/*
* Copyright © 2015 Thomas Helland
*
* 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 "nir.h"
#include "nir_constant_expressions.h"
#include "nir_loop_analyze.h"
typedef enum {
undefined,
invariant,
not_invariant,
basic_induction
} nir_loop_variable_type;
struct nir_basic_induction_var;
typedef struct {
/* A link for the work list */
struct list_head process_link;
bool in_loop;
/* The ssa_def associated with this info */
nir_ssa_def *def;
/* The type of this ssa_def */
nir_loop_variable_type type;
/* If this is of type basic_induction */
struct nir_basic_induction_var *ind;
/* True if variable is in an if branch or a nested loop */
bool in_control_flow;
} nir_loop_variable;
typedef struct nir_basic_induction_var {
nir_op alu_op; /* The type of alu-operation */
nir_loop_variable *alu_def; /* The def of the alu-operation */
nir_loop_variable *invariant; /* The invariant alu-operand */
nir_loop_variable *def_outside_loop; /* The phi-src outside the loop */
} nir_basic_induction_var;
typedef struct {
/* The loop we store information for */
nir_loop *loop;
/* Loop_variable for all ssa_defs in function */
nir_loop_variable *loop_vars;
/* A list of the loop_vars to analyze */
struct list_head process_list;
nir_variable_mode indirect_mask;
} loop_info_state;
static nir_loop_variable *
get_loop_var(nir_ssa_def *value, loop_info_state *state)
{
return &(state->loop_vars[value->index]);
}
typedef struct {
loop_info_state *state;
bool in_control_flow;
} init_loop_state;
static bool
init_loop_def(nir_ssa_def *def, void *void_init_loop_state)
{
init_loop_state *loop_init_state = void_init_loop_state;
nir_loop_variable *var = get_loop_var(def, loop_init_state->state);
if (loop_init_state->in_control_flow) {
var->in_control_flow = true;
} else {
/* Add to the tail of the list. That way we start at the beginning of
* the defs in the loop instead of the end when walking the list. This
* means less recursive calls. Only add defs that are not in nested
* loops or conditional blocks.
*/
list_addtail(&var->process_link, &loop_init_state->state->process_list);
}
var->in_loop = true;
return true;
}
static bool
init_loop_block(nir_block *block, loop_info_state *state,
bool in_control_flow)
{
init_loop_state init_state = {.in_control_flow = in_control_flow,
.state = state };
nir_foreach_instr(instr, block) {
if (instr->type == nir_instr_type_intrinsic ||
instr->type == nir_instr_type_alu ||
instr->type == nir_instr_type_tex) {
state->loop->info->num_instructions++;
}
nir_foreach_ssa_def(instr, init_loop_def, &init_state);
}
return true;
}
static inline bool
is_var_alu(nir_loop_variable *var)
{
return var->def->parent_instr->type == nir_instr_type_alu;
}
static inline bool
is_var_constant(nir_loop_variable *var)
{
return var->def->parent_instr->type == nir_instr_type_load_const;
}
static inline bool
is_var_phi(nir_loop_variable *var)
{
return var->def->parent_instr->type == nir_instr_type_phi;
}
static inline bool
mark_invariant(nir_ssa_def *def, loop_info_state *state)
{
nir_loop_variable *var = get_loop_var(def, state);
if (var->type == invariant)
return true;
if (!var->in_loop) {
var->type = invariant;
return true;
}
if (var->type == not_invariant)
return false;
if (is_var_alu(var)) {
nir_alu_instr *alu = nir_instr_as_alu(def->parent_instr);
for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
if (!mark_invariant(alu->src[i].src.ssa, state)) {
var->type = not_invariant;
return false;
}
}
var->type = invariant;
return true;
}
/* Phis shouldn't be invariant except if one operand is invariant, and the
* other is the phi itself. These should be removed by opt_remove_phis.
