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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.
+ */
+
+#include "compiler/glsl_types.h"
+#include "loop_analysis.h"
+#include "ir_hierarchical_visitor.h"
+
+static bool is_loop_terminator(ir_if *ir);
+
+static bool all_expression_operands_are_loop_constant(ir_rvalue *,
+ hash_table *);
+
+static ir_rvalue *get_basic_induction_increment(ir_assignment *, hash_table *);
+
+
+/**
+ * Record the fact that the given loop variable was referenced inside the loop.
+ *
+ * \arg in_assignee is true if the reference was on the LHS of an assignment.
+ *
+ * \arg in_conditional_code_or_nested_loop is true if the reference occurred
+ * inside an if statement or a nested loop.
+ *
+ * \arg current_assignment is the ir_assignment node that the loop variable is
+ * on the LHS of, if any (ignored if \c in_assignee is false).
+ */
+void
+loop_variable::record_reference(bool in_assignee,
+ bool in_conditional_code_or_nested_loop,
+ ir_assignment *current_assignment)
+{
+ if (in_assignee) {
+ assert(current_assignment != NULL);
+
+ if (in_conditional_code_or_nested_loop ||
+ current_assignment->condition != NULL) {
+ this->conditional_or_nested_assignment = true;
+ }
+
+ if (this->first_assignment == NULL) {
+ assert(this->num_assignments == 0);
+
+ this->first_assignment = current_assignment;
+ }
+
+ this->num_assignments++;
+ } else if (this->first_assignment == current_assignment) {
+ /* This catches the case where the variable is used in the RHS of an
+ * assignment where it is also in the LHS.
+ */
+ this->read_before_write = true;
+ }
+}
+
+
+loop_state::loop_state()
+{
+ this->ht = hash_table_ctor(0, hash_table_pointer_hash,
+ hash_table_pointer_compare);
+ this->mem_ctx = ralloc_context(NULL);
+ this->loop_found = false;
+}
+
+
+loop_state::~loop_state()
+{
+ hash_table_dtor(this->ht);
+ ralloc_free(this->mem_ctx);
+}
+
+
+loop_variable_state *
+loop_state::insert(ir_loop *ir)
+{
+ loop_variable_state *ls = new(this->mem_ctx) loop_variable_state;
+
+ hash_table_insert(this->ht, ls, ir);
+ this->loop_found = true;
+
+ return ls;
+}
+
+
+loop_variable_state *
+loop_state::get(const ir_loop *ir)
+{
+ return (loop_variable_state *) hash_table_find(this->ht, ir);
+}
+
+
+loop_variable *
+loop_variable_state::get(const ir_variable *ir)
+{
+ return (loop_variable *) hash_table_find(this->var_hash, ir);
+}
+
+
+loop_variable *
+loop_variable_state::insert(ir_variable *var)
+{
+ void *mem_ctx = ralloc_parent(this);
+ loop_variable *lv = rzalloc(mem_ctx, loop_variable);
+
+ lv->var = var;
+
+ hash_table_insert(this->var_hash, lv, lv->var);
+ this->variables.push_tail(lv);
+
+ return lv;
+}
+
+
+loop_terminator *
+loop_variable_state::insert(ir_if *if_stmt)
+{
+ void *mem_ctx = ralloc_parent(this);
+ loop_terminator *t = new(mem_ctx) loop_terminator();
+
+ t->ir = if_stmt;
+ this->terminators.push_tail(t);
+
+ return t;
+}
+
+
+/**
+ * If the given variable already is recorded in the state for this loop,
+ * return the corresponding loop_variable object that records information
+ * about it.
+ *
+ * Otherwise, create a new loop_variable object to record information about
+ * the variable, and set its \c read_before_write field appropriately based on
+ * \c in_assignee.
+ *
+ * \arg in_assignee is true if this variable was encountered on the LHS of an
+ * assignment.
