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/*

 * 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

 * - INT_DIV_TO_MUL_RCP

 * - EXP_TO_EXP2

 * - POW_TO_EXP2

 * - LOG_TO_LOG2

 * - MOD_TO_FRACT

 * - LRP_TO_ARITH

 * - BITFIELD_INSERT_TO_BFM_BFI

 *

 * 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 and INT_DIV_TO_MUL_RCP:

 * --------------------------------------

 * Breaks an ir_binop_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.

 *

 * 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

 * 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_binop_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.

 *

 * LRP_TO_ARITH:

 * -------------

 * Converts ir_triop_lrp to (op0 * (1.0f - op2)) + (op1 * op2).

 *

 * BITFIELD_INSERT_TO_BFM_BFI:

 * ---------------------------

 * Breaks ir_quadop_bitfield_insert into ir_binop_bfm (bitfield mask) and

 * ir_triop_bfi (bitfield insert).

 *

 * Many GPUs implement the bitfieldInsert() built-in from ARB_gpu_shader_5

 * with a pair of instructions.

 *

 */

#include "main/core.h" /* for M_LOG2E */

#include "glsl_types.h"

#include "ir.h"

#include "ir_builder.h"

#include "ir_optimization.h"

using namespace ir_builder;

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 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 *);

   void log_to_log2(ir_expression *);

   void lrp_to_arith(ir_expression *);

   void bitfield_insert_to_bfm_bfi(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)

{

   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 {

      ir->operation = ir_unop_i2u;

      ir->operands[0] = new(ir) ir_expression(ir_unop_f2i, 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;

}

void

lower_instructions_visitor::lrp_to_arith(ir_expression *ir)

{

   /* (lrp x y a) -> x*(1-a) + y*a */

   /* Save op2 */

   ir_variable *temp = new(ir) ir_variable(ir->operands[2]->type, "lrp_factor",

					   ir_var_temporary);

   this->base_ir->insert_before(temp);

   this->base_ir->insert_before(assign(temp, ir->operands[2]));

   ir_constant *one = new(ir) ir_constant(1.0f);

   ir->operation = ir_binop_add;

   ir->operands[0] = mul(ir->operands[0], sub(one, temp));

   ir->operands[1] = mul(ir->operands[1], temp);

   ir->operands[2] = NULL;

   this->progress = true;

}

void

lower_instructions_visitor::bitfield_insert_to_bfm_bfi(ir_expression *ir)

{

   /* Translates

    *    ir_quadop_bitfield_insert base insert offset bits

    * into

    *    ir_triop_bfi (ir_binop_bfm bits offset) insert base

    */

   ir_rvalue *base_expr = ir->operands[0];

   ir->operation = ir_triop_bfi;

   ir->operands[0] = new(ir) ir_expression(ir_binop_bfm,

                                           ir->type->get_base_type(),

                                           ir->operands[3],

                                           ir->operands[2]);

   /* ir->operands[1] is still the value to insert. */

   ir->operands[2] = base_expr;

   ir->operands[3] = NULL;

   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 (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;

   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) && ir->type->is_float())

	 mod_to_fract(ir);

      break;

   case ir_binop_pow:

      if (lowering(POW_TO_EXP2))

	 pow_to_exp2(ir);

      break;

   case ir_triop_lrp:

      if (lowering(LRP_TO_ARITH))

	 lrp_to_arith(ir);

      break;

   case ir_quadop_bitfield_insert:

      if (lowering(BITFIELD_INSERT_TO_BFM_BFI))

         bitfield_insert_to_bfm_bfi(ir);

      break;

   default:

      return visit_continue;

   }

   return visit_continue;

}