[Mesa-dev] [PATCH 091/133] nir: Add a pass to lower local variable accesses to SSA values
Jason Ekstrand
jason at jlekstrand.net
Mon Jan 5 22:28:19 PST 2015
On Sun, Jan 4, 2015 at 1:01 PM, Connor Abbott <cwabbott0 at gmail.com> wrote:
> Ok, I'm going to try reviewing this again. I'm pasting the latest version
> of the file from review/nir-v1 and replying to that so that I won't get
> confused between all the various changes and reorganizing things. Here we
> go!
>
> > /*
> > * 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 at jlekstrand.net)
> > *
> > */
> >
> > #include "nir.h"
> >
> > struct deref_node {
> > struct deref_node *parent;
> > const struct glsl_type *type;
> >
> > bool lower_to_ssa;
> >
> > struct set *loads;
> > struct set *stores;
> > struct set *copies;
> >
> > nir_ssa_def **def_stack;
> > nir_ssa_def **def_stack_tail;
> >
> > struct deref_node *wildcard;
> > struct deref_node *indirect;
> > struct deref_node *children[0];
> > };
> >
> > struct lower_variables_state {
> > void *mem_ctx;
> > 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 dereference leaves to deref_node data. A
> deref
> > * is considered a leaf if it is fully-qualified (no wildcards) and
> > * direct. In short, these are the derefs we can actually consider
> > * lowering to SSA values.
> > */
>
> I was mislead by the "leaf" name the first time I reviewed this; having a
> comment explaining what it does helps, but I still think that it's a pretty
> misleading name. "Leaf," at least to me, implies that it's a leaf of the
> dereference tree, which in this case isn't true unless I'm missing
> something here. I think "direct" is the right term here. You already say
> that dereference leaves are "fully qualified (no wild cards) and direct" --
> I would just call something potentially with wildcards + direct references
> "not indirect," and then what you're calling "leaf" becomes just "direct."
>
Yes, "leaf" is a crappy name, but I'm not sure I like the distinction
between "direct" and "not indirect" either. A double-negative should be a
positive. I'm all for a better name, I just haven't found one.
> Also, it was only after reading through the entire thing and thinking
> about it that I realized why we have this hash table -- it's because we can
> only figure out if direct dereferences alias indirect dereferences, so we
> only consider lowering them. Of course, we may have to expand some wildcard
> copies since they're copying the direct dereference we're trying to lower
> to SSA, but otherwise we don't care about them. Idk if you want to explain
> this here.
>
Yes, a comment about that would probably be a good plan.
>
> > struct hash_table *deref_leaves;
> >
> > /* A hash table mapping phi nodes to deref_state data */
> > struct hash_table *phi_table;
> > };
> >
> > /* The following two functions implement a hash and equality check for
> > * variable dreferences. When the hash or equality function encounters
> an
> > * array, all indirects are treated as equal and are never equal to a
> > * direct dereference or a wildcard.
> > *
> > * Some of the magic numbers here were taken from _mesa_hash_data and one
> > * was just a big prime I found on the internet.
> > */
> > static uint32_t
> > hash_deref(const void *void_deref)
> > {
> > const nir_deref *deref = void_deref;
> >
> > uint32_t hash;
> > if (deref->child) {
> > hash = hash_deref(deref->child);
> > } else {
> > hash = 2166136261ul;
> > }
> >
> > switch (deref->deref_type) {
> > case nir_deref_type_var:
> > hash ^= _mesa_hash_pointer(nir_deref_as_var(deref)->var);
> > break;
> > case nir_deref_type_array: {
> > nir_deref_array *array = nir_deref_as_array(deref);
> > hash += 268435183 * array->deref_array_type;
> > if (array->deref_array_type == nir_deref_array_type_direct)
> > hash ^= array->base_offset; /* Some prime */
> > break;
> > }
> > case nir_deref_type_struct:
> > hash ^= nir_deref_as_struct(deref)->index;
> > break;
> > }
> >
> > return hash * 0x01000193;
> > }
>
> I know I complained about this already but... could we just use
> _mesa_hash_data directly here, or at least properly implement FNV-1a here?
> It should be the same or less code either way (FNV-1a is really, really
> easy), and we can use something with a (presumably) solid mathematical
> basis that's been proven in practice. To me, that sounds better than
> multiplying by random primes found on the Internet and praying that we get
> a good distribution.
>
Meh... I'm not convinced it's hurting us, but I also don't care. I'll add
the stuff to hash_table.h
> Another orthogonal thing which I may have also mentioned before, is that I
> think we should be using a for loop here. C doesn't have guaranteed
> optimized tail recursion, so when people (including me) see a function that
> uses recursion, we assume it's because it's doing something that couldn't
> be done using a simple loop, which isn't true here. I don't think recursion
> makes it more readable, since walking linked lists using a loop is already
> a pretty common thing for us to do, and that's exactly what we're doing
> here. So IMHO, a while loop is more readable here. In addition, a number of
> things that I wrote to traverse dereference lists are using a loop already,
> and so does get_deref_node() below.
