/*
* Copyright © 2014 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.
*
* Authors:
* Jason Ekstrand (jason@jlekstrand.net)
*
*/
#include "nir.h"
#include "nir_builder.h"
#include "nir_phi_builder.h"
#include "nir_vla.h"
struct deref_node {
struct deref_node *parent;
const struct glsl_type *type;
bool lower_to_ssa;
/* Only valid for things that end up in the direct list.
* Note that multiple nir_deref_vars may correspond to this node, but they
* will all be equivalent, so any is as good as the other.
*/
nir_deref_var *deref;
struct exec_node direct_derefs_link;
struct set *loads;
struct set *stores;
struct set *copies;
struct nir_phi_builder_value *pb_value;
struct deref_node *wildcard;
struct deref_node *indirect;
struct deref_node *children[0];
};
struct lower_variables_state {
nir_shader *shader;
void *dead_ctx;
nir_function_impl *impl;
/* A hash table mapping variables to deref_node data */
struct hash_table *deref_var_nodes;
/* A hash table mapping fully-qualified direct dereferences, i.e.
* dereferences with no indirect or wildcard array dereferences, to
* deref_node data.
*
* At the moment, we only lower loads, stores, and copies that can be
* trivially lowered to loads and stores, i.e. copies with no indirects
* and no wildcards. If a part of a variable that is being loaded from
* and/or stored into is also involved in a copy operation with
* wildcards, then we lower that copy operation to loads and stores, but
* otherwise we leave copies with wildcards alone. Since the only derefs
* used in these loads, stores, and trivial copies are ones with no
* wildcards and no indirects, these are precisely the derefs that we
* can actually consider lowering.
*/
struct exec_list direct_deref_nodes;
/* Controls whether get_deref_node will add variables to the
* direct_deref_nodes table. This is turned on when we are initially
* scanning for load/store instructions. It is then turned off so we
* don't accidentally change the direct_deref_nodes table while we're
* iterating throug it.
*/
bool add_to_direct_deref_nodes;
struct nir_phi_builder *phi_builder;
};
static struct deref_node *
deref_node_create(struct deref_node *parent,
const struct glsl_type *type, nir_shader *shader)
{
size_t size = sizeof(struct deref_node) +
glsl_get_length(type) * sizeof(struct deref_node *);
struct deref_node *node = rzalloc_size(shader, size);
node->type = type;
node->parent = parent;
node->deref = NULL;
exec_node_init(&node->direct_derefs_link);
return node;
}
/* Returns the deref node associated with the given variable. This will be
* the root of the tree representing all of the derefs of the given variable.
*/
static struct deref_node *
get_deref_node_for_var(nir_variable *var, struct lower_variables_state *state)
{
struct deref_node *node;
struct hash_entry *var_entry =
_mesa_hash_table_search(state->deref_var_nodes, var);
if (var_entry) {
return var_entry->data;
} else {
node = deref_node_create(NULL, var->type, state->dead_ctx);
_mesa_hash_table_insert(state->deref_var_nodes, var, node);
return node;
}
}
/* Gets the deref_node for the given deref chain and creates it if it
* doesn't yet exist. If the deref is fully-qualified and direct and
* state->add_to_direct_deref_nodes is true, it will be added to the hash
* table of of fully-qualified direct derefs.
*/
static struct deref_node *
get_deref_node(nir_deref_var *deref, struct lower_variables_state *state)
{
bool is_direct = true;
/* Start at the base of the chain. */
struct deref_node *node = get_deref_node_for_var(deref->var, state);
assert(deref->deref.type == node->type);
for (nir_deref *tail = deref->deref.child; tail; tail = tail->child) {
switch (tail->deref_type) {
case nir_deref_type_struct: {
nir_deref_struct *deref_struct = nir_deref_as_struct(tail);
assert(deref_struct->index < glsl_get_length(node->type));
if (node->children[deref_struct->index] == NULL)
node->children[deref_struct->index] =
deref_node_create(node, tail->type, state->dead_ctx);
node = node->children[deref_struct->index];
break;
}
case nir_deref_type_array: {
nir_deref_array *arr = nir_deref_as_array(tail);
switch (arr->deref_array_type) {
case nir_deref_array_type_direct:
/* This is possible if a loop unrolls and generates an
* out-of-bounds offset. We need to handle this at least
* somewhat gracefully.
