[Mesa-dev] [PATCH 2/2] i965/vec4: Clamp indirect tes input array reads with 0x0fffffff

[Ian Romanick]

On 08/29/2018 02:22 PM, Jason Ekstrand wrote:
> Have you seen this cause an actual problem?  There's no way we can
> actually end up with an input array that big...  I guess this is for the
> crazy OOB case?

The array can't be that big due to other compiler limits.  This is just
to prevent a garbage index from being used.  If the previous patch is
reverted, the test case mentioned in that patch will have this problem
because the index will be negative.

> On Wed, Aug 29, 2018 at 3:12 PM Ian Romanick <idr at freedesktop.org
> <mailto:idr at freedesktop.org>> wrote:
> 
>     From: Ian Romanick <ian.d.romanick at intel.com
>     <mailto:ian.d.romanick at intel.com>>
> 
>     Page 190 of "Volume 7: 3D Media GPGPU Engine (Haswell)" says the valid
>     range of the offset is [0, 0FFFFFFFh].
> 
>     Signed-off-by: Ian Romanick <ian.d.romanick at intel.com
>     <mailto:ian.d.romanick at intel.com>>
>     Cc: mesa-stable at lists.freedesktop.org
>     <mailto:mesa-stable at lists.freedesktop.org>
>     Cc: Kenneth Graunke <kenneth at whitecape.org
>     <mailto:kenneth at whitecape.org>>
>     ---
>      src/intel/compiler/brw_vec4_tes.cpp | 12 +++++++++++-
>      1 file changed, 11 insertions(+), 1 deletion(-)
> 
>     diff --git a/src/intel/compiler/brw_vec4_tes.cpp
>     b/src/intel/compiler/brw_vec4_tes.cpp
>     index 35aff0f4b78..cf1bff42aa9 100644
>     --- a/src/intel/compiler/brw_vec4_tes.cpp
>     +++ b/src/intel/compiler/brw_vec4_tes.cpp
>     @@ -185,9 +185,19 @@
>     vec4_tes_visitor::nir_emit_intrinsic(nir_intrinsic_instr *instr)
>               first_component /= 2;
> 
>            if (indirect_offset.file != BAD_FILE) {
>     +         src_reg clamped_indirect_offset = src_reg(this,
>     glsl_type::uvec4_type);
>     +
>     +         /* Page 190 of "Volume 7: 3D Media GPGPU Engine (Haswell)"
>     says the
>     +          * valid range of the offset is [0, 0FFFFFFFh].
>     +          */
>     +         emit_minmax(BRW_CONDITIONAL_L,
>     +                     dst_reg(clamped_indirect_offset),
>     +                     retype(indirect_offset, BRW_REGISTER_TYPE_UD),
>     +                     brw_imm_ud(0x0fffffffu));
>     +
>               header = src_reg(this, glsl_type::uvec4_type);
>               emit(TES_OPCODE_ADD_INDIRECT_URB_OFFSET, dst_reg(header),
>     -              input_read_header, indirect_offset);
>     +              input_read_header, clamped_indirect_offset);
>            } else {
>               /* Arbitrarily only push up to 24 vec4 slots worth of data,
>                * which is 12 registers (since each holds 2 vec4 slots).
>     -- 
>     2.14.4
> 
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