* load_consts are already set to invariant and constant during init,
* and so should return earlier. Remaining op_codes are set undefined.
*/
var->type = not_invariant;
return false;
}
static void
compute_invariance_information(loop_info_state *state)
{
/* An expression is invariant in a loop L if:
* (base cases)
* – it’s a constant
* – it’s a variable use, all of whose single defs are outside of L
* (inductive cases)
* – it’s a pure computation all of whose args are loop invariant
* – it’s a variable use whose single reaching def, and the
* rhs of that def is loop-invariant
*/
list_for_each_entry_safe(nir_loop_variable, var, &state->process_list,
process_link) {
assert(!var->in_control_flow);
if (mark_invariant(var->def, state))
list_del(&var->process_link);
}
}
static bool
compute_induction_information(loop_info_state *state)
{
bool found_induction_var = false;
list_for_each_entry_safe(nir_loop_variable, var, &state->process_list,
process_link) {
/* It can't be an induction variable if it is invariant. Invariants and
* things in nested loops or conditionals should have been removed from
* the list by compute_invariance_information().
*/
assert(!var->in_control_flow && var->type != invariant);
/* We are only interested in checking phis for the basic induction
* variable case as its simple to detect. All basic induction variables
* have a phi node
*/
if (!is_var_phi(var))
continue;
nir_phi_instr *phi = nir_instr_as_phi(var->def->parent_instr);
nir_basic_induction_var *biv = rzalloc(state, nir_basic_induction_var);
nir_foreach_phi_src(src, phi) {
nir_loop_variable *src_var = get_loop_var(src->src.ssa, state);
/* If one of the sources is in a conditional or nested block then
* panic.
*/
if (src_var->in_control_flow)
break;
if (!src_var->in_loop) {
biv->def_outside_loop = src_var;
} else if (is_var_alu(src_var)) {
nir_alu_instr *alu = nir_instr_as_alu(src_var->def->parent_instr);
if (nir_op_infos[alu->op].num_inputs == 2) {
biv->alu_def = src_var;
biv->alu_op = alu->op;
for (unsigned i = 0; i < 2; i++) {
/* Is one of the operands const, and the other the phi */
if (alu->src[i].src.ssa->parent_instr->type == nir_instr_type_load_const &&
alu->src[1-i].src.ssa == &phi->dest.ssa)
biv->invariant = get_loop_var(alu->src[i].src.ssa, state);
}
}
}
}
if (biv->alu_def && biv->def_outside_loop && biv->invariant &&
is_var_constant(biv->def_outside_loop)) {
assert(is_var_constant(biv->invariant));
biv->alu_def->type = basic_induction;
biv->alu_def->ind = biv;
var->type = basic_induction;
var->ind = biv;
found_induction_var = true;
} else {
ralloc_free(biv);
}
}
return found_induction_var;
}
static bool
initialize_ssa_def(nir_ssa_def *def, void *void_state)
{
loop_info_state *state = void_state;
nir_loop_variable *var = get_loop_var(def, state);
var->in_loop = false;
var->def = def;
if (def->parent_instr->type == nir_instr_type_load_const) {
var->type = invariant;
} else {
var->type = undefined;
}
return true;
}
static inline bool
ends_in_break(nir_block *block)
{
if (exec_list_is_empty(&block->instr_list))
return false;
nir_instr *instr = nir_block_last_instr(block);
return instr->type == nir_instr_type_jump &&
nir_instr_as_jump(instr)->type == nir_jump_break;
}
static bool
find_loop_terminators(loop_info_state *state)
{
bool success = false;
foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
if (node->type == nir_cf_node_if) {
nir_if *nif = nir_cf_node_as_if(node);
nir_block *break_blk = NULL;
nir_block *continue_from_blk = NULL;
bool continue_from_then = true;
nir_block *last_then = nir_if_last_then_block(nif);
nir_block *last_else = nir_if_last_else_block(nif);
if (ends_in_break(last_then)) {
break_blk = last_then;
continue_from_blk = last_else;
