[Mesa-dev] [PATCH v2 41/53] intel/compiler: assert that lower conversions produces valid strides

[Pohjolainen, Topi]

Subject reads a little odd, maybe just: "assert strides in conversion
lowering". The assert itself seems useful:

Reviewed-by: Topi Pohjolainen <topi.pohjolainen at intel.com>

On Wed, Dec 19, 2018 at 12:51:09PM +0100, Iago Toral Quiroga wrote:
> The hardware only has two bits to specify the horizontal stride, so the
> maximum horizontal stride we can use is 4. The pass calculates strides
> based on the sizes of the types involved, and for conversions between
> 64-bit and 8-bit types that can lead to strides of 8.
> 
> The compiler should make sure that such conversions are handled in two
> steps to avoid that situation. If we fail to do this properly, the
> generated assembly will be invalid and validation will fail, but
> asserting here makes debugging easier.
> ---
>  src/intel/compiler/brw_fs_lower_conversions.cpp | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/src/intel/compiler/brw_fs_lower_conversions.cpp b/src/intel/compiler/brw_fs_lower_conversions.cpp
> index 145fb55f995..00781e824e8 100644
> --- a/src/intel/compiler/brw_fs_lower_conversions.cpp
> +++ b/src/intel/compiler/brw_fs_lower_conversions.cpp
> @@ -90,6 +90,13 @@ fs_visitor::lower_conversions()
>              fs_reg temp = ibld.vgrf(get_exec_type(inst));
>              fs_reg strided_temp = subscript(temp, dst.type, 0);
>  
> +            /* Make sure we don't exceed hardware limits here. If we have code
> +             * that hits this assertion it means that we need to split the
> +             * instruction in two, using intermediary types (see for
> +             * example nir_op_i2i8).
> +             */
> +            assert(strided_temp.stride <= 4);
> +
>              assert(inst->size_written == inst->dst.component_size(inst->exec_size));
>              inst->dst = strided_temp;
>              inst->saturate = false;
> -- 
> 2.17.1
> 
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