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* Copyright © 2012 Vincent Lejeune
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* Copyright © 2012 Intel Corporation
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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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* 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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* 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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#include "util/hash_table.h"
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* \file lower_output_reads.cpp
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* In GLSL, shader output variables (such as varyings) can be both read and
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* written. However, on some hardware, reading an output register causes
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* This pass creates temporary shadow copies of every (used) shader output,
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* and replaces all accesses to use those instead. It also adds code to the
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* main() function to copy the final values to the actual shader outputs.
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class output_read_remover : public ir_hierarchical_visitor {
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* A hash table mapping from the original ir_variable shader outputs
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* (ir_var_shader_out mode) to the new temporaries to be used instead.
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hash_table *replacements;
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output_read_remover(unsigned stage);
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~output_read_remover();
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virtual ir_visitor_status visit(class ir_dereference_variable *);
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virtual ir_visitor_status visit_leave(class ir_emit_vertex *);
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virtual ir_visitor_status visit_leave(class ir_return *);
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virtual ir_visitor_status visit_leave(class ir_function_signature *);
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} /* anonymous namespace */
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* Hash function for the output variables - computes the hash of the name.
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* NOTE: We're using the name string to ensure that the hash doesn't depend
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* on any random factors, otherwise the output_read_remover could produce
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* the random order of the assignments.
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* NOTE: If you want to reuse this function please take into account that
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* generally the names of the variables are non-unique.
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hash_table_var_hash(const void *key)
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const ir_variable * var = static_cast<const ir_variable *>(key);
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return _mesa_hash_string(var->name);
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output_read_remover::output_read_remover(unsigned stage)
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replacements = _mesa_hash_table_create(NULL, hash_table_var_hash,
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_mesa_key_pointer_equal);
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output_read_remover::~output_read_remover()
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_mesa_hash_table_destroy(replacements, NULL);
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output_read_remover::visit(ir_dereference_variable *ir)
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if (ir->var->data.mode != ir_var_shader_out || ir->var->data.fb_fetch_output)
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return visit_continue;
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hash_entry *entry = _mesa_hash_table_search(replacements, ir->var);
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ir_variable *temp = entry ? (ir_variable *) entry->data : NULL;
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/* If we don't have an existing temporary, create one. */
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void *var_ctx = ralloc_parent(ir->var);
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temp = new(var_ctx) ir_variable(ir->var->type, ir->var->name,
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/* copy flags which affect arithematical precision */
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temp->data.invariant = ir->var->data.invariant;
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temp->data.precise = ir->var->data.precise;
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temp->data.precision = ir->var->data.precision;
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_mesa_hash_table_insert(replacements, ir->var, temp);
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ir->var->insert_after(temp);
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/* Update the dereference to use the temporary */
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return visit_continue;
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* Create an assignment to copy a temporary value back to the actual output.
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static ir_assignment *
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copy(void *ctx, ir_variable *output, ir_variable *temp)
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ir_dereference_variable *lhs = new(ctx) ir_dereference_variable(output);
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ir_dereference_variable *rhs = new(ctx) ir_dereference_variable(temp);
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return new(ctx) ir_assignment(lhs, rhs);
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/** Insert a copy-back assignment before a "return" statement or a call to
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emit_return_copy(const void *key, void *data, void *closure)
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ir_return *ir = (ir_return *) closure;
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ir->insert_before(copy(ir, (ir_variable *) key, (ir_variable *) data));
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/** Insert a copy-back assignment at the end of the main() function */
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emit_main_copy(const void *key, void *data, void *closure)
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ir_function_signature *sig = (ir_function_signature *) closure;
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sig->body.push_tail(copy(sig, (ir_variable *) key, (ir_variable *) data));
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output_read_remover::visit_leave(ir_return *ir)
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hash_table_call_foreach(replacements, emit_return_copy, ir);
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return visit_continue;
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output_read_remover::visit_leave(ir_emit_vertex *ir)
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hash_table_call_foreach(replacements, emit_return_copy, ir);
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return visit_continue;
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output_read_remover::visit_leave(ir_function_signature *sig)
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if (strcmp(sig->function_name(), "main") != 0)
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return visit_continue;
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hash_table_call_foreach(replacements, emit_main_copy, sig);
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return visit_continue;
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lower_output_reads(unsigned stage, exec_list *instructions)
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/* Due to the possible interactions between multiple tessellation control
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* shader invocations, we leave output variables as-is.
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if (stage == MESA_SHADER_TESS_CTRL)
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output_read_remover v(stage);
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visit_list_elements(&v, instructions);