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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_discard_flow.cpp
*
* Implements the GLSL 1.30 revision 9 rule for fragment shader
* discard handling:
*
* "Control flow exits the shader, and subsequent implicit or
* explicit derivatives are undefined when this control flow is
* non-uniform (meaning different fragments within the primitive
* take different control paths)."
*
* There seem to be two conflicting things here. "Control flow exits
* the shader" sounds like the discarded fragments should effectively
* jump to the end of the shader, but that breaks derivatives in the
* case of uniform control flow and causes rendering failure in the
* bushes in Unigine Tropics.
*
* The question, then, is whether the intent was "loops stop at the
* point that the only active channels left are discarded pixels" or
* "discarded pixels become inactive at the point that control flow
* returns to the top of a loop". This implements the second
* interpretation.
*/
#include "glsl_types.h"
#include "ir.h"
#include "program/hash_table.h"
class lower_discard_flow_visitor : public ir_hierarchical_visitor {
public:
lower_discard_flow_visitor(ir_variable *discarded)
: discarded(discarded)
{
mem_ctx = ralloc_parent(discarded);
}
~lower_discard_flow_visitor()
{
}
ir_visitor_status visit_enter(ir_discard *ir);
ir_visitor_status visit_enter(ir_loop_jump *ir);
ir_visitor_status visit_enter(ir_loop *ir);
ir_visitor_status visit_enter(ir_function_signature *ir);
ir_if *generate_discard_break();
ir_variable *discarded;
void *mem_ctx;
};
ir_visitor_status
lower_discard_flow_visitor::visit_enter(ir_loop_jump *ir)
{
if (ir->mode != ir_loop_jump::jump_continue)
return visit_continue;
ir->insert_before(generate_discard_break());
return visit_continue;
}
ir_visitor_status
lower_discard_flow_visitor::visit_enter(ir_discard *ir)
{
ir_dereference *lhs = new(mem_ctx) ir_dereference_variable(discarded);
ir_rvalue *rhs = new(mem_ctx) ir_constant(true);
ir_assignment *assign = new(mem_ctx) ir_assignment(lhs, rhs);
ir->insert_before(assign);
return visit_continue;
}
ir_visitor_status
lower_discard_flow_visitor::visit_enter(ir_loop *ir)
{
ir->body_instructions.push_tail(generate_discard_break());
return visit_continue;
}
ir_visitor_status
lower_discard_flow_visitor::visit_enter(ir_function_signature *ir)
{
if (strcmp(ir->function_name(), "main") != 0)
return visit_continue;
ir_dereference *lhs = new(mem_ctx) ir_dereference_variable(discarded);
ir_rvalue *rhs = new(mem_ctx) ir_constant(false);
ir_assignment *assign = new(mem_ctx) ir_assignment(lhs, rhs);
ir->body.push_head(assign);
return visit_continue;
}
ir_if *
lower_discard_flow_visitor::generate_discard_break()
{
ir_rvalue *if_condition = new(mem_ctx) ir_dereference_variable(discarded);
ir_if *if_inst = new(mem_ctx) ir_if(if_condition);
ir_instruction *br = new(mem_ctx) ir_loop_jump(ir_loop_jump::jump_break);
if_inst->then_instructions.push_tail(br);
return if_inst;
}
void
lower_discard_flow(exec_list *ir)
{
void *mem_ctx = ir;
ir_variable *var = new(mem_ctx) ir_variable(glsl_type::bool_type,
"discarded",
ir_var_temporary);
ir->push_head(var);
lower_discard_flow_visitor v(var);
visit_list_elements(&v, ir);
}
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