/*
* 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"
#include "util/bitset.h"
typedef enum {
undefined,
invariant,
not_invariant,
basic_induction
} nir_loop_variable_type;
typedef struct nir_basic_induction_var {
nir_alu_instr *alu; /* The def of the alu-operation */
nir_ssa_def *def_outside_loop; /* The phi-src outside the loop */
} 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 */
bool in_if_branch;
/* True if variable is in a nested loop */
bool in_nested_loop;
/* Could be a basic_induction if following uniforms are inlined */
nir_src *init_src;
nir_alu_src *update_src;
} nir_loop_variable;
typedef struct {
/* The loop we store information for */
nir_loop *loop;
/* Loop_variable for all ssa_defs in function */
nir_loop_variable *loop_vars;
BITSET_WORD *loop_vars_init;
/* 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)
{
nir_loop_variable *var = &(state->loop_vars[value->index]);
if (!BITSET_TEST(state->loop_vars_init, value->index)) {
var->in_loop = false;
var->def = value;
var->in_if_branch = false;
var->in_nested_loop = false;
var->init_src = NULL;
var->update_src = NULL;
if (value->parent_instr->type == nir_instr_type_load_const)
var->type = invariant;
else
var->type = undefined;
BITSET_SET(state->loop_vars_init, value->index);
}
return var;
}
typedef struct {
loop_info_state *state;
bool in_if_branch;
bool in_nested_loop;
} 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_nested_loop) {
var->in_nested_loop = true;
} else if (loop_init_state->in_if_branch) {
var->in_if_branch = 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;
}
/** Calculate an estimated cost in number of instructions
*
* We do this so that we don't unroll loops which will later get massively
* inflated due to int64 or fp64 lowering. The estimates provided here don't
* have to be massively accurate; they just have to be good enough that loop
* unrolling doesn't cause things to blow up too much.
*/
static unsigned
instr_cost(nir_instr *instr, const nir_shader_compiler_options *options)
{
if (instr->type == nir_instr_type_intrinsic ||
instr->type == nir_instr_type_tex)
return 1;
if (instr->type != nir_instr_type_alu)
return 0;
nir_alu_instr *alu = nir_instr_as_alu(instr);
const nir_op_info *info = &nir_op_infos[alu->op];
unsigned cost = 1;
if (alu->op == nir_op_flrp) {
if ((options->lower_flrp16 && nir_dest_bit_size(alu->dest.dest) == 16) ||
(options->lower_flrp32 && nir_dest_bit_size(alu->dest.dest) == 32) ||
(options->lower_flrp64 && nir_dest_bit_size(alu->dest.dest) == 64))
cost *= 3;
}
/* Assume everything 16 or 32-bit is cheap.
*
* There are no 64-bit ops that don't have a 64-bit thing as their
* destination or first source.
*/
if (nir_dest_bit_size(alu->dest.dest) < 64 &&
nir_src_bit_size(alu->src[0].src) < 64)
return cost;
bool is_fp64 = nir_dest_bit_size(alu->dest.dest) == 64 &&
nir_alu_type_get_base_type(info->output_type) == nir_type_float;
for (unsigned i = 0; i < info->num_inputs; i++) {
if (nir_src_bit_size(alu->src[i].src) == 64 &&
nir_alu_type_get_base_type(info->input_types[i]) == nir_type_float)
is_fp64 = true;
}
if (is_fp64) {
/* If it's something lowered normally, it's expensive. */
if (options->lower_doubles_options &
nir_lower_doubles_op_to_options_mask(alu->op))
cost *= 20;
/* If it's full software, it's even more expensive */
if (options->lower_doubles_options & nir_lower_fp64_full_software)
cost *= 100;
return cost;
} else {
if (options->lower_int64_options &
nir_lower_int64_op_to_options_mask(alu->op)) {
/* These require a doing the division algorithm. */
if (alu->op == nir_op_idiv || alu->op == nir_op_udiv ||
alu->op == nir_op_imod || alu->op == nir_op_umod ||
alu->op == nir_op_irem)
return cost * 100;
/* Other int64 lowering isn't usually all that expensive */
return cost * 5;
}
return cost;
}
}
static bool
init_loop_block(nir_block *block, loop_info_state *state,
bool in_if_branch, bool in_nested_loop,
const nir_shader_compiler_options *options)
{
init_loop_state init_state = {.in_if_branch = in_if_branch,
.in_nested_loop = in_nested_loop,
.state = state };
nir_foreach_instr(instr, block) {
state->loop->info->instr_cost += instr_cost(instr, options);
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_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_if_branch && !var->in_nested_loop);
if (mark_invariant(var->def, state))
list_del(&var->process_link);
}
}
/* If all of the instruction sources point to identical ALU instructions (as
* per nir_instrs_equal), return one of the ALU instructions. Otherwise,
* return NULL.
