[Mesa-dev] [PATCH 3/3] nir: Rewrite lower_regs_to_ssa to use the phi builder
Jason Ekstrand
jason at jlekstrand.net
Wed Dec 14 18:38:40 UTC 2016
This keeps some of Connor's original code. However, while I was at it,
I updated this very old pass to a bit more modern NIR.
---
src/compiler/nir/nir_lower_regs_to_ssa.c | 583 +++++++++----------------------
1 file changed, 156 insertions(+), 427 deletions(-)
diff --git a/src/compiler/nir/nir_lower_regs_to_ssa.c b/src/compiler/nir/nir_lower_regs_to_ssa.c
index 74c1961..d7ecd42 100644
--- a/src/compiler/nir/nir_lower_regs_to_ssa.c
+++ b/src/compiler/nir/nir_lower_regs_to_ssa.c
@@ -26,513 +26,242 @@
*/
#include "nir.h"
-#include <stdlib.h>
+#include "nir_builder.h"
+#include "nir_phi_builder.h"
+#include "nir_vla.h"
-/*
- * Implements the classic to-SSA algorithm described by Cytron et. al. in
- * "Efficiently Computing Static Single Assignment Form and the Control
- * Dependence Graph."
- */
+struct regs_to_ssa_state {
+ nir_shader *shader;
-/* inserts a phi node of the form reg = phi(reg, reg, reg, ...) */
+ struct nir_phi_builder_value **values;
+};
-static void
-insert_trivial_phi(nir_register *reg, nir_block *block, void *mem_ctx)
-{
- nir_phi_instr *instr = nir_phi_instr_create(mem_ctx);
-
- instr->dest.reg.reg = reg;
- struct set_entry *entry;
- set_foreach(block->predecessors, entry) {
- nir_block *pred = (nir_block *) entry->key;
-
- nir_phi_src *src = ralloc(instr, nir_phi_src);
- src->pred = pred;
- src->src.is_ssa = false;
- src->src.reg.base_offset = 0;
- src->src.reg.indirect = NULL;
- src->src.reg.reg = reg;
- exec_list_push_tail(&instr->srcs, &src->node);
- }
-
- nir_instr_insert_before_block(block, &instr->instr);
-}
-
-static void
-insert_phi_nodes(nir_function_impl *impl)
+static bool
+rewrite_src(nir_src *src, void *_state)
{
- void *mem_ctx = ralloc_parent(impl);
-
- unsigned *work = calloc(impl->num_blocks, sizeof(unsigned));
- unsigned *has_already = calloc(impl->num_blocks, sizeof(unsigned));
-
- /*
- * 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_block **W = malloc(impl->num_blocks * sizeof(nir_block *));
- unsigned w_start, w_end;
-
- unsigned iter_count = 0;
-
- nir_index_blocks(impl);
-
- foreach_list_typed(nir_register, reg, node, &impl->registers) {
- if (reg->num_array_elems != 0)
- continue;
-
- w_start = w_end = 0;
- iter_count++;
-
- nir_foreach_def(dest, reg) {
- nir_instr *def = dest->reg.parent_instr;
- if (work[def->block->index] < iter_count)
- W[w_end++] = def->block;
- work[def->block->index] = iter_count;
- }
+ struct regs_to_ssa_state *state = _state;
- while (w_start != w_end) {
- nir_block *cur = W[w_start++];
- struct set_entry *entry;
- set_foreach(cur->dom_frontier, entry) {
- nir_block *next = (nir_block *) 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 == impl->end_block)
- continue;
-
- if (has_already[next->index] < iter_count) {
- insert_trivial_phi(reg, next, mem_ctx);
- has_already[next->index] = iter_count;
- if (work[next->index] < iter_count) {
- work[next->index] = iter_count;
- W[w_end++] = next;
- }
- }
- }
- }
- }
+ if (src->is_ssa)
+ return true;
- free(work);
- free(has_already);
- free(W);
-}
+ nir_instr *instr = src->parent_instr;
+ nir_register *reg = src->reg.reg;
+ struct nir_phi_builder_value *value = state->values[reg->index];
-typedef struct {
- nir_ssa_def **stack;
- int index;
- unsigned num_defs; /** < used to add indices to debug names */
-#ifndef NDEBUG
- unsigned stack_size;
