[Mesa-dev] [PATCH 12/13] nir: add a loop unrolling pass
Connor Abbott
cwabbott0 at gmail.com
Tue Aug 30 00:34:56 UTC 2016
On Mon, Aug 29, 2016 at 12:59 AM, Timothy Arceri
<timothy.arceri at collabora.com> wrote:
> ---
> src/compiler/Makefile.sources | 1 +
> src/compiler/nir/nir.h | 2 +
> src/compiler/nir/nir_opt_loop_unroll.c | 394 +++++++++++++++++++++++++++++++++
> 3 files changed, 397 insertions(+)
> create mode 100644 src/compiler/nir/nir_opt_loop_unroll.c
>
> diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
> index 79de484..a9f104d 100644
> --- a/src/compiler/Makefile.sources
> +++ b/src/compiler/Makefile.sources
> @@ -231,6 +231,7 @@ NIR_FILES = \
> nir/nir_opt_dead_cf.c \
> nir/nir_opt_gcm.c \
> nir/nir_opt_global_to_local.c \
> + nir/nir_opt_loop_unroll.c \
> nir/nir_opt_peephole_select.c \
> nir/nir_opt_remove_phis.c \
> nir/nir_opt_undef.c \
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index 9083bd0..81d9dfc 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2676,6 +2676,8 @@ bool nir_opt_dead_cf(nir_shader *shader);
>
> void nir_opt_gcm(nir_shader *shader);
>
> +bool nir_opt_loop_unroll(nir_shader *shader);
> +
> bool nir_opt_peephole_select(nir_shader *shader);
>
> bool nir_opt_remove_phis(nir_shader *shader);
> diff --git a/src/compiler/nir/nir_opt_loop_unroll.c b/src/compiler/nir/nir_opt_loop_unroll.c
> new file mode 100644
> index 0000000..22530c9
> --- /dev/null
> +++ b/src/compiler/nir/nir_opt_loop_unroll.c
> @@ -0,0 +1,394 @@
> +/*
> + * Copyright © 2016 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.
> + */
> +
> +#include "nir.h"
> +#include "nir_builder.h"
> +#include "nir_control_flow.h"
> +
> +typedef struct {
> + /* Array of loops */
> + nir_loop *loops;
> +
> + /* Array of unroll factors */
> + int *factors;
> +} unroll_vector;
> +
> +typedef struct {
> + /* Array of loop infos for the loop nest */
> + nir_loop_info *li;
> +
> + /* List of unroll vectors */
> + struct list_head unroll_vectors;
> +
> + nir_shader_compiler_options *options;
> +} loop_unroll_state;
> +
> +static void
> +extract_loop_body(nir_cf_list *extracted, nir_cf_node *node, nir_shader *ns)
The shader argument is unused, you can delete it.
> +{
> + nir_cf_node *end = node;
> + while (!nir_cf_node_is_last(end))
> + end = nir_cf_node_next(end);
> +
> + nir_cf_loop_list_extract(extracted, node, end);
> +}
> +
> +static void
> +clone_list(nir_shader *ns, nir_loop *loop, nir_cf_list *src_cf_list,
> + nir_cf_list *cloned_cf_list, struct hash_table *remap_table,
> + struct hash_table *phi_remap)
> +{
> + /* Dest list needs to at least have one block */
> + nir_block *nblk = nir_block_create(ns);
> + nblk->cf_node.parent = loop->cf_node.parent;
> + exec_list_push_tail(&cloned_cf_list->list, &nblk->cf_node.node);
> +
> + nir_clone_loop_list(&cloned_cf_list->list, &src_cf_list->list,
> + remap_table, phi_remap, ns);
> +}
> +
> +static void
> +remove_unrolled_loop(nir_cf_node *loop, nir_block *block_before_loop,
> + struct hash_table *remap_table,
> + struct hash_table *phi_remap,
> + nir_function_impl *impl)
> +{
> + /* Fixup LCSSA-phi srcs */
> + nir_block *prev_block = nir_cf_node_as_block(nir_cf_node_prev(loop));
> + nir_cf_node *cf_node = nir_cf_node_next(loop);
> + assert(cf_node->type == nir_cf_node_block);
> +
> + nir_block *block = nir_cf_node_as_block(cf_node);
> + nir_foreach_instr_safe(instr, block) {
> + if (instr->type == nir_instr_type_phi) {
> + nir_phi_instr *phi = nir_instr_as_phi(instr);
> + assert(phi->is_lcssa_phi);
> +
> + if (nir_cf_node_as_loop(loop)->info->trip_count != 0) {
> + nir_foreach_phi_src_safe(src, phi) {
> + /* Update predecessor */
> + src->pred = prev_block;
> +
> + /* Update src */
> + struct hash_entry *hte =
> + _mesa_hash_table_search(phi_remap, src->src.ssa);
> + if (hte) {
> + nir_src new_src = nir_src_for_ssa((nir_ssa_def *) hte->data);
> + nir_instr_rewrite_src(instr, &src->src, new_src);
> + } else {
> + /* If the LCSSA src was not a phi fallback to following the
> + * the remappings in the remap table.