>
That should be easy enough too.
>
> >
> > static bool
> > derefs_equal(const void *void_a, const void *void_b)
> > {
> > const nir_deref *a = void_a;
> > const nir_deref *b = void_b;
> >
> > if (a->deref_type != b->deref_type)
> > return false;
> >
> > switch (a->deref_type) {
> > case nir_deref_type_var:
> > if (nir_deref_as_var(a)->var != nir_deref_as_var(b)->var)
> > return false;
> > break;
> > case nir_deref_type_array: {
> > nir_deref_array *a_arr = nir_deref_as_array(a);
> > nir_deref_array *b_arr = nir_deref_as_array(b);
> >
> > if (a_arr->deref_array_type != b_arr->deref_array_type)
> > return false;
> >
> > if (a_arr->deref_array_type == nir_deref_array_type_direct &&
> > a_arr->base_offset != b_arr->base_offset)
> > return false;
> > break;
> > }
> > case nir_deref_type_struct:
> > if (nir_deref_as_struct(a)->index != nir_deref_as_struct(b)->index)
> > return false;
> > break;
> > default:
> > unreachable("Invalid dreference type");
> > }
> >
> > assert((a->child == NULL) == (b->child == NULL));
> > if (a->child)
> > return derefs_equal(a->child, b->child);
> > else
> > return true;
> > }
>
> Same comment about using a loop here.
>
> >
> > static int
> > type_get_length(const struct glsl_type *type)
> > {
> > switch (glsl_get_base_type(type)) {
> > case GLSL_TYPE_STRUCT:
> > case GLSL_TYPE_ARRAY:
> > return glsl_get_length(type);
> > case GLSL_TYPE_FLOAT:
> > case GLSL_TYPE_INT:
> > case GLSL_TYPE_UINT:
> > case GLSL_TYPE_BOOL:
> > if (glsl_type_is_matrix(type))
> > return glsl_get_matrix_columns(type);
> > else
> > return glsl_get_vector_elements(type);
> > default:
> > unreachable("Invalid deref base type");
> > }
> > }
> >
> > static struct deref_node *
> > deref_node_create(struct deref_node *parent,
> > const struct glsl_type *type, void *mem_ctx)
> > {
> > size_t size = sizeof(struct deref_node) +
> > type_get_length(type) * sizeof(struct deref_node *);
> >
> > struct deref_node *node = rzalloc_size(mem_ctx, size);
> > node->type = type;
> > node->parent = parent;
> >
> > return node;
> > }
> >
> > /* Gets the deref_node for the given deref chain and creates it if it
> > * doesn't yet exist. If the deref is a leaf (fully-qualified and
> direct)
>
> (a leaf -> direct)
>
> > * and add_to_leaves is true, it will be added to the hash table of
> leaves.
> > */
> > static struct deref_node *
> > get_deref_node(nir_deref_var *deref, bool add_to_leaves,
> > struct lower_variables_state *state)
> > {
> > bool is_leaf = true;
> > struct deref_node *parent = NULL;
>
> If it were me, I'd call this node_parent to emphasize that it's a node and
> not a dereference. I got confused and had to look at the definition again
> to realize that.
>
> > nir_deref *tail = &deref->deref;
> > while (tail) {
>
> Maybe use a for loop instead? Something like
>
> for (nir_deref *tail = &deref->deref; tail; tail = tail->child)
>
> to be more up-front that we're doing.
>
> > struct deref_node *node;
> >
> > switch (tail->deref_type) {
> > case nir_deref_type_var: {
> > assert(tail == &deref->deref);
> > assert(parent == NULL);
> >
> > uint32_t var_hash = _mesa_hash_pointer(deref->var);
> > struct hash_entry *entry =
> > _mesa_hash_table_search(state->deref_var_nodes,
> > var_hash, deref->var);
> > if (entry) {
> > node = entry->data;
> > } else {
> > node = deref_node_create(NULL, tail->type, state->dead_ctx);
> > _mesa_hash_table_insert(state->deref_var_nodes,
> > var_hash, deref->var, node);
> > }
> > break;
> > }
>
> Since this case is guaranteed to happen only once at the beginning of the
> chain, it might make more sense to move it above the loop to make that more
> explicit rather than having the asserts. This will also make the other
> parent != NULL asserts unnecessary since parent will never be set to NULL.
>
Yeah, I'll see what I can do about reworking this. I kind of like my
recursion, but loops are ok too.
