[Mesa-dev] [PATCH 10/13] nir: add a loop unrolling pass
Timothy Arceri
timothy.arceri at collabora.com
Thu Dec 22 02:26:13 UTC 2016
V2:
- tidy ups suggested by Connor.
- tidy up cloning logic and handle copy propagation
based of suggestion by Connor.
- use nir_ssa_def_rewrite_uses to fix up lcssa phis
suggested by Connor.
- add support for complex loop unrolling (two terminators)
- handle case were the ssa defs use outside the loop is already a phi
- support unrolling loops with multiple terminators when trip count
is know for each terminator
V3:
- set correct num_components when creating phi in complex unroll
- rewrite update remap table based on Jasons suggestions.
- remove unrequired extract_loop_body() helper as suggested by Jason.
- simplify the lcssa phi fix up code for simple loops as per Jasons suggestions.
- use mem context to keep track of hash table memory as suggested by Jason.
- move is_{complex,simple}_loop helpers to the unroll code
- require nir_metadata_block_index
- partially rewrote complex unroll to be simpler and easier to follow.
V4:
- use rzalloc() when creating nir_phi_src but not setting pred right away
fixes regression cause by ralloc() no longer zeroing memory.
V5:
- simplify calling of complex_unroll()
- use new loop terminator fields to get the break/continue from blocks
and simplify loop unrolling code
- handle slightly less trivial loop terminators. if branches can
now have instructions but can only contain a single block.
- use nir print type IR snippets in unroll function descriptions
- add better explanation and variable for why we need to clone
additional times when the second terminator it the limiting
terminator.
- partially convert out of ssa before unrolling loops (suggested by Jason)
v6:
- remove unused nir_builder
- use Jasons new from ssa helper
- tidy/fixup cursor use
- unroll terminators that contain control flow correctly
- unroll complex loops with control flow before the terminators
correctly
---
src/compiler/Makefile.sources | 1 +
src/compiler/nir/nir.h | 2 +
src/compiler/nir/nir_opt_loop_unroll.c | 566 +++++++++++++++++++++++++++++++++
3 files changed, 569 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 f551449..566e246 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -241,6 +241,7 @@ 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 fd35bd0..0fd6a77 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2555,6 +2555,8 @@ bool nir_opt_dead_cf(nir_shader *shader);
bool nir_opt_gcm(nir_shader *shader, bool value_number);
+bool nir_opt_loop_unroll(nir_shader *shader, nir_variable_mode indirect_mask);
+
bool nir_opt_peephole_select(nir_shader *shader, unsigned limit);
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..6d27c6b
--- /dev/null
+++ b/src/compiler/nir/nir_opt_loop_unroll.c
@@ -0,0 +1,566 @@
+/*
+ * 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"
+#include "nir_loop_analyze.h"
+
+/* Convert the phis from the loops first block and the block that follows the
+ * loop into regs. Partially converting out of SSA allows us to unroll the
+ * loop without having to keep track of and update phis along the way which
+ * gets tricky and doesn't add much value over conveting to regs.
+ */
+static void
+convert_loop_phis_to_reg(nir_loop *loop,
+ nir_block *header_blk)
+{
+ nir_lower_phis_to_regs_block(header_blk);
+
+ nir_block *block_after_loop =
+ nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node));
+
+ nir_lower_phis_to_regs_block(block_after_loop);
+}
+
+static void
+get_first_blocks_in_terminator(nir_loop_terminator *term,
+ nir_block **first_break_block,
+ nir_block **first_continue_block)
+{
+ if (term->continue_from_then) {
+ *first_continue_block = nir_if_first_then_block(term->nif);
+ *first_break_block = nir_if_first_else_block(term->nif);
+ } else {
+ *first_continue_block = nir_if_first_else_block(term->nif);
+ *first_break_block = nir_if_first_then_block(term->nif);
+ }
+}
+
+/**
+ * Unroll a loop where we know exactly how many iterations there are and there
+ * is only a single exit point. Note here we can unroll loops with multiple
+ * theoretical exits that only have a single terminating exit that we always
+ * know is the "real" exit.
+ *
+ * loop {
+ * ...instrs...
+ * }
+ *
+ * And the iteration count is 3, the output will be:
+ *
+ * ...instrs... ...instrs... ...instrs...
