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On 08/29/2011 10:52 AM, Kenneth Graunke wrote:
> From: Bryan Cain <bryanca...@gmail.com>
>
> Using multiply and reciprocal for integer division involves potentially
> lossy floating point conversions. This is okay for older GPUs that
> represent integers as floating point, but undesirable for GPUs with
> native integer division instructions.
>
> TGSI, for example, has UDIV/IDIV instructions for integer division,
> so it makes sense to handle this directly. Likewise for i965.
>
> Signed-off-by: Bryan Cain <bryanca...@gmail.com>
> Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.roman...@intel.com>
> ---
> v3: Check for int/float explicitly, fixing a mistake where div_to_mul_rcp
> would be run on integers when !lowering(INT_DIV_TO_MUL_RCP) and
> lowering(DIV_TO_MUL_RCP).
>
> src/glsl/ir_optimization.h | 13 ++--
> src/glsl/lower_instructions.cpp | 125
> ++++++++++++++++------------
> src/mesa/drivers/dri/i965/brw_shader.cpp | 1 +
> src/mesa/program/ir_to_mesa.cpp | 2 +-
> src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 2 +-
> 5 files changed, 80 insertions(+), 63 deletions(-)
>
> diff --git a/src/glsl/ir_optimization.h b/src/glsl/ir_optimization.h
> index f7808bd..48448d4 100644
> --- a/src/glsl/ir_optimization.h
> +++ b/src/glsl/ir_optimization.h
> @@ -29,12 +29,13 @@
> */
>
> /* Operations for lower_instructions() */
> -#define SUB_TO_ADD_NEG 0x01
> -#define DIV_TO_MUL_RCP 0x02
> -#define EXP_TO_EXP2 0x04
> -#define POW_TO_EXP2 0x08
> -#define LOG_TO_LOG2 0x10
> -#define MOD_TO_FRACT 0x20
> +#define SUB_TO_ADD_NEG 0x01
> +#define DIV_TO_MUL_RCP 0x02
> +#define EXP_TO_EXP2 0x04
> +#define POW_TO_EXP2 0x08
> +#define LOG_TO_LOG2 0x10
> +#define MOD_TO_FRACT 0x20
> +#define INT_DIV_TO_MUL_RCP 0x40
>
> bool do_common_optimization(exec_list *ir, bool linked, unsigned
> max_unroll_iterations);
>
> diff --git a/src/glsl/lower_instructions.cpp b/src/glsl/lower_instructions.cpp
> index 23aa19b..d79eb0a 100644
> --- a/src/glsl/lower_instructions.cpp
> +++ b/src/glsl/lower_instructions.cpp
> @@ -32,6 +32,7 @@
> * Currently supported transformations:
> * - SUB_TO_ADD_NEG
> * - DIV_TO_MUL_RCP
> + * - INT_DIV_TO_MUL_RCP
> * - EXP_TO_EXP2
> * - POW_TO_EXP2
> * - LOG_TO_LOG2
> @@ -47,8 +48,8 @@
> * want to recognize add(op0, neg(op1)) or the other way around to
> * produce a subtract anyway.
> *
> - * DIV_TO_MUL_RCP:
> - * ---------------
> + * DIV_TO_MUL_RCP and INT_DIV_TO_MUL_RCP:
> + * --------------------------------------
> * Breaks an ir_unop_div expression down to op0 * (rcp(op1)).
> *
> * Many GPUs don't have a divide instruction (945 and 965 included),
> @@ -56,6 +57,10 @@
> * reciprocal. By breaking the operation down, constant reciprocals
> * can get constant folded.
> *
> + * DIV_TO_MUL_RCP only lowers floating point division; INT_DIV_TO_MUL_RCP
> + * handles the integer case, converting to and from floating point so that
> + * RCP is possible.
