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/*
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 * Copyright © 2010 Intel Corporation
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 *
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 * Permission is hereby granted, free of charge, to any person obtaining a
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 * copy of this software and associated documentation files (the "Software"),
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 * to deal in the Software without restriction, including without limitation
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 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
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 * and/or sell copies of the Software, and to permit persons to whom the
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 * Software is furnished to do so, subject to the following conditions:
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 *
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 * The above copyright notice and this permission notice (including the next
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 * paragraph) shall be included in all copies or substantial portions of the
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 * Software.
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 *
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 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
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 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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 * DEALINGS IN THE SOFTWARE.
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 */
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/**
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 * \file opt_constant_folding.cpp
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 * Replace constant-valued expressions with references to constant values.
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 */
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#include "ir.h"
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#include "ir_visitor.h"
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#include "ir_rvalue_visitor.h"
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#include "ir_optimization.h"
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#include "glsl_types.h"
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namespace {
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/**
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 * Visitor class for replacing expressions with ir_constant values.
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 */
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class ir_constant_folding_visitor : public ir_rvalue_visitor {
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public:
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   ir_constant_folding_visitor()
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   {
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      this->progress = false;
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   }
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   virtual ~ir_constant_folding_visitor()
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   {
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      /* empty */
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   }
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   virtual ir_visitor_status visit_enter(ir_assignment *ir);
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   virtual ir_visitor_status visit_enter(ir_call *ir);
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   virtual void handle_rvalue(ir_rvalue **rvalue);
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   bool progress;
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};
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} /* unnamed namespace */
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void
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ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
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{
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   if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
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      return;
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   /* Note that we do rvalue visitoring on leaving.  So if an
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    * expression has a non-constant operand, no need to go looking
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    * down it to find if it's constant.  This cuts the time of this
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    * pass down drastically.
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    */
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   ir_expression *expr = (*rvalue)->as_expression();
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   if (expr) {
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      for (unsigned int i = 0; i < expr->get_num_operands(); i++) {
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	 if (!expr->operands[i]->as_constant())
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	    return;
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      }
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   }
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   ir_constant *constant = (*rvalue)->constant_expression_value();
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   if (constant) {
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      *rvalue = constant;
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      this->progress = true;
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   } else {
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      (*rvalue)->accept(this);
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   }
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}
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ir_visitor_status
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ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
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{
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   ir->rhs->accept(this);
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   handle_rvalue(&ir->rhs);
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   if (ir->condition) {
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      ir->condition->accept(this);
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      handle_rvalue(&ir->condition);
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      ir_constant *const_val = ir->condition->as_constant();
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      /* If the condition is constant, either remove the condition or
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       * remove the never-executed assignment.
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       */
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      if (const_val) {
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	 if (const_val->value.b[0])
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	    ir->condition = NULL;
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	 else
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	    ir->remove();
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	 this->progress = true;
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      }
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   }
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   /* Don't descend into the LHS because we want it to stay as a
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    * variable dereference.  FINISHME: We probably should to get array
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    * indices though.
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    */
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   return visit_continue_with_parent;
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}
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ir_visitor_status
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ir_constant_folding_visitor::visit_enter(ir_call *ir)
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{
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   /* Attempt to constant fold parameters */
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   exec_list_iterator sig_iter = ir->callee->parameters.iterator();
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   foreach_iter(exec_list_iterator, iter, *ir) {
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      ir_rvalue *param_rval = (ir_rvalue *)iter.get();
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      ir_variable *sig_param = (ir_variable *)sig_iter.get();
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      if (sig_param->mode == ir_var_function_in
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          || sig_param->mode == ir_var_const_in) {
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	 ir_rvalue *new_param = param_rval;
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	 handle_rvalue(&new_param);
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	 if (new_param != param_rval) {
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	    param_rval->replace_with(new_param);
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	 }
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      }
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      sig_iter.next();
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   }
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   /* Next, see if the call can be replaced with an assignment of a constant */
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   ir_constant *const_val = ir->constant_expression_value();
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   if (const_val != NULL) {
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      ir_assignment *assignment =
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	 new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
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      ir->replace_with(assignment);
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   }
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   return visit_continue_with_parent;
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}
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bool
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do_constant_folding(exec_list *instructions)
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{
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   ir_constant_folding_visitor constant_folding;
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   visit_list_elements(&constant_folding, instructions);
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   return constant_folding.progress;
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}