+ */
+loop_variable *
+loop_variable_state::get_or_insert(ir_variable *var, bool in_assignee)
+{
+ loop_variable *lv = this->get(var);
+
+ if (lv == NULL) {
+ lv = this->insert(var);
+ lv->read_before_write = !in_assignee;
+ }
+
+ return lv;
+}
+
+
+namespace {
+
+class loop_analysis : public ir_hierarchical_visitor {
+public:
+ loop_analysis(loop_state *loops);
+
+ virtual ir_visitor_status visit(ir_loop_jump *);
+ virtual ir_visitor_status visit(ir_dereference_variable *);
+
+ virtual ir_visitor_status visit_enter(ir_call *);
+
+ virtual ir_visitor_status visit_enter(ir_loop *);
+ virtual ir_visitor_status visit_leave(ir_loop *);
+ virtual ir_visitor_status visit_enter(ir_assignment *);
+ virtual ir_visitor_status visit_leave(ir_assignment *);
+ virtual ir_visitor_status visit_enter(ir_if *);
+ virtual ir_visitor_status visit_leave(ir_if *);
+
+ loop_state *loops;
+
+ int if_statement_depth;
+
+ ir_assignment *current_assignment;
+
+ exec_list state;
+};
+
+} /* anonymous namespace */
+
+loop_analysis::loop_analysis(loop_state *loops)
+ : loops(loops), if_statement_depth(0), current_assignment(NULL)
+{
+ /* empty */
+}
+
+
+ir_visitor_status
+loop_analysis::visit(ir_loop_jump *ir)
+{
+ (void) ir;
+
+ assert(!this->state.is_empty());
+
+ loop_variable_state *const ls =
+ (loop_variable_state *) this->state.get_head();
+
+ ls->num_loop_jumps++;
+
+ return visit_continue;
+}
+
+
+ir_visitor_status
+loop_analysis::visit_enter(ir_call *)
+{
+ /* Mark every loop that we're currently analyzing as containing an ir_call
+ * (even those at outer nesting levels).
+ */
+ foreach_in_list(loop_variable_state, ls, &this->state) {
+ ls->contains_calls = true;
+ }
+
+ return visit_continue_with_parent;
+}
+
+
+ir_visitor_status
+loop_analysis::visit(ir_dereference_variable *ir)
+{
+ /* If we're not somewhere inside a loop, there's nothing to do.
+ */
+ if (this->state.is_empty())
+ return visit_continue;
+
+ bool nested = false;
+
+ foreach_in_list(loop_variable_state, ls, &this->state) {
+ ir_variable *var = ir->variable_referenced();
+ loop_variable *lv = ls->get_or_insert(var, this->in_assignee);
+
+ lv->record_reference(this->in_assignee,
+ nested || this->if_statement_depth > 0,
+ this->current_assignment);
+ nested = true;
+ }
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_enter(ir_loop *ir)
+{
+ loop_variable_state *ls = this->loops->insert(ir);
+ this->state.push_head(ls);
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_leave(ir_loop *ir)
+{
+ loop_variable_state *const ls =
+ (loop_variable_state *) this->state.pop_head();
+
+ /* Function calls may contain side effects. These could alter any of our
+ * variables in ways that cannot be known, and may even terminate shader
+ * execution (say, calling discard in the fragment shader). So we can't
+ * rely on any of our analysis about assignments to variables.
+ *
+ * We could perform some conservative analysis (prove there's no statically
+ * possible assignment, etc.) but it isn't worth it for now; function
+ * inlining will allow us to unroll loops anyway.
+ */
+ if (ls->contains_calls)
+ return visit_continue;
+
+ foreach_in_list(ir_instruction, node, &ir->body_instructions) {
+ /* Skip over declarations at the start of a loop.
+ */
+ if (node->as_variable())
+ continue;
+
+ ir_if *if_stmt = ((ir_instruction *) node)->as_if();
+
+ if ((if_stmt != NULL) && is_loop_terminator(if_stmt))
+ ls->insert(if_stmt);
+ else
+ break;
+ }
+
+
+ foreach_in_list_safe(loop_variable, lv, &ls->variables) {
+ /* Move variables that are already marked as being loop constant to
+ * a separate list. These trivially don't need to be tested.
+ */
+ if (lv->is_loop_constant()) {
+ lv->remove();
+ ls->constants.push_tail(lv);
+ }
+ }
+
+ /* Each variable assigned in the loop that isn't already marked as being loop
+ * constant might still be loop constant. The requirements at this point
+ * are:
+ *
+ * - Variable is written before it is read.
+ *
+ * - Only one assignment to the variable.
+ *
+ * - All operands on the RHS of the assignment are also loop constants.
+ *
+ * The last requirement is the reason for the progress loop. A variable
+ * marked as a loop constant on one pass may allow other variables to be
+ * marked as loop constant on following passes.
