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nir/vars_to_ssa: Use the new nir_phi_builder helper

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The efficiency should be approximately the same.  We do a little more work
per phi node because we have to sort the predecessors.  However, we no
longer have to walk the blocks a second time to pop things off the stack.
The bigger advantage, however, is that we can now re-use the phi placement
and per-block SSA value tracking in other passes.
This commit is contained in:
Jason Ekstrand
2016-01-18 08:40:16 -08:00
parent 8aab4a7bd2
commit a7a5e8a2de
1 changed files with 136 additions and 404 deletions
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src/glsl/nir/nir_lower_vars_to_ssa.c
+136 -404
View File
@@ -27,6 +27,7 @@
#include "nir.h"
#include "nir_builder.h"
#include "nir_phi_builder.h"
#include "nir_vla.h"
@@ -47,8 +48,7 @@ struct deref_node {
struct set *stores;
struct set *copies;
nir_ssa_def **def_stack;
nir_ssa_def **def_stack_tail;
struct nir_phi_builder_value *pb_value;
struct deref_node *wildcard;
struct deref_node *indirect;
@@ -87,8 +87,7 @@ struct lower_variables_state {
*/
bool add_to_direct_deref_nodes;
/* A hash table mapping phi nodes to deref_state data */
struct hash_table *phi_table;
struct nir_phi_builder *phi_builder;
};
static struct deref_node *
@@ -473,141 +472,6 @@ lower_copies_to_load_store(struct deref_node *node,
return true;
}
/** 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->shader,
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.
* 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, phi);
if (!entry)
continue;
struct deref_node *node = entry->data;
nir_phi_src *src = ralloc(phi, nir_phi_src);
src->pred = pred;
src->src.parent_instr = &phi->instr;
src->src.is_ssa = true;
src->src.ssa = get_ssa_def_for_block(node, pred, state);
list_addtail(&src->src.use_link, &src->src.ssa->uses);
exec_list_push_tail(&phi->srcs, &src->node);
}
}
static void
add_undef_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);
nir_ssa_undef_instr *undef =
nir_ssa_undef_instr_create(state->shader,
phi->dest.ssa.num_components);
nir_instr_insert(nir_before_cf_list(&state->impl->body), &undef->instr);
nir_phi_src *src = ralloc(phi, nir_phi_src);
src->pred = pred;
src->src.parent_instr = &phi->instr;
src->src.is_ssa = true;
src->src.ssa = &undef->def;
list_addtail(&src->src.use_link, &undef->def.uses);
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
@@ -622,282 +486,126 @@ rename_variables_block(nir_block *block, struct lower_variables_state *state)
nir_builder_init(&b, state->impl);
nir_foreach_instr_safe(block, instr) {
if (instr->type == nir_instr_type_phi) {
nir_phi_instr *phi = nir_instr_as_phi(instr);
if (instr->type != nir_instr_type_intrinsic)
continue;
struct hash_entry *entry =
_mesa_hash_table_search(state->phi_table, phi);
nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
/* This can happen if we already have phi nodes in the program
* that were not created in this pass.
*/
if (!entry)
continue;
switch (intrin->intrinsic) {
case nir_intrinsic_load_var: {
struct deref_node *node =
get_deref_node(intrin->variables[0], state);
struct deref_node *node = entry->data;
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);
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], 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);
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.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;
nir_ssa_dest_init(&mov->instr, &mov->dest.dest,
intrin->num_components, NULL);
nir_instr_insert_before(&intrin->instr, &mov->instr);
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(&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);
if (intrin->const_index[0] == (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 = get_ssa_def_for_block(node, block, state);
/* 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 (intrin->const_index[0] & (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);
def_stack_push(node, new_def, state);
/* We'll wait to remove the instruction until the next pass
* 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, 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], state);
if (!node)
nir_src_for_ssa(&undef->def));
continue;
}
if (!node->lower_to_ssa)
continue;
def_stack_pop_if_in_block(node, block);
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, NULL);
nir_instr_insert_before(&intrin->instr, &mov->instr);
nir_instr_remove(&intrin->instr);
}
}
return true;
}
static bool
add_unreachable_phi_srcs_block(nir_block *block, void *void_state)
{
struct lower_variables_state *state = void_state;
/* Only run on unreachable blocks */
if (block->imm_dom || block == nir_start_block(state->impl))
return true;
if (block->successors[0])
add_undef_phi_sources(block->successors[0], block, state);
if (block->successors[1])
add_undef_phi_sources(block->successors[1], block, state);
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)
{
NIR_VLA_ZERO(unsigned, work, state->impl->num_blocks);
NIR_VLA_ZERO(unsigned, has_already, state->impl->num_blocks);
/*
* Since the work flags already prevent us from inserting a node that has
* ever been inserted into W, we don't need to use a set to represent W.
