/*
* This file implements an out-of-SSA pass as described in "Revisiting
* Out-of-SSA Translation for Correctness, Code Quality, and Efficiency" by
- * Boissinot et. al.
+ * Boissinot et al.
*/
struct from_ssa_state {
bool phi_webs_only;
struct hash_table *merge_node_table;
nir_instr *instr;
+ bool progress;
};
/* Returns true if a dominates b */
/* The following data structure, which I have named merge_set is a way of
* representing a set registers of non-interfering registers. This is
- * based on the concept of a "dominence forest" presented in "Fast Copy
- * Coalescing and Live-Range Identification" by Budimlic et. al. but the
+ * based on the concept of a "dominance forest" presented in "Fast Copy
+ * Coalescing and Live-Range Identification" by Budimlic et al. but the
* implementation concept is taken from "Revisiting Out-of-SSA Translation
- * for Correctness, Code Quality, and Efficiency" by Boissinot et. al..
+ * for Correctness, Code Quality, and Efficiency" by Boissinot et al.
*
* Each SSA definition is associated with a merge_node and the association
* is represented by a combination of a hash table and the "def" parameter
* in the merge_node structure. The merge_set stores a linked list of
- * merge_node's in dominence order of the ssa definitions. (Since the
- * liveness analysis pass indexes the SSA values in dominence order for us,
+ * merge_nodes in dominance order of the ssa definitions. (Since the
+ * liveness analysis pass indexes the SSA values in dominance order for us,
* this is an easy thing to keep up.) It is assumed that no pair of the
* nodes in a given set interfere. Merging two sets or checking for
* interference can be done in a single linear-time merge-sort walk of the
*
* This is an implementation of Algorithm 2 in "Revisiting Out-of-SSA
* Translation for Correctness, Code Quality, and Efficiency" by
- * Boissinot et. al.
+ * Boissinot et al.
*/
static bool
merge_sets_interfere(merge_set *a, merge_set *b)
last_phi_instr = instr;
}
- /* If we don't have any phi's, then there's nothing for us to do. */
+ /* If we don't have any phis, then there's nothing for us to do. */
if (last_phi_instr == NULL)
return true;
}
nir_ssa_def_rewrite_uses(def, nir_src_for_reg(reg));
- assert(list_empty(&def->uses) && list_empty(&def->if_uses));
+ assert(list_is_empty(&def->uses) && list_is_empty(&def->if_uses));
if (def->parent_instr->type == nir_instr_type_ssa_undef) {
/* If it's an ssa_undef instruction, remove it since we know we just got
nir_instr *parent_instr = def->parent_instr;
nir_instr_remove(parent_instr);
ralloc_steal(state->dead_ctx, parent_instr);
+ state->progress = true;
return true;
}
nir_dest *dest = exec_node_data(nir_dest, def, ssa);
nir_instr_rewrite_dest(state->instr, dest, nir_dest_for_reg(reg));
-
+ state->progress = true;
return true;
}
/* Resolves ssa definitions to registers. While we're at it, we also
* remove phi nodes.
*/
-static bool
+static void
resolve_registers_block(nir_block *block, struct from_ssa_state *state)
{
nir_foreach_instr_safe(instr, block) {
if (instr->type == nir_instr_type_phi) {
nir_instr_remove(instr);
ralloc_steal(state->dead_ctx, instr);
+ state->progress = true;
}
}
state->instr = NULL;
-
- return true;
}
static void
else
assert(src.reg.reg->num_components >= dest_src.reg.reg->num_components);
- nir_alu_instr *mov = nir_alu_instr_create(b->shader, nir_op_imov);
+ nir_alu_instr *mov = nir_alu_instr_create(b->shader, nir_op_mov);
nir_src_copy(&mov->src[0].src, &src, mov);
mov->dest.dest = nir_dest_for_reg(dest_src.reg.reg);
mov->dest.write_mask = (1 << dest_src.reg.reg->num_components) - 1;
nir_builder_instr_insert(b, &mov->instr);
}
-/* Resolves a single parallel copy operation into a sequence of mov's
+/* Resolves a single parallel copy operation into a sequence of movs
*
* This is based on Algorithm 1 from "Revisiting Out-of-SSA Translation for
- * Correctness, Code Quality, and Efficiency" by Boissinot et. al..