> + *
> * EXP_TO_EXP2 and LOG_TO_LOG2:
> * ----------------------------
> * Many GPUs don't have a base e log or exponent instruction, but they
> @@ -95,6 +100,7 @@ private:
>
> void sub_to_add_neg(ir_expression *);
> void div_to_mul_rcp(ir_expression *);
> + void int_div_to_mul_rcp(ir_expression *);
> void mod_to_fract(ir_expression *);
> void exp_to_exp2(ir_expression *);
> void pow_to_exp2(ir_expression *);
> @@ -127,60 +133,67 @@
> lower_instructions_visitor::sub_to_add_neg(ir_expression *ir)
> void
> lower_instructions_visitor::div_to_mul_rcp(ir_expression *ir)
> {
> - if (!ir->operands[1]->type->is_integer()) {
> - /* New expression for the 1.0 / op1 */
> - ir_rvalue *expr;
> - expr = new(ir) ir_expression(ir_unop_rcp,
> - ir->operands[1]->type,
> - ir->operands[1],
> - NULL);
> -
> - /* op0 / op1 -> op0 * (1.0 / op1) */
> - ir->operation = ir_binop_mul;
> - ir->operands[1] = expr;
> + assert(ir->operands[1]->type->is_float());
> +
> + /* New expression for the 1.0 / op1 */
> + ir_rvalue *expr;
> + expr = new(ir) ir_expression(ir_unop_rcp,
> + ir->operands[1]->type,
> + ir->operands[1]);
> +
> + /* op0 / op1 -> op0 * (1.0 / op1) */
> + ir->operation = ir_binop_mul;
> + ir->operands[1] = expr;
> +
> + this->progress = true;
> +}
> +
> +void
> +lower_instructions_visitor::int_div_to_mul_rcp(ir_expression *ir)
> +{
> + assert(ir->operands[1]->type->is_integer());
> +
> + /* Be careful with integer division -- we need to do it as a
> + * float and re-truncate, since rcp(n > 1) of an integer would
> + * just be 0.
> + */
> + ir_rvalue *op0, *op1;
> + const struct glsl_type *vec_type;
> +
> + vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
> + ir->operands[1]->type->vector_elements,
> + ir->operands[1]->type->matrix_columns);
> +
> + if (ir->operands[1]->type->base_type == GLSL_TYPE_INT)
> + op1 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[1],
> NULL);
> + else
> + op1 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[1],
> NULL);
> +
> + op1 = new(ir) ir_expression(ir_unop_rcp, op1->type, op1, NULL);
> +
> + vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
> + ir->operands[0]->type->vector_elements,
> + ir->operands[0]->type->matrix_columns);
> +
> + if (ir->operands[0]->type->base_type == GLSL_TYPE_INT)
> + op0 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[0],
> NULL);
> + else
> + op0 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[0],
> NULL);
> +
> + vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
> + ir->type->vector_elements,
> + ir->type->matrix_columns);
> +
> + op0 = new(ir) ir_expression(ir_binop_mul, vec_type, op0, op1);
> +
> + if (ir->operands[1]->type->base_type == GLSL_TYPE_INT) {
> + ir->operation = ir_unop_f2i;
> + ir->operands[0] = op0;
> } else {
> - /* Be careful with integer division -- we need to do it as a
> - * float and re-truncate, since rcp(n > 1) of an integer would
> - * just be 0.