+ */
+static void
+simple_unroll(nir_loop *loop)
+{
+ nir_loop_terminator *limiting_term = loop->info->limiting_terminator;
+ assert(nir_is_trivial_loop_if(limiting_term->nif,
+ limiting_term->break_block));
+
+ nir_convert_loop_to_lcssa(loop);
+
+ nir_block *header_blk = nir_loop_first_block(loop);
+ convert_loop_phis_to_reg(loop, header_blk);
+
+ /* Skip over loop terminator and get the loop body. */
+ list_for_each_entry(nir_loop_terminator, terminator,
+ &loop->info->loop_terminator_list,
+ loop_terminator_link) {
+
+ /* Remove all but the limiting terminator as we know the other exit
+ * conditions can never be met. Note we need to extract any instructions
+ * in the continue from branch and insert then into the loop body before
+ * removing it.
+ */
+ if (terminator->nif != limiting_term->nif) {
+ nir_block *first_break_block;
+ nir_block *first_continue_block;
+ get_first_blocks_in_terminator(terminator, &first_break_block,
+ &first_continue_block);
+
+ assert(nir_is_trivial_loop_if(terminator->nif,
+ terminator->break_block));
+
+ nir_cf_list continue_from_lst;
+ nir_cf_extract(&continue_from_lst,
+ nir_before_block(first_continue_block),
+ nir_after_block(terminator->continue_from_block));
+ nir_cf_reinsert(&continue_from_lst,
+ nir_after_cf_node(&terminator->nif->cf_node));
+
+ nir_cf_node_remove(&terminator->nif->cf_node);
+ }
+ }
+
+ nir_block *first_break_block;
+ nir_block *first_continue_block;
+ get_first_blocks_in_terminator(limiting_term, &first_break_block,
+ &first_continue_block);
+
+ /* Pluck out the loop header */
+ nir_cf_list lp_header;
+ nir_cf_extract(&lp_header, nir_before_block(header_blk),
+ nir_before_cf_node(&limiting_term->nif->cf_node));
+
+ /* Add the continue from block of the limiting terminator to the loop body
+ */
+ nir_cf_list continue_from_lst;
+ nir_cf_extract(&continue_from_lst, nir_before_block(first_continue_block),
+ nir_after_block(limiting_term->continue_from_block));
+ nir_cf_reinsert(&continue_from_lst,
+ nir_after_cf_node(&limiting_term->nif->cf_node));
+
+ /* Pluck out the loop body */
+ nir_cf_list loop_body;
+ nir_cf_extract(&loop_body, nir_after_cf_node(&limiting_term->nif->cf_node),
+ nir_after_block(nir_loop_last_block(loop)));
+
+ struct hash_table *remap_table =
+ _mesa_hash_table_create(NULL, _mesa_hash_pointer,
+ _mesa_key_pointer_equal);
+
+ /* Clone the loop header */
+ nir_cf_list cloned_header;
+ nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent,
+ remap_table);
+
+ /* Insert cloned loop header before the loop */
+ nir_cf_reinsert(&cloned_header, nir_before_cf_node(&loop->cf_node));
+
+ /* Temp list to store the cloned loop body as we unroll */
+ nir_cf_list unrolled_lp_body;
+
+ /* Clone loop header and append to the loop body */
+ for (unsigned i = 0; i < loop->info->trip_count; i++) {
+ /* Clone loop body */
+ nir_cf_list_clone(&unrolled_lp_body, &loop_body, loop->cf_node.parent,
+ remap_table);
+
+ /* Insert unrolled loop body before the loop */
+ nir_cf_reinsert(&unrolled_lp_body, nir_before_cf_node(&loop->cf_node));
+
+ /* Clone loop header */
+ nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent,
+ remap_table);
+
+ /* Insert loop header after loop body */
+ nir_cf_reinsert(&cloned_header, nir_before_cf_node(&loop->cf_node));
+ }
+
+ /* Remove the break from the loop terminator and add instructions from
+ * the break block after the unrolled loop.