+ * Correctness, Code Quality, and Efficiency" by Boissinot et al.
* However, I never got the algorithm to work as written, so this version
* is slightly modified.
*
int a = pred[b];
emit_copy(&state->builder, values[loc[a]], values[b]);
- /* If any other copies want a they can find it at b */
- loc[a] = b;
-
/* b has been filled, mark it as not needing to be copied */
pred[b] = -1;
- /* If a needs to be filled, it's ready for copying now */
- if (pred[a] != -1)
+ /* If a needs to be filled... */
+ if (pred[a] != -1) {
+ /* If any other copies want a they can find it at b */
+ loc[a] = b;
+
+ /* It's ready for copying now */
ready[++ready_idx] = a;
+ }
}
int b = to_do[to_do_idx--];
if (pred[b] == -1)
nir_register *reg = nir_local_reg_create(state->builder.impl);
reg->name = "copy_temp";
reg->num_array_elems = 0;
- if (values[b].is_ssa)
+ if (values[b].is_ssa) {
reg->num_components = values[b].ssa->num_components;
- else
+ reg->bit_size = values[b].ssa->bit_size;
+ } else {
reg->num_components = values[b].reg.reg->num_components;
+ reg->bit_size = values[b].reg.reg->bit_size;
+ }
values[num_vals].is_ssa = false;
values[num_vals].reg.reg = reg;
return true;
}
-static void
+static bool
nir_convert_from_ssa_impl(nir_function_impl *impl, bool phi_webs_only)
{
struct from_ssa_state state;
nir_builder_init(&state.builder, impl);
state.dead_ctx = ralloc_context(NULL);
state.phi_webs_only = phi_webs_only;
- state.merge_node_table = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
- _mesa_key_pointer_equal);
+ state.merge_node_table = _mesa_pointer_hash_table_create(NULL);
+ state.progress = false;
nir_foreach_block(block, impl) {
add_parallel_copy_to_end_of_block(block, state.dead_ctx);
/* Clean up dead instructions and the hash tables */
_mesa_hash_table_destroy(state.merge_node_table, NULL);
ralloc_free(state.dead_ctx);
+ return state.progress;
}
-void
+bool
nir_convert_from_ssa(nir_shader *shader, bool phi_webs_only)
{
+ bool progress = false;
+
nir_foreach_function(function, shader) {
if (function->impl)
- nir_convert_from_ssa_impl(function->impl, phi_webs_only);
+ progress |= nir_convert_from_ssa_impl(function->impl, phi_webs_only);
}
+
+ return progress;
}
static void
-place_phi_read(nir_shader *shader, nir_register *reg,
- nir_ssa_def *def, nir_block *block)
+place_phi_read(nir_builder *b, nir_register *reg,
+ nir_ssa_def *def, nir_block *block, unsigned depth)
{
if (block != def->parent_instr->block) {
/* Try to go up the single-successor tree */
bool all_single_successors = true;
- struct set_entry *entry;
set_foreach(block->predecessors, entry) {
nir_block *pred = (nir_block *)entry->key;
if (pred->successors[0] && pred->successors[1]) {
}
}
- if (all_single_successors) {
+ if (all_single_successors && depth < 32) {
/* All predecessors of this block have exactly one successor and it
* is this block so they must eventually lead here without
* intersecting each other. Place the reads in the predecessors
* instead of this block.
+ *
+ * We only let this function recurse 32 times because it can recurse
+ * indefinitely in the presence of infinite loops. Because we're
+ * crawling a single-successor chain, it doesn't matter where we
+ * place it so it's ok to stop at an arbitrary distance.
+ *
+ * TODO: One day, we could detect back edges and avoid the recursion
+ * that way.