continue_from_then = false;
} else if (ends_in_break(last_else)) {
break_blk = last_else;
continue_from_blk = last_then;
}
/* If there is a break then we should find a terminator. If we can
* not find a loop terminator, but there is a break-statement then
* we should return false so that we do not try to find trip-count
*/
if (!nir_is_trivial_loop_if(nif, break_blk))
return false;
/* Continue if the if contained no jumps at all */
if (!break_blk)
continue;
if (nif->condition.ssa->parent_instr->type == nir_instr_type_phi)
return false;
nir_loop_terminator *terminator =
rzalloc(state->loop->info, nir_loop_terminator);
list_add(&terminator->loop_terminator_link,
&state->loop->info->loop_terminator_list);
terminator->nif = nif;
terminator->break_block = break_blk;
terminator->continue_from_block = continue_from_blk;
terminator->continue_from_then = continue_from_then;
terminator->conditional_instr = nif->condition.ssa->parent_instr;
success = true;
}
}
return success;
}
static int32_t
get_iteration(nir_op cond_op, nir_const_value *initial, nir_const_value *step,
nir_const_value *limit)
{
int32_t iter;
switch (cond_op) {
case nir_op_ige:
case nir_op_ilt:
case nir_op_ieq:
case nir_op_ine: {
int32_t initial_val = initial->i32[0];
int32_t span = limit->i32[0] - initial_val;
iter = span / step->i32[0];
break;
}
case nir_op_uge:
case nir_op_ult: {
uint32_t initial_val = initial->u32[0];
uint32_t span = limit->u32[0] - initial_val;
iter = span / step->u32[0];
break;
}
case nir_op_fge:
case nir_op_flt:
case nir_op_feq:
case nir_op_fne: {
float initial_val = initial->f32[0];
float span = limit->f32[0] - initial_val;
iter = span / step->f32[0];
break;
}
default:
return -1;
}
return iter;
}
static bool
test_iterations(int32_t iter_int, nir_const_value *step,
nir_const_value *limit, nir_op cond_op, unsigned bit_size,
nir_alu_type induction_base_type,
nir_const_value *initial, bool limit_rhs, bool invert_cond)
{
assert(nir_op_infos[cond_op].num_inputs == 2);
nir_const_value iter_src = { {0, } };
nir_op mul_op;
nir_op add_op;
switch (induction_base_type) {
case nir_type_float:
iter_src.f32[0] = (float) iter_int;
mul_op = nir_op_fmul;
add_op = nir_op_fadd;
break;
case nir_type_int:
case nir_type_uint:
iter_src.i32[0] = iter_int;
mul_op = nir_op_imul;
add_op = nir_op_iadd;
break;
default:
unreachable("Unhandled induction variable base type!");
}
/* Multiple the iteration count we are testing by the number of times we
* step the induction variable each iteration.
*/
nir_const_value mul_src[2] = { iter_src, *step };
nir_const_value mul_result =
nir_eval_const_opcode(mul_op, 1, bit_size, mul_src);
/* Add the initial value to the accumulated induction variable total */
nir_const_value add_src[2] = { mul_result, *initial };
nir_const_value add_result =
nir_eval_const_opcode(add_op, 1, bit_size, add_src);
nir_const_value src[2] = { { {0, } }, { {0, } } };
src[limit_rhs ? 0 : 1] = add_result;
src[limit_rhs ? 1 : 0] = *limit;
/* Evaluate the loop exit condition */
nir_const_value result = nir_eval_const_opcode(cond_op, 1, bit_size, src);
return invert_cond ? (result.u32[0] == 0) : (result.u32[0] != 0);
}
static int
calculate_iterations(nir_const_value *initial, nir_const_value *step,
nir_const_value *limit, nir_loop_variable *alu_def,
nir_alu_instr *cond_alu, bool limit_rhs, bool invert_cond)
{
assert(initial != NULL && step != NULL && limit != NULL);
nir_alu_instr *alu = nir_instr_as_alu(alu_def->def->parent_instr);
/* nir_op_isub should have been lowered away by this point */
assert(alu->op != nir_op_isub);
/* Make sure the alu type for our induction variable is compatible with the
* conditional alus input type. If its not something has gone really wrong.