*/
if (arr->base_offset >= glsl_get_length(node->type))
return NULL;
if (node->children[arr->base_offset] == NULL)
node->children[arr->base_offset] =
deref_node_create(node, tail->type, state->dead_ctx);
node = node->children[arr->base_offset];
break;
case nir_deref_array_type_indirect:
if (node->indirect == NULL)
node->indirect = deref_node_create(node, tail->type,
state->dead_ctx);
node = node->indirect;
is_direct = false;
break;
case nir_deref_array_type_wildcard:
if (node->wildcard == NULL)
node->wildcard = deref_node_create(node, tail->type,
state->dead_ctx);
node = node->wildcard;
is_direct = false;
break;
default:
unreachable("Invalid array deref type");
}
break;
}
default:
unreachable("Invalid deref type");
}
}
assert(node);
/* Only insert if it isn't already in the list. */
if (is_direct && state->add_to_direct_deref_nodes &&
node->direct_derefs_link.next == NULL) {
node->deref = deref;
assert(deref->var != NULL);
exec_list_push_tail(&state->direct_deref_nodes,
&node->direct_derefs_link);
}
return node;
}
/* \sa foreach_deref_node_match */
static bool
foreach_deref_node_worker(struct deref_node *node, nir_deref *deref,
bool (* cb)(struct deref_node *node,
struct lower_variables_state *state),
struct lower_variables_state *state)
{
if (deref->child == NULL) {
return cb(node, state);
} else {
switch (deref->child->deref_type) {
case nir_deref_type_array: {
nir_deref_array *arr = nir_deref_as_array(deref->child);
assert(arr->deref_array_type == nir_deref_array_type_direct);
if (node->children[arr->base_offset] &&
!foreach_deref_node_worker(node->children[arr->base_offset],
deref->child, cb, state))
return false;
if (node->wildcard &&
!foreach_deref_node_worker(node->wildcard,
deref->child, cb, state))
return false;
return true;
}
case nir_deref_type_struct: {
nir_deref_struct *str = nir_deref_as_struct(deref->child);
if (node->children[str->index] &&
!foreach_deref_node_worker(node->children[str->index],
deref->child, cb, state))
return false;
return true;
}
default:
unreachable("Invalid deref child type");
}
}
}
/* Walks over every "matching" deref_node and calls the callback. A node
* is considered to "match" if either refers to that deref or matches up t
* a wildcard. In other words, the following would match a[6].foo[3].bar:
*
* a[6].foo[3].bar
* a[*].foo[3].bar
* a[6].foo[*].bar
* a[*].foo[*].bar
*
* The given deref must be a full-length and fully qualified (no wildcards
* or indirects) deref chain.
*/
static bool
foreach_deref_node_match(nir_deref_var *deref,
bool (* cb)(struct deref_node *node,
struct lower_variables_state *state),
struct lower_variables_state *state)
{
nir_deref_var var_deref = *deref;
var_deref.deref.child = NULL;
struct deref_node *node = get_deref_node(&var_deref, state);
if (node == NULL)
return false;
return foreach_deref_node_worker(node, &deref->deref, cb, state);
}
/* \sa deref_may_be_aliased */
static bool
deref_may_be_aliased_node(struct deref_node *node, nir_deref *deref,
struct lower_variables_state *state)
{
if (deref->child == NULL) {
return false;
} else {
switch (deref->child->deref_type) {
case nir_deref_type_array: {
nir_deref_array *arr = nir_deref_as_array(deref->child);
if (arr->deref_array_type == nir_deref_array_type_indirect)
return true;
/* If there is an indirect at this level, we're aliased. */
if (node->indirect)
return true;
assert(arr->deref_array_type == nir_deref_array_type_direct);
if (node->children[arr->base_offset] &&
deref_may_be_aliased_node(node->children[arr->base_offset],
deref->child, state))
return true;
if (node->wildcard &&
deref_may_be_aliased_node(node->wildcard, deref->child, state))
return true;
return false;
}
case nir_deref_type_struct: {
nir_deref_struct *str = nir_deref_as_struct(deref->child);
if (node->children[str->index]) {
return deref_may_be_aliased_node(node->children[str->index],
deref->child, state);
} else {
return false;
}
}
default:
unreachable("Invalid nir_deref child type");
}
}
}
/* Returns true if there are no indirects that can ever touch this deref.
