On Tue, May 6, 2014 at 3:53 AM, Juha-Pekka Heikkila
<juhapekka.heikk...@gmail.com> wrote:
> Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikk...@gmail.com>
> ---
> src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> index d2dc5fa..22ca528 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> @@ -293,10 +293,6 @@ fs_visitor::try_emit_saturate(ir_expression *ir)
> bool
> fs_visitor::try_emit_mad(ir_expression *ir)
> {
> - /* 3-src instructions were introduced in gen6. */
> - if (brw->gen < 6)
> - return false;
> -
> /* MAD can only handle floating-point data. */
> if (ir->type != glsl_type::float_type)
> return false;
> @@ -327,7 +323,16 @@ fs_visitor::try_emit_mad(ir_expression *ir)
> fs_reg src2 = this->result;
>
> this->result = fs_reg(this, ir->type);
> - emit(BRW_OPCODE_MAD, this->result, src0, src1, src2);
> +
> + /* 3-src instructions were introduced in gen6. */
> + if (brw->gen < 6) {
> + fs_reg temp = fs_reg(this, glsl_type::float_type);
> +
> + emit(MUL(temp, src1, src2));
> + emit(ADD(this->result, src0, temp));
> + } else {
> + emit(BRW_OPCODE_MAD, this->result, src0, src1, src2);
> + }
>
> return true;
> }
> --
> 1.8.1.2
try_emit_mad is called every time we visit an add-expression, and on
platforms that don't have MAD it fails and the compiler generates
standard code for the expression tree.
So, if your expression tree was a a multiply-add the compiler will
generate a multiply and an add instruction. Adding code to make
try_emit_mad do that doesn't actually change anything.
I've made a branch that uses the LINE instruction to perform
multiply-adds when the arguments are immediates. Minus the shader size
explosion in unigine tropics, it seems to be a pretty nice
improvement. But the problem with unigine will have to be sorted out
before it can be committed.
Maybe you'd be interested in taking a look at that?
See https://bugs.freedesktop.org/show_bug.cgi?id=77544
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