+ */
+ bool progress;
+ do {
+ progress = false;
+
+ foreach_in_list_safe(loop_variable, lv, &ls->variables) {
+ if (lv->conditional_or_nested_assignment || (lv->num_assignments > 1))
+ continue;
+
+ /* Process the RHS of the assignment. If all of the variables
+ * accessed there are loop constants, then add this
+ */
+ ir_rvalue *const rhs = lv->first_assignment->rhs;
+ if (all_expression_operands_are_loop_constant(rhs, ls->var_hash)) {
+ lv->rhs_clean = true;
+
+ if (lv->is_loop_constant()) {
+ progress = true;
+
+ lv->remove();
+ ls->constants.push_tail(lv);
+ }
+ }
+ }
+ } while (progress);
+
+ /* The remaining variables that are not loop invariant might be loop
+ * induction variables.
+ */
+ foreach_in_list_safe(loop_variable, lv, &ls->variables) {
+ /* If there is more than one assignment to a variable, it cannot be a
+ * loop induction variable. This isn't strictly true, but this is a
+ * very simple induction variable detector, and it can't handle more
+ * complex cases.
+ */
+ if (lv->num_assignments > 1)
+ continue;
+
+ /* All of the variables with zero assignments in the loop are loop
+ * invariant, and they should have already been filtered out.
+ */
+ assert(lv->num_assignments == 1);
+ assert(lv->first_assignment != NULL);
+
+ /* The assignment to the variable in the loop must be unconditional and
+ * not inside a nested loop.
+ */
+ if (lv->conditional_or_nested_assignment)
+ continue;
+
+ /* Basic loop induction variables have a single assignment in the loop
+ * that has the form 'VAR = VAR + i' or 'VAR = VAR - i' where i is a
+ * loop invariant.
+ */
+ ir_rvalue *const inc =
+ get_basic_induction_increment(lv->first_assignment, ls->var_hash);
+ if (inc != NULL) {
+ lv->increment = inc;
+
+ lv->remove();
+ ls->induction_variables.push_tail(lv);
+ }
+ }
+
+ /* Search the loop terminating conditions for those of the form 'i < c'
+ * where i is a loop induction variable, c is a constant, and < is any
+ * relative operator. From each of these we can infer an iteration count.
+ * Also figure out which terminator (if any) produces the smallest
+ * iteration count--this is the limiting terminator.
+ */
+ foreach_in_list(loop_terminator, t, &ls->terminators) {
+ ir_if *if_stmt = t->ir;
+
+ /* If-statements can be either 'if (expr)' or 'if (deref)'. We only care
+ * about the former here.
+ */
+ ir_expression *cond = if_stmt->condition->as_expression();
+ if (cond == NULL)
+ continue;
+
+ switch (cond->operation) {
+ case ir_binop_less:
+ case ir_binop_greater:
+ case ir_binop_lequal:
+ case ir_binop_gequal: {
+ /* The expressions that we care about will either be of the form
+ * 'counter < limit' or 'limit < counter'. Figure out which is
+ * which.
+ */
+ ir_rvalue *counter = cond->operands[0]->as_dereference_variable();
+ ir_constant *limit = cond->operands[1]->as_constant();
+ enum ir_expression_operation cmp = cond->operation;
+
+ if (limit == NULL) {
+ counter = cond->operands[1]->as_dereference_variable();
+ limit = cond->operands[0]->as_constant();
+
+ switch (cmp) {
+ case ir_binop_less: cmp = ir_binop_greater; break;
+ case ir_binop_greater: cmp = ir_binop_less; break;
+ case ir_binop_lequal: cmp = ir_binop_gequal; break;
+ case ir_binop_gequal: cmp = ir_binop_lequal; break;
+ default: assert(!"Should not get here.");
+ }
+ }
+
+ if ((counter == NULL) || (limit == NULL))
+ break;
+
+ ir_variable *var = counter->variable_referenced();
+
+ ir_rvalue *init = find_initial_value(ir, var);
+
+ loop_variable *lv = ls->get(var);
+ if (lv != NULL && lv->is_induction_var()) {
+ t->iterations = calculate_iterations(init, limit, lv->increment,
+ cmp);
+
+ if (t->iterations >= 0 &&
+ (ls->limiting_terminator == NULL ||
+ t->iterations < ls->limiting_terminator->iterations)) {
+ ls->limiting_terminator = t;
+ }
+ }
+ break;
+ }
+
+ default:
+ break;
+ }
+ }
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_enter(ir_if *ir)
+{
+ (void) ir;
+
+ if (!this->state.is_empty())
+ this->if_statement_depth++;
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_leave(ir_if *ir)
+{
+ (void) ir;
+
+ if (!this->state.is_empty())
+ this->if_statement_depth--;
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_enter(ir_assignment *ir)
+{
+ /* If we're not somewhere inside a loop, there's nothing to do.
