/*
* 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 *);
/**
* 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;
}