[Mesa-dev] [PATCH] glsl: skip mul by zero opt for floating point expression

[Ilia Mirkin]

On Mon, Jul 2, 2018 at 11:22 AM, vadym.shovkoplias
<vadim.shovkoplias at gmail.com> wrote:
> From: Vadym Shovkoplias <vadym.shovkoplias at globallogic.com>
>
> One of the operands can be NaN and multiplication by zero
> should also result to NaN value. E.g:

See my comment in https://bugs.freedesktop.org/show_bug.cgi?id=107089#c1

>
> float Temp = 0.0;
> void main()
> {
>         Temp = log2(Temp);
>         Temp = Temp * 0.0;
>         isnan(Temp);
>         ...
> }
>
> here Temp should be NaN and isnan() should return true.
>
> Signed-off-by: Vadym Shovkoplias <vadym.shovkoplias at globallogic.com>
> ---
>  src/compiler/glsl/opt_algebraic.cpp | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/src/compiler/glsl/opt_algebraic.cpp b/src/compiler/glsl/opt_algebraic.cpp
> index ff4be26957..2d01575bb3 100644
> --- a/src/compiler/glsl/opt_algebraic.cpp
> +++ b/src/compiler/glsl/opt_algebraic.cpp
> @@ -590,7 +590,8 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
>        if (is_vec_one(op_const[1]))
>          return ir->operands[0];
>
> -      if (is_vec_zero(op_const[0]) || is_vec_zero(op_const[1]))
> +      if ((is_vec_zero(op_const[0]) || is_vec_zero(op_const[1])) &&
> +       !ir->type->is_float() && !ir->type->is_double())
>          return ir_constant::zero(ir, ir->type);
>
>        if (is_vec_negative_one(op_const[0]))
> --
> 2.18.0
>
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