>
> >
> > case nir_deref_type_struct: {
> > assert(parent != NULL);
> >
> > nir_deref_struct *deref_struct = nir_deref_as_struct(tail);
> > assert(deref_struct->index < type_get_length(parent->type));
> > if (parent->children[deref_struct->index]) {
> > node = parent->children[deref_struct->index];
> > } else {
> > node = deref_node_create(parent, tail->type,
> state->dead_ctx);
> > parent->children[deref_struct->index] = node;
> > }
> > break;
> > }
> >
> > case nir_deref_type_array: {
> > assert(parent != NULL);
> >
> > nir_deref_array *arr = nir_deref_as_array(tail);
> > switch (arr->deref_array_type) {
> > case nir_deref_array_type_direct:
> > if (arr->base_offset >= type_get_length(parent->type)) {
> > /* This is possible if a loop unrolls and generates an
> > * out-of-bounds offset. We need to handle this at least
> > * somewhat gracefully.
> > */
> > return NULL;
> > } else if (parent->children[arr->base_offset]) {
> > node = parent->children[arr->base_offset];
> > } else {
> > node = deref_node_create(parent, tail->type,
> state->dead_ctx);
> > parent->children[arr->base_offset] = node;
> > }
> > break;
> > case nir_deref_array_type_indirect:
> > if (parent->indirect) {
> > node = parent->indirect;
> > } else {
> > node = deref_node_create(parent, tail->type,
> state->dead_ctx);
> > parent->indirect = node;
> > }
> > is_leaf = false;
> > break;
> > case nir_deref_array_type_wildcard:
> > if (parent->wildcard) {
> > node = parent->wildcard;
> > } else {
> > node = deref_node_create(parent, tail->type,
> state->dead_ctx);
> > parent->wildcard = node;
> > }
> > is_leaf = false;
> > break;
> > default:
> > unreachable("Invalid array deref type");
> > }
> > break;
> > }
> > default:
> > unreachable("Invalid deref type");
> > }
> >
> > parent = node;
> > tail = tail->child;
> > }
> >
> > assert(parent);
> >
> > if (is_leaf && add_to_leaves)
> > _mesa_hash_table_insert(state->deref_leaves,
> > hash_deref(deref), deref, parent);
> >
> > return parent;
> > }
> >
> > /* \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);
> > return foreach_deref_node_worker(node->children[str->index],
> > deref->child, cb, state);
> > }
> >
> > 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 indirexcts) deref chain.
>
> indirects
>
> > */
> > 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, false, 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;
> >
> > 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.
> > * This question can only be asked about fully-qualified derefs.
> > * Obviously, it's pointless to ask this about indirects, but we also
> > * rule-out wildcards. For example, if the given deref is a[6].foo, then
>
> I think I'd like to see this spelled out a little more. Maybe something
> like:
>
> We don't handle wildcard dereferences, since that would involve checking
> each array index to make sure that there aren't any indirect references.
>
> I couldn't think of anything that would allow us to figure out if
> dereferences with wildcards aliased any indirect dereferences without
> having to check every array index (which seems like a bad idea). I guess
> it's not clear if we should do that anyways, since it might help cases like
> these:
>
> temp[*].thing = foo[*].thing;
> bar[*].thing = temp[*].thing;
>
> since after lowering temp[*].thing to SSA we can recognize the copy and
> turn it into:
> bar[*].thing = foo[*].thing
>
> but for more complicated cases like:
> if (...) {
> temp[*].thing = foo[*].thing;
> } else {
> temp[*].thing = bar[*].thing;
> }
> baz[*].thing = temp[*].thing;
>
> it'll just kill our register pressure if temp is large enough... and this
> is all very theoretical anyways.
>
>
> > * any uses of a[i].foo would case 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.
> > */
> > static bool
> > deref_may_be_aliased(nir_deref_var *deref,
> > 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, false, state);
>
> We're only looking for the root node corresponding to the variable, and
> we've already populated the deref_var_nodes table, so we can just look it
> up here.
>
> >
> > /* An invalid dereference can't be aliased. */
> > if (node == NULL)
> > return false;
> >
> > return deref_may_be_aliased_node(node, &deref->deref, state);
> > }
> >
> > static void
> > register_load_instr(nir_intrinsic_instr *load_instr, bool create_node,
> > struct lower_variables_state *state)
> > {
> > struct deref_node *node = get_deref_node(load_instr->variables[0],
> > create_node, state);
> > if (node == NULL)
> > return;
> >
> > if (node->loads == NULL)
> > node->loads = _mesa_set_create(state->dead_ctx,
> > _mesa_key_pointer_equal);
> >
> > _mesa_set_add(node->loads, _mesa_hash_pointer(load_instr),
> load_instr);
> > }
> >
> > static void
> > register_store_instr(nir_intrinsic_instr *store_instr, bool create_node,
> > struct lower_variables_state *state)
> > {
> > struct deref_node *node = get_deref_node(store_instr->variables[0],
> > create_node, state);
> > if (node == NULL)
> > return;
> >
> > if (node->stores == NULL)
> > node->stores = _mesa_set_create(state->dead_ctx,
> > _mesa_key_pointer_equal);
> >
> > _mesa_set_add(node->stores, _mesa_hash_pointer(store_instr),
> store_instr);
> > }
>
> I would call these "add_load_instr" and "add_store_instr" since "register"
> already has another meaning. I don't have a strong preference though.
