glsl: Implement the GLSL 1.30+ discard control flow rule in GLSL IR.
Previously, I tried implementing this in the i965 driver, but did so in a way that violated the intent of the spec, and broke Tropics. Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
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@ -51,6 +51,7 @@ LIBGLSL_CXX_FILES := \
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loop_unroll.cpp \
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loop_unroll.cpp \
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lower_clip_distance.cpp \
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lower_clip_distance.cpp \
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lower_discard.cpp \
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lower_discard.cpp \
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lower_discard_flow.cpp \
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lower_if_to_cond_assign.cpp \
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lower_if_to_cond_assign.cpp \
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lower_instructions.cpp \
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lower_instructions.cpp \
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lower_jumps.cpp \
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lower_jumps.cpp \
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@ -66,6 +66,7 @@ bool do_tree_grafting(exec_list *instructions);
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bool do_vec_index_to_cond_assign(exec_list *instructions);
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bool do_vec_index_to_cond_assign(exec_list *instructions);
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bool do_vec_index_to_swizzle(exec_list *instructions);
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bool do_vec_index_to_swizzle(exec_list *instructions);
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bool lower_discard(exec_list *instructions);
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bool lower_discard(exec_list *instructions);
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bool lower_discard_flow(exec_list *instructions);
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bool lower_instructions(exec_list *instructions, unsigned what_to_lower);
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bool lower_instructions(exec_list *instructions, unsigned what_to_lower);
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bool lower_noise(exec_list *instructions);
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bool lower_noise(exec_list *instructions);
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bool lower_variable_index_to_cond_assign(exec_list *instructions,
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bool lower_variable_index_to_cond_assign(exec_list *instructions,
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@ -2296,6 +2296,17 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
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prog->LinkStatus = true;
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prog->LinkStatus = true;
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}
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}
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/* Implement the GLSL 1.30+ rule for discard vs infinite loops Do
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* it before optimization because we want most of the checks to get
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* dropped thanks to constant propagation.
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*/
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if (max_version >= 130) {
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struct gl_shader *sh = prog->_LinkedShaders[MESA_SHADER_FRAGMENT];
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if (sh) {
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lower_discard_flow(sh->ir);
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}
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}
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/* Do common optimization before assigning storage for attributes,
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/* Do common optimization before assigning storage for attributes,
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* uniforms, and varyings. Later optimization could possibly make
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* uniforms, and varyings. Later optimization could possibly make
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* some of that unused.
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* some of that unused.
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@ -0,0 +1,144 @@
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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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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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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 = new(mem_ctx) ir_constant(true);
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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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}
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