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/*

 * Copyright © 2010 Intel Corporation

 *

 * Permission is hereby granted, free of charge, to any person obtaining a

 * constant of this software and associated documentation files (the "Software"),

 * to deal in the Software without restriction, including without limitation

 * the rights to use, constant, 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 constantright 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 CONSTANTRIGHT 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 opt_constant_propagation.cpp

 *

 * Tracks assignments of constants to channels of variables, and

 * usage of those constant channels with direct usage of the constants.

 *

 * This can lead to constant folding and algebraic optimizations in

 * those later expressions, while causing no increase in instruction

 * count (due to constants being generally free to load from a

 * constant push buffer or as instruction immediate values) and

 * possibly reducing register pressure.

 */

#include "ir.h"

#include "ir_visitor.h"

#include "ir_rvalue_visitor.h"

#include "ir_basic_block.h"

#include "ir_optimization.h"

#include "glsl_types.h"

namespace {

class acp_entry : public exec_node

{

public:

   acp_entry(ir_variable *var, unsigned write_mask, ir_constant *constant)

   {

      assert(var);

      assert(constant);

      this->var = var;

      this->write_mask = write_mask;

      this->constant = constant;

      this->initial_values = write_mask;

   }

   acp_entry(const acp_entry *src)

   {

      this->var = src->var;

      this->write_mask = src->write_mask;

      this->constant = src->constant;

      this->initial_values = src->initial_values;

   }

   ir_variable *var;

   ir_constant *constant;

   unsigned write_mask;

   /** Mask of values initially available in the constant. */

   unsigned initial_values;

};

class kill_entry : public exec_node

{

public:

   kill_entry(ir_variable *var, unsigned write_mask)

   {

      assert(var);

      this->var = var;

      this->write_mask = write_mask;

   }

   ir_variable *var;

   unsigned write_mask;

};

class ir_constant_propagation_visitor : public ir_rvalue_visitor {

public:

   ir_constant_propagation_visitor()

   {

      progress = false;

      killed_all = false;

      mem_ctx = ralloc_context(0);

      this->acp = new(mem_ctx) exec_list;

      this->kills = new(mem_ctx) exec_list;

   }

   ~ir_constant_propagation_visitor()

   {

      ralloc_free(mem_ctx);

   }

   virtual ir_visitor_status visit_enter(class ir_loop *);

   virtual ir_visitor_status visit_enter(class ir_function_signature *);

   virtual ir_visitor_status visit_enter(class ir_function *);

   virtual ir_visitor_status visit_leave(class ir_assignment *);

   virtual ir_visitor_status visit_enter(class ir_call *);

   virtual ir_visitor_status visit_enter(class ir_if *);

   void add_constant(ir_assignment *ir);

   void kill(ir_variable *ir, unsigned write_mask);

   void handle_if_block(exec_list *instructions);

   void handle_rvalue(ir_rvalue **rvalue);

   /** List of acp_entry: The available constants to propagate */

   exec_list *acp;

   /**

    * List of kill_entry: The masks of variables whose values were

    * killed in this block.

    */

   exec_list *kills;

   bool progress;

   bool killed_all;

   void *mem_ctx;

};

void

ir_constant_propagation_visitor::handle_rvalue(ir_rvalue **rvalue)

{

   if (this->in_assignee || !*rvalue)

      return;

   const glsl_type *type = (*rvalue)->type;

   if (!type->is_scalar() && !type->is_vector())

      return;

   ir_swizzle *swiz = NULL;

   ir_dereference_variable *deref = (*rvalue)->as_dereference_variable();

   if (!deref) {

      swiz = (*rvalue)->as_swizzle();

      if (!swiz)

	 return;

      deref = swiz->val->as_dereference_variable();

      if (!deref)

	 return;

   }

   ir_constant_data data;

   memset(&data, 0, sizeof(data));

   for (unsigned int i = 0; i < type->components(); i++) {

      int channel;

      acp_entry *found = NULL;

      if (swiz) {

	 switch (i) {

	 case 0: channel = swiz->mask.x; break;

	 case 1: channel = swiz->mask.y; break;

	 case 2: channel = swiz->mask.z; break;

	 case 3: channel = swiz->mask.w; break;

	 default: assert(!"shouldn't be reached"); channel = 0; break;

	 }

      } else {

	 channel = i;