>
> >
> > static void
> > register_copy_instr(nir_intrinsic_instr *copy_instr, bool create_node,
> > struct lower_variables_state *state)
>
> Same here...
>
> > {
> > for (unsigned idx = 0; idx < 2; idx++) {
> > struct deref_node *node =
> get_deref_node(copy_instr->variables[idx],
> > create_node, state);
> > if (node == NULL)
> > continue;
> >
> > if (node->copies == NULL)
> > node->copies = _mesa_set_create(state->dead_ctx,
> > _mesa_key_pointer_equal);
> >
> > _mesa_set_add(node->copies, _mesa_hash_pointer(copy_instr),
> copy_instr);
> > }
> > }
> >
> > /* Registers all variable uses in the given block. */
> > static bool
> > register_variable_uses_block(nir_block *block, void *void_state)
>
> and here.
>
> > {
> > struct lower_variables_state *state = void_state;
> >
> > nir_foreach_instr_safe(block, instr) {
> > 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, true, state);
> > break;
> >
> > case nir_intrinsic_store_var:
> > register_store_instr(intrin, true, state);
> > break;
> >
> > case nir_intrinsic_copy_var:
> > register_copy_instr(intrin, true, state);
> > break;
> >
> > default:
> > continue;
> > }
> > }
> >
> > return true;
> > }
> >
> > /* Walks down the deref chain and returns the next deref in the chain
> whose
> > * child is a wildcard. In other words, given the chain
> a[1].foo[*].bar,
> > * this function will return the deref to foo. Calling it a second time
> > * with the [*].bar, it will return NULL.
> > */
> > static nir_deref *
> > deref_next_wildcard_parent(nir_deref *deref)
> > {
> > for (nir_deref *tail = deref; tail->child; tail = tail->child) {
> > if (tail->child->deref_type != nir_deref_type_array)
> > continue;
> >
> > nir_deref_array *arr = nir_deref_as_array(tail->child);
> >
> > if (arr->deref_array_type == nir_deref_array_type_wildcard)
> > return tail;
> > }
> >
> > return NULL;
> > }
> >
> > /* Returns the last deref in the chain.
> > */
> > static nir_deref *
> > get_deref_tail(nir_deref *deref)
> > {
> > while (deref->child)
> > deref = deref->child;
> >
> > return deref;
> > }
> >
> > /* This function recursively walks the given deref chain and replaces the
> > * given copy instruction with an equivalent sequence load/store
> > * operations.
> > *
> > * @copy_instr The copy instruction to replace; new instructions will
> be
> > * inserted before this one
> > *
> > * @dest_head The head of the destination variable deref chain
> > *
> > * @src_head The head of the source variable deref chain
> > *
> > * @dest_tail The current tail of the destination variable deref
> chain;
> > * this is used for recursion and external callers of this
> > * function should call it with tail == head
> > *
> > * @src_tail The current tail of the source variable deref chain;
> > * this is used for recursion and external callers of this
> > * function should call it with tail == head
> > *
> > * @state The current variable lowering state
> > */
> > static void
> > emit_copy_load_store(nir_intrinsic_instr *copy_instr,
> > nir_deref_var *dest_head, nir_deref_var *src_head,
> > nir_deref *dest_tail, nir_deref *src_tail,
> > struct lower_variables_state *state)
> > {
> > /* Find the next pair of wildcards */
> > nir_deref *src_arr_parent = deref_next_wildcard_parent(src_tail);
> > nir_deref *dest_arr_parent = deref_next_wildcard_parent(dest_tail);
> >
> > if (src_arr_parent || dest_arr_parent) {
> > /* Wildcards had better come in matched pairs */
> > assert(dest_arr_parent && dest_arr_parent);
> >
> > nir_deref_array *src_arr =
> nir_deref_as_array(src_arr_parent->child);
> > nir_deref_array *dest_arr =
> nir_deref_as_array(dest_arr_parent->child);
> >
> > unsigned length = type_get_length(src_arr_parent->type);
> > /* The wildcards should represent the same number of elements */
> > assert(length == type_get_length(dest_arr_parent->type));
> > assert(length > 0);
> >
> > /* Walk over all of the elements that this wildcard refers to and
> > * call emit_copy_load_store on each one of them */
> > src_arr->deref_array_type = nir_deref_array_type_direct;
> > dest_arr->deref_array_type = nir_deref_array_type_direct;
> > for (unsigned i = 0; i < length; i++) {
> > src_arr->base_offset = i;
> > dest_arr->base_offset = i;