> + */
> + nir_ssa_def *ssa_def = src->src.ssa;
> + while ((hte = _mesa_hash_table_search(remap_table,
> + ssa_def))) {
> + ssa_def = (nir_ssa_def *) hte->data;
> + }
> +
> + if (ssa_def != src->src.ssa){
> + nir_src new_src = nir_src_for_ssa(ssa_def);
> + nir_instr_rewrite_src(instr, &src->src, new_src);
> + }
> + }
> + }
> + }
> + nir_opt_remove_phi(phi);
> + } else {
> + /* There should be no more LCSSA-phis */
> + break;
> + }
> + }
> +
> + /* After cloning the loop and fixing up the LCSSA-phis we need to remove
> + * any obsolete phis at the beginning of the new unrolled block. To avoid
> + * failing validation.
> + */
> + nir_foreach_instr_safe(instr, block_before_loop) {
> + if (instr->type != nir_instr_type_phi)
> + continue;
> +
> + /* Replace phi */
> + nir_phi_instr *phi = nir_instr_as_phi(instr);
> + nir_opt_remove_phi(phi);
> + }
> +
> + /* Remove the loop */
> + nir_loop *nir_loop = nir_cf_node_as_loop(loop);
> + foreach_list_typed(nir_cf_node, child, node, &nir_loop->body)
> + nir_cleanup_cf_node(child, impl, false);
> +
> + exec_node_remove(&loop->node);
> +
> + stitch_blocks(prev_block, block);
oof... I think you can just use nir_cf_node_delete() here. No need to
use private CF functions.
> +}
> +
> +/**
> + * Unroll a loop which does not contain any jumps. For example, if the input
> + * is:
> + *
> + * (loop (...) ...instrs...)
> + *
> + * And the iteration count is 3, the output will be:
> + *
> + * ...instrs... ...instrs... ...instrs...
> + */
> +static void
> +simple_unroll(nir_function *fn, nir_loop *loop, nir_builder *b)
> +{
> + nir_shader *ns = fn->shader;
> + nir_block *prev_block =
> + nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
> +
> + struct exec_node *loop_node = exec_list_get_head(&loop->body);
> + nir_cf_node *lp_header_cf_node = exec_node_data(nir_cf_node, loop_node,
> + node);
There's a helper for this, nir_loop_first_cf_node().
> +
> + struct hash_table *remap_table =
> + _mesa_hash_table_create(NULL, _mesa_hash_pointer,
> + _mesa_key_pointer_equal);
> +
> + struct hash_table *phi_remap =
> + _mesa_hash_table_create(NULL, _mesa_hash_pointer,
> + _mesa_key_pointer_equal);
> +
> + /* Get the loop header this contains a bunch of phis and the loops
> + * conditional.
> + */
> + assert(lp_header_cf_node->type == nir_cf_node_block);
> + nir_block *loop_header_blk = nir_cf_node_as_block(lp_header_cf_node);
> +
> + /* Remove any phi preds that are from the loop itself nir_opt_remove_phi()
> + * will clean this up further for us.
