[Mesa-dev] [PATCH 03/10] intel/fs: Fix bug in lower_simd_width while splitting an instruction which was already split.

[Francisco Jerez]

Iago Toral <itoral at igalia.com> writes:

> On Mon, 2019-01-07 at 11:58 -0800, Francisco Jerez wrote:
>> Iago Toral <itoral at igalia.com> writes:
>> 
>> > On Sat, 2018-12-29 at 12:38 -0800, Francisco Jerez wrote:
>> > > This seems to be a problem in combination with the
>> > > lower_regioning
>> > > pass introduced by a future commit, which can modify a SIMD-split
>> > > instruction causing its execution size to become illegal
>> > > again.  A
>> > > subsequent call to lower_simd_width() would hit this bug on a
>> > > future
>> > > platform.
>> > > 
>> > > Cc: mesa-stable at lists.freedesktop.org
>> > > ---
>> > >  src/intel/compiler/brw_fs.cpp | 4 ++--
>> > >  1 file changed, 2 insertions(+), 2 deletions(-)
>> > > 
>> > > diff --git a/src/intel/compiler/brw_fs.cpp
>> > > b/src/intel/compiler/brw_fs.cpp
>> > > index 97544fdf465..4aacc72a1b7 100644
>> > > --- a/src/intel/compiler/brw_fs.cpp
>> > > +++ b/src/intel/compiler/brw_fs.cpp
>> > > @@ -5666,7 +5666,7 @@ static fs_reg
>> > >  emit_unzip(const fs_builder &lbld, fs_inst *inst, unsigned i)
>> > >  {
>> > >     /* Specified channel group from the source region. */
>> > > -   const fs_reg src = horiz_offset(inst->src[i], lbld.group());
>> > > +   const fs_reg src = horiz_offset(inst->src[i], lbld.group() -
>> > > inst->group);
>> > 
>> > Should we assert that lbld.group >= inst->group? Same below.
>> > 
>> 
>> The IR will fail validation anytime that's not the case.  But I can
>> add
>> the assertions in both places if that makes you feel more
>> comfortable.
>
> I guess you are referring to this assert at codegen time:
>
> assert(inst->force_writemask_all || inst->group % inst->exec_size ==
> 0);
>
> I guess that is probably enough, but I would still prefer to add the
> asserts here too if that's okay.
>

Nah, I was thinking of the i965 IR validator that checks for
out-of-bounds VGRF register accesses.  But the asserts would be more
strict -- Just added them locally.

Thanks!

>> > >     if (needs_src_copy(lbld, inst, i)) {
>> > >        /* Builder of the right width to perform the copy avoiding
>> > > uninitialized
>> > > @@ -5757,7 +5757,7 @@ emit_zip(const fs_builder &lbld_before,
>> > > const
>> > > fs_builder &lbld_after,
>> > >     assert(lbld_before.group() == lbld_after.group());
>> > >  
>> > >     /* Specified channel group from the destination region. */
>> > > -   const fs_reg dst = horiz_offset(inst->dst,
>> > > lbld_after.group());
>> > > +   const fs_reg dst = horiz_offset(inst->dst, lbld_after.group()
>> > > -
>> > > inst->group);
>> > >     const unsigned dst_size = inst->size_written /
>> > >        inst->dst.component_size(inst->exec_size);
>> > >  
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