> > emit_copy_load_store(copy_instr, dest_head, src_head,
> > &dest_arr->deref, &src_arr->deref, state);
> > }
> > src_arr->deref_array_type = nir_deref_array_type_wildcard;
> > dest_arr->deref_array_type = nir_deref_array_type_wildcard;
> > } else {
> > /* In this case, we have no wildcards anymore, so all we have to do
> > * is just emit the load and store operations. */
> > src_tail = get_deref_tail(src_tail);
> > dest_tail = get_deref_tail(dest_tail);
> >
> > assert(src_tail->type == dest_tail->type);
> >
> > unsigned num_components = glsl_get_vector_elements(src_tail->type);
> >
> > nir_deref *src_deref = nir_copy_deref(state->mem_ctx,
> &src_head->deref);
> > nir_deref *dest_deref = nir_copy_deref(state->mem_ctx,
> &dest_head->deref);
> >
> > nir_intrinsic_instr *load =
> > nir_intrinsic_instr_create(state->mem_ctx,
> nir_intrinsic_load_var);
> > load->num_components = num_components;
> > load->variables[0] = nir_deref_as_var(src_deref);
> > load->dest.is_ssa = true;
> > nir_ssa_def_init(&load->instr, &load->dest.ssa, num_components,
> NULL);
> >
> > nir_instr_insert_before(©_instr->instr, &load->instr);
> > register_load_instr(load, false, state);
> >
> > nir_intrinsic_instr *store =
> > nir_intrinsic_instr_create(state->mem_ctx,
> nir_intrinsic_store_var);
> > store->num_components = num_components;
> > store->variables[0] = nir_deref_as_var(dest_deref);
> > store->src[0].is_ssa = true;
> > store->src[0].ssa = &load->dest.ssa;
> >
> > nir_instr_insert_before(©_instr->instr, &store->instr);
> > register_store_instr(store, false, state);
> > }
> > }
> >
> > /* 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;
> >
> > emit_copy_load_store(copy, copy->variables[0], copy->variables[1],
> > ©->variables[0]->deref,
> > ©->variables[1]->deref,
> > state);
> >
> > for (unsigned i = 0; i < 2; ++i) {
> > struct deref_node *arg_node = get_deref_node(copy->variables[i],
> > false, state);
> > if (arg_node == NULL)
> > continue;
> >
> > struct set_entry *arg_entry = _mesa_set_search(arg_node->copies,
> > copy_entry->hash,
> > copy);
> > assert(arg_entry);
> > _mesa_set_remove(node->copies, arg_entry);
> > }
> >
> > nir_instr_remove(©->instr);
> > }
> >
> > return true;
> > }
> >
> > /* Returns a load_const instruction that represents the constant
> > * initializer for the given deref chain. The caller is responsible for
> > * ensuring that there actually is a constant initializer.
> > */
> > static nir_load_const_instr *
> > get_const_initializer_load(const nir_deref_var *deref,
> > struct lower_variables_state *state)
> > {
> > nir_constant *constant = deref->var->constant_initializer;
> > const nir_deref *tail = &deref->deref;
> > unsigned matrix_offset = 0;
> > while (tail->child) {
> > switch (tail->child->deref_type) {
> > case nir_deref_type_array: {
> > nir_deref_array *arr = nir_deref_as_array(tail->child);
> > assert(arr->deref_array_type == nir_deref_array_type_direct);
> > if (glsl_type_is_matrix(tail->type)) {
> > assert(arr->deref.child == NULL);
> > matrix_offset = arr->base_offset;
> > } else {
> > constant = constant->elements[arr->base_offset];
> > }
> > break;
> > }
> >
> > case nir_deref_type_struct: {
> > constant =
> constant->elements[nir_deref_as_struct(tail->child)->index];
> > break;
> > }
> >
> > default:
> > unreachable("Invalid deref child type");
> > }
> >
> > tail = tail->child;
> > }
> >
> > nir_load_const_instr *load =
> > nir_load_const_instr_create(state->mem_ctx,
> > glsl_get_vector_elements(tail->type));
> >
> > matrix_offset *= load->def.num_components;
> > for (unsigned i = 0; i < load->def.num_components; i++) {
> > switch (glsl_get_base_type(tail->type)) {
> > case GLSL_TYPE_FLOAT:
> > case GLSL_TYPE_INT:
> > case GLSL_TYPE_UINT:
> > load->value.u[i] = constant->value.u[matrix_offset + i];
> > break;
> > case GLSL_TYPE_BOOL:
> > load->value.u[i] = constant->value.b[matrix_offset + i] ?
> > NIR_TRUE : NIR_FALSE;
>
> I see you sneakily squashed in my fix :P
>
> > break;
> > default:
> > unreachable("Invalid immediate type");
> > }
> > }
> >
> > return load;
> > }
> >
> > /** Pushes an SSA def onto the def stack for the given node
> > *
> > * Each node is potentially associated with a stack of SSA definitions.