+ */
+ nir_instr *break_instr = nir_block_last_instr(limiting_term->break_block);
+ nir_instr_remove(break_instr);
+ nir_cf_list break_list;
+ nir_cf_extract(&break_list, nir_before_block(first_break_block),
+ nir_after_block(limiting_term->break_block));
+
+ /* Clone so things get properly remapped */
+ nir_cf_list cloned_break_list;
+ nir_cf_list_clone(&cloned_break_list, &break_list, loop->cf_node.parent,
+ remap_table);
+
+ nir_cf_reinsert(&cloned_break_list, nir_before_cf_node(&loop->cf_node));
+
+ /* Remove the loop */
+ nir_cf_node_remove(&loop->cf_node);
+
+ /* Delete the original loop body, break block & header */
+ nir_cf_delete(&lp_header);
+ nir_cf_delete(&loop_body);
+ nir_cf_delete(&break_list);
+
+ _mesa_hash_table_destroy(remap_table, NULL);
+}
+
+static void
+move_cf_list_into_loop_term(nir_cf_list *lst, nir_loop_terminator *term)
+{
+ /* Move the rest of the loop inside the continue-from-block */
+ nir_cf_reinsert(lst, nir_after_block(term->continue_from_block));
+
+ /* Remove the break */
+ nir_instr_remove(nir_block_last_instr(term->break_block));
+}
+
+static nir_cursor
+get_complex_unroll_insert_location(nir_cf_node *node, bool continue_from_then)
+{
+ if (node->type == nir_cf_node_loop) {
+ return nir_before_cf_node(node);
+ } else {
+ nir_if *if_stmt = nir_cf_node_as_if(node);
+ if (continue_from_then) {
+ return nir_after_block(nir_if_last_then_block(if_stmt));
+ } else {
+ return nir_after_block(nir_if_last_else_block(if_stmt));
+ }
+ }
+}
+
+/**
+ * Unroll a loop with two exists when the trip count of one of the exits is
+ * unknown. If continue_from_then is true, the loop is repeated only when the
+ * "then" branch of the if is taken; otherwise it is repeated only
+ * when the "else" branch of the if is taken.
+ *
+ * For example, if the input is:
+ *
+ * loop {
+ * ...phis/condition...
+ * if condition {
+ * ...then instructions...
+ * } else {
+ * ...continue instructions...
+ * break
+ * }
+ * ...body...
+ * }
+ *
+ * And the iteration count is 3, and unlimit_term->continue_from_then is true,
+ * then the output will be:
+ *
+ * ...condition...
+ * if condition {
+ * ...then instructions...
+ * ...body...
+ * if condition {
+ * ...then instructions...
+ * ...body...
+ * if condition {
+ * ...then instructions...
+ * ...body...
+ * } else {
+ * ...continue instructions...
+ * }
+ * } else {
+ * ...continue instructions...
+ * }
+ * } else {
+ * ...continue instructions...
+ * }
+ */
+static void
+complex_unroll(nir_loop *loop, nir_loop_terminator *unlimit_term,
+ bool limiting_term_second)
+{
+ assert(nir_is_trivial_loop_if(unlimit_term->nif,
+ unlimit_term->break_block));
+
+ nir_loop_terminator *limiting_term = loop->info->limiting_terminator;
+ assert(nir_is_trivial_loop_if(limiting_term->nif,
+ limiting_term->break_block));
+
+ nir_convert_loop_to_lcssa(loop);
+
+ nir_block *header_blk = nir_loop_first_block(loop);
+ convert_loop_phis_to_reg(loop, header_blk);
+
+ nir_cf_list lp_header;
+ nir_cf_list limit_break_list;
+ unsigned num_times_to_clone;
+ if (limiting_term_second) {
+ /* Pluck out the loop header */
+ nir_cf_extract(&lp_header, nir_before_block(header_blk),
+ nir_before_cf_node(&unlimit_term->nif->cf_node));
+
+ /* We need some special handling when its the second terminator causing
+ * us to exit the loop for example:
+ *
+ * for (int i = 0; i < uniform_lp_count; i++) {
+ * colour = vec4(0.0, 1.0, 0.0, 1.0);
+ *
+ * if (i == 1) {
+ * break;
+ * }
+ * ... any further code is unreachable after i == 1 ...
+ * }
+ */
+ nir_cf_list after_lt;
+ nir_if *limit_if = limiting_term->nif;
+ nir_cf_extract(&after_lt, nir_after_cf_node(&limit_if->cf_node),
+ nir_after_block(nir_loop_last_block(loop)));
+ move_cf_list_into_loop_term(&after_lt, limiting_term);
+
+ /* Because the trip count is the number of times we pass over the entire
+ * loop before hitting a break when the second terminator is the
+ * limiting terminator we can actually execute code inside the loop when
+ * trip count == 0 e.g. the code above the break. So we need to bump
+ * the trip_count in order for the code below to clone anything. When
+ * trip count == 1 we execute the code above the break twice and the
+ * code below it once so we need clone things twice and so on.
