src/compiler/glsl/lower_if_to_cond_assign.cpp - platform/external/mesa3d - Git at Google

 /*
  * 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_if_to_cond_assign.cpp
  *
  * This flattens if-statements to conditional assignments if:
  *
  * - the GPU has limited or no flow control support
  *   (controlled by max_depth)
  *
  * - small conditional branches are more expensive than conditional assignments
  *   (controlled by min_branch_cost, that's the cost for a branch to be
  *    preserved)
  *
  * It can't handle other control flow being inside of its block, such
  * as calls or loops.  Hopefully loop unrolling and inlining will take
  * care of those.
  *
  * Drivers for GPUs with no control flow support should simply call
  *
  *    lower_if_to_cond_assign(instructions)
  *
  * to attempt to flatten all if-statements.
  *
  * Some GPUs (such as i965 prior to gen6) do support control flow, but have a
  * maximum nesting depth N.  Drivers for such hardware can call
  *
  *    lower_if_to_cond_assign(instructions, N)
  *
  * to attempt to flatten any if-statements appearing at depth > N.
  */

 #include "compiler/glsl_types.h"
 #include "ir.h"
 #include "util/set.h"
 #include "util/hash_table.h" /* Needed for the hashing functions */
 #include "main/macros.h" /* for MAX2 */

 namespace {

 class ir_if_to_cond_assign_visitor : public ir_hierarchical_visitor {
 public:
    ir_if_to_cond_assign_visitor(gl_shader_stage stage,
                                 unsigned max_depth,
                                 unsigned min_branch_cost)
    {
       this->progress = false;
       this->stage = stage;
       this->max_depth = max_depth;
       this->min_branch_cost = min_branch_cost;
       this->depth = 0;

       this->condition_variables = _mesa_pointer_set_create(NULL);
    }

    ~ir_if_to_cond_assign_visitor()
    {
       _mesa_set_destroy(this->condition_variables, NULL);
    }

    ir_visitor_status visit_enter(ir_if *);
    ir_visitor_status visit_leave(ir_if *);

    bool found_unsupported_op;
    bool found_expensive_op;
    bool found_dynamic_arrayref;
    bool is_then;
    bool progress;
    gl_shader_stage stage;
    unsigned then_cost;
    unsigned else_cost;
    unsigned min_branch_cost;
    unsigned max_depth;
    unsigned depth;

    struct set *condition_variables;
 };

 } /* anonymous namespace */

 bool
 lower_if_to_cond_assign(gl_shader_stage stage, exec_list *instructions,
                         unsigned max_depth, unsigned min_branch_cost)
 {
    if (max_depth == UINT_MAX)
       return false;

    ir_if_to_cond_assign_visitor v(stage, max_depth, min_branch_cost);

    visit_list_elements(&v, instructions);

    return v.progress;
 }

 static void
 check_ir_node(ir_instruction *ir, void *data)
 {
    ir_if_to_cond_assign_visitor *v = (ir_if_to_cond_assign_visitor *)data;

    switch (ir->ir_type) {
    case ir_type_call:
    case ir_type_discard:
    case ir_type_loop:
    case ir_type_loop_jump:
    case ir_type_return:
    case ir_type_emit_vertex:
    case ir_type_end_primitive:
    case ir_type_barrier:
       v->found_unsupported_op = true;
       break;

    case ir_type_dereference_variable: {
       ir_variable *var = ir->as_dereference_variable()->variable_referenced();

       /* Lowering branches with TCS output accesses breaks many piglit tests,
        * so don't touch them for now.
        */
       if (v->stage == MESA_SHADER_TESS_CTRL &&
           var->data.mode == ir_var_shader_out)
          v->found_unsupported_op = true;
       break;
    }