> + */
> + nir_foreach_instr_safe(instr, loop_header_blk) {
> + if (instr->type != nir_instr_type_phi)
> + break;
> +
> + nir_phi_instr *phi = nir_instr_as_phi(instr);
> + nir_foreach_phi_src_safe(src, phi) {
> + /* Is the pred from the block itself? */
> + if (src->pred->index > phi->instr.block->index &&
> + src->pred->cf_node.parent == &loop->cf_node) {
> +
> + /* Store the phi dest and src to be used for remaping */
> + _mesa_hash_table_insert(phi_remap, &phi->dest.ssa, src->src.ssa);
> +
> + list_del(&src->src.use_link);
> + exec_node_remove(&src->node);
> + }
> + }
> + }
> +
> + /* Skip over if node (loop condition) and get the real loop body we need
> + * to do this now because we are about to start messing with the control
> + * flow.
> + */
> + nir_cf_node *if_node = nir_cf_node_next(lp_header_cf_node);
> + nir_cf_node *cf_node = nir_cf_node_next(if_node);
> + assert(cf_node->type == nir_cf_node_block);
> +
> + /* Pluck out the loop header */
> + nir_cf_list lp_header;
> + nir_cf_extract(&lp_header, nir_before_cf_node(lp_header_cf_node),
> + nir_after_cf_node(lp_header_cf_node));
> +
> + loop_node = exec_list_get_head(&loop->body);
> + lp_header_cf_node = exec_node_data(nir_cf_node, loop_node, node);
again, nir_loop_first_cf_node()
> +
> + /* Extract phis from loop header and place before the loop */
> + nir_cf_list lp_header_phis;
> + nir_cf_loop_list_extract(&lp_header_phis, lp_header_cf_node,
> + lp_header_cf_node);
> + b->cursor = nir_before_cf_node(&loop->cf_node);
> + nir_cf_reinsert(&lp_header_phis, b->cursor);
Why do we need to do this? I thought we didn't need to touch the phi's
anymore and we were just going to delete them.
> +
> + /* Pluck out the loop body */
> + nir_cf_list loop_body;
> + extract_loop_body(&loop_body, cf_node, ns);
> +
> + /* Initialise remap table with phi remap table */
> + struct hash_entry *hte;
> + hash_table_foreach(phi_remap, hte) {
> + _mesa_hash_table_insert(remap_table, hte->key, hte->data);
> + }
> +
> + /* Clone loop header and append to the loop body */
> + if (loop->info->trip_count > 0) {
> + nir_cf_list cloned_header;
> + exec_list_make_empty(&cloned_header.list);
> + cloned_header.impl = loop_body.impl;
> +
> + clone_list(ns, loop, &lp_header, &cloned_header, remap_table, phi_remap);
> +
> + /* Append loop body with header instructions */
> + struct exec_node *lp_body_node = exec_list_get_tail(&loop_body.list);
> + nir_cf_node *end = exec_node_data(nir_cf_node, lp_body_node, node);
> + nir_block *lp_body_blk = nir_cf_node_as_block(end);
> +
> + struct exec_node *lp_header_node =
> + exec_list_get_head(&cloned_header.list);
> + nir_block *lp_header_blk =
> + nir_cf_node_as_block(exec_node_data(nir_cf_node, lp_header_node,
> + node));
> +
> + foreach_list_typed(nir_instr, instr, node, &lp_header_blk->instr_list) {
> + instr->block = lp_body_blk;
> + }
> +
> + exec_list_append(&lp_body_blk->instr_list, &lp_header_blk->instr_list);
> + }
This is kinda ugly, but I don't have any suggestions on how to improve
it... I think in the future, we should rewrite all loops into do-while
form right before unrolling them and then this will go away.