*/
nir_alu_type induction_base_type =
nir_alu_type_get_base_type(nir_op_infos[alu->op].output_type);
if (induction_base_type == nir_type_int || induction_base_type == nir_type_uint) {
assert(nir_alu_type_get_base_type(nir_op_infos[cond_alu->op].input_types[1]) == nir_type_int ||
nir_alu_type_get_base_type(nir_op_infos[cond_alu->op].input_types[1]) == nir_type_uint);
} else {
assert(nir_alu_type_get_base_type(nir_op_infos[cond_alu->op].input_types[0]) ==
induction_base_type);
}
/* Check for nsupported alu operations */
if (alu->op != nir_op_iadd && alu->op != nir_op_fadd)
return -1;
/* do-while loops can increment the starting value before the condition is
* checked. e.g.
*
* do {
* ndx++;
* } while (ndx < 3);
*
* Here we check if the induction variable is used directly by the loop
* condition and if so we assume we need to step the initial value.
*/
unsigned trip_offset = 0;
if (cond_alu->src[0].src.ssa == alu_def->def ||
cond_alu->src[1].src.ssa == alu_def->def) {
trip_offset = 1;
}
int iter_int = get_iteration(cond_alu->op, initial, step, limit);
/* If iter_int is negative the loop is ill-formed or is the conditional is
* unsigned with a huge iteration count so don't bother going any further.
*/
if (iter_int < 0)
return -1;
/* An explanation from the GLSL unrolling pass:
*
* 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);
*/
assert(nir_src_bit_size(alu->src[0].src) ==
nir_src_bit_size(alu->src[1].src));
unsigned bit_size = nir_src_bit_size(alu->src[0].src);
for (int bias = -1; bias <= 1; bias++) {
const int iter_bias = iter_int + bias;
if (test_iterations(iter_bias, step, limit, cond_alu->op, bit_size,
induction_base_type, initial,
limit_rhs, invert_cond)) {
return iter_bias > 0 ? iter_bias - trip_offset : iter_bias;
}
}
return -1;
}
/* Run through each of the terminators of the loop and try to infer a possible
* trip-count. We need to check them all, and set the lowest trip-count as the
* trip-count of our loop. If one of the terminators has an undecidable
* trip-count we can not safely assume anything about the duration of the
* loop.
*/
static void
find_trip_count(loop_info_state *state)
{
bool trip_count_known = true;
nir_loop_terminator *limiting_terminator = NULL;
int min_trip_count = -1;
list_for_each_entry(nir_loop_terminator, terminator,
&state->loop->info->loop_terminator_list,
loop_terminator_link) {
if (terminator->conditional_instr->type != nir_instr_type_alu) {
/* If we get here the loop is dead and will get cleaned up by the
* nir_opt_dead_cf pass.
*/
trip_count_known = false;
continue;
}
nir_alu_instr *alu = nir_instr_as_alu(terminator->conditional_instr);
nir_loop_variable *basic_ind = NULL;
nir_loop_variable *limit = NULL;
bool limit_rhs = true;
switch (alu->op) {
case nir_op_fge: case nir_op_ige: case nir_op_uge:
case nir_op_flt: case nir_op_ilt: case nir_op_ult:
case nir_op_feq: case nir_op_ieq:
case nir_op_fne: case nir_op_ine:
/* We assume that the limit is the "right" operand */
basic_ind = get_loop_var(alu->src[0].src.ssa, state);
limit = get_loop_var(alu->src[1].src.ssa, state);
if (basic_ind->type != basic_induction) {
/* We had it the wrong way, flip things around */
basic_ind = get_loop_var(alu->src[1].src.ssa, state);
limit = get_loop_var(alu->src[0].src.ssa, state);
limit_rhs = false;
}
/* The comparison has to have a basic induction variable
* and a constant for us to be able to find trip counts
*/
if (basic_ind->type != basic_induction || !is_var_constant(limit)) {
trip_count_known = false;
continue;
}
/* We have determined that we have the following constants:
* (With the typical int i = 0; i < x; i++; as an example)
* - Upper limit.