> > * This stack is used for determining what SSA definition reaches a given
> > * point in the program for variable renaming. The stack is always kept
> in
> > * dominance-order with at most one SSA def per block. If the SSA
> > * definition on the top of the stack is in the same block as the one
> being
> > * pushed, the top element is replaced.
> > */
> > static void
> > def_stack_push(struct deref_node *node, nir_ssa_def *def,
> > struct lower_variables_state *state)
> > {
> > if (node->def_stack == NULL) {
> > node->def_stack = ralloc_array(state->dead_ctx, nir_ssa_def *,
> > state->impl->num_blocks);
> > node->def_stack_tail = node->def_stack - 1;
> > }
> >
> > if (node->def_stack_tail >= node->def_stack) {
> > nir_ssa_def *top_def = *node->def_stack_tail;
> >
> > if (def->parent_instr->block == top_def->parent_instr->block) {
> > /* They're in the same block, just replace the top */
> > *node->def_stack_tail = def;
> > return;
> > }
> > }
> >
> > *(++node->def_stack_tail) = def;
> > }
> >
> > /* Pop the top of the def stack if it's in the given block */
> > static void
> > def_stack_pop_if_in_block(struct deref_node *node, nir_block *block)
> > {
> > /* If we're popping, then we have presumably pushed at some time in
> the
> > * past so this should exist.
> > */
> > assert(node->def_stack != NULL);
> >
> > /* The stack is already empty. Do nothing. */
> > if (node->def_stack_tail < node->def_stack)
> > return;
> >
> > nir_ssa_def *def = *node->def_stack_tail;
> > if (def->parent_instr->block == block)
> > node->def_stack_tail--;
> > }
> >
> > /** Retrieves the SSA definition on the top of the stack for the given
> > * node, if one exists. If the stack is empty, then we return the
> constant
> > * initializer (if it exists) or an SSA undef.
> > */
> > static nir_ssa_def *
> > get_ssa_def_for_block(struct deref_node *node, nir_block *block,
> > struct lower_variables_state *state)
> > {
> > /* If we have something on the stack, go ahead and return it. We're
> > * assuming that the top of the stack dominates the given block.
> > */
> > if (node->def_stack && node->def_stack_tail >= node->def_stack)
> > return *node->def_stack_tail;
> >
> > /* If we got here then we don't have a definition that dominates the
> > * given block. This means that we need to add an undef and use that.
> > */
> > nir_ssa_undef_instr *undef =
> > nir_ssa_undef_instr_create(state->mem_ctx,
> > glsl_get_vector_elements(node->type));
> > nir_instr_insert_before_cf_list(&state->impl->body, &undef->instr);
> > def_stack_push(node, &undef->def, state);
> > return &undef->def;
> > }
> >
> > /* Given a block and one of its predecessors, this function fills in the
> > * souces of the phi nodes to take SSA defs from the given predecessor.
>
> sources
>
> > * This function must be called exactly once per block/predecessor pair.
> > */
> > static void
> > add_phi_sources(nir_block *block, nir_block *pred,
> > struct lower_variables_state *state)
> > {
> > nir_foreach_instr(block, instr) {
> > if (instr->type != nir_instr_type_phi)
> > break;
> >
> > nir_phi_instr *phi = nir_instr_as_phi(instr);
> >
> > struct hash_entry *entry =
> > _mesa_hash_table_search(state->phi_table,
> > _mesa_hash_pointer(phi), phi);
> > if (!entry)
> > continue;
> >
> > struct deref_node *node = entry->data;
> >
> > nir_phi_src *src = ralloc(state->mem_ctx, nir_phi_src);
> > src->pred = pred;
> > src->src.is_ssa = true;
> > src->src.ssa = get_ssa_def_for_block(node, pred, state);
> >
> > _mesa_set_add(src->src.ssa->uses, _mesa_hash_pointer(instr),
> instr);
> >
> > exec_list_push_tail(&phi->srcs, &src->node);
> > }
> > }
> >
> > /* Performs variable renaming by doing a DFS of the dominance tree
> > *
> > * 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_block(nir_block *block, struct lower_variables_state
> *state)
> > {
> > nir_foreach_instr_safe(block, instr) {
> > if (instr->type == nir_instr_type_phi) {
> > nir_phi_instr *phi = nir_instr_as_phi(instr);
> >
> > struct hash_entry *entry =
> > _mesa_hash_table_search(state->phi_table,
> > _mesa_hash_pointer(phi), phi);
> >
> > /* This can happen if we already have phi nodes in the program
> > * that were not created in this pass.