-#endif
-} reg_state;
-
-typedef struct {
- reg_state *states;
- void *mem_ctx;
- nir_instr *parent_instr;
- nir_if *parent_if;
- nir_function_impl *impl;
-
- /* map from SSA value -> original register */
- struct hash_table *ssa_map;
-} rewrite_state;
-
-static nir_ssa_def *get_ssa_src(nir_register *reg, rewrite_state *state)
-{
- unsigned index = reg->index;
+ nir_ssa_def *def = nir_phi_builder_value_get_block_def(value, instr->block);
+ nir_instr_rewrite_src(instr, src, nir_src_for_ssa(def));
- if (state->states[index].index == -1) {
- /*
- * We're using an undefined register, create a new undefined SSA value
- * to preserve the information that this source is undefined
- */
- nir_ssa_undef_instr *instr =
- nir_ssa_undef_instr_create(state->mem_ctx, reg->num_components,
- reg->bit_size);
-
- /*
- * We could just insert the undefined instruction before the instruction
- * we're rewriting, but we could be rewriting a phi source in which case
- * we can't do that, so do the next easiest thing - insert it at the
- * beginning of the program. In the end, it doesn't really matter where
- * the undefined instructions are because they're going to be ignored
- * in the backend.
- */
- nir_instr_insert_before_cf_list(&state->impl->body, &instr->instr);
- return &instr->def;
- }
-
- return state->states[index].stack[state->states[index].index];
+ return true;
}
-static bool
-rewrite_use(nir_src *src, void *_state)
+static void
+rewrite_if_condition(nir_if *nif, struct regs_to_ssa_state *state)
{
- rewrite_state *state = (rewrite_state *) _state;
-
- if (src->is_ssa)
- return true;
-
- unsigned index = src->reg.reg->index;
-
- if (state->states[index].stack == NULL)
- return true;
+ if (nif->condition.is_ssa)
+ return;
- nir_ssa_def *def = get_ssa_src(src->reg.reg, state);
- if (state->parent_instr)
- nir_instr_rewrite_src(state->parent_instr, src, nir_src_for_ssa(def));
- else
- nir_if_rewrite_condition(state->parent_if, nir_src_for_ssa(def));
+ nir_block *block = nir_cf_node_as_block(nir_cf_node_prev(&nif->cf_node));
+ nir_register *reg = nif->condition.reg.reg;
+ struct nir_phi_builder_value *value = state->values[reg->index];
- return true;
+ nir_ssa_def *def = nir_phi_builder_value_get_block_def(value, block);
+ nir_if_rewrite_condition(nif, nir_src_for_ssa(def));
}
static bool
-rewrite_def_forwards(nir_dest *dest, void *_state)
+rewrite_dest(nir_dest *dest, void *_state)
{
- rewrite_state *state = (rewrite_state *) _state;
+ struct regs_to_ssa_state *state = _state;
if (dest->is_ssa)
return true;
+ nir_instr *instr = dest->reg.parent_instr;
nir_register *reg = dest->reg.reg;
- unsigned index = reg->index;
-
- if (state->states[index].stack == NULL)
- return true;
-
- char *name = NULL;
- if (dest->reg.reg->name)
- name = ralloc_asprintf(state->mem_ctx, "%s_%u", dest->reg.reg->name,
- state->states[index].num_defs);
+ struct nir_phi_builder_value *value = state->values[reg->index];
list_del(&dest->reg.def_link);
- nir_ssa_dest_init(state->parent_instr, dest, reg->num_components,
- reg->bit_size, name);
- ralloc_free(name);
-
- /* push our SSA destination on the stack */
- state->states[index].index++;
- assert(state->states[index].index < state->states[index].stack_size);
- state->states[index].stack[state->states[index].index] = &dest->ssa;
- state->states[index].num_defs++;
+ nir_ssa_dest_init(instr, dest, reg->num_components,
+ reg->bit_size, reg->name);
- _mesa_hash_table_insert(state->ssa_map, &dest->ssa, reg);
