[Mesa-dev] [PATCH] state_tracker: Fix bug in conditional discards with native ints.

[Brian Paul]

On 09/03/2014 03:04 PM, Eric Anholt wrote:
> A bool is 0 or ~0, and KILL_IF takes a float arg that's <0 for discard or
>> = 0 for not.  By negating it, we ended up doing a floating point subtract
> of (0 - ~0), which ended up as an inf.  To make this actually work, we
> need to convert the bool to a float.
> ---
>   src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> index dd9c84f..62e4101 100644
> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> @@ -3091,8 +3091,18 @@ glsl_to_tgsi_visitor::visit(ir_discard *ir)
>   {
>      if (ir->condition) {
>         ir->condition->accept(this);
> -      this->result.negate = ~this->result.negate;
> -      emit(ir, TGSI_OPCODE_KILL_IF, undef_dst, this->result);
> +      st_src_reg condition = this->result;
> +
> +      /* Convert the bool condition to a float so we can negate. */
> +      if (native_integers) {
> +         st_src_reg temp = get_temp(ir->condition->type);
> +         emit(ir, TGSI_OPCODE_AND, st_dst_reg(temp),
> +              condition, st_src_reg_for_float(1.0));
> +         condition = temp;
> +      }
> +
> +      condition.negate = ~condition.negate;
> +      emit(ir, TGSI_OPCODE_KILL_IF, undef_dst, condition);
>      } else {
>         /* unconditional kil */
>         emit(ir, TGSI_OPCODE_KILL);
>

Reviewed-by: Brian Paul <brianp at vmware.com>

Tag for stable branches?