[Mesa-dev] [Mesa-stable] [PATCH v2] llvmpipe: disable vsx in ppc due to LLVM PPC bug

[Jan Vesely]

On Tue, Nov 17, 2015 at 12:37 PM, Oded Gabbay <oded.gabbay at gmail.com> wrote:

> On Tue, Nov 17, 2015 at 6:15 PM, Emil Velikov <emil.l.velikov at gmail.com>
> wrote:
> > On 17 November 2015 at 16:02, Oded Gabbay <oded.gabbay at gmail.com> wrote:
> >> This patch makes sure that if we use altivec (VMX) instructions, we
> don't
> >> use VSX instructions as well, as this cause piglit tests to fail
> >>
> >> For more details, see: https://llvm.org/bugs/show_bug.cgi?id=25503#c7
> >>
> >> With this patch, ppc64le reaches parity with x86-64 as far as piglit
> test
> >> suite is concerned.
> >>
> >> v2:
> >> - Added check that we have at least LLVM 3.4
> >> - Added the LLVM bug URL as a comment in the code
> >>
> >> Signed-off-by: Oded Gabbay <oded.gabbay at gmail.com>
> >> Cc: "11.0" <mesa-stable at lists.freedesktop.org>
> >> ---
> >>  src/gallium/auxiliary/gallivm/lp_bld_misc.cpp | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
> b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
> >> index 7bda118..152593a 100644
> >> --- a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
> >> +++ b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
> >> @@ -536,6 +536,10 @@
> lp_build_create_jit_compiler_for_module(LLVMExecutionEngineRef *OutJIT,
> >>
> >>  #if defined(PIPE_ARCH_PPC)
> >>     MAttrs.push_back(util_cpu_caps.has_altivec ? "+altivec" :
> "-altivec");
> >> +#if HAVE_LLVM >= 0x0304
> >> +   /* See LLVM bug https://llvm.org/bugs/show_bug.cgi?id=25503#c7 */
> >> +   MAttrs.push_back("-vsx");
> > The commit message does not reflect what the patch actually does. I
> > cannot object against the patch in any way, although the two should be
> > in sync imho.
> >
> > Base of a very quick look at the llvm bug, I'm leaning that the commit
> > msg is correct and the patch is off ?
> >
> > Thanks
> > Emil
>
> Hmm, I'm not sure I understand what you mean.
>
> The commit message says: "This patch makes sure that if we use altivec
> (VMX) instructions, we don't
> use VSX instructions as well, as this cause piglit tests to fail"
>
> And the patch itself disables the VSX attribute in LLVM backend in
> case we use Altivec (VMX) - meaning that no VSX instructions will be
> generated alongside Altivec instructions.
>
> So unless I completely misunderstood something, the commit message and
> the patch match.
>

sorry to meddle. the commit message suggests that you only want to disable
vsx if altivec is enabled. However, the patch adds -vsx unconditionally. Do
you want to ever have "-altivec -vsx"?

Jan


>
> The llvm bug description maybe a little misleading, because I started
> it last week and then I had a different impression. But that's why I
> pointed to comment #7 which is where I wrote the updated description,
> which matches this patch (workaround).
>
>       Oded
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