    /* SSBO, images, atomic counters are handled by ir_type_call */
    case ir_type_texture:
       v->found_expensive_op = true;
       break;

    case ir_type_dereference_array: {
       ir_dereference_array *deref = ir->as_dereference_array();

       if (deref->array_index->ir_type != ir_type_constant)
          v->found_dynamic_arrayref = true;
    } /* fall-through */
    case ir_type_expression:
    case ir_type_dereference_record:
       if (v->is_then)
          v->then_cost++;
       else
          v->else_cost++;
       break;

    default:
       break;
    }
 }

 static void
 move_block_to_cond_assign(void *mem_ctx,
                           ir_if *if_ir, ir_rvalue *cond_expr,
                           exec_list *instructions,
                           struct set *set)
 {
    foreach_in_list_safe(ir_instruction, ir, instructions) {
       if (ir->ir_type == ir_type_assignment) {
          ir_assignment *assign = (ir_assignment *)ir;

          if (_mesa_set_search(set, assign) == NULL) {
             _mesa_set_add(set, assign);

             /* If the LHS of the assignment is a condition variable that was
              * previously added, insert an additional assignment of false to
              * the variable.
              */
             const bool assign_to_cv =
                _mesa_set_search(
                   set, assign->lhs->variable_referenced()) != NULL;

             if (!assign->condition) {
                if (assign_to_cv) {
                   assign->rhs =
                      new(mem_ctx) ir_expression(ir_binop_logic_and,
                                                 glsl_type::bool_type,
                                                 cond_expr->clone(mem_ctx, NULL),
                                                 assign->rhs);
                } else {
                   assign->condition = cond_expr->clone(mem_ctx, NULL);
                }
             } else {
                assign->condition =
                   new(mem_ctx) ir_expression(ir_binop_logic_and,
                                              glsl_type::bool_type,
                                              cond_expr->clone(mem_ctx, NULL),
                                              assign->condition);
             }
          }
       }

       /* Now, move from the if block to the block surrounding it. */
       ir->remove();
       if_ir->insert_before(ir);
    }
 }

 ir_visitor_status
 ir_if_to_cond_assign_visitor::visit_enter(ir_if *)
 {
    this->depth++;

    return visit_continue;
 }

 ir_visitor_status
 ir_if_to_cond_assign_visitor::visit_leave(ir_if *ir)
 {
    bool must_lower = this->depth-- > this->max_depth;

    /* Only flatten when beyond the GPU's maximum supported nesting depth. */
    if (!must_lower && this->min_branch_cost == 0)
       return visit_continue;

    this->found_unsupported_op = false;
    this->found_expensive_op = false;
    this->found_dynamic_arrayref = false;
    this->then_cost = 0;
    this->else_cost = 0;

    ir_assignment *assign;

    /* Check that both blocks don't contain anything we can't support. */
    this->is_then = true;
    foreach_in_list(ir_instruction, then_ir, &ir->then_instructions) {
       visit_tree(then_ir, check_ir_node, this);
    }

    this->is_then = false;
    foreach_in_list(ir_instruction, else_ir, &ir->else_instructions) {
       visit_tree(else_ir, check_ir_node, this);
    }

    if (this->found_unsupported_op)
       return visit_continue; /* can't handle inner unsupported opcodes */

    /* Skip if the branch cost is high enough or if there's an expensive op.
     *
     * Also skip if non-constant array indices were encountered, since those
     * can be out-of-bounds for a not-taken branch, and so generating an
     * assignment would be incorrect. In the case of must_lower, it's up to the
     * backend to deal with any potential fall-out (perhaps by translating the
     * assignments to hardware-predicated moves).
     */
    if (!must_lower &&
        (this->found_expensive_op ||
         this->found_dynamic_arrayref ||
         MAX2(this->then_cost, this->else_cost) >= this->min_branch_cost))
       return visit_continue;

    void *mem_ctx = ralloc_parent(ir);