+ nir_phi_builder_value_set_block_def(value, instr->block, &dest->ssa);
return true;
}
static void
-rewrite_alu_instr_forward(nir_alu_instr *instr, rewrite_state *state)
+rewrite_alu_instr(nir_alu_instr *alu, struct regs_to_ssa_state *state)
{
- state->parent_instr = &instr->instr;
+ for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++)
+ rewrite_src(&alu->src[i].src, state);
- nir_foreach_src(&instr->instr, rewrite_use, state);
-
- if (instr->dest.dest.is_ssa)
+ if (alu->dest.dest.is_ssa)
return;
- nir_register *reg = instr->dest.dest.reg.reg;
- unsigned index = reg->index;
+ nir_register *reg = alu->dest.dest.reg.reg;
+ struct nir_phi_builder_value *value = state->values[reg->index];
- if (state->states[index].stack == NULL)
+ unsigned write_mask = alu->dest.write_mask;
+ if (write_mask == (1 << reg->num_components) - 1) {
+ /* This is the simple case where the instruction writes all the
+ * components. We can handle that the same as any other destination.
+ */
+ rewrite_dest(&alu->dest.dest, state);
return;
+ }
- unsigned write_mask = instr->dest.write_mask;
- if (write_mask != (1 << instr->dest.dest.reg.reg->num_components) - 1) {
- /*
- * Calculate the number of components the final instruction, which for
- * per-component things is the number of output components of the
- * instruction and non-per-component things is the number of enabled
- * channels in the write mask.
+ /* Calculate the number of components the final instruction, which for
+ * per-component things is the number of output components of the
+ * per-component things is the number of output components of the
+ * instruction and non-per-component things is the number of enabled
+ * channels in the write mask.
+ */
+ unsigned num_components;
+ unsigned vec_swizzle[4] = { 0, 1, 2, 3 };
+ if (nir_op_infos[alu->op].output_size == 0) {
+ /* Figure out the swizzle we need on the vecN operation and compute
+ * the number of components in the SSA def at the same time.
*/
- unsigned num_components;
- if (nir_op_infos[instr->op].output_size == 0) {
- unsigned temp = (write_mask & 0x5) + ((write_mask >> 1) & 0x5);
- num_components = (temp & 0x3) + ((temp >> 2) & 0x3);
- } else {
- num_components = nir_op_infos[instr->op].output_size;
+ num_components = 0;
+ for (unsigned index = 0; index < 4; index++) {
+ if (write_mask & (1 << index))
+ vec_swizzle[index] = num_components++;
}
- char *name = NULL;
- if (instr->dest.dest.reg.reg->name)
- name = ralloc_asprintf(state->mem_ctx, "%s_%u",
- reg->name, state->states[index].num_defs);
-
- instr->dest.write_mask = (1 << num_components) - 1;
- list_del(&instr->dest.dest.reg.def_link);
- nir_ssa_dest_init(&instr->instr, &instr->dest.dest, num_components,
- reg->bit_size, name);
- ralloc_free(name);
+ /* When we change the output writemask, we need to change
+ * the swizzles for per-component inputs too
+ */
+ for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
+ if (nir_op_infos[alu->op].input_sizes[i] != 0)
+ continue;
- if (nir_op_infos[instr->op].output_size == 0) {
/*
- * When we change the output writemask, we need to change the
- * swizzles for per-component inputs too
+ * We keep two indices:
+ * 1. The index of the original (non-SSA) component
+ * 2. The index of the post-SSA, compacted, component
+ *
+ * We need to map the swizzle component at index 1 to the swizzle
+ * component at index 2. Since index 1 is always larger than
+ * index 2, we can do it in a single loop.