*
* For example, if the given deref is a[6].foo, then any uses of a[i].foo
* would cause this to return false, but a[i].bar would not affect it
* because it's a different structure member. A var_copy involving of
* a[*].bar also doesn't affect it because that can be lowered to entirely
* direct load/stores.
*
* We only support asking this question about fully-qualified derefs.
* Obviously, it's pointless to ask this about indirects, but we also
* rule-out wildcards. Handling Wildcard dereferences would involve
* checking each array index to make sure that there aren't any indirect
* references.
*/
static bool
deref_may_be_aliased(nir_deref_var *deref,
struct lower_variables_state *state)
{
return deref_may_be_aliased_node(get_deref_node_for_var(deref->var, state),
&deref->deref, state);
}
static void
register_load_instr(nir_intrinsic_instr *load_instr,
struct lower_variables_state *state)
{
struct deref_node *node = get_deref_node(load_instr->variables[0], state);
if (node == NULL)
return;
if (node->loads == NULL)
node->loads = _mesa_set_create(state->dead_ctx, _mesa_hash_pointer,
_mesa_key_pointer_equal);
_mesa_set_add(node->loads, load_instr);
}
static void
register_store_instr(nir_intrinsic_instr *store_instr,
struct lower_variables_state *state)
{
struct deref_node *node = get_deref_node(store_instr->variables[0], state);
if (node == NULL)
return;
if (node->stores == NULL)
node->stores = _mesa_set_create(state->dead_ctx, _mesa_hash_pointer,
_mesa_key_pointer_equal);
_mesa_set_add(node->stores, store_instr);
}
static void
register_copy_instr(nir_intrinsic_instr *copy_instr,
struct lower_variables_state *state)
{
for (unsigned idx = 0; idx < 2; idx++) {
struct deref_node *node =
get_deref_node(copy_instr->variables[idx], state);
if (node == NULL)
continue;
if (node->copies == NULL)
node->copies = _mesa_set_create(state->dead_ctx, _mesa_hash_pointer,
_mesa_key_pointer_equal);
_mesa_set_add(node->copies, copy_instr);
}
}
/* Registers all variable uses in the given block. */
static bool
register_variable_uses_block(nir_block *block,
struct lower_variables_state *state)
{
nir_foreach_instr_safe(instr, block) {
if (instr->type != nir_instr_type_intrinsic)
continue;
nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
switch (intrin->intrinsic) {
case nir_intrinsic_load_var:
register_load_instr(intrin, state);
break;
case nir_intrinsic_store_var:
register_store_instr(intrin, state);
break;
case nir_intrinsic_copy_var:
register_copy_instr(intrin, state);
break;
default:
continue;
}
}
return true;
}
/* Walks over all of the copy instructions to or from the given deref_node
* and lowers them to load/store intrinsics.
*/
static bool
lower_copies_to_load_store(struct deref_node *node,
struct lower_variables_state *state)
{
if (!node->copies)
return true;
struct set_entry *copy_entry;
set_foreach(node->copies, copy_entry) {
nir_intrinsic_instr *copy = (void *)copy_entry->key;
nir_lower_var_copy_instr(copy, state->shader);
for (unsigned i = 0; i < 2; ++i) {
struct deref_node *arg_node =
get_deref_node(copy->variables[i], state);
/* Only bother removing copy entries for other nodes */
if (arg_node == NULL || arg_node == node)
continue;
struct set_entry *arg_entry = _mesa_set_search(arg_node->copies, copy);
assert(arg_entry);
_mesa_set_remove(arg_node->copies, arg_entry);
}
nir_instr_remove(©->instr);
}
node->copies = NULL;
return true;
}
/* Performs variable renaming
*
* This algorithm is very similar to the one outlined in "Efficiently
* Computing Static Single Assignment Form and the Control Dependence
* Graph" by Cytron et al. The primary difference is that we only put one
* SSA def on the stack per block.
