On Wed, Mar 20, 2013 at 12:06 PM, Pekka Jääskeläinen <
[email protected]> wrote:
> On 03/20/2013 05:49 PM, Erik Schnetter wrote:
>
> With gcc, memcpy is completely optimized away. With clang as well -- I
>> am using memcpy internally e.g. to convert doubles into integers to
>> access certain bits, and this translates to no instruction at all,
>> things are just kept in the same register. I would therefore hope that
>> the pocl->vecmathlib transition would be similarly ideal.
>>
>
> Let's hope so. Anyways, the generic type version is useful to ensure
> portability to other targets. Afterall, the most important thing is to
> have an inlineable math library. Other optimizations are secondary
> at this point.
>
> I cannot compile vecmathlib separately to produce the 'test' binary:
>
> [ 2%] Building CXX object CMakeFiles/bench.dir/bench.cc.**o
> make[2]: clang++-mp-3.3: Command not found
> make[2]: *** [CMakeFiles/bench.dir/bench.**cc.o] Error 127
> make[1]: *** [CMakeFiles/bench.dir/all] Error 2
>
There is a file CMakeLists.txt that hard-codes (didn't use autoconf here)
the clang compiler name and compiler options. If you modify these manually,
you should be able to build.
> But I know it uses the SSE2 optimized header as I inserted an
> #warning there where it includes them. I do not have AVX.
>
> cat /proc/cpuinfo
> ...
> flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
> cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx
> rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology
> nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2
> ssse3 cx16 xtpr pdcm sse4_1 sse4_2 popcnt aes lahf_lm ida arat dtherm
> tpr_shadow vnmi flexpriority ept vpid
On this system, round() should translate to a single machine instruction.
With optimization, clang should inline all function calls, and there should
not be a long string of calls.
I'm continuing to investigate.
-erik
--
Erik Schnetter <[email protected]>
http://www.perimeterinstitute.ca/personal/eschnetter/
AIM: eschnett247, Skype: eschnett, Google Talk: [email protected]
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