I haven't really looked at the other patches yet, but the subject of
this one caught my eye.
I'm not sure this is useful. I believe we lower A-B to A+neg(B) for all
architectures. I'm pretty sure we also already have a pass that
converts A+neg(neg(B)) to A+B. Did you write any shaders to try to
tickle this code? What did something like the following produce before
and after this change?
uniform vec4 a;
uniform vec4 b;
void main()
{
gl_Position = a - (-b);
}
For the neg(A)-B case, I think the existing code is better for most
architectures. You end up with a single
ADD r2, -r1, -r0
instruction currently. With this change you would potentially need an
extra move to apply the negation. I believe at least the i965 backend
has a pass to push those negations "down" the tree... effectively
undoing what your pass does. :)
On 07/14/2014 03:22 PM, thomashellan...@gmail.com wrote:
> From: Thomas Helland <thomashellan...@gmail.com>
>
> ...and neg(A) - B == neg(A + B)
>
> Signed-off-by: Thomas Helland <thomashellan...@gmail.com>
> ---
> src/glsl/opt_algebraic.cpp | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
> index 2361d0f..fba9de6 100644
> --- a/src/glsl/opt_algebraic.cpp
> +++ b/src/glsl/opt_algebraic.cpp
> @@ -454,6 +454,12 @@ ir_algebraic_visitor::handle_expression(ir_expression
> *ir)
> /* X - X == 0 */
> if (ir->operands[0]->equals(ir->operands[1]))
> return ir_constant::zero(ir, ir->type);
> + /* A - neg(B) = A + B */
> + if (op_expr[1] && op_expr[1]->operation == ir_unop_neg)
> + return add(ir->operands[0], op_expr[1]->operands[0]);
> + /* neg(A) - B = neg(A + B) */
> + if (op_expr[0] && op_expr[0]->operation == ir_unop_neg)
> + return neg(add(op_expr[0]->operands[0], ir->operands[1]));
> break;
>
> case ir_binop_mul:
>
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