*/
- set_foreach(block->predecessors, entry)
- place_phi_read(shader, reg, def, (nir_block *)entry->key);
+ set_foreach(block->predecessors, entry) {
+ place_phi_read(b, reg, def, (nir_block *)entry->key, depth + 1);
+ }
return;
}
}
- nir_alu_instr *mov = nir_alu_instr_create(shader, nir_op_imov);
- mov->src[0].src = nir_src_for_ssa(def);
- mov->dest.dest = nir_dest_for_reg(reg);
- mov->dest.write_mask = (1 << reg->num_components) - 1;
- nir_instr_insert(nir_after_block_before_jump(block), &mov->instr);
+ b->cursor = nir_after_block_before_jump(block);
+ nir_store_reg(b, reg, def, ~0);
}
-/** Lower all of the phi nodes in a block to imov's to and from a register
+/** Lower all of the phi nodes in a block to imovs to and from a register
*
* This provides a very quick-and-dirty out-of-SSA pass that you can run on a
- * single block to convert all of it's phis to a register and some imov's.
+ * single block to convert all of its phis to a register and some imovs.
* The code that is generated, while not optimal for actual codegen in a
* back-end, is easy to generate, correct, and will turn into the same set of
* phis after you call regs_to_ssa and do some copy propagation.
bool
nir_lower_phis_to_regs_block(nir_block *block)
{
- nir_function_impl *impl = nir_cf_node_get_function(&block->cf_node);
- nir_shader *shader = impl->function->shader;
+ nir_builder b;
+ nir_builder_init(&b, nir_cf_node_get_function(&block->cf_node));
bool progress = false;
nir_foreach_instr_safe(instr, block) {
nir_phi_instr *phi = nir_instr_as_phi(instr);
assert(phi->dest.is_ssa);
- nir_register *reg = create_reg_for_ssa_def(&phi->dest.ssa, impl);
+ nir_register *reg = create_reg_for_ssa_def(&phi->dest.ssa, b.impl);
- nir_alu_instr *mov = nir_alu_instr_create(shader, nir_op_imov);
- mov->src[0].src = nir_src_for_reg(reg);
- mov->dest.write_mask = (1 << phi->dest.ssa.num_components) - 1;
- nir_ssa_dest_init(&mov->instr, &mov->dest.dest,
- phi->dest.ssa.num_components, phi->dest.ssa.bit_size,
- phi->dest.ssa.name);
- nir_instr_insert(nir_after_instr(&phi->instr), &mov->instr);
+ b.cursor = nir_after_instr(&phi->instr);
+ nir_ssa_def *def = nir_load_reg(&b, reg);
- nir_ssa_def_rewrite_uses(&phi->dest.ssa,
- nir_src_for_ssa(&mov->dest.dest.ssa));
+ nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(def));
nir_foreach_phi_src(src, phi) {
assert(src->src.is_ssa);
- place_phi_read(shader, reg, src->src.ssa, src->pred);
+ place_phi_read(&b, reg, src->src.ssa, src->pred, 0);
}
nir_instr_remove(&phi->instr);
return true;
}
+static bool
+ssa_def_is_local_to_block(nir_ssa_def *def, UNUSED void *state)
+{
+ nir_block *block = def->parent_instr->block;
+ nir_foreach_use(use_src, def) {
+ if (use_src->parent_instr->block != block ||
+ use_src->parent_instr->type == nir_instr_type_phi) {
+ return false;
+ }
+ }
+
+ if (!list_is_empty(&def->if_uses))
+ return false;
+
+ return true;
+}
+
/** Lower all of the SSA defs in a block to registers
*
* This performs the very simple operation of blindly replacing all of the SSA
nir_register *reg = create_reg_for_ssa_def(&load->def, state.impl);
nir_ssa_def_rewrite_uses(&load->def, nir_src_for_reg(reg));
- nir_alu_instr *mov = nir_alu_instr_create(shader, nir_op_imov);
+ nir_alu_instr *mov = nir_alu_instr_create(shader, nir_op_mov);
mov->src[0].src = nir_src_for_ssa(&load->def);
mov->dest.dest = nir_dest_for_reg(reg);
mov->dest.write_mask = (1 << reg->num_components) - 1;
nir_instr_insert(nir_after_instr(&load->instr), &mov->instr);
+ } else if (nir_foreach_ssa_def(instr, ssa_def_is_local_to_block, NULL)) {
+ /* If the SSA def produced by this instruction is only in the block
+ * in which it is defined and is not used by ifs or phis, then we
+ * don't have a reason to convert it to a register.
+ */
} else {
nir_foreach_dest(instr, dest_replace_ssa_with_reg, &state);
}
projects / mesa.git / blobdiff