*/
static nir_alu_instr *
phi_instr_as_alu(nir_phi_instr *phi)
{
nir_alu_instr *first = NULL;
nir_foreach_phi_src(src, phi) {
assert(src->src.is_ssa);
if (src->src.ssa->parent_instr->type != nir_instr_type_alu)
return NULL;
nir_alu_instr *alu = nir_instr_as_alu(src->src.ssa->parent_instr);
if (first == NULL) {
first = alu;
} else {
if (!nir_instrs_equal(&first->instr, &alu->instr))
return NULL;
}
}
return first;
}
static bool
alu_src_has_identity_swizzle(nir_alu_instr *alu, unsigned src_idx)
{
assert(nir_op_infos[alu->op].input_sizes[src_idx] == 0);
assert(alu->dest.dest.is_ssa);
for (unsigned i = 0; i < alu->dest.dest.ssa.num_components; i++) {
if (alu->src[src_idx].swizzle[i] != i)
return false;
}
return true;
}
static bool
is_only_uniform_src(nir_src *src)
{
if (!src->is_ssa)
return false;
nir_instr *instr = src->ssa->parent_instr;
switch (instr->type) {
case nir_instr_type_alu: {
/* Return true if all sources return true. */
nir_alu_instr *alu = nir_instr_as_alu(instr);
for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
if (!is_only_uniform_src(&alu->src[i].src))
return false;
}
return true;
}
case nir_instr_type_intrinsic: {
nir_intrinsic_instr *inst = nir_instr_as_intrinsic(instr);
/* current uniform inline only support load ubo */
return inst->intrinsic == nir_intrinsic_load_ubo;
}
case nir_instr_type_load_const:
/* Always return true for constants. */
return true;
default:
return false;
}
}
static bool
compute_induction_information(loop_info_state *state)
{
bool found_induction_var = false;
unsigned num_induction_vars = 0;
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_if_branch && !var->in_nested_loop &&
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_src *init_src = NULL;
nir_loop_variable *alu_src_var = NULL;
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 an if branch or nested loop then don't
* attempt to go any further.
*/
if (src_var->in_if_branch || src_var->in_nested_loop)
break;
/* Detect inductions variables that are incremented in both branches
* of an unnested if rather than in a loop block.
*/
if (is_var_phi(src_var)) {
nir_phi_instr *src_phi =
nir_instr_as_phi(src_var->def->parent_instr);
nir_alu_instr *src_phi_alu = phi_instr_as_alu(src_phi);
if (src_phi_alu) {
src_var = get_loop_var(&src_phi_alu->dest.dest.ssa, state);
if (!src_var->in_if_branch)
break;
}
}
if (!src_var->in_loop && !biv->def_outside_loop) {
biv->def_outside_loop = src_var->def;
init_src = &src->src;
} else if (is_var_alu(src_var) && !biv->alu) {
alu_src_var = src_var;
nir_alu_instr *alu = nir_instr_as_alu(src_var->def->parent_instr);
/* Check for unsupported alu operations */
if (alu->op != nir_op_iadd && alu->op != nir_op_fadd)
break;
if (nir_op_infos[alu->op].num_inputs == 2) {
for (unsigned i = 0; i < 2; i++) {
/* Is one of the operands const or uniform, and the other the phi.
* The phi source can't be swizzled in any way.