* - Starting value
* - Step / iteration size
* Thats all thats needed to calculate the trip-count
*/
nir_const_value initial_val =
nir_instr_as_load_const(basic_ind->ind->def_outside_loop->
def->parent_instr)->value;
nir_const_value step_val =
nir_instr_as_load_const(basic_ind->ind->invariant->def->
parent_instr)->value;
nir_const_value limit_val =
nir_instr_as_load_const(limit->def->parent_instr)->value;
int iterations = calculate_iterations(&initial_val, &step_val,
&limit_val,
basic_ind->ind->alu_def, alu,
limit_rhs,
terminator->continue_from_then);
/* Where we not able to calculate the iteration count */
if (iterations == -1) {
trip_count_known = false;
continue;
}
/* If this is the first run or we have found a smaller amount of
* iterations than previously (we have identified a more limiting
* terminator) set the trip count and limiting terminator.
*/
if (min_trip_count == -1 || iterations < min_trip_count) {
min_trip_count = iterations;
limiting_terminator = terminator;
}
break;
default:
trip_count_known = false;
}
}
state->loop->info->is_trip_count_known = trip_count_known;
if (min_trip_count > -1)
state->loop->info->trip_count = min_trip_count;
state->loop->info->limiting_terminator = limiting_terminator;
}
/* Checks if we should force the loop to be unrolled regardless of size
* due to array access heuristics.
*/
static bool
force_unroll_array_access(loop_info_state *state, nir_shader *ns,
nir_deref_var *variable)
{
nir_deref *tail = &variable->deref;
while (tail->child != NULL) {
tail = tail->child;
if (tail->deref_type == nir_deref_type_array) {
nir_deref_array *deref_array = nir_deref_as_array(tail);
if (deref_array->deref_array_type != nir_deref_array_type_indirect)
continue;
nir_loop_variable *array_index =
get_loop_var(deref_array->indirect.ssa, state);
if (array_index->type != basic_induction)
continue;
/* If an array is indexed by a loop induction variable, and the
* array size is exactly the number of loop iterations, this is
* probably a simple for-loop trying to access each element in
* turn; the application may expect it to be unrolled.
*/
if (glsl_get_length(variable->deref.type) ==
state->loop->info->trip_count) {
state->loop->info->force_unroll = true;
return state->loop->info->force_unroll;
}
if (variable->var->data.mode & state->indirect_mask) {
state->loop->info->force_unroll = true;
return state->loop->info->force_unroll;
}
}
}
return false;
}
static bool
force_unroll_heuristics(loop_info_state *state, nir_shader *ns,
nir_block *block)
{
nir_foreach_instr(instr, block) {
if (instr->type != nir_instr_type_intrinsic)
continue;
nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
/* Check for arrays variably-indexed by a loop induction variable.
* Unrolling the loop may convert that access into constant-indexing.