      }

      foreach_iter(exec_list_iterator, iter, *this->acp) {

	 acp_entry *entry = (acp_entry *)iter.get();

	 if (entry->var == deref->var && entry->write_mask & (1 << channel)) {

	    found = entry;

	    break;

	 }

      }

      if (!found)

	 return;

      int rhs_channel = 0;

      for (int j = 0; j < 4; j++) {

	 if (j == channel)

	    break;

	 if (found->initial_values & (1 << j))

	    rhs_channel++;

      }

      switch (type->base_type) {

      case GLSL_TYPE_FLOAT:

	 data.f[i] = found->constant->value.f[rhs_channel];

	 break;

      case GLSL_TYPE_INT:

	 data.i[i] = found->constant->value.i[rhs_channel];

	 break;

      case GLSL_TYPE_UINT:

	 data.u[i] = found->constant->value.u[rhs_channel];

	 break;

      case GLSL_TYPE_BOOL:

	 data.b[i] = found->constant->value.b[rhs_channel];

	 break;

      default:

	 assert(!"not reached");

	 break;

      }

   }

   *rvalue = new(ralloc_parent(deref)) ir_constant(type, &data);

   this->progress = true;

}

ir_visitor_status

ir_constant_propagation_visitor::visit_enter(ir_function_signature *ir)

{

   /* Treat entry into a function signature as a completely separate

    * block.  Any instructions at global scope will be shuffled into

    * main() at link time, so they're irrelevant to us.

    */

   exec_list *orig_acp = this->acp;

   exec_list *orig_kills = this->kills;

   bool orig_killed_all = this->killed_all;

   this->acp = new(mem_ctx) exec_list;

   this->kills = new(mem_ctx) exec_list;

   this->killed_all = false;

   visit_list_elements(this, &ir->body);

   this->kills = orig_kills;

   this->acp = orig_acp;

   this->killed_all = orig_killed_all;

   return visit_continue_with_parent;

}

ir_visitor_status

ir_constant_propagation_visitor::visit_leave(ir_assignment *ir)

{

   if (this->in_assignee)

      return visit_continue;

   unsigned kill_mask = ir->write_mask;

   if (ir->lhs->as_dereference_array()) {

      /* The LHS of the assignment uses an array indexing operator (e.g. v[i]

       * = ...;).  Since we only try to constant propagate vectors and

       * scalars, this means that either (a) array indexing is being used to

       * select a vector component, or (b) the variable in question is neither

       * a scalar or a vector, so we don't care about it.  In the former case,

       * we want to kill the whole vector, since in general we can't predict

       * which vector component will be selected by array indexing.  In the

       * latter case, it doesn't matter what we do, so go ahead and kill the

       * whole variable anyway.

       *

       * Note that if the array index is constant (e.g. v[2] = ...;), we could

       * in principle be smarter, but we don't need to, because a future

       * optimization pass will convert it to a simple assignment with the

       * correct mask.

       */

      kill_mask = ~0;

   }

   kill(ir->lhs->variable_referenced(), kill_mask);

   add_constant(ir);

   return visit_continue;

}

ir_visitor_status

ir_constant_propagation_visitor::visit_enter(ir_function *ir)

{

   (void) ir;

   return visit_continue;

}

ir_visitor_status

ir_constant_propagation_visitor::visit_enter(ir_call *ir)

{

   /* Do constant propagation on call parameters, but skip any out params */

   exec_list_iterator sig_param_iter = ir->callee->parameters.iterator();

   foreach_iter(exec_list_iterator, iter, ir->actual_parameters) {

      ir_variable *sig_param = (ir_variable *)sig_param_iter.get();

      ir_rvalue *param = (ir_rvalue *)iter.get();

      if (sig_param->mode != ir_var_function_out

          && sig_param->mode != ir_var_function_inout) {

	 ir_rvalue *new_param = param;

	 handle_rvalue(&new_param);

         if (new_param != param)

	    param->replace_with(new_param);

	 else

	    param->accept(this);

      }

      sig_param_iter.next();

   }

   /* Since we're unlinked, we don't (necssarily) know the side effects of

    * this call.  So kill all copies.

