On Thu, Nov 17, 2016 at 12:03:18AM +0100, Thomas Koenig wrote:
> >Don't you need to test in configure if the assembler supports AVX?
> >Otherwise if somebody is bootstrapping gcc with older assembler, it will
> >just fail to bootstrap.
>
> That's a good point. The AVX instructions were added in binutils 2.19,
> which was released in 2011. This could be put in the prerequisites.
>
> What should the test do? Fail with an error message "you need newer
> binutils" or simply (and silently) not compile the AVX vesion?
>From what I understood, you want those functions just to be implementation
details, not exported from libgfortran.so*. Thus the test would do
something similar to what gcc/testsuite/lib/target-supports.exp
(check_effective_target_avx)
does, but of course in autoconf way, not in tcl.
Also, from what I see, target_clones just use IFUNCs, so you probably also
need some configure test whether ifuncs are supported (the
gcc.target/i386/mvc* tests use dg-require-ifunc, so you'd need something
similar again in configure. But if so, then I have no idea why you use
a wrapper around the function, instead of using it on the exported APIs.
> >For matmul_i*, wouldn't it make more sense to use avx2 instead of avx,
> >or both avx and avx2 and maybe avx512f?
>
> I did a vdiff of the disassembled code generated or avx and avx2, and
> (somewhat to my surprise) there was no difference. Maybe, with more
> unrolling, something more might have happened. I didn't check for
> AVX512f, but I can do that.
For the float/double code it wouldn't surprise me (assuming you don't need
gather insns and similar stuff). But for integers generally most of the
avx instructions can only handle 128-bit vectors, while avx2 has 256-bit
ones.
Jakub
