014/09/09 13:10:48, Sven Panne wrote:
> I think that
> 
>    return (((res ^ lhs) & (res ^ rhs) & (1U << 31)) != 0;
> 
> is a bit clearer and involves no implicit conversion, similar below.

Done.

[Benedikt Meurer, 2014-09-09 14:18:28]

Committed patchset #3 (id:40001) manually as 23809 (presubmit successful).