+ */
+ num_times_to_clone = loop->info->trip_count + 1;
+ } else {
+ /* Pluck out the loop header */
+ nir_cf_extract(&lp_header, nir_before_block(header_blk),
+ nir_before_cf_node(&limiting_term->nif->cf_node));
+
+ nir_block *first_break_block;
+ nir_block *first_continue_block;
+ get_first_blocks_in_terminator(limiting_term, &first_break_block,
+ &first_continue_block);
+
+ /* Remove the break then extract instructions from the break block so we
+ * can insert them in the innermost else of the unrolled loop.
+ */
+ nir_instr *break_instr = nir_block_last_instr(limiting_term->break_block);
+ nir_instr_remove(break_instr);
+ nir_cf_extract(&limit_break_list, nir_before_block(first_break_block),
+ nir_after_block(limiting_term->break_block));
+
+ nir_cf_list continue_list;
+ nir_cf_extract(&continue_list, nir_before_block(first_continue_block),
+ nir_after_block(limiting_term->continue_from_block));
+
+ nir_cf_reinsert(&continue_list,
+ nir_after_cf_node(&limiting_term->nif->cf_node));
+
+ nir_cf_node_remove(&limiting_term->nif->cf_node);
+
+ num_times_to_clone = loop->info->trip_count;
+ }
+
+ /* In the terminator that we have no trip count for move everything after
+ * the terminator into the continue from branch.
+ */
+ nir_cf_list loop_end;
+ nir_cf_extract(&loop_end, nir_after_cf_node(&unlimit_term->nif->cf_node),
+ nir_after_block(nir_loop_last_block(loop)));
+ move_cf_list_into_loop_term(&loop_end, unlimit_term);
+
+ /* Pluck out the loop body. */
+ nir_cf_list loop_body;
+ nir_cf_extract(&loop_body, nir_before_block(nir_loop_first_block(loop)),
+ nir_after_block(nir_loop_last_block(loop)));
+
+ struct hash_table *remap_table =
+ _mesa_hash_table_create(NULL, _mesa_hash_pointer,
+ _mesa_key_pointer_equal);
+
+ /* Set unroll_loc to the loop as we will insert the unrolled loop before it
+ */
+ nir_cf_node *unroll_loc = &loop->cf_node;
+
+ /* Temp lists to store the cloned loop as we unroll */
+ nir_cf_list unrolled_lp_body;
+ nir_cf_list cloned_header;
+
+ for (unsigned i = 0; i < num_times_to_clone; i++) {
+ /* Clone loop header */
+ nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent,
+ remap_table);
+
+ nir_cursor cursor =
+ get_complex_unroll_insert_location(unroll_loc,
+ unlimit_term->continue_from_then);
+
+ /* Insert cloned loop header */
+ nir_cf_reinsert(&cloned_header, cursor);
+
+ cursor =
+ get_complex_unroll_insert_location(unroll_loc,
+ unlimit_term->continue_from_then);
+
+ /* Clone loop body */
+ nir_cf_list_clone(&unrolled_lp_body, &loop_body, loop->cf_node.parent,
+ remap_table);
+
+ unroll_loc = exec_node_data(nir_cf_node,
+ exec_list_get_tail(&unrolled_lp_body.list),
+ node);
+ assert(unroll_loc->type == nir_cf_node_block &&
+ exec_list_is_empty(&nir_cf_node_as_block(unroll_loc)->instr_list));
+
+ /* Get the unrolled if node */
+ unroll_loc = nir_cf_node_prev(unroll_loc);
+
+ /* Insert unrolled loop body */
+ nir_cf_reinsert(&unrolled_lp_body, cursor);
+ }
+
+ if (!limiting_term_second) {
+ assert(unroll_loc->type == nir_cf_node_if);
+
+ nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent,
+ remap_table);
+
+ nir_cursor cursor =
+ get_complex_unroll_insert_location(unroll_loc,
+ unlimit_term->continue_from_then);
+
+ /* Insert cloned loop header */
+ nir_cf_reinsert(&cloned_header, cursor);
+
+ /* Clone so things get properly remapped, and insert break block from
+ * the limiting terminator.