*/
- for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {
- if (nir_op_infos[instr->op].input_sizes[i] != 0)
- continue;
-
- unsigned new_swizzle[4] = {0, 0, 0, 0};
-
- /*
- * We keep two indices:
- * 1. The index of the original (non-SSA) component
- * 2. The index of the post-SSA, compacted, component
- *
- * We need to map the swizzle component at index 1 to the swizzle
- * component at index 2.
- */
-
- unsigned ssa_index = 0;
- for (unsigned index = 0; index < 4; index++) {
- if (!((write_mask >> index) & 1))
- continue;
-
- new_swizzle[ssa_index] = instr->src[i].swizzle[index];
- ssa_index++;
- }
-
- for (unsigned j = 0; j < 4; j++)
- instr->src[i].swizzle[j] = new_swizzle[j];
- }
- }
-
- nir_op op;
- switch (reg->num_components) {
- case 2: op = nir_op_vec2; break;
- case 3: op = nir_op_vec3; break;
- case 4: op = nir_op_vec4; break;
- default: unreachable("not reached");
- }
-
- nir_alu_instr *vec = nir_alu_instr_create(state->mem_ctx, op);
- vec->dest.dest.reg.reg = reg;
- vec->dest.write_mask = (1 << reg->num_components) - 1;
-
- nir_ssa_def *old_src = get_ssa_src(reg, state);
- nir_ssa_def *new_src = &instr->dest.dest.ssa;
+ unsigned ssa_index = 0;
+ for (unsigned index = 0; index < 4; index++) {
+ if (!((write_mask >> index) & 1))
+ continue;
- unsigned ssa_index = 0;
- for (unsigned i = 0; i < reg->num_components; i++) {
- vec->src[i].src.is_ssa = true;
- if ((write_mask >> i) & 1) {
- vec->src[i].src.ssa = new_src;
- if (nir_op_infos[instr->op].output_size == 0)
- vec->src[i].swizzle[0] = ssa_index;
- else
- vec->src[i].swizzle[0] = i;
- ssa_index++;
- } else {
- vec->src[i].src.ssa = old_src;
- vec->src[i].swizzle[0] = i;
+ alu->src[i].swizzle[ssa_index++] = alu->src[i].swizzle[index];
}
+ assert(ssa_index == num_components);
}
-
- nir_instr_insert_after(&instr->instr, &vec->instr);
-
- state->parent_instr = &vec->instr;
- rewrite_def_forwards(&vec->dest.dest, state);
} else {
- rewrite_def_forwards(&instr->dest.dest, state);
+ num_components = nir_op_infos[alu->op].output_size;
+ }
+ assert(num_components <= 4);
+
+ alu->dest.write_mask = (1 << num_components) - 1;
+ list_del(&alu->dest.dest.reg.def_link);
+ nir_ssa_dest_init(&alu->instr, &alu->dest.dest, num_components,
+ reg->bit_size, reg->name);
+
+ nir_op vecN_op;
+ switch (reg->num_components) {
+ case 2: vecN_op = nir_op_vec2; break;
+ case 3: vecN_op = nir_op_vec3; break;
+ case 4: vecN_op = nir_op_vec4; break;
+ default: unreachable("not reached");
}
-}
-static void
-rewrite_phi_instr(nir_phi_instr *instr, rewrite_state *state)
-{
- state->parent_instr = &instr->instr;
- rewrite_def_forwards(&instr->dest, state);
-}
+ nir_alu_instr *vec = nir_alu_instr_create(state->shader, vecN_op);
-static void
-rewrite_instr_forward(nir_instr *instr, rewrite_state *state)
-{
- if (instr->type == nir_instr_type_alu) {
- rewrite_alu_instr_forward(nir_instr_as_alu(instr), state);
- return;
- }
+ nir_ssa_def *old_src =