*/
if (alu->src[1-i].src.ssa == &phi->dest.ssa &&
alu_src_has_identity_swizzle(alu, 1 - i)) {
nir_src *src = &alu->src[i].src;
if (nir_src_is_const(*src))
biv->alu = alu;
else if (is_only_uniform_src(src)) {
/* Update value of induction variable is a statement
* contains only uniform and constant
*/
var->update_src = alu->src + i;
biv->alu = alu;
}
}
}
}
if (!biv->alu)
break;
} else {
biv->alu = NULL;
break;
}
}
if (biv->alu && biv->def_outside_loop) {
nir_instr *inst = biv->def_outside_loop->parent_instr;
if (inst->type == nir_instr_type_load_const) {
/* Initial value of induction variable is a constant */
if (var->update_src) {
alu_src_var->update_src = var->update_src;
ralloc_free(biv);
} else {
alu_src_var->type = basic_induction;
alu_src_var->ind = biv;
var->type = basic_induction;
var->ind = biv;
found_induction_var = true;
}
num_induction_vars += 2;
} else if (is_only_uniform_src(init_src)) {
/* Initial value of induction variable is a uniform */
var->init_src = init_src;
alu_src_var->init_src = var->init_src;
alu_src_var->update_src = var->update_src;
num_induction_vars += 2;
ralloc_free(biv);
} else {
var->update_src = NULL;
ralloc_free(biv);
}
} else {
var->update_src = NULL;
ralloc_free(biv);
}
}
nir_loop_info *info = state->loop->info;
ralloc_free(info->induction_vars);
info->num_induction_vars = 0;
/* record induction variables into nir_loop_info */
if (num_induction_vars) {
info->induction_vars = ralloc_array(info, nir_loop_induction_variable,
num_induction_vars);
list_for_each_entry(nir_loop_variable, var, &state->process_list,
process_link) {
if (var->type == basic_induction || var->init_src || var->update_src) {
nir_loop_induction_variable *ivar =
&info->induction_vars[info->num_induction_vars++];
ivar->def = var->def;
ivar->init_src = var->init_src;
ivar->update_src = var->update_src;
}
}
/* don't overflow */
assert(info->num_induction_vars <= num_induction_vars);
}
return found_induction_var;
}
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 (nir_block_ends_in_break(last_then)) {
break_blk = last_then;
continue_from_blk = last_else;
continue_from_then = false;
} else if (nir_block_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)) {
state->loop->info->complex_loop = true;
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) {
state->loop->info->complex_loop = true;
return false;
}
nir_loop_terminator *terminator =
rzalloc(state->loop->info, nir_loop_terminator);
list_addtail(&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;
}
/* This function looks for an array access within a loop that uses an
* induction variable for the array index. If found it returns the size of the
* array, otherwise 0 is returned. If we find an induction var we pass it back
* to the caller via array_index_out.
*/
static unsigned
find_array_access_via_induction(loop_info_state *state,
nir_deref_instr *deref,
nir_loop_variable **array_index_out)
{
for (nir_deref_instr *d = deref; d; d = nir_deref_instr_parent(d)) {
if (d->deref_type != nir_deref_type_array)
continue;
assert(d->arr.index.is_ssa);
nir_loop_variable *array_index = get_loop_var(d->arr.index.ssa, state);
if (array_index->type != basic_induction)
continue;
if (array_index_out)
*array_index_out = array_index;
nir_deref_instr *parent = nir_deref_instr_parent(d);
if (glsl_type_is_array_or_matrix(parent->type)) {
return glsl_get_length(parent->type);
} else {
assert(glsl_type_is_vector(parent->type));
return glsl_get_vector_elements(parent->type);
}
}
return 0;
}
static bool
guess_loop_limit(loop_info_state *state, nir_const_value *limit_val,
nir_ssa_scalar basic_ind)
{
unsigned min_array_size = 0;
nir_foreach_block_in_cf_node(block, &state->loop->cf_node) {
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. */
if (intrin->intrinsic == nir_intrinsic_load_deref ||