> +
> + /* Reinsert original header before the loop */
> + nir_cf_reinsert(&lp_header, b->cursor);
> +
> + nir_cf_list *prev_lp = &loop_body;
> +
> + /* Create temp array to store the cloned loop body as we unroll */
> + nir_cf_list unrolled_lp_body[2];
> + exec_list_make_empty(&unrolled_lp_body[0].list);
> + exec_list_make_empty(&unrolled_lp_body[1].list);
> + unrolled_lp_body[0].impl = loop_body.impl;
> + unrolled_lp_body[1].impl = loop_body.impl;
> +
> + for (unsigned i = 1; i < loop->info->trip_count; i++) {
> +
> + /* Clone the loop body */
> + if (exec_list_is_empty(&unrolled_lp_body[0].list)){
> + clone_list(ns, loop, prev_lp, &unrolled_lp_body[0], remap_table,
> + phi_remap);
> +
> + /* Insert unrolled loop body before the loop. */
> + b->cursor = nir_before_cf_node(&loop->cf_node);
> + nir_cf_reinsert(prev_lp, b->cursor);
> +
> + prev_lp = &unrolled_lp_body[0];
> + } else {
> + clone_list(ns, loop, prev_lp, &unrolled_lp_body[1], remap_table,
> + phi_remap);
> +
> + /* Insert unrolled loop body before the loop. */
> + b->cursor = nir_before_cf_node(&loop->cf_node);
> + nir_cf_reinsert(prev_lp, b->cursor);
> +
> + prev_lp = &unrolled_lp_body[1];
> + }
> + }
> +
> + b->cursor = nir_before_cf_node(&loop->cf_node);
> + if (loop->info->trip_count != 0) {
> + nir_cf_reinsert(prev_lp, b->cursor);
> + } else {
> + /* Its possible to end up with a trip count of zero. For example:
> + *
> + * int 0;
> + * do res = res.yzwx; while (++i < 1);
> + *
> + * In this case we simple delete the loop and fix up the LCSSA phis.
> + */
> + nir_cf_delete(prev_lp);
> + }
> +
> + /* The loop has been unrolled so remove it. */
> + remove_unrolled_loop(&loop->cf_node, prev_block, remap_table, phi_remap,
> + fn->impl);
> +
> + _mesa_hash_table_destroy(remap_table, NULL);
> + _mesa_hash_table_destroy(phi_remap, NULL);
> +}
> +
> +static bool
> +process_loops(nir_cf_node *cf_node, nir_builder *b, bool *innermost_loop)
> +{
> + bool progress = false;
> + nir_loop *loop;
> +
> + switch (cf_node->type) {
> + case nir_cf_node_block:
> + return progress;
> + case nir_cf_node_if: {
> + nir_if *if_stmt = nir_cf_node_as_if(cf_node);
> + foreach_list_typed_safe(nir_cf_node, nested_node, node, &if_stmt->then_list)
> + progress |= process_loops(nested_node, b, innermost_loop);
> + foreach_list_typed_safe(nir_cf_node, nested_node, node, &if_stmt->else_list)
> + progress |= process_loops(nested_node, b, innermost_loop);
> + return progress;
> + }
> + case nir_cf_node_loop: {
> + loop = nir_cf_node_as_loop(cf_node);
> + foreach_list_typed_safe(nir_cf_node, nested_node, node, &loop->body)
> + progress |= process_loops(nested_node, b, innermost_loop);
> + break;
> + }
> + default:
> + unreachable("unknown cf node type");
> + }
> +
> + if (*innermost_loop) {
> + nir_function *fn = nir_cf_node_get_function(&loop->cf_node)->function;
> + if (is_simple_for_loop(fn->shader, loop->info)) {
> + simple_unroll(fn, loop, b);
> + progress = true;
> + /* Don't unroll outer loops loops until after loop analysis have run
> + * again.
> + */
> + *innermost_loop = false;
> + } else {
> + /* We couldn't unroll the innermost loop so don't try to unroll the
> + * outerloop.
> + */
> + *innermost_loop = false;
> + }
> + }
> +
> + return progress;
> +}
> +
> +static bool
> +nir_opt_loop_unroll_impl(nir_function_impl *impl)
> +{
> + bool progress = false;
> + nir_metadata_require(impl, nir_metadata_loop_analysis);
> +
> + nir_builder b;
> + nir_builder_init(&b, impl);
> +
> + foreach_list_typed_safe(nir_cf_node, node, node, &impl->body) {
> + bool innermost_loop = true;
> + progress |= process_loops(node, &b, &innermost_loop);
> + }
> +
> + return progress;
> +}
> +
> +bool
> +nir_opt_loop_unroll(nir_shader *shader)
> +{
> + bool progress = false;
> +
> + nir_foreach_function(function, shader) {
> + if (function->impl) {
> + progress |= nir_opt_loop_unroll_impl(function->impl);
> + }
> + }
> + return false;
> +}
> --
> 2.7.4
>
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