This thing has been trouble since I wrote it. Nice to see it go.
Both patches are:
Reviewed-by: Chris Forbes <chrisf at ijw.co.nz>
On May 30, 2015 6:28 AM, "Matt Turner" <mattst88 at gmail.com> wrote:
> On Fri, May 29, 2015 at 6:53 AM, Neil Roberts <neil at linux.intel.com>
> wrote:
> > Previously when generating the send instruction for a sample
> > instruction with an indirect sampler it would use the destination
> > register as a temporary store. This breaks when used in combination
> > with the opt_sampler_eot optimisation because that forces the
> > destination to be null. This patch fixes that by avoiding the temp
> > register altogether.
> >
> > The reason the temporary register was needed was because it was trying
> > to ensure the binding table index doesn't overflow a byte by and'ing
> > it with 0xff. The result is then or'd with samper_index<<8. This patch
> > instead just and's the whole thing by 0xfff. This will ensure that a
> > bogus sampler index won't overflow into the rest of the message
> > descriptor but unlike the previous code it won't ensure that the
> > binding table index doesn't overflow into the sampler index. It
> > doesn't seem like that should matter very much though because if the
> > shader is generating a bogus sampler index then it's going to just get
> > garbage out either way.
> >
> > Instead of doing sampler_index<<8|(sampler_index+base_table_index) the
> > new code avoids one operation by doing
> > sampler_index*0x101+base_table_index which should be equivalent.
> > However if we wanted to avoid the multiply for some reason we could do
> > this by adding an extra or instruction still without needing the
> > temporary register.
> >
> > This fixes a number of Piglit tests on Skylake that were using
> > indirect samplers such as:
> >
> > spec at arb_gpu_shader5@execution at sampler_array_indexing@fs-simple
> > ---
> > src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 17 ++++-------------
> > src/mesa/drivers/dri/i965/brw_vec4_generator.cpp | 16 ++++------------
> > 2 files changed, 8 insertions(+), 25 deletions(-)
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> > index 0be0f86..ea46b1a 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> > @@ -779,27 +779,18 @@ fs_generator::generate_tex(fs_inst *inst, struct
> brw_reg dst, struct brw_reg src
> > brw_mark_surface_used(prog_data, sampler +
> base_binding_table_index);
> > } else {
> > /* Non-const sampler index */
> > - /* Note: this clobbers `dst` as a temporary before emitting the
> send */
> >
> > struct brw_reg addr = vec1(retype(brw_address_reg(0),
> BRW_REGISTER_TYPE_UD));
> > - struct brw_reg temp = vec1(retype(dst, BRW_REGISTER_TYPE_UD));
> > -
> > struct brw_reg sampler_reg = vec1(retype(sampler_index,
> BRW_REGISTER_TYPE_UD));
> >
> > brw_push_insn_state(p);
> > brw_set_default_mask_control(p, BRW_MASK_DISABLE);
> > brw_set_default_access_mode(p, BRW_ALIGN_1);
> >
> > - /* Some care required: `sampler` and `temp` may alias:
> > - * addr = sampler & 0xff
> > - * temp = (sampler << 8) & 0xf00
> > - * addr = addr | temp
> > - */
> > - brw_ADD(p, addr, sampler_reg,
> brw_imm_ud(base_binding_table_index));
> > - brw_SHL(p, temp, sampler_reg, brw_imm_ud(8u));
> > - brw_AND(p, temp, temp, brw_imm_ud(0x0f00));
> > - brw_AND(p, addr, addr, brw_imm_ud(0x0ff));
> > - brw_OR(p, addr, addr, temp);
> > + /* addr = ((sampler * 0x101) + base_binding_table_index) & 0xfff
> */
> > + brw_MUL(p, addr, sampler_reg, brw_imm_ud(0x101));
> > + brw_ADD(p, addr, addr, brw_imm_ud(base_binding_table_index));
> > + brw_AND(p, addr, addr, brw_imm_ud(0xfff));
> >
> > brw_pop_insn_state(p);
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
> b/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
> > index 20d096c..1d3f5ed 100644
> > --- a/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
> > @@ -398,10 +398,8 @@ vec4_generator::generate_tex(vec4_instruction *inst,
> > brw_mark_surface_used(&prog_data->base, sampler +
> base_binding_table_index);
> > } else {
> > /* Non-constant sampler index. */
> > - /* Note: this clobbers `dst` as a temporary before emitting the
> send */
> >
> > struct brw_reg addr = vec1(retype(brw_address_reg(0),
> BRW_REGISTER_TYPE_UD));
> > - struct brw_reg temp = vec1(retype(dst, BRW_REGISTER_TYPE_UD));
> >
>
> I'd delete the blank line here as well to match the fs code.
>
> Really nice solution. I'd been trying to figure out the best way to
> get an additional temporary in here, but this is clearly better.
>
> Reviewed-by: Matt Turner <mattst88 at gmail.com>
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