text: /*
   * 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
   *
   * 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).
   */
  
  #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 *);
  };
  
  /**
   * 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, precision_from_ir(ir->operands[1]));
     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, precision_from_ir(ir->operands[2]));
     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;
  }
  
  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;
  
     default:
        return visit_continue;
     }
  
     return visit_continue;
  }
  