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* Copyright © 2010 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 "main/compiler.h"
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#include "glsl_types.h"
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#include "loop_analysis.h"
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#include "ir_hierarchical_visitor.h"
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* Find an initializer of a variable outside a loop
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* Works backwards from the loop to find the pre-loop value of the variable.
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* This is used, for example, to find the initial value of loop induction
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* \param loop Loop where \c var is an induction variable
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* \param var Variable whose initializer is to be found
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* The \c ir_rvalue assigned to the variable outside the loop. May return
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* \c NULL if no initializer can be found.
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find_initial_value(ir_loop *loop, ir_variable *var)
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for (exec_node *node = loop->prev;
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!node->is_head_sentinel();
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ir_instruction *ir = (ir_instruction *) node;
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switch (ir->ir_type) {
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case ir_type_loop_jump:
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case ir_type_function:
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case ir_type_function_signature:
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assert(!"Should not get here.");
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case ir_type_assignment: {
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ir_assignment *assign = ir->as_assignment();
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ir_variable *assignee = assign->lhs->whole_variable_referenced();
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return (assign->condition != NULL) ? NULL : assign->rhs;
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calculate_iterations(ir_rvalue *from, ir_rvalue *to, ir_rvalue *increment,
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enum ir_expression_operation op)
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void *mem_ctx = talloc_init(__func__);
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ir_expression *const sub =
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new(mem_ctx) ir_expression(ir_binop_sub, from->type, to, from);
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ir_expression *const div =
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new(mem_ctx) ir_expression(ir_binop_div, sub->type, sub, increment);
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ir_constant *iter = div->constant_expression_value();
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if (!iter->type->is_integer()) {
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new(mem_ctx) ir_expression(ir_unop_f2i, glsl_type::int_type, iter,
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iter = cast->constant_expression_value();
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int iter_value = iter->get_int_component(0);
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/* Make sure that the calculated number of iterations satisfies the exit
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* condition. This is needed to catch off-by-one errors and some types of
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* ill-formed loops. For example, we need to detect that the following
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* loop does not have a maximum iteration count.
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* for (float x = 0.0; x != 0.9; x += 0.2)
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const int bias[] = { -1, 0, 1 };
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bool valid_loop = false;
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for (unsigned i = 0; i < Elements(bias); i++) {
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iter = (increment->type->is_integer())
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? new(mem_ctx) ir_constant(iter_value + bias[i])
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: new(mem_ctx) ir_constant(float(iter_value + bias[i]));
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ir_expression *const mul =
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new(mem_ctx) ir_expression(ir_binop_mul, increment->type, iter,
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ir_expression *const add =
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new(mem_ctx) ir_expression(ir_binop_add, mul->type, mul, from);
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ir_expression *const cmp =
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new(mem_ctx) ir_expression(op, glsl_type::bool_type, add, to);
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ir_constant *const cmp_result = cmp->constant_expression_value();
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assert(cmp_result != NULL);
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if (cmp_result->get_bool_component(0)) {
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iter_value += bias[i];
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talloc_free(mem_ctx);
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return (valid_loop) ? iter_value : -1;
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class loop_control_visitor : public ir_hierarchical_visitor {
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loop_control_visitor(loop_state *state)
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this->progress = false;
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virtual ir_visitor_status visit_leave(ir_loop *ir);
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loop_control_visitor::visit_leave(ir_loop *ir)
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loop_variable_state *const ls = this->state->get(ir);
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/* If we've entered a loop that hasn't been analyzed, something really,
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* really bad has happened.
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return visit_continue;
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/* Search the loop terminating conditions for one of the form 'i < c' where
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* i is a loop induction variable, c is a constant, and < is any relative
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int max_iterations = (ls->max_iterations < 0) ? INT_MAX : ls->max_iterations;
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foreach_list(node, &ls->terminators) {
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loop_terminator *t = (loop_terminator *) node;
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ir_if *if_stmt = t->ir;
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/* If-statements can be either 'if (expr)' or 'if (deref)'. We only care
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* about the former here.
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ir_expression *cond = if_stmt->condition->as_expression();
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switch (cond->operation) {
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case ir_binop_greater:
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case ir_binop_lequal:
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case ir_binop_gequal: {
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/* The expressions that we care about will either be of the form
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* 'counter < limit' or 'limit < counter'. Figure out which is
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ir_rvalue *counter = cond->operands[0]->as_dereference_variable();
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ir_constant *limit = cond->operands[1]->as_constant();
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enum ir_expression_operation cmp = cond->operation;
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counter = cond->operands[1]->as_dereference_variable();
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limit = cond->operands[0]->as_constant();
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case ir_binop_less: cmp = ir_binop_gequal; break;
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case ir_binop_greater: cmp = ir_binop_lequal; break;
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case ir_binop_lequal: cmp = ir_binop_greater; break;
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case ir_binop_gequal: cmp = ir_binop_less; break;
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default: assert(!"Should not get here.");
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if ((counter == NULL) || (limit == NULL))
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ir_variable *var = counter->variable_referenced();
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ir_rvalue *init = find_initial_value(ir, var);
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foreach_list(iv_node, &ls->induction_variables) {
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loop_variable *lv = (loop_variable *) iv_node;
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if (lv->var == var) {
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const int iterations = calculate_iterations(init, limit,
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if (iterations >= 0) {
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/* If the new iteration count is lower than the previously
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* believed iteration count, update the loop control values.
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if (iterations < max_iterations) {
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ir->from = init->clone(ir, NULL);
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ir->to = limit->clone(ir, NULL);
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ir->increment = lv->increment->clone(ir, NULL);
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ir->counter = lv->var;
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max_iterations = iterations;
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/* Remove the conditional break statement. The loop
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* controls are now set such that the exit condition will be
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assert(ls->num_loop_jumps > 0);
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ls->num_loop_jumps--;
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this->progress = true;
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/* If we have proven the one of the loop exit conditions is satisifed before
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* running the loop once, remove the loop.
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if (max_iterations == 0)
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ls->max_iterations = max_iterations;
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return visit_continue;
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set_loop_controls(exec_list *instructions, loop_state *ls)
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loop_control_visitor v(ls);