intrin->intrinsic == nir_intrinsic_store_deref ||
intrin->intrinsic == nir_intrinsic_copy_deref) {
nir_loop_variable *array_idx = NULL;
unsigned array_size =
find_array_access_via_induction(state,
nir_src_as_deref(intrin->src[0]),
&array_idx);
if (array_idx && basic_ind.def == array_idx->def &&
(min_array_size == 0 || min_array_size > array_size)) {
/* Array indices are scalars */
assert(basic_ind.def->num_components == 1);
min_array_size = array_size;
}
if (intrin->intrinsic != nir_intrinsic_copy_deref)
continue;
array_size =
find_array_access_via_induction(state,
nir_src_as_deref(intrin->src[1]),
&array_idx);
if (array_idx && basic_ind.def == array_idx->def &&
(min_array_size == 0 || min_array_size > array_size)) {
/* Array indices are scalars */
assert(basic_ind.def->num_components == 1);
min_array_size = array_size;
}
}
}
}
if (min_array_size) {
*limit_val = nir_const_value_for_uint(min_array_size,
basic_ind.def->bit_size);
return true;
}
return false;
}
static bool
try_find_limit_of_alu(nir_ssa_scalar limit, nir_const_value *limit_val,
nir_loop_terminator *terminator, loop_info_state *state)
{
if (!nir_ssa_scalar_is_alu(limit))
return false;
nir_op limit_op = nir_ssa_scalar_alu_op(limit);
if (limit_op == nir_op_imin || limit_op == nir_op_fmin) {
for (unsigned i = 0; i < 2; i++) {
nir_ssa_scalar src = nir_ssa_scalar_chase_alu_src(limit, i);
if (nir_ssa_scalar_is_const(src)) {
*limit_val = nir_ssa_scalar_as_const_value(src);
terminator->exact_trip_count_unknown = true;
return true;
}
}
}
return false;
}
static nir_const_value
eval_const_unop(nir_op op, unsigned bit_size, nir_const_value src0,
unsigned execution_mode)
{
assert(nir_op_infos[op].num_inputs == 1);
nir_const_value dest;
nir_const_value *src[1] = { &src0 };
nir_eval_const_opcode(op, &dest, 1, bit_size, src, execution_mode);
return dest;
}
static nir_const_value
eval_const_binop(nir_op op, unsigned bit_size,
nir_const_value src0, nir_const_value src1,
unsigned execution_mode)
{
assert(nir_op_infos[op].num_inputs == 2);
nir_const_value dest;
nir_const_value *src[2] = { &src0, &src1 };
nir_eval_const_opcode(op, &dest, 1, bit_size, src, execution_mode);
return dest;
}
static int32_t
get_iteration(nir_op cond_op, nir_const_value initial, nir_const_value step,
nir_const_value limit, unsigned bit_size,
unsigned execution_mode)
{
nir_const_value span, iter;
switch (cond_op) {
case nir_op_ige:
case nir_op_ilt:
case nir_op_ieq:
case nir_op_ine:
span = eval_const_binop(nir_op_isub, bit_size, limit, initial,
execution_mode);
iter = eval_const_binop(nir_op_idiv, bit_size, span, step,
execution_mode);
break;
case nir_op_uge:
case nir_op_ult:
span = eval_const_binop(nir_op_isub, bit_size, limit, initial,
execution_mode);
iter = eval_const_binop(nir_op_udiv, bit_size, span, step,
execution_mode);
break;
case nir_op_fge:
case nir_op_flt:
case nir_op_feq:
case nir_op_fneu:
span = eval_const_binop(nir_op_fsub, bit_size, limit, initial,
execution_mode);
iter = eval_const_binop(nir_op_fdiv, bit_size, span,
step, execution_mode);
iter = eval_const_unop(nir_op_f2i64, bit_size, iter, execution_mode);
break;
default:
return -1;
}
uint64_t iter_u64 = nir_const_value_as_uint(iter, bit_size);
return iter_u64 > INT_MAX ? -1 : (int)iter_u64;
}
static bool
will_break_on_first_iteration(nir_const_value step,
nir_alu_type induction_base_type,
unsigned trip_offset,
nir_op cond_op, unsigned bit_size,
nir_const_value initial,
nir_const_value limit,
bool limit_rhs, bool invert_cond,
unsigned execution_mode)
{
if (trip_offset == 1) {
nir_op add_op;
switch (induction_base_type) {
case nir_type_float:
add_op = nir_op_fadd;
break;
case nir_type_int:
case nir_type_uint:
add_op = nir_op_iadd;
break;
default:
unreachable("Unhandled induction variable base type!");
}
initial = eval_const_binop(add_op, bit_size, initial, step,