+ */
+ nir_cf_list cloned_break_blk;
+ nir_cf_list_clone(&cloned_break_blk, &limit_break_list,
+ loop->cf_node.parent, remap_table);
+
+ cursor =
+ get_complex_unroll_insert_location(unroll_loc,
+ unlimit_term->continue_from_then);
+
+ nir_cf_reinsert(&cloned_break_blk, cursor);
+ nir_cf_delete(&limit_break_list);
+ }
+
+ /* The loop has been unrolled so remove it. */
+ nir_cf_node_remove(&loop->cf_node);
+
+ /* Delete the original loop header and body */
+ nir_cf_delete(&lp_header);
+ nir_cf_delete(&loop_body);
+
+ _mesa_hash_table_destroy(remap_table, NULL);
+}
+
+static bool
+is_loop_small_enough_to_unroll(nir_shader *shader, nir_loop_info *li)
+{
+ unsigned max_iter = shader->options->max_unroll_iterations;
+
+ if (li->trip_count > max_iter)
+ return false;
+
+ if (li->force_unroll)
+ return true;
+
+ bool loop_not_too_large =
+ li->num_instructions * li->trip_count <= max_iter * 25;
+
+ return loop_not_too_large;
+}
+
+static bool
+process_loops(nir_shader *sh, nir_cf_node *cf_node, 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(sh, nested_node, innermost_loop);
+ foreach_list_typed_safe(nir_cf_node, nested_node, node, &if_stmt->else_list)
+ progress |= process_loops(sh, nested_node, 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(sh, nested_node, innermost_loop);
+ break;
+ }
+ default:
+ unreachable("unknown cf node type");
+ }
+
+ if (*innermost_loop) {
+ /* Don't attempt to unroll outer loops or a second inner loop in
+ * this pass wait until the next pass as we have altered the cf.
+ */
+ *innermost_loop = false;
+
+ if (loop->info->limiting_terminator == NULL)
+ return progress;
+
+ if (!is_loop_small_enough_to_unroll(sh, loop->info))
+ return progress;
+
+ if (loop->info->is_trip_count_known) {
+ simple_unroll(loop);
+ progress = true;
+ } else {
+ /* Attempt to unroll loops with two terminators. */
+ unsigned num_lt = list_length(&loop->info->loop_terminator_list);
+ if (num_lt == 2) {
+ bool limiting_term_second = true;
+ nir_loop_terminator *terminator =
+ list_last_entry(&loop->info->loop_terminator_list,
+ nir_loop_terminator, loop_terminator_link);
+
+
+ if (terminator->nif == loop->info->limiting_terminator->nif) {
+ limiting_term_second = false;
+ terminator =
+ list_first_entry(&loop->info->loop_terminator_list,
+ nir_loop_terminator, loop_terminator_link);
+ }
+
+ /* If the first terminator has a trip count of zero and is the
+ * limiting terminator just do a simple unroll as the second
+ * terminator can never be reached.
+ */
+ if (loop->info->trip_count == 0 && !limiting_term_second) {
+ simple_unroll(loop);
+ } else {
+ complex_unroll(loop, terminator, limiting_term_second);
+ }
+ progress = true;
+ }
+ }
+ }
+
+ return progress;
+}
+
+static bool
+nir_opt_loop_unroll_impl(nir_function_impl *impl,
+ nir_variable_mode indirect_mask)
+{
+ bool progress = false;
+ nir_metadata_require(impl, nir_metadata_loop_analysis, indirect_mask);
+ nir_metadata_require(impl, nir_metadata_block_index);
+
+ foreach_list_typed_safe(nir_cf_node, node, node, &impl->body) {
+ bool innermost_loop = true;
+ progress |= process_loops(impl->function->shader, node,
+ &innermost_loop);
+ }
+
+ if (progress)
+ nir_convert_to_ssa_impl(impl);
+
+ return progress;
+}
+
+bool
+nir_opt_loop_unroll(nir_shader *shader, nir_variable_mode indirect_mask)
+{
+ bool progress = false;
+
+ nir_foreach_function(function, shader) {
+ if (function->impl) {
+ progress |= nir_opt_loop_unroll_impl(function->impl, indirect_mask);
+ }
+ }
+ return progress;
+}
--
2.9.3
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