+ nir_phi_builder_value_get_block_def(value, alu->instr.block);
+ nir_ssa_def *new_src = &alu->dest.dest.ssa;
- if (instr->type == nir_instr_type_phi) {
- rewrite_phi_instr(nir_instr_as_phi(instr), state);
- return;
+ for (unsigned i = 0; i < reg->num_components; i++) {
+ if (write_mask & (1 << i)) {
+ vec->src[i].src = nir_src_for_ssa(new_src);
+ vec->src[i].swizzle[0] = vec_swizzle[i];
+ } else {
+ vec->src[i].src = nir_src_for_ssa(old_src);
+ vec->src[i].swizzle[0] = i;
+ }
}
- state->parent_instr = instr;
+ nir_ssa_dest_init(&vec->instr, &vec->dest.dest, reg->num_components,
+ reg->bit_size, reg->name);
+ nir_instr_insert(nir_after_instr(&alu->instr), &vec->instr);
- nir_foreach_src(instr, rewrite_use, state);
- nir_foreach_dest(instr, rewrite_def_forwards, state);
+ nir_phi_builder_value_set_block_def(value, alu->instr.block,
+ &vec->dest.dest.ssa);
}
static void
-rewrite_phi_sources(nir_block *block, nir_block *pred, rewrite_state *state)
-{
- nir_foreach_instr(instr, block) {
- if (instr->type != nir_instr_type_phi)
- break;
-
- nir_phi_instr *phi_instr = nir_instr_as_phi(instr);
-
- state->parent_instr = instr;
-
- nir_foreach_phi_src(src, phi_instr) {
- if (src->pred == pred) {
- rewrite_use(&src->src, state);
- break;
- }
- }
- }
-}
-
-static bool
-rewrite_def_backwards(nir_dest *dest, void *_state)
+lower_regs_to_ssa_impl(nir_function_impl *impl)
{
- rewrite_state *state = (rewrite_state *) _state;
+ if (exec_list_is_empty(&impl->registers))
+ return;
- if (!dest->is_ssa)
- return true;
+ nir_metadata_require(impl, nir_metadata_block_index |
+ nir_metadata_dominance);
+ nir_index_local_regs(impl);
- struct hash_entry *entry =
- _mesa_hash_table_search(state->ssa_map, &dest->ssa);
+ struct regs_to_ssa_state state;
+ state.shader = impl->function->shader;
+ state.values = malloc(impl->reg_alloc * sizeof(*state.values));
- if (!entry)
- return true;
+ struct nir_phi_builder *phi_build = nir_phi_builder_create(impl);
- nir_register *reg = (nir_register *) entry->data;
- unsigned index = reg->index;
+ const unsigned block_set_words = BITSET_WORDS(impl->num_blocks);
+ NIR_VLA(BITSET_WORD, defs, block_set_words);
- state->states[index].index--;
- assert(state->states[index].index >= -1);
+ nir_foreach_register(reg, &impl->registers) {
+ /* This only works on "plain" registers */
+ assert(reg->num_array_elems == 0);
+ assert(!reg->is_packed);
- return true;
-}
+ memset(defs, 0, block_set_words * sizeof(*defs));
-static void
-rewrite_instr_backwards(nir_instr *instr, rewrite_state *state)
-{
- nir_foreach_dest(instr, rewrite_def_backwards, state);
-}
+ nir_foreach_def(dest, reg)
+ BITSET_SET(defs, dest->reg.parent_instr->block->index);
-static void
-rewrite_block(nir_block *block, rewrite_state *state)
-{
- /* This will skip over any instructions after the current one, which is
- * what we want because those instructions (vector gather, conditional
- * select) will already be in SSA form.