execution_mode);
}
nir_const_value *src[2];
src[limit_rhs ? 0 : 1] = &initial;
src[limit_rhs ? 1 : 0] = &limit;
/* Evaluate the loop exit condition */
nir_const_value result;
nir_eval_const_opcode(cond_op, &result, 1, bit_size, src, execution_mode);
return invert_cond ? !result.b : result.b;
}
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,
unsigned execution_mode)
{
assert(nir_op_infos[cond_op].num_inputs == 2);
nir_const_value iter_src;
nir_op mul_op;
nir_op add_op;
switch (induction_base_type) {
case nir_type_float:
iter_src = nir_const_value_for_float(iter_int, bit_size);
mul_op = nir_op_fmul;
add_op = nir_op_fadd;
break;
case nir_type_int:
case nir_type_uint:
iter_src = nir_const_value_for_int(iter_int, bit_size);
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_result =
eval_const_binop(mul_op, bit_size, iter_src, step, execution_mode);
/* Add the initial value to the accumulated induction variable total */
nir_const_value add_result =
eval_const_binop(add_op, bit_size, mul_result, initial, execution_mode);
nir_const_value *src[2];
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, &result, 1, bit_size, src, execution_mode);
return invert_cond ? !result.b : result.b;
}
static int
calculate_iterations(nir_const_value initial, nir_const_value step,
nir_const_value limit, nir_alu_instr *alu,
nir_ssa_scalar cond, nir_op alu_op, bool limit_rhs,
bool invert_cond, unsigned execution_mode)
{
/* 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[alu_op].input_types[1]) == nir_type_int ||
nir_alu_type_get_base_type(nir_op_infos[alu_op].input_types[1]) == nir_type_uint);
} else {
assert(nir_alu_type_get_base_type(nir_op_infos[alu_op].input_types[0]) ==
induction_base_type);
}
/* Only variable with these update ops were marked as induction. */
assert(alu->op == nir_op_iadd || alu->op == nir_op_fadd);
/* 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;
nir_alu_instr *cond_alu = nir_instr_as_alu(cond.def->parent_instr);
if (cond_alu->src[0].src.ssa == &alu->dest.dest.ssa ||
cond_alu->src[1].src.ssa == &alu->dest.dest.ssa) {
trip_offset = 1;
}
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);
/* get_iteration works under assumption that iterator will be
* incremented or decremented until it hits the limit,
* however if the loop condition is false on the first iteration
* get_iteration's assumption is broken. Handle such loops first.
*/
if (will_break_on_first_iteration(step, induction_base_type, trip_offset,
alu_op, bit_size, initial,
limit, limit_rhs, invert_cond,
execution_mode)) {
return 0;
}
int iter_int = get_iteration(alu_op, initial, step, limit, bit_size,
execution_mode);
/* 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);
*/
for (int bias = -1; bias <= 1; bias++) {
const int iter_bias = iter_int + bias;
if (test_iterations(iter_bias, step, limit, alu_op, bit_size,
induction_base_type, initial,
limit_rhs, invert_cond, execution_mode)) {
return iter_bias > 0 ? iter_bias - trip_offset : iter_bias;
}
}
return -1;
}
static nir_op
inverse_comparison(nir_op alu_op)
{
switch (alu_op) {
case nir_op_fge:
return nir_op_flt;
case nir_op_ige:
return nir_op_ilt;
case nir_op_uge:
return nir_op_ult;
case nir_op_flt:
return nir_op_fge;
case nir_op_ilt:
return nir_op_ige;
case nir_op_ult:
return nir_op_uge;
case nir_op_feq:
return nir_op_fneu;
case nir_op_ieq:
return nir_op_ine;
case nir_op_fneu:
return nir_op_feq;
case nir_op_ine:
return nir_op_ieq;
default:
unreachable("Unsuported comparison!");
}
}
static bool
get_induction_and_limit_vars(nir_ssa_scalar cond,
nir_ssa_scalar *ind,
nir_ssa_scalar *limit,
bool *limit_rhs,
loop_info_state *state)
{
nir_ssa_scalar rhs, lhs;
lhs = nir_ssa_scalar_chase_alu_src(cond, 0);
rhs = nir_ssa_scalar_chase_alu_src(cond, 1);
if (get_loop_var(lhs.def, state)->type == basic_induction) {
