[Mesa-dev] [PATCH] i965/fs: retype offset_reg to UD at load_ssbo

[Ian Romanick]

On 04/18/2018 01:57 PM, Jose Maria Casanova Crespo wrote:
> All operations with offset_reg at do_vector_read are done
> with UD type. So copy propagation was not working through
> the generated MOVs:
> 
> mov(8) vgrf9:UD, vgrf7:D

I have noticed other cases of this.  Copy propagation doesn't work
across moves that change the type because int->float and float->int
actually change the bit pattern.  unsigned->signed doesn't do anything,
so it seems like we should allow that case.  This is a few steps down on
my to-do list, but if someone else gets to it first...

> This change allows removing the MOV generated for reading the
> first components for 16-bit and 64-bit ssbo reads with
> non-constant offsets.
> ---
>  src/intel/compiler/brw_fs_nir.cpp | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/intel/compiler/brw_fs_nir.cpp b/src/intel/compiler/brw_fs_nir.cpp
> index 6c4bcd1c113..0ebaab96634 100644
> --- a/src/intel/compiler/brw_fs_nir.cpp
> +++ b/src/intel/compiler/brw_fs_nir.cpp
> @@ -4142,7 +4142,7 @@ fs_visitor::nir_emit_intrinsic(const fs_builder &bld, nir_intrinsic_instr *instr
>        if (const_offset) {
>           offset_reg = brw_imm_ud(const_offset->u32[0]);
>        } else {
> -         offset_reg = get_nir_src(instr->src[1]);
> +         offset_reg = retype(get_nir_src(instr->src[1]), BRW_REGISTER_TYPE_UD);
>        }
>  
>        /* Read the vector */
>