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