+ */
+ if (this->state.is_empty())
+ return visit_continue_with_parent;
+
+ this->current_assignment = ir;
+
+ return visit_continue;
+}
+
+ir_visitor_status
+loop_analysis::visit_leave(ir_assignment *ir)
+{
+ /* Since the visit_enter exits with visit_continue_with_parent for this
+ * case, the loop state stack should never be empty here.
+ */
+ assert(!this->state.is_empty());
+
+ assert(this->current_assignment == ir);
+ this->current_assignment = NULL;
+
+ return visit_continue;
+}
+
+
+class examine_rhs : public ir_hierarchical_visitor {
+public:
+ examine_rhs(hash_table *loop_variables)
+ {
+ this->only_uses_loop_constants = true;
+ this->loop_variables = loop_variables;
+ }
+
+ virtual ir_visitor_status visit(ir_dereference_variable *ir)
+ {
+ loop_variable *lv =
+ (loop_variable *) hash_table_find(this->loop_variables, ir->var);
+
+ assert(lv != NULL);
+
+ if (lv->is_loop_constant()) {
+ return visit_continue;
+ } else {
+ this->only_uses_loop_constants = false;
+ return visit_stop;
+ }
+ }
+
+ hash_table *loop_variables;
+ bool only_uses_loop_constants;
+};
+
+
+bool
+all_expression_operands_are_loop_constant(ir_rvalue *ir, hash_table *variables)
+{
+ examine_rhs v(variables);
+
+ ir->accept(&v);
+
+ return v.only_uses_loop_constants;
+}
+
+
+ir_rvalue *
+get_basic_induction_increment(ir_assignment *ir, hash_table *var_hash)
+{
+ /* The RHS must be a binary expression.
+ */
+ ir_expression *const rhs = ir->rhs->as_expression();
+ if ((rhs == NULL)
+ || ((rhs->operation != ir_binop_add)
+ && (rhs->operation != ir_binop_sub)))
+ return NULL;
+
+ /* One of the of operands of the expression must be the variable assigned.
+ * If the operation is subtraction, the variable in question must be the
+ * "left" operand.
+ */
+ ir_variable *const var = ir->lhs->variable_referenced();
+
+ ir_variable *const op0 = rhs->operands[0]->variable_referenced();
+ ir_variable *const op1 = rhs->operands[1]->variable_referenced();
+
+ if (((op0 != var) && (op1 != var))
+ || ((op1 == var) && (rhs->operation == ir_binop_sub)))
+ return NULL;
+
+ ir_rvalue *inc = (op0 == var) ? rhs->operands[1] : rhs->operands[0];
+
+ if (inc->as_constant() == NULL) {
+ ir_variable *const inc_var = inc->variable_referenced();
+ if (inc_var != NULL) {
+ loop_variable *lv =
+ (loop_variable *) hash_table_find(var_hash, inc_var);
+
+ if (lv == NULL || !lv->is_loop_constant()) {
+ assert(lv != NULL);
+ inc = NULL;
+ }
+ } else
+ inc = NULL;
+ }
+
+ if ((inc != NULL) && (rhs->operation == ir_binop_sub)) {
+ void *mem_ctx = ralloc_parent(ir);
+
+ inc = new(mem_ctx) ir_expression(ir_unop_neg,
+ inc->type,
+ inc->clone(mem_ctx, NULL),
+ NULL);
+ }
+
+ return inc;
+}
+
+
+/**
+ * Detect whether an if-statement is a loop terminating condition
+ *
+ * Detects if-statements of the form
+ *
+ * (if (expression bool ...) (break))
+ */
+bool
+is_loop_terminator(ir_if *ir)
+{
+ if (!ir->else_instructions.is_empty())
+ return false;
+
+ ir_instruction *const inst =
+ (ir_instruction *) ir->then_instructions.get_head();
+ if (inst == NULL)
+ return false;
+
+ if (inst->ir_type != ir_type_loop_jump)
+ return false;
+
+ ir_loop_jump *const jump = (ir_loop_jump *) inst;
+ if (jump->mode != ir_loop_jump::jump_break)
+ return false;
+
+ return true;
+}
+
+
+loop_state *
+analyze_loop_variables(exec_list *instructions)
+{
+ loop_state *loops = new loop_state;
+ loop_analysis v(loops);
+
+ v.run(instructions);
+ return v.loops;
+}
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