- */
- nir_foreach_instr_safe(instr, block) {
- rewrite_instr_forward(instr, state);
- }
-
- if (block != state->impl->end_block &&
- !nir_cf_node_is_last(&block->cf_node) &&
- nir_cf_node_next(&block->cf_node)->type == nir_cf_node_if) {
- nir_if *if_stmt = nir_cf_node_as_if(nir_cf_node_next(&block->cf_node));
- state->parent_instr = NULL;
- state->parent_if = if_stmt;
- rewrite_use(&if_stmt->condition, state);
+ state.values[reg->index] =
+ nir_phi_builder_add_value(phi_build, reg->num_components,
+ reg->bit_size, defs);
}
- if (block->successors[0])
- rewrite_phi_sources(block->successors[0], block, state);
- if (block->successors[1])
- rewrite_phi_sources(block->successors[1], block, state);
-
- for (unsigned i = 0; i < block->num_dom_children; i++)
- rewrite_block(block->dom_children[i], state);
+ nir_foreach_block(block, impl) {
+ nir_foreach_instr(instr, block) {
+ if (instr->type == nir_instr_type_alu) {
+ rewrite_alu_instr(nir_instr_as_alu(instr), &state);
+ } else {
+ nir_foreach_src(instr, rewrite_src, &state);
+ nir_foreach_dest(instr, rewrite_dest, &state);
+ }
+ }
- nir_foreach_instr_reverse(instr, block) {
- rewrite_instr_backwards(instr, state);
+ nir_if *following_if = nir_block_get_following_if(block);
+ if (following_if)
+ rewrite_if_condition(following_if, &state);
}
-}
-static void
-remove_unused_regs(nir_function_impl *impl, rewrite_state *state)
-{
- foreach_list_typed_safe(nir_register, reg, node, &impl->registers) {
- if (state->states[reg->index].stack != NULL)
- exec_node_remove(®->node);
- }
-}
+ nir_phi_builder_finish(phi_build);
+ free(state.values);
-static void
-init_rewrite_state(nir_function_impl *impl, rewrite_state *state)
-{
- state->impl = impl;
- state->mem_ctx = ralloc_parent(impl);
- state->ssa_map = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
- _mesa_key_pointer_equal);
- state->states = rzalloc_array(NULL, reg_state, impl->reg_alloc);
-
- foreach_list_typed(nir_register, reg, node, &impl->registers) {
- assert(reg->index < impl->reg_alloc);
- if (reg->num_array_elems > 0) {
- state->states[reg->index].stack = NULL;
- } else {
- /*
- * Calculate a conservative estimate of the stack size based on the
- * number of definitions there are. Note that this function *must* be
- * called after phi nodes are inserted so we can count phi node
- * definitions too.
- */
- unsigned stack_size = list_length(®->defs);
-
- state->states[reg->index].stack = ralloc_array(state->states,
- nir_ssa_def *,
- stack_size);
-#ifndef NDEBUG
- state->states[reg->index].stack_size = stack_size;
-#endif
- state->states[reg->index].index = -1;
- state->states[reg->index].num_defs = 0;
- }
+ nir_foreach_register(reg, &impl->registers) {
+ assert(list_empty(®->uses));
+ assert(list_empty(®->if_uses));
+ assert(list_empty(®->defs));
}
-}
-
-static void
-destroy_rewrite_state(rewrite_state *state)
-{
- _mesa_hash_table_destroy(state->ssa_map, NULL);
- ralloc_free(state->states);
-}
-
-static void
-lower_regs_to_ssa_impl(nir_function_impl *impl)
-{
- nir_metadata_require(impl, nir_metadata_dominance);
-
- insert_phi_nodes(impl);
-
- rewrite_state state;
- init_rewrite_state(impl, &state);
- rewrite_block(nir_start_block(impl), &state);
-
- remove_unused_regs(impl, &state);
-
- nir_metadata_preserve(impl, nir_metadata_block_index |
- nir_metadata_dominance);
-
- destroy_rewrite_state(&state);
+ exec_list_make_empty(&impl->registers);
}
void
nir_lower_regs_to_ssa(nir_shader *shader)
{
+ assert(exec_list_is_empty(&shader->registers));
+
nir_foreach_function(function, shader) {
if (function->impl)
lower_regs_to_ssa_impl(function->impl);
--
2.5.0.400.gff86faf
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