How to define multiple processor families?

[Xi Ruoyao]

On 2018-05-08 10:17 +0800, Feng Longda wrote:
> This is just for broadwell, but if the processor is skylake or some
> newer type, it can't full use of the processor new microcode.

Jonathan means that if "-march=skylake" has only 0.22% performance
increase than "-march=broadwell", you can just use "-march=broadwell"
happily.

> Does we have better solution for this kind of use case.

The target_clones attribute should work.

> It seems intel ICC provide this kind of solution.

Where?  I can't find that in ICC documentation.

> 2018-05-08 3:26 GMT+08:00 Jonathan Wakely <jwakely.gcc@gmail.com>:
> > On 7 May 2018 at 11:46, Xi Ruoyao wrote:
> > > On 2018-05-07 18:30 +0800, Feng Longda wrote:
> > > > If we set -march/tune to define processor, we can obtain some extra
> > > > performance improvement.
> > > > 
> > > > I want to run my application on different intel processor family, for
> > > > example: broadwell, skylake, haswell, skylake-avx512.
> > > > 
> > > > What should I set? Does It like the following ?
> > > > 
> > > > -march=broadwell   -mtune=intel -mmmx -msse -msse -msse2 -msse3 -mavx
> > > > -mavx2 -mavx=512f -mavx512pf ...
> > > 
> > > No.  Then GCC would use AVX-512, and the program can't run on processors
> > > without AVX-512.  (You'll see "Illegal Instruction - Core Dumped").
> > > 
> > > You should use target_clone attribute.
> > > c.f. https://gcc.gnu.org/onlinedocs/gcc-8.1.0/gcc/Common-Function-Attributes.html
> > 
> > Or just use -march=broadwell and see if the performance is good enough.
-- 
Xi Ruoyao <ryxi@stu.xidian.edu.cn>
School of Aerospace Science and Technology, Xidian University