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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);
+}