    /* Store the condition to a variable.  Move all of the instructions from
     * the then-clause of the if-statement.  Use the condition variable as a
     * condition for all assignments.
     */
    ir_variable *const then_var =
       new(mem_ctx) ir_variable(glsl_type::bool_type,
                                "if_to_cond_assign_then",
                                ir_var_temporary);
    ir->insert_before(then_var);

    ir_dereference_variable *then_cond =
       new(mem_ctx) ir_dereference_variable(then_var);

    assign = new(mem_ctx) ir_assignment(then_cond, ir->condition);
    ir->insert_before(assign);

    move_block_to_cond_assign(mem_ctx, ir, then_cond,
                              &ir->then_instructions,
                              this->condition_variables);

    /* Add the new condition variable to the hash table.  This allows us to
     * find this variable when lowering other (enclosing) if-statements.
     */
    _mesa_set_add(this->condition_variables, then_var);

    /* If there are instructions in the else-clause, store the inverse of the
     * condition to a variable.  Move all of the instructions from the
     * else-clause if the if-statement.  Use the (inverse) condition variable
     * as a condition for all assignments.
     */
    if (!ir->else_instructions.is_empty()) {
       ir_variable *const else_var =
          new(mem_ctx) ir_variable(glsl_type::bool_type,
                                   "if_to_cond_assign_else",
                                   ir_var_temporary);
       ir->insert_before(else_var);

       ir_dereference_variable *else_cond =
          new(mem_ctx) ir_dereference_variable(else_var);

       ir_rvalue *inverse =
          new(mem_ctx) ir_expression(ir_unop_logic_not,
                                     then_cond->clone(mem_ctx, NULL));

       assign = new(mem_ctx) ir_assignment(else_cond, inverse);
       ir->insert_before(assign);

       move_block_to_cond_assign(mem_ctx, ir, else_cond,
                                 &ir->else_instructions,
                                 this->condition_variables);

       /* Add the new condition variable to the hash table.  This allows us to
        * find this variable when lowering other (enclosing) if-statements.
        */
       _mesa_set_add(this->condition_variables, else_var);
    }

    ir->remove();

    this->progress = true;

    return visit_continue;
 }
	/*
	* 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_if_to_cond_assign.cpp
	*
	* This flattens if-statements to conditional assignments if:
	*
	* - the GPU has limited or no flow control support
	* (controlled by max_depth)
	*
	* - small conditional branches are more expensive than conditional assignments
	* (controlled by min_branch_cost, that's the cost for a branch to be
	* preserved)
	*
	* It can't handle other control flow being inside of its block, such
	* as calls or loops. Hopefully loop unrolling and inlining will take
	* care of those.
	*
	* Drivers for GPUs with no control flow support should simply call
	*
	* lower_if_to_cond_assign(instructions)
	*
	* to attempt to flatten all if-statements.
	*
	* Some GPUs (such as i965 prior to gen6) do support control flow, but have a
	* maximum nesting depth N. Drivers for such hardware can call
	*
	* lower_if_to_cond_assign(instructions, N)
	*
	* to attempt to flatten any if-statements appearing at depth > N.
	*/

	#include "compiler/glsl_types.h"
	#include "ir.h"
	#include "util/set.h"
	#include "util/hash_table.h" /* Needed for the hashing functions */
	#include "main/macros.h" /* for MAX2 */

	namespace {

	class ir_if_to_cond_assign_visitor : public ir_hierarchical_visitor {
	public:
	ir_if_to_cond_assign_visitor(gl_shader_stage stage,
	unsigned max_depth,
	unsigned min_branch_cost)
	{
	this->progress = false;
	this->stage = stage;
	this->max_depth = max_depth;
	this->min_branch_cost = min_branch_cost;
	this->depth = 0;

	this->condition_variables = _mesa_pointer_set_create(NULL);
	}

	~ir_if_to_cond_assign_visitor()
	{
	_mesa_set_destroy(this->condition_variables, NULL);
	}

	ir_visitor_status visit_enter(ir_if *);
	ir_visitor_status visit_leave(ir_if *);

	bool found_unsupported_op;
	bool found_expensive_op;
	bool found_dynamic_arrayref;
	bool is_then;
	bool progress;
	gl_shader_stage stage;
	unsigned then_cost;
	unsigned else_cost;
	unsigned min_branch_cost;
	unsigned max_depth;
	unsigned depth;

	struct set *condition_variables;
	};