> > */
> > if (!entry)
> > continue;
> >
> > struct deref_node *node = entry->data;
> >
> > def_stack_push(node, &phi->dest.ssa, state);
> > } else if (instr->type == nir_instr_type_intrinsic) {
> > 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],
> > false, 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->mem_ctx,
> > intrin->num_components);
> >
> > nir_instr_insert_before(&intrin->instr, &undef->instr);
> > nir_instr_remove(&intrin->instr);
> >
> > nir_src new_src = {
> > .is_ssa = true,
> > .ssa = &undef->def,
> > };
> >
> > nir_ssa_def_rewrite_uses(&intrin->dest.ssa, new_src,
> > state->mem_ctx);
> > continue;
> > }
> >
> > if (!node->lower_to_ssa)
> > continue;
> >
> > nir_alu_instr *mov = nir_alu_instr_create(state->mem_ctx,
> > nir_op_imov);
> > mov->src[0].src.is_ssa = true;
> > mov->src[0].src.ssa = get_ssa_def_for_block(node, block,
> state);
> > 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;
> > mov->dest.dest.is_ssa = true;
> > nir_ssa_def_init(&mov->instr, &mov->dest.dest.ssa,
> > intrin->num_components, NULL);
> >
> > nir_instr_insert_before(&intrin->instr, &mov->instr);
> > nir_instr_remove(&intrin->instr);
> >
> > nir_src new_src = {
> > .is_ssa = true,
> > .ssa = &mov->dest.dest.ssa,
> > };
> >
> > nir_ssa_def_rewrite_uses(&intrin->dest.ssa, new_src,
> > state->mem_ctx);
> > break;
> > }
> >
> > case nir_intrinsic_store_var: {
> > struct deref_node *node =
> get_deref_node(intrin->variables[0],
> > false, 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_alu_instr *mov = nir_alu_instr_create(state->mem_ctx,
> > nir_op_imov);
> > mov->src[0].src.is_ssa = true;
> > mov->src[0].src.ssa = intrin->src[0].ssa;
> > for (unsigned i = intrin->num_components; i < 4; i++)
> > mov->src[0].swizzle[i] = 0;
> >
> > mov->dest.write_mask = (1 << intrin->num_components) - 1;
> > mov->dest.dest.is_ssa = true;
> > nir_ssa_def_init(&mov->instr, &mov->dest.dest.ssa,
> > intrin->num_components, NULL);
> >
> > nir_instr_insert_before(&intrin->instr, &mov->instr);
> >
> > def_stack_push(node, &mov->dest.dest.ssa, state);
> >
> > /* We'll wait to remove the unstruction until the next pass
>
> instruction (although I'm kind of curious about what an unstruction would
> be...)
>
lol
>
> > * where we pop the node we just pushed back off the stack.
> > */
> > break;
> > }
> >
> > default:
> > break;
> > }
> > }
> > }
> >
> > if (block->successors[0])
> > add_phi_sources(block->successors[0], block, state);
> > if (block->successors[1])
> > add_phi_sources(block->successors[1], block, state);
> >
> > for (unsigned i = 0; i < block->num_dom_children; ++i)
> > rename_variables_block(block->dom_children[i], state);
> >
> > /* Now we iterate over the instructions and pop off any SSA defs that
> we
> > * pushed in the first loop.
> > */
> > nir_foreach_instr_safe(block, instr) {
> > if (instr->type == nir_instr_type_phi) {
> > nir_phi_instr *phi = nir_instr_as_phi(instr);
> >
> > struct hash_entry *entry =
> > _mesa_hash_table_search(state->phi_table,
> > _mesa_hash_pointer(phi), phi);
> >
> > /* This can happen if we already have phi nodes in the program
> > * that were not created in this pass.
> > */
> > if (!entry)
> > continue;
> >
> > struct deref_node *node = entry->data;
> >
> > def_stack_pop_if_in_block(node, block);
> > } else if (instr->type == nir_instr_type_intrinsic) {
> > nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
> >
> > if (intrin->intrinsic != nir_intrinsic_store_var)
> > continue;
> >
> > struct deref_node *node = get_deref_node(intrin->variables[0],
> > false, state);
> > if (!node)
> > continue;
> >
> > if (!node->lower_to_ssa)
> > continue;
> >
> > def_stack_pop_if_in_block(node, block);
> > nir_instr_remove(&intrin->instr);
> > }
> > }
> >
> > return true;
> > }
> >
> > /* Inserts phi nodes for all variables marked lower_to_ssa
> > *
> > * This is the same algorithm as presented in "Efficiently Computing
> Static
> > * Single Assignment Form and the Control Dependence Graph" by Cytron et.
> > * al.
> > */
> > static void
> > insert_phi_nodes(struct lower_variables_state *state)
> > {
> > unsigned work[state->impl->num_blocks];
> > unsigned has_already[state->impl->num_blocks];
> > nir_block *W[state->impl->num_blocks];
>
> In the original code I had a comment that explained why W can be an array
> here (since it was a set in the original paper). Can we add it back?
>
Yeah, we should do that.