> - */
> - ir_rvalue *op0, *op1;
> - const struct glsl_type *vec_type;
> -
> - vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
> - ir->operands[1]->type->vector_elements,
> - ir->operands[1]->type->matrix_columns);
> -
> - if (ir->operands[1]->type->base_type == GLSL_TYPE_INT)
> - op1 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[1],
> NULL);
> - else
> - op1 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[1],
> NULL);
> -
> - op1 = new(ir) ir_expression(ir_unop_rcp, op1->type, op1, NULL);
> -
> - vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
> - ir->operands[0]->type->vector_elements,
> - ir->operands[0]->type->matrix_columns);
> -
> - if (ir->operands[0]->type->base_type == GLSL_TYPE_INT)
> - op0 = new(ir) ir_expression(ir_unop_i2f, vec_type, ir->operands[0],
> NULL);
> - else
> - op0 = new(ir) ir_expression(ir_unop_u2f, vec_type, ir->operands[0],
> NULL);
> -
> - vec_type = glsl_type::get_instance(GLSL_TYPE_FLOAT,
> - ir->type->vector_elements,
> - ir->type->matrix_columns);
> -
> - op0 = new(ir) ir_expression(ir_binop_mul, vec_type, op0, op1);
> -
> - if (ir->operands[1]->type->base_type == GLSL_TYPE_INT) {
> - ir->operation = ir_unop_f2i;
> - ir->operands[0] = op0;
> - } else {
> - ir->operation = ir_unop_i2u;
> - ir->operands[0] = new(ir) ir_expression(ir_unop_f2i, op0);
> - }
> - ir->operands[1] = NULL;
> + ir->operation = ir_unop_i2u;
> + ir->operands[0] = new(ir) ir_expression(ir_unop_f2i, op0);
> }
> + ir->operands[1] = NULL;
>
> this->progress = true;
> }
> @@ -265,7 +278,9 @@ lower_instructions_visitor::visit_leave(ir_expression *ir)
> break;
>
> case ir_binop_div:
> - if (lowering(DIV_TO_MUL_RCP))
> + if (ir->operands[1]->type->is_integer() &&
> lowering(INT_DIV_TO_MUL_RCP))
> + int_div_to_mul_rcp(ir);
> + else if (ir->operands[1]->type->is_float() && lowering(DIV_TO_MUL_RCP))
> div_to_mul_rcp(ir);
> break;
>
> diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp
> b/src/mesa/drivers/dri/i965/brw_shader.cpp
> index 3ff6bba..7e53097 100644
> --- a/src/mesa/drivers/dri/i965/brw_shader.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
> @@ -100,6 +100,7 @@ brw_link_shader(struct gl_context *ctx, struct
> gl_shader_program *prog)
> lower_instructions(shader->ir,
> MOD_TO_FRACT |
> DIV_TO_MUL_RCP |
> + INT_DIV_TO_MUL_RCP |
> SUB_TO_ADD_NEG |
> EXP_TO_EXP2 |
> LOG_TO_LOG2);
> diff --git a/src/mesa/program/ir_to_mesa.cpp b/src/mesa/program/ir_to_mesa.cpp
> index 6820e4c..dd154db 100644
> --- a/src/mesa/program/ir_to_mesa.cpp
> +++ b/src/mesa/program/ir_to_mesa.cpp
> @@ -3232,7 +3232,7 @@ _mesa_ir_link_shader(struct gl_context *ctx, struct
> gl_shader_program *prog)
> /* Lowering */
> do_mat_op_to_vec(ir);
> lower_instructions(ir, (MOD_TO_FRACT | DIV_TO_MUL_RCP | EXP_TO_EXP2
> - | LOG_TO_LOG2
> + | LOG_TO_LOG2 | INT_DIV_TO_MUL_RCP
> | ((options->EmitNoPow) ? POW_TO_EXP2 : 0)));
>
> progress = do_lower_jumps(ir, true, true, options->EmitNoMainReturn,
> options->EmitNoCont, options->EmitNoLoops) || progress;
> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> index 9cac309..ec42742 100644
> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> @@ -5012,7 +5012,7 @@ st_link_shader(struct gl_context *ctx, struct
> gl_shader_program *prog)
> /* Lowering */
> do_mat_op_to_vec(ir);
> lower_instructions(ir, (MOD_TO_FRACT | DIV_TO_MUL_RCP | EXP_TO_EXP2
> - | LOG_TO_LOG2
> + | LOG_TO_LOG2 | INT_DIV_TO_MUL_RCP
> | ((options->EmitNoPow) ? POW_TO_EXP2 : 0)));
>
> progress = do_lower_jumps(ir, true, true,
> options->EmitNoMainReturn, options->EmitNoCont, options->EmitNoLoops) ||
> progress;
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