*/
static bool
rename_variables(struct lower_variables_state *state)
{
nir_builder b;
nir_builder_init(&b, state->impl);
nir_foreach_block(block, state->impl) {
nir_foreach_instr_safe(instr, block) {
if (instr->type != nir_instr_type_intrinsic)
continue;
nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
switch (intrin->intrinsic) {
case nir_intrinsic_load_var: {
struct deref_node *node =
get_deref_node(intrin->variables[0], state);
if (node == NULL) {
/* If we hit this path then we are referencing an invalid
* value. Most likely, we unrolled something and are
* reading past the end of some array. In any case, this
* should result in an undefined value.
*/
nir_ssa_undef_instr *undef =
nir_ssa_undef_instr_create(state->shader,
intrin->num_components,
intrin->dest.ssa.bit_size);
nir_instr_insert_before(&intrin->instr, &undef->instr);
nir_instr_remove(&intrin->instr);
nir_ssa_def_rewrite_uses(&intrin->dest.ssa,
nir_src_for_ssa(&undef->def));
continue;
}
if (!node->lower_to_ssa)
continue;
nir_alu_instr *mov = nir_alu_instr_create(state->shader,
nir_op_imov);
mov->src[0].src = nir_src_for_ssa(
nir_phi_builder_value_get_block_def(node->pb_value, block));
for (unsigned i = intrin->num_components; i < 4; i++)
mov->src[0].swizzle[i] = 0;
assert(intrin->dest.is_ssa);
mov->dest.write_mask = (1 << intrin->num_components) - 1;
nir_ssa_dest_init(&mov->instr, &mov->dest.dest,
intrin->num_components,
intrin->dest.ssa.bit_size, NULL);
nir_instr_insert_before(&intrin->instr, &mov->instr);
nir_instr_remove(&intrin->instr);
nir_ssa_def_rewrite_uses(&intrin->dest.ssa,
nir_src_for_ssa(&mov->dest.dest.ssa));
break;
}
case nir_intrinsic_store_var: {
struct deref_node *node =
get_deref_node(intrin->variables[0], state);
if (node == NULL) {
/* Probably an out-of-bounds array store. That should be a
* no-op. */
nir_instr_remove(&intrin->instr);
continue;
}
if (!node->lower_to_ssa)
continue;
assert(intrin->num_components ==
glsl_get_vector_elements(node->type));
assert(intrin->src[0].is_ssa);
nir_ssa_def *new_def;
b.cursor = nir_before_instr(&intrin->instr);
unsigned wrmask = nir_intrinsic_write_mask(intrin);
if (wrmask == (1 << intrin->num_components) - 1) {
/* Whole variable store - just copy the source. Note that
* intrin->num_components and intrin->src[0].ssa->num_components
* may differ.
*/
unsigned swiz[4];
for (unsigned i = 0; i < 4; i++)
swiz[i] = i < intrin->num_components ? i : 0;
new_def = nir_swizzle(&b, intrin->src[0].ssa, swiz,
intrin->num_components, false);
} else {
nir_ssa_def *old_def =
nir_phi_builder_value_get_block_def(node->pb_value, block);
/* For writemasked store_var intrinsics, we combine the newly
* written values with the existing contents of unwritten
* channels, creating a new SSA value for the whole vector.
*/
nir_ssa_def *srcs[4];
for (unsigned i = 0; i < intrin->num_components; i++) {
if (wrmask & (1 << i)) {
srcs[i] = nir_channel(&b, intrin->src[0].ssa, i);
} else {
srcs[i] = nir_channel(&b, old_def, i);
}
}
new_def = nir_vec(&b, srcs, intrin->num_components);
}
assert(new_def->num_components == intrin->num_components);
nir_phi_builder_value_set_block_def(node->pb_value, block, new_def);
nir_instr_remove(&intrin->instr);
break;
}
default:
break;
}
}
}
return true;
}
/** Implements a pass to lower variable uses to SSA values
*
* This path walks the list of instructions and tries to lower as many
* local variable load/store operations to SSA defs and uses as it can.