*ind = lhs;
*limit = rhs;
*limit_rhs = true;
return true;
} else if (get_loop_var(rhs.def, state)->type == basic_induction) {
*ind = rhs;
*limit = lhs;
*limit_rhs = false;
return true;
} else {
return false;
}
}
static bool
try_find_trip_count_vars_in_iand(nir_ssa_scalar *cond,
nir_ssa_scalar *ind,
nir_ssa_scalar *limit,
bool *limit_rhs,
loop_info_state *state)
{
const nir_op alu_op = nir_ssa_scalar_alu_op(*cond);
assert(alu_op == nir_op_ieq || alu_op == nir_op_inot);
nir_ssa_scalar iand = nir_ssa_scalar_chase_alu_src(*cond, 0);
if (alu_op == nir_op_ieq) {
nir_ssa_scalar zero = nir_ssa_scalar_chase_alu_src(*cond, 1);
if (!nir_ssa_scalar_is_alu(iand) || !nir_ssa_scalar_is_const(zero)) {
/* Maybe we had it the wrong way, flip things around */
nir_ssa_scalar tmp = zero;
zero = iand;
iand = tmp;
/* If we still didn't find what we need then return */
if (!nir_ssa_scalar_is_const(zero))
return false;
}
/* If the loop is not breaking on (x && y) == 0 then return */
if (nir_ssa_scalar_as_uint(zero) != 0)
return false;
}
if (!nir_ssa_scalar_is_alu(iand))
return false;
if (nir_ssa_scalar_alu_op(iand) != nir_op_iand)
return false;
/* Check if iand src is a terminator condition and try get induction var
* and trip limit var.
*/
bool found_induction_var = false;
for (unsigned i = 0; i < 2; i++) {
nir_ssa_scalar src = nir_ssa_scalar_chase_alu_src(iand, i);
if (nir_is_supported_terminator_condition(src) &&
get_induction_and_limit_vars(src, ind, limit, limit_rhs, state)) {
*cond = src;
found_induction_var = true;
/* If we've found one with a constant limit, stop. */
if (nir_ssa_scalar_is_const(*limit))
return true;
}
}
return found_induction_var;
}
/* 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, unsigned execution_mode)
{
bool trip_count_known = true;
bool guessed_trip_count = false;
nir_loop_terminator *limiting_terminator = NULL;
int max_trip_count = -1;
list_for_each_entry(nir_loop_terminator, terminator,
&state->loop->info->loop_terminator_list,
loop_terminator_link) {
assert(terminator->nif->condition.is_ssa);
nir_ssa_scalar cond = { terminator->nif->condition.ssa, 0 };
if (!nir_ssa_scalar_is_alu(cond)) {
/* 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_op alu_op = nir_ssa_scalar_alu_op(cond);
bool limit_rhs;
nir_ssa_scalar basic_ind = { NULL, 0 };
nir_ssa_scalar limit;
if ((alu_op == nir_op_inot || alu_op == nir_op_ieq) &&
try_find_trip_count_vars_in_iand(&cond, &basic_ind, &limit,
&limit_rhs, state)) {
/* The loop is exiting on (x && y) == 0 so we need to get the
* inverse of x or y (i.e. which ever contained the induction var) in
* order to compute the trip count.
*/
alu_op = inverse_comparison(nir_ssa_scalar_alu_op(cond));
trip_count_known = false;
terminator->exact_trip_count_unknown = true;
}
if (!basic_ind.def) {
if (nir_is_supported_terminator_condition(cond)) {
get_induction_and_limit_vars(cond, &basic_ind,
&limit, &limit_rhs, state);
}
}
/* The comparison has to have a basic induction variable for us to be
* able to find trip counts.
*/
if (!basic_ind.def) {
trip_count_known = false;
continue;
}
terminator->induction_rhs = !limit_rhs;
/* Attempt to find a constant limit for the loop */
nir_const_value limit_val;
if (nir_ssa_scalar_is_const(limit)) {
limit_val = nir_ssa_scalar_as_const_value(limit);
} else {
trip_count_known = false;
if (!try_find_limit_of_alu(limit, &limit_val, terminator, state)) {
/* Guess loop limit based on array access */
if (!guess_loop_limit(state, &limit_val, basic_ind)) {
continue;
}
guessed_trip_count = true;
}
}
/* 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_basic_induction_var *ind_var =
get_loop_var(basic_ind.def, state)->ind;
/* The basic induction var might be a vector but, because we guarantee
* earlier that the phi source has a scalar swizzle, we can take the
* component from basic_ind.