	} /* anonymous namespace */

	bool
	lower_if_to_cond_assign(gl_shader_stage stage, exec_list *instructions,
	unsigned max_depth, unsigned min_branch_cost)
	{
	if (max_depth == UINT_MAX)
	return false;

	ir_if_to_cond_assign_visitor v(stage, max_depth, min_branch_cost);

	visit_list_elements(&v, instructions);

	return v.progress;
	}

	static void
	check_ir_node(ir_instruction ir, void data)
	{
	ir_if_to_cond_assign_visitor v = (ir_if_to_cond_assign_visitor )data;

	switch (ir->ir_type) {
	case ir_type_call:
	case ir_type_discard:
	case ir_type_loop:
	case ir_type_loop_jump:
	case ir_type_return:
	case ir_type_emit_vertex:
	case ir_type_end_primitive:
	case ir_type_barrier:
	v->found_unsupported_op = true;
	break;

	case ir_type_dereference_variable: {
	ir_variable *var = ir->as_dereference_variable()->variable_referenced();

	/* Lowering branches with TCS output accesses breaks many piglit tests,
	* so don't touch them for now.
	*/
	if (v->stage == MESA_SHADER_TESS_CTRL &&
	var->data.mode == ir_var_shader_out)
	v->found_unsupported_op = true;
	break;
	}

	/* SSBO, images, atomic counters are handled by ir_type_call */
	case ir_type_texture:
	v->found_expensive_op = true;
	break;

	case ir_type_dereference_array: {
	ir_dereference_array *deref = ir->as_dereference_array();

	if (deref->array_index->ir_type != ir_type_constant)
	v->found_dynamic_arrayref = true;
	} /* fall-through */
	case ir_type_expression:
	case ir_type_dereference_record:
	if (v->is_then)
	v->then_cost++;
	else
	v->else_cost++;
	break;

	default:
	break;
	}
	}

	static void
	move_block_to_cond_assign(void *mem_ctx,
	ir_if if_ir, ir_rvalue cond_expr,
	exec_list *instructions,
	struct set *set)
	{
	foreach_in_list_safe(ir_instruction, ir, instructions) {
	if (ir->ir_type == ir_type_assignment) {
	ir_assignment assign = (ir_assignment )ir;

	if (_mesa_set_search(set, assign) == NULL) {
	_mesa_set_add(set, assign);

	/* If the LHS of the assignment is a condition variable that was
	* previously added, insert an additional assignment of false to
	* the variable.
	*/
	const bool assign_to_cv =
	_mesa_set_search(
	set, assign->lhs->variable_referenced()) != NULL;

	if (!assign->condition) {
	if (assign_to_cv) {
	assign->rhs =
	new(mem_ctx) ir_expression(ir_binop_logic_and,
	glsl_type::bool_type,
	cond_expr->clone(mem_ctx, NULL),
	assign->rhs);
	} else {
	assign->condition = cond_expr->clone(mem_ctx, NULL);
	}
	} else {
	assign->condition =
	new(mem_ctx) ir_expression(ir_binop_logic_and,
	glsl_type::bool_type,
	cond_expr->clone(mem_ctx, NULL),
	assign->condition);
	}
	}
	}

	/* Now, move from the if block to the block surrounding it. */
	ir->remove();
	if_ir->insert_before(ir);
	}
	}

	ir_visitor_status
	ir_if_to_cond_assign_visitor::visit_enter(ir_if *)
	{
	this->depth++;

	return visit_continue;
	}

	ir_visitor_status
	ir_if_to_cond_assign_visitor::visit_leave(ir_if *ir)
	{
	bool must_lower = this->depth-- > this->max_depth;