*/
if (intrin->intrinsic == nir_intrinsic_load_var ||
intrin->intrinsic == nir_intrinsic_store_var ||
intrin->intrinsic == nir_intrinsic_copy_var) {
unsigned num_vars =
nir_intrinsic_infos[intrin->intrinsic].num_variables;
for (unsigned i = 0; i < num_vars; i++) {
if (force_unroll_array_access(state, ns, intrin->variables[i]))
return true;
}
}
}
return false;
}
static void
get_loop_info(loop_info_state *state, nir_function_impl *impl)
{
/* Initialize all variables to "outside_loop". This also marks defs
* invariant and constant if they are nir_instr_type_load_consts
*/
nir_foreach_block(block, impl) {
nir_foreach_instr(instr, block)
nir_foreach_ssa_def(instr, initialize_ssa_def, state);
}
/* Add all entries in the outermost part of the loop to the processing list
* Mark the entries in conditionals or in nested loops accordingly
*/
foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
switch (node->type) {
case nir_cf_node_block:
init_loop_block(nir_cf_node_as_block(node), state, false);
break;
case nir_cf_node_if:
nir_foreach_block_in_cf_node(block, node)
init_loop_block(block, state, true);
break;
case nir_cf_node_loop:
nir_foreach_block_in_cf_node(block, node) {
init_loop_block(block, state, true);
}
break;
case nir_cf_node_function:
break;
}
}
/* Induction analysis needs invariance information so get that first */
compute_invariance_information(state);
/* We have invariance information so try to find induction variables */
if (!compute_induction_information(state))
return;
/* Try to find all simple terminators of the loop. If we can't find any,
* or we find possible terminators that have side effects then bail.
*/
if (!find_loop_terminators(state)) {
list_for_each_entry_safe(nir_loop_terminator, terminator,
&state->loop->info->loop_terminator_list,
loop_terminator_link) {
list_del(&terminator->loop_terminator_link);
ralloc_free(terminator);
}
return;
}
/* Run through each of the terminators and try to compute a trip-count */
find_trip_count(state);
nir_shader *ns = impl->function->shader;
foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
if (node->type == nir_cf_node_block) {
if (force_unroll_heuristics(state, ns, nir_cf_node_as_block(node)))
break;
} else {
nir_foreach_block_in_cf_node(block, node) {
if (force_unroll_heuristics(state, ns, block))
break;
}
}
}
}
static loop_info_state *
initialize_loop_info_state(nir_loop *loop, void *mem_ctx,
nir_function_impl *impl)
{
loop_info_state *state = rzalloc(mem_ctx, loop_info_state);
state->loop_vars = rzalloc_array(mem_ctx, nir_loop_variable,
impl->ssa_alloc);
state->loop = loop;
list_inithead(&state->process_list);
if (loop->info)
ralloc_free(loop->info);
loop->info = rzalloc(loop, nir_loop_info);
list_inithead(&loop->info->loop_terminator_list);
return state;
}
static void
process_loops(nir_cf_node *cf_node, nir_variable_mode indirect_mask)
{
switch (cf_node->type) {
case nir_cf_node_block:
return;
case nir_cf_node_if: {
nir_if *if_stmt = nir_cf_node_as_if(cf_node);
foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->then_list)
process_loops(nested_node, indirect_mask);
foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->else_list)
process_loops(nested_node, indirect_mask);
return;
}
case nir_cf_node_loop: {
nir_loop *loop = nir_cf_node_as_loop(cf_node);
foreach_list_typed(nir_cf_node, nested_node, node, &loop->body)
process_loops(nested_node, indirect_mask);
break;
}
default:
unreachable("unknown cf node type");
}
nir_loop *loop = nir_cf_node_as_loop(cf_node);
nir_function_impl *impl = nir_cf_node_get_function(cf_node);
void *mem_ctx = ralloc_context(NULL);
loop_info_state *state = initialize_loop_info_state(loop, mem_ctx, impl);
state->indirect_mask = indirect_mask;
get_loop_info(state, impl);
ralloc_free(mem_ctx);
}
void
nir_loop_analyze_impl(nir_function_impl *impl,
nir_variable_mode indirect_mask)
{
nir_index_ssa_defs(impl);
foreach_list_typed(nir_cf_node, node, node, &impl->body)
process_loops(node, indirect_mask);
}