    */

   acp->make_empty();

   this->killed_all = true;

   return visit_continue_with_parent;

}

void

ir_constant_propagation_visitor::handle_if_block(exec_list *instructions)

{

   exec_list *orig_acp = this->acp;

   exec_list *orig_kills = this->kills;

   bool orig_killed_all = this->killed_all;

   this->acp = new(mem_ctx) exec_list;

   this->kills = new(mem_ctx) exec_list;

   this->killed_all = false;

   /* Populate the initial acp with a constant of the original */

   foreach_iter(exec_list_iterator, iter, *orig_acp) {

      acp_entry *a = (acp_entry *)iter.get();

      this->acp->push_tail(new(this->mem_ctx) acp_entry(a));

   }

   visit_list_elements(this, instructions);

   if (this->killed_all) {

      orig_acp->make_empty();

   }

   exec_list *new_kills = this->kills;

   this->kills = orig_kills;

   this->acp = orig_acp;

   this->killed_all = this->killed_all || orig_killed_all;

   foreach_iter(exec_list_iterator, iter, *new_kills) {

      kill_entry *k = (kill_entry *)iter.get();

      kill(k->var, k->write_mask);

   }

}

ir_visitor_status

ir_constant_propagation_visitor::visit_enter(ir_if *ir)

{

   ir->condition->accept(this);

   handle_rvalue(&ir->condition);

   handle_if_block(&ir->then_instructions);

   handle_if_block(&ir->else_instructions);

   /* handle_if_block() already descended into the children. */

   return visit_continue_with_parent;

}

ir_visitor_status

ir_constant_propagation_visitor::visit_enter(ir_loop *ir)

{

   exec_list *orig_acp = this->acp;

   exec_list *orig_kills = this->kills;

   bool orig_killed_all = this->killed_all;

   /* FINISHME: For now, the initial acp for loops is totally empty.

    * We could go through once, then go through again with the acp

    * cloned minus the killed entries after the first run through.

    */

   this->acp = new(mem_ctx) exec_list;

   this->kills = new(mem_ctx) exec_list;

   this->killed_all = false;

   visit_list_elements(this, &ir->body_instructions);

   if (this->killed_all) {

      orig_acp->make_empty();

   }

   exec_list *new_kills = this->kills;

   this->kills = orig_kills;

   this->acp = orig_acp;

   this->killed_all = this->killed_all || orig_killed_all;

   foreach_iter(exec_list_iterator, iter, *new_kills) {

      kill_entry *k = (kill_entry *)iter.get();

      kill(k->var, k->write_mask);

   }

   /* already descended into the children. */

   return visit_continue_with_parent;

}

void

ir_constant_propagation_visitor::kill(ir_variable *var, unsigned write_mask)

{

   assert(var != NULL);

   /* We don't track non-vectors. */

   if (!var->type->is_vector() && !var->type->is_scalar())

      return;

   /* Remove any entries currently in the ACP for this kill. */

   foreach_iter(exec_list_iterator, iter, *this->acp) {

      acp_entry *entry = (acp_entry *)iter.get();

      if (entry->var == var) {

	 entry->write_mask &= ~write_mask;

	 if (entry->write_mask == 0)

	    entry->remove();

      }

   }

   /* Add this writemask of the variable to the list of killed

    * variables in this block.

    */

   foreach_iter(exec_list_iterator, iter, *this->kills) {

      kill_entry *entry = (kill_entry *)iter.get();

      if (entry->var == var) {

	 entry->write_mask |= write_mask;

	 return;

      }

   }

   /* Not already in the list.  Make new entry. */

   this->kills->push_tail(new(this->mem_ctx) kill_entry(var, write_mask));

}

/**

 * Adds an entry to the available constant list if it's a plain assignment

 * of a variable to a variable.

 */

void

ir_constant_propagation_visitor::add_constant(ir_assignment *ir)

{

   acp_entry *entry;

   if (ir->condition)

      return;

   if (!ir->write_mask)

      return;

   ir_dereference_variable *deref = ir->lhs->as_dereference_variable();

   ir_constant *constant = ir->rhs->as_constant();

   if (!deref || !constant)

      return;

   /* Only do constant propagation on vectors.  Constant matrices,

    * arrays, or structures would require more work elsewhere.

    */

   if (!deref->var->type->is_vector() && !deref->var->type->is_scalar())

      return;

   entry = new(this->mem_ctx) acp_entry(deref->var, ir->write_mask, constant);

   this->acp->push_tail(entry);

}

} /* unnamed namespace */

/**

 * Does a constant propagation pass on the code present in the instruction stream.

 */

bool

do_constant_propagation(exec_list *instructions)

{

   ir_constant_propagation_visitor v;

   visit_list_elements(&v, instructions);

   return v.progress;

}