>
> >
> > memset(work, 0, sizeof work);
> > memset(has_already, 0, sizeof has_already);
> >
> > unsigned w_start, w_end;
> > unsigned iter_count = 0;
> >
> > struct hash_entry *deref_entry;
> > hash_table_foreach(state->deref_leaves, deref_entry) {
> > struct deref_node *node = deref_entry->data;
> >
> > if (node->stores == NULL)
> > continue;
> >
> > if (!node->lower_to_ssa)
> > continue;
> >
> > w_start = w_end = 0;
> > iter_count++;
> >
> > struct set_entry *store_entry;
> > set_foreach(node->stores, store_entry) {
> > nir_intrinsic_instr *store = (nir_intrinsic_instr
> *)store_entry->key;
> > if (work[store->instr.block->index] < iter_count)
> > W[w_end++] = store->instr.block;
> > work[store->instr.block->index] = iter_count;
> > }
> >
> > while (w_start != w_end) {
> > nir_block *cur = W[w_start++];
> > struct set_entry *dom_entry;
> > set_foreach(cur->dom_frontier, dom_entry) {
> > nir_block *next = (nir_block *) dom_entry->key;
> >
> > /*
> > * If there's more than one return statement, then the end
> block
> > * can be a join point for some definitions. However, there
> are
> > * no instructions in the end block, so nothing would use
> those
> > * phi nodes. Of course, we couldn't place those phi nodes
> > * anyways due to the restriction of having no instructions
> in the
> > * end block...
> > */
> > if (next == state->impl->end_block)
> > continue;
> >
> > if (has_already[next->index] < iter_count) {
> > nir_phi_instr *phi = nir_phi_instr_create(state->mem_ctx);
> > phi->dest.is_ssa = true;
> > nir_ssa_def_init(&phi->instr, &phi->dest.ssa,
> > glsl_get_vector_elements(node->type),
> NULL);
> > nir_instr_insert_before_block(next, &phi->instr);
> >
> > _mesa_hash_table_insert(state->phi_table,
> > _mesa_hash_pointer(phi), phi,
> node);
> >
> > has_already[next->index] = iter_count;
> > if (work[next->index] < iter_count) {
> > work[next->index] = iter_count;
> > W[w_end++] = next;
> > }
> > }
> > }
> > }
> > }
> > }
> >
> > static bool
> > nir_lower_variables_impl(nir_function_impl *impl)
> > {
> > struct lower_variables_state state;
> >
> > state.mem_ctx = ralloc_parent(impl);
> > state.dead_ctx = ralloc_context(state.mem_ctx);
> > state.impl = impl;
> >
> > state.deref_var_nodes = _mesa_hash_table_create(state.dead_ctx,
> >
> _mesa_key_pointer_equal);
> > state.deref_leaves = _mesa_hash_table_create(state.dead_ctx,
> > derefs_equal);
> > state.phi_table = _mesa_hash_table_create(state.dead_ctx,
> > _mesa_key_pointer_equal);
> >
> > nir_foreach_block(impl, register_variable_uses_block, &state);
> >
> > struct set *outputs = _mesa_set_create(state.dead_ctx,
> > _mesa_key_pointer_equal);
> >
> > bool progress = false;
> >
> > nir_metadata_require(impl, nir_metadata_block_index);
> >
> > struct hash_entry *entry;
> > hash_table_foreach(state.deref_leaves, entry) {
> > nir_deref_var *deref = (void *)entry->key;
> > struct deref_node *node = entry->data;
> >
> > if (deref->var->data.mode != nir_var_local) {
> > _mesa_hash_table_remove(state.deref_leaves, entry);
> > continue;
> > }
> >
> > if (deref_may_be_aliased(deref, &state)) {
> > _mesa_hash_table_remove(state.deref_leaves, entry);
> > continue;
> > }
> >
> > node->lower_to_ssa = true;
> > progress = true;
> >
> > if (deref->var->constant_initializer) {
> > nir_load_const_instr *load = get_const_initializer_load(deref,
> &state);
> > nir_ssa_def_init(&load->instr, &load->def,
> > glsl_get_vector_elements(node->type), NULL);
> > nir_instr_insert_before_cf_list(&impl->body, &load->instr);
> > def_stack_push(node, &load->def, &state);
> > }
> >
> > if (deref->var->data.mode == nir_var_shader_out)
> > _mesa_set_add(outputs, _mesa_hash_pointer(node), node);
> >
> > foreach_deref_node_match(deref, lower_copies_to_load_store,
> &state);
> > }
> >
> > if (!progress)
> > return false;
> >
> > nir_metadata_require(impl, nir_metadata_dominance);
> >
> > insert_phi_nodes(&state);
> > rename_variables_block(impl->start_block, &state);
> >
> > nir_metadata_preserve(impl, nir_metadata_block_index |
> > nir_metadata_dominance);
> >
> > ralloc_free(state.dead_ctx);
> >
> > return progress;
> > }
> >
> > void
> > nir_lower_variables(nir_shader *shader)
> > {
> > nir_foreach_overload(shader, overload) {
> > if (overload->impl)
> > nir_lower_variables_impl(overload->impl);
> > }
> > }
>
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