* Also, since no block can ever be inserted into W more than once, we know
* that the maximum size of W is the number of basic blocks in the
* function. So all we need to handle W is an array and a pointer to the
* next element to be inserted and the next element to be removed.
*/
NIR_VLA(nir_block *, W, state->impl->num_blocks);
unsigned w_start, w_end;
unsigned iter_count = 0;
foreach_list_typed(struct deref_node, node, direct_derefs_link,
&state->direct_deref_nodes) {
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;
nir_ssa_def_rewrite_uses(&intrin->dest.ssa,
nir_src_for_ssa(&mov->dest.dest.ssa));
break;
}
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;
case nir_intrinsic_store_var: {
struct deref_node *node =
get_deref_node(intrin->variables[0], state);
/*
* 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 (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);
if (intrin->const_index[0] == (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.
*/
if (next == state->impl->end_block)
continue;
unsigned swiz[4];
for (unsigned i = 0; i < 4; i++)
swiz[i] = i < intrin->num_components ? i : 0;
if (has_already[next->index] < iter_count) {
nir_phi_instr *phi = nir_phi_instr_create(state->shader);
nir_ssa_dest_init(&phi->instr, &phi->dest,
glsl_get_vector_elements(node->type), NULL);
nir_instr_insert_before_block(next, &phi->instr);
_mesa_hash_table_insert(state->phi_table, phi, node);
has_already[next->index] = iter_count;
if (work[next->index] < iter_count) {
work[next->index] = iter_count;
W[w_end++] = next;
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 (intrin->const_index[0] & (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;
}
}
}
for (unsigned i = 0; i < block->num_dom_children; ++i)
rename_variables_block(block->dom_children[i], state);
return true;
}
/** Implements a pass to lower variable uses to SSA values
*
@@ -939,9 +647,6 @@ nir_lower_vars_to_ssa_impl(nir_function_impl *impl)
_mesa_hash_pointer,
_mesa_key_pointer_equal);
exec_list_make_empty(&state.direct_deref_nodes);
state.phi_table = _mesa_hash_table_create(state.dead_ctx,
_mesa_hash_pointer,
_mesa_key_pointer_equal);
/* Build the initial deref structures and direct_deref_nodes table */
state.add_to_direct_deref_nodes = true;
@@ -971,15 +676,6 @@ nir_lower_vars_to_ssa_impl(nir_function_impl *impl)
node->lower_to_ssa = true;
progress = true;
if (deref->var->constant_initializer) {
nir_load_const_instr *load =
nir_deref_get_const_initializer_load(state.shader, deref);
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);
}
foreach_deref_node_match(deref, lower_copies_to_load_store, &state);
}
@@ -996,10 +692,46 @@ nir_lower_vars_to_ssa_impl(nir_function_impl *impl)
*/
nir_foreach_block(impl, register_variable_uses_block, &state);
insert_phi_nodes(&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));
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);
}
}
if (node->deref->var->constant_initializer)
BITSET_SET(store_blocks, 0);
node->pb_value =
nir_phi_builder_add_value(state.phi_builder,
glsl_get_vector_elements(node->type),
store_blocks);
if (node->deref->var->constant_initializer) {
nir_load_const_instr *load =
nir_deref_get_const_initializer_load(state.shader, node->deref);
nir_instr_insert_before_cf_list(&impl->body, &load->instr);
nir_phi_builder_value_set_block_def(node->pb_value,
nir_start_block(impl), &load->def);
}
}
rename_variables_block(nir_start_block(impl), &state);
nir_foreach_block(impl, add_unreachable_phi_srcs_block, &state);
nir_phi_builder_finish(state.phi_builder);
nir_metadata_preserve(impl, nir_metadata_block_index |
nir_metadata_dominance);