On Wed, Apr 25, 2012 at 1:24 AM, Alexandre Rames <[email protected]> wrote: > Not using the intrinsic shouldn't make any difference here. > > But __popcnt is the intrinsic, not the instruction. Shouldn't MS compiler > automatically detect hardware support and use another solution if the popcnt > isn't available.
Maybe it should, but it's not what the MSDN page says it does. If it did, this code code would have to check some global flag every time, which would be more expensive than the operation itself, or require some patching in runtime. -- Vitaly > > On Wed, Apr 25, 2012 at 9:22 AM, Florian Schneider <[email protected]> > wrote: >> >> Hm, interesting. I assume that we don't instruct g++ or msvc to generate >> any fancy SSE4.1 instructions anyway because V8 has to run on old non-SSE >> hardware - in which case the benefit of using the compiler intrinsics is >> probably void. >> >> Den 24. apr. 2012 19.20 skrev Vitaly Repeshko <[email protected]>: >> >>> FYI. http://msdn.microsoft.com/en-us/library/bb385231.aspx says "If >>> you run code that uses this intrinsic on hardware that does not >>> support the popcnt instruction, the results are unpredictable." >>> >>> >>> -- Vitaly >>> >>> On Tue, Apr 24, 2012 at 10:03 AM, Florian Schneider >>> <[email protected]> wrote: >>> > You're welcome. The Win32 builder still not happy. I'm not so familiar >>> > with >>> > our Windows buildbot configuration, so I'm fixing it for now by just >>> > avoiding the problematic compiler intrinsic >>> > (http://code.google.com/p/v8/source/detail?r=11428) It should not make >>> > a big >>> > difference, should it? >>> > >>> > >>> > >>> > Den 24. apr. 2012 18.14 skrev Alexandre Rames >>> > <[email protected]>: >>> > >>> >> Thanks! >>> >> >>> >> >>> >> On Tue, Apr 24, 2012 at 4:36 PM, <[email protected]> wrote: >>> >>> >>> >>> Thanks. Still LGTM. >>> >>> >>> >>> I'll re-land it >>> >>> >>> >>> http://codereview.chromium.org/9638018/ >>> >> >>> >> >>> > >>> > -- >>> > v8-dev mailing list >>> > [email protected] >>> > http://groups.google.com/group/v8-dev >>> >>> -- >>> v8-dev mailing list >>> [email protected] >>> http://groups.google.com/group/v8-dev >> >> > > -- > v8-dev mailing list > [email protected] > http://groups.google.com/group/v8-dev -- v8-dev mailing list [email protected] http://groups.google.com/group/v8-dev
