/*
* 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 "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 *);
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 = rzalloc(mem_ctx, loop_terminator);
t->ir = if_stmt;
this->terminators.push_tail(t);
return t;
}
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;
};
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 *ir)
{
/* If we're not somewhere inside a loop, there's nothing to do. */
if (this->state.is_empty())
return visit_continue;
loop_variable_state *const ls =
(loop_variable_state *) this->state.get_head();
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;
loop_variable_state *const ls =
(loop_variable_state *) this->state.get_head();
ir_variable *var = ir->variable_referenced();
loop_variable *lv = ls->get(var);
if (lv == NULL) {
lv = ls->insert(var);
lv->read_before_write = !this->in_assignee;
}
if (this->in_assignee) {
assert(this->current_assignment != NULL);
lv->conditional_assignment = (this->if_statement_depth > 0)
|| (this->current_assignment->condition != NULL);
if (lv->first_assignment == NULL) {
assert(lv->num_assignments == 0);
lv->first_assignment = this->current_assignment;
}
lv->num_assignments++;
} else if (lv->first_assignment == this->current_assignment) {
/* This catches the case where the variable is used in the RHS of an
* assignment where it is also in the LHS.
*/
lv->read_before_write = 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_list(node, &ir->body_instructions) {
/* Skip over declarations at the start of a loop.
*/
if (((ir_instruction *) 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_list_safe(node, &ls->variables) {
loop_variable *lv = (loop_variable *) node;
/* 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_list_safe(node, &ls->variables) {
loop_variable *lv = (loop_variable *) node;
if (lv->conditional_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_list_safe(node, &ls->variables) {
loop_variable *lv = (loop_variable *) node;
/* 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 assignmnet to the variable in the loop must be unconditional.
*/
if (lv->conditional_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->iv_scale = NULL;
lv->biv = lv->var;
lv->increment = inc;
lv->remove();
ls->induction_variables.push_tail(lv);
}
}
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->is_loop_constant())
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;
}