[Mesa-dev] [PATCH 2/2] glsl: Use bitfieldInsert in ldexp() lowering.

[Ian Romanick]

On 01/27/2014 01:02 PM, Matt Turner wrote:
> Shaves a few instructions off of lowered ldexp().
> ---
>  src/glsl/lower_instructions.cpp | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/src/glsl/lower_instructions.cpp b/src/glsl/lower_instructions.cpp
> index 8f8d448..44a6e80 100644
> --- a/src/glsl/lower_instructions.cpp
> +++ b/src/glsl/lower_instructions.cpp
> @@ -384,10 +384,10 @@ lower_instructions_visitor::ldexp_to_arith(ir_expression *ir)
>     /* Constants */
>     ir_constant *zeroi = ir_constant::zero(ir, ivec);
>  
> -   ir_constant *sign_mantissa_mask = new(ir) ir_constant(0x807fffffu, vec_elem);
>     ir_constant *sign_mask = new(ir) ir_constant(0x80000000u, vec_elem);
>  
>     ir_constant *exp_shift = new(ir) ir_constant(23u, vec_elem);
> +   ir_constant *exp_width = new(ir) ir_constant(8u, vec_elem);
>  
>     /* Temporary variables */
>     ir_variable *x = new(ir) ir_variable(ir->type, "x", ir_var_temporary);
> @@ -449,11 +449,17 @@ lower_instructions_visitor::ldexp_to_arith(ir_expression *ir)
>      */
>  
>     ir_constant *exp_shift_clone = exp_shift->clone(ir, NULL);
> -   ir->operation = ir_unop_bitcast_u2f;
> -   ir->operands[0] = bit_or(bit_and(bitcast_f2u(x), sign_mantissa_mask),
> -                            lshift(i2u(resulting_biased_exp), exp_shift_clone));
> +   ir->operation = ir_unop_bitcast_i2f;
> +   ir->operands[0] = bitfield_insert(bitcast_f2i(x), resulting_biased_exp,
> +                                     exp_shift_clone, exp_width);
>     ir->operands[1] = NULL;
>  
> +   /* Don't generate new IR that would need to be lowered in an additional
> +    * pass.
> +    */
> +   if (lowering(BITFIELD_INSERT_TO_BFM_BFI))
> +      bitfield_insert_to_bfm_bfi(ir->operands[0]->as_expression());
> +

I was waffling about ways to do this without as_expression, but meh.

Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>

>     this->progress = true;
>  }
>