/*
* Copyright © 2010 Intel Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
/**
* \file lower_instructions.cpp
*
* Many GPUs lack native instructions for certain expression operations, and
* must replace them with some other expression tree. This pass lowers some
* of the most common cases, allowing the lowering code to be implemented once
* rather than in each driver backend.
*
* Currently supported transformations:
* - SUB_TO_ADD_NEG
* - DIV_TO_MUL_RCP
* - EXP_TO_EXP2
* - POW_TO_EXP2
* - LOG_TO_LOG2
* - MOD_TO_FRACT
*
* SUB_TO_ADD_NEG:
* ---------------
* Breaks an ir_binop_sub expression down to add(op0, neg(op1))
*
* This simplifies expression reassociation, and for many backends
* there is no subtract operation separate from adding the negation.
* For backends with native subtract operations, they will probably
* want to recognize add(op0, neg(op1)) or the other way around to
* produce a subtract anyway.
*
* 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),
* but they do have an RCP instruction to compute an approximate
* reciprocal. By breaking the operation down, constant reciprocals
* can get constant folded.
*
* EXP_TO_EXP2 and LOG_TO_LOG2:
* ----------------------------
* Many GPUs don't have a base e log or exponent instruction, but they
* do have base 2 versions, so this pass converts exp and log to exp2
* and log2 operations.
*
* POW_TO_EXP2:
* -----------
* Many older GPUs don't have an x**y instruction. For these GPUs, convert
* x**y to 2**(y * log2(x)).
*
* MOD_TO_FRACT:
* -------------
* Breaks an ir_unop_mod expression down to (op1 * fract(op0 / op1))
*
* Many GPUs don't have a MOD instruction (945 and 965 included), and
* if we have to break it down like this anyway, it gives an
* opportunity to do things like constant fold the (1.0 / op1) easily.
*/
#include "main/core.h" /* for M_LOG2E */
#include "glsl_types.h"
#include "ir.h"
#include "ir_optimization.h"
class lower_instructions_visitor : public ir_hierarchical_visitor {
public:
lower_instructions_visitor(unsigned lower)
: progress(false), lower(lower) { }
ir_visitor_status visit_leave(ir_expression *);
bool progress;
private:
unsigned lower; /** Bitfield of which operations to lower */
void sub_to_add_neg(ir_expression *);
void div_to_mul_rcp(ir_expression *);
void mod_to_fract(ir_expression *);
void exp_to_exp2(ir_expression *);
void pow_to_exp2(ir_expression *);
void log_to_log2(ir_expression *);
};
/**
* Determine if a particular type of lowering should occur
*/
#define lowering(x) (this->lower & x)
bool
lower_instructions(exec_list *instructions, unsigned what_to_lower)
{
lower_instructions_visitor v(what_to_lower);
visit_list_elements(&v, instructions);
return v.progress;
}
void
lower_instructions_visitor::sub_to_add_neg(ir_expression *ir)
{
ir->operation = ir_binop_add;
ir->operands[1] = new(ir) ir_expression(ir_unop_neg, ir->operands[1]->type,
ir->operands[1], NULL);
this->progress = true;
}
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;
} 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);
op0 = new(ir) ir_expression(ir_binop_mul, vec_type, op0, op1);
ir->operation = ir_unop_f2i;
ir->operands[0] = op0;
ir->operands[1] = NULL;
}
this->progress = true;
}
void
lower_instructions_visitor::exp_to_exp2(ir_expression *ir)
{
ir_constant *log2_e = new(ir) ir_constant(float(M_LOG2E));
ir->operation = ir_unop_exp2;
ir->operands[0] = new(ir) ir_expression(ir_binop_mul, ir->operands[0]->type,
ir->operands[0], log2_e);
this->progress = true;
}
void
lower_instructions_visitor::pow_to_exp2(ir_expression *ir)
{
ir_expression *const log2_x =
new(ir) ir_expression(ir_unop_log2, ir->operands[0]->type,
ir->operands[0]);
ir->operation = ir_unop_exp2;
ir->operands[0] = new(ir) ir_expression(ir_binop_mul, ir->operands[1]->type,
ir->operands[1], log2_x);
ir->operands[1] = NULL;
this->progress = true;
}
void
lower_instructions_visitor::log_to_log2(ir_expression *ir)
{
ir->operation = ir_binop_mul;
ir->operands[0] = new(ir) ir_expression(ir_unop_log2, ir->operands[0]->type,
ir->operands[0], NULL);
ir->operands[1] = new(ir) ir_constant(float(1.0 / M_LOG2E));
this->progress = true;
}
void
lower_instructions_visitor::mod_to_fract(ir_expression *ir)
{
ir_variable *temp = new(ir) ir_variable(ir->operands[1]->type, "mod_b",
ir_var_temporary);
this->base_ir->insert_before(temp);
ir_assignment *const assign =
new(ir) ir_assignment(new(ir) ir_dereference_variable(temp),
ir->operands[1], NULL);
this->base_ir->insert_before(assign);
ir_expression *const div_expr =
new(ir) ir_expression(ir_binop_div, ir->operands[0]->type,
ir->operands[0],
new(ir) ir_dereference_variable(temp));
/* Don't generate new IR that would need to be lowered in an additional
* pass.
*/
if (lowering(DIV_TO_MUL_RCP))
div_to_mul_rcp(div_expr);
ir_rvalue *expr = new(ir) ir_expression(ir_unop_fract,
ir->operands[0]->type,
div_expr,
NULL);
ir->operation = ir_binop_mul;
ir->operands[0] = new(ir) ir_dereference_variable(temp);
ir->operands[1] = expr;
this->progress = true;
}
ir_visitor_status
lower_instructions_visitor::visit_leave(ir_expression *ir)
{
switch (ir->operation) {
case ir_binop_sub:
if (lowering(SUB_TO_ADD_NEG))
sub_to_add_neg(ir);
break;
case ir_binop_div:
if (lowering(DIV_TO_MUL_RCP))
div_to_mul_rcp(ir);
break;
case ir_unop_exp:
if (lowering(EXP_TO_EXP2))
exp_to_exp2(ir);
break;
case ir_unop_log:
if (lowering(LOG_TO_LOG2))
log_to_log2(ir);
break;
case ir_binop_mod:
if (lowering(MOD_TO_FRACT))
mod_to_fract(ir);
break;
case ir_binop_pow:
if (lowering(POW_TO_EXP2))
pow_to_exp2(ir);
break;
default:
return visit_continue;
}
return visit_continue;
}