* The process involves four passes:
*
* 1) Iterate over all of the instructions and mark where each local
* variable deref is used in a load, store, or copy. While we're at
* it, we keep track of all of the fully-qualified (no wildcards) and
* fully-direct references we see and store them in the
* direct_deref_nodes hash table.
*
* 2) Walk over the list of fully-qualified direct derefs generated in
* the previous pass. For each deref, we determine if it can ever be
* aliased, i.e. if there is an indirect reference anywhere that may
* refer to it. If it cannot be aliased, we mark it for lowering to an
* SSA value. At this point, we lower any var_copy instructions that
* use the given deref to load/store operations.
*
* 3) Walk over the list of derefs we plan to lower to SSA values and
* insert phi nodes as needed.
*
* 4) Perform "variable renaming" by replacing the load/store instructions
* with SSA definitions and SSA uses.
*/
static bool
nir_lower_vars_to_ssa_impl(nir_function_impl *impl)
{
struct lower_variables_state state;
state.shader = impl->function->shader;
state.dead_ctx = ralloc_context(state.shader);
state.impl = impl;
state.deref_var_nodes = _mesa_hash_table_create(state.dead_ctx,
_mesa_hash_pointer,
_mesa_key_pointer_equal);
exec_list_make_empty(&state.direct_deref_nodes);
/* Build the initial deref structures and direct_deref_nodes table */
state.add_to_direct_deref_nodes = true;
nir_foreach_block(block, impl) {
register_variable_uses_block(block, &state);
}
bool progress = false;
nir_metadata_require(impl, nir_metadata_block_index);
/* We're about to iterate through direct_deref_nodes. Don't modify it. */
state.add_to_direct_deref_nodes = false;
foreach_list_typed_safe(struct deref_node, node, direct_derefs_link,
&state.direct_deref_nodes) {
nir_deref_var *deref = node->deref;
if (deref->var->data.mode != nir_var_local) {
exec_node_remove(&node->direct_derefs_link);
continue;
}
if (deref_may_be_aliased(deref, &state)) {
exec_node_remove(&node->direct_derefs_link);
continue;
}
node->lower_to_ssa = true;
progress = true;
foreach_deref_node_match(deref, lower_copies_to_load_store, &state);
}
if (!progress)
return false;
nir_metadata_require(impl, nir_metadata_dominance);
/* We may have lowered some copy instructions to load/store
* instructions. The uses from the copy instructions hav already been
* removed but we need to rescan to ensure that the uses from the newly
* added load/store instructions are registered. We need this
* information for phi node insertion below.
*/
nir_foreach_block(block, impl) {
register_variable_uses_block(block, &state);
}
state.phi_builder = nir_phi_builder_create(state.impl);
NIR_VLA(BITSET_WORD, store_blocks, BITSET_WORDS(state.impl->num_blocks));
foreach_list_typed(struct deref_node, node, direct_derefs_link,
&state.direct_deref_nodes) {
if (!node->lower_to_ssa)
continue;
memset(store_blocks, 0,
BITSET_WORDS(state.impl->num_blocks) * sizeof(*store_blocks));
assert(node->deref->var->constant_initializer == NULL);
if (node->stores) {
struct set_entry *store_entry;
set_foreach(node->stores, store_entry) {
nir_intrinsic_instr *store =
(nir_intrinsic_instr *)store_entry->key;
BITSET_SET(store_blocks, store->instr.block->index);
}
}
node->pb_value =
nir_phi_builder_add_value(state.phi_builder,
glsl_get_vector_elements(node->type),
glsl_get_bit_size(node->type),
store_blocks);
}
rename_variables(&state);
nir_phi_builder_finish(state.phi_builder);
nir_metadata_preserve(impl, nir_metadata_block_index |
nir_metadata_dominance);
ralloc_free(state.dead_ctx);
return progress;
}
bool
nir_lower_vars_to_ssa(nir_shader *shader)
{
bool progress = false;
nir_foreach_function(function, shader) {
if (function->impl)
progress |= nir_lower_vars_to_ssa_impl(function->impl);
}
return progress;
}