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