	/* Only flatten when beyond the GPU's maximum supported nesting depth. */
	if (!must_lower && this->min_branch_cost == 0)
	return visit_continue;

	this->found_unsupported_op = false;
	this->found_expensive_op = false;
	this->found_dynamic_arrayref = false;
	this->then_cost = 0;
	this->else_cost = 0;

	ir_assignment *assign;

	/* Check that both blocks don't contain anything we can't support. */
	this->is_then = true;
	foreach_in_list(ir_instruction, then_ir, &ir->then_instructions) {
	visit_tree(then_ir, check_ir_node, this);
	}

	this->is_then = false;
	foreach_in_list(ir_instruction, else_ir, &ir->else_instructions) {
	visit_tree(else_ir, check_ir_node, this);
	}

	if (this->found_unsupported_op)
	return visit_continue; /* can't handle inner unsupported opcodes */

	/* Skip if the branch cost is high enough or if there's an expensive op.
	*
	* Also skip if non-constant array indices were encountered, since those
	* can be out-of-bounds for a not-taken branch, and so generating an
	* assignment would be incorrect. In the case of must_lower, it's up to the
	* backend to deal with any potential fall-out (perhaps by translating the
	* assignments to hardware-predicated moves).
	*/
	if (!must_lower &&
	(this->found_expensive_op \|\|
	this->found_dynamic_arrayref \|\|
	MAX2(this->then_cost, this->else_cost) >= this->min_branch_cost))
	return visit_continue;

	void *mem_ctx = ralloc_parent(ir);

	/* Store the condition to a variable. Move all of the instructions from
	* the then-clause of the if-statement. Use the condition variable as a
	* condition for all assignments.
	*/
	ir_variable *const then_var =
	new(mem_ctx) ir_variable(glsl_type::bool_type,
	"if_to_cond_assign_then",
	ir_var_temporary);
	ir->insert_before(then_var);

	ir_dereference_variable *then_cond =
	new(mem_ctx) ir_dereference_variable(then_var);

	assign = new(mem_ctx) ir_assignment(then_cond, ir->condition);
	ir->insert_before(assign);

	move_block_to_cond_assign(mem_ctx, ir, then_cond,
	&ir->then_instructions,
	this->condition_variables);

	/* Add the new condition variable to the hash table. This allows us to
	* find this variable when lowering other (enclosing) if-statements.
	*/
	_mesa_set_add(this->condition_variables, then_var);

	/* If there are instructions in the else-clause, store the inverse of the
	* condition to a variable. Move all of the instructions from the
	* else-clause if the if-statement. Use the (inverse) condition variable
	* as a condition for all assignments.
	*/
	if (!ir->else_instructions.is_empty()) {
	ir_variable *const else_var =
	new(mem_ctx) ir_variable(glsl_type::bool_type,
	"if_to_cond_assign_else",
	ir_var_temporary);
	ir->insert_before(else_var);

	ir_dereference_variable *else_cond =
	new(mem_ctx) ir_dereference_variable(else_var);

	ir_rvalue *inverse =
	new(mem_ctx) ir_expression(ir_unop_logic_not,
	then_cond->clone(mem_ctx, NULL));

	assign = new(mem_ctx) ir_assignment(else_cond, inverse);
	ir->insert_before(assign);

	move_block_to_cond_assign(mem_ctx, ir, else_cond,
	&ir->else_instructions,
	this->condition_variables);

	/* Add the new condition variable to the hash table. This allows us to
	* find this variable when lowering other (enclosing) if-statements.
	*/
	_mesa_set_add(this->condition_variables, else_var);
	}

	ir->remove();

	this->progress = true;

	return visit_continue;
	}