*/
nir_ssa_scalar initial_s = { ind_var->def_outside_loop, basic_ind.comp };
nir_ssa_scalar alu_s = { &ind_var->alu->dest.dest.ssa, basic_ind.comp };
nir_const_value initial_val = nir_ssa_scalar_as_const_value(initial_s);
/* We are guaranteed by earlier code that at least one of these sources
* is a constant but we don't know which.
*/
nir_const_value step_val;
memset(&step_val, 0, sizeof(step_val));
UNUSED bool found_step_value = false;
assert(nir_op_infos[ind_var->alu->op].num_inputs == 2);
for (unsigned i = 0; i < 2; i++) {
nir_ssa_scalar alu_src = nir_ssa_scalar_chase_alu_src(alu_s, i);
if (nir_ssa_scalar_is_const(alu_src)) {
found_step_value = true;
step_val = nir_ssa_scalar_as_const_value(alu_src);
break;
}
}
assert(found_step_value);
int iterations = calculate_iterations(initial_val, step_val, limit_val,
ind_var->alu, cond,
alu_op, limit_rhs,
terminator->continue_from_then,
execution_mode);
/* Where we not able to calculate the iteration count */
if (iterations == -1) {
trip_count_known = false;
guessed_trip_count = false;
continue;
}
if (guessed_trip_count) {
guessed_trip_count = false;
if (state->loop->info->guessed_trip_count == 0 ||
state->loop->info->guessed_trip_count > iterations)
state->loop->info->guessed_trip_count = iterations;
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 (max_trip_count == -1 || iterations < max_trip_count) {
max_trip_count = iterations;
limiting_terminator = terminator;
}
}
state->loop->info->exact_trip_count_known = trip_count_known;
if (max_trip_count > -1)
state->loop->info->max_trip_count = max_trip_count;
state->loop->info->limiting_terminator = limiting_terminator;
}
static bool
force_unroll_array_access(loop_info_state *state, nir_deref_instr *deref)
{
unsigned array_size = find_array_access_via_induction(state, deref, NULL);
if (array_size) {
if ((array_size == state->loop->info->max_trip_count) &&
nir_deref_mode_must_be(deref, nir_var_shader_in |
nir_var_shader_out |
nir_var_shader_temp |
nir_var_function_temp))
return true;
if (nir_deref_mode_must_be(deref, state->indirect_mask))
return true;
}
return false;
}
static bool
force_unroll_heuristics(loop_info_state *state, 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_deref ||
intrin->intrinsic == nir_intrinsic_store_deref ||
intrin->intrinsic == nir_intrinsic_copy_deref) {
if (force_unroll_array_access(state,
nir_src_as_deref(intrin->src[0])))
return true;
if (intrin->intrinsic == nir_intrinsic_copy_deref &&
force_unroll_array_access(state,
nir_src_as_deref(intrin->src[1])))
return true;
}
}
return false;
}
static void
get_loop_info(loop_info_state *state, nir_function_impl *impl)
{
nir_shader *shader = impl->function->shader;
const nir_shader_compiler_options *options = shader->options;
/* 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, false, options);
break;
case nir_cf_node_if:
nir_foreach_block_in_cf_node(block, node)
init_loop_block(block, state, true, false, options);
break;
case nir_cf_node_loop:
nir_foreach_block_in_cf_node(block, node) {
init_loop_block(block, state, false, true, options);
}
break;
case nir_cf_node_function:
break;
}
}
/* 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;
}
/* 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;
/* Run through each of the terminators and try to compute a trip-count */
find_trip_count(state, impl->function->shader->info.float_controls_execution_mode);
nir_foreach_block_in_cf_node(block, &state->loop->cf_node) {
if (force_unroll_heuristics(state, block)) {
state->loop->info->force_unroll = true;
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 = ralloc_array(mem_ctx, nir_loop_variable,
impl->ssa_alloc);
state->loop_vars_init = rzalloc_array(mem_ctx, BITSET_WORD,
BITSET_WORDS(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);
}