nir: add a loop unrolling pass
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
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
This commit is contained in:
Timothy Arceri
@@ -241,6 +241,7 @@ NIR_FILES = \
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nir/nir_opt_dead_cf.c \
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nir/nir_opt_gcm.c \
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nir/nir_opt_global_to_local.c \
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nir/nir_opt_loop_unroll.c \
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nir/nir_opt_peephole_select.c \
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nir/nir_opt_remove_phis.c \
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nir/nir_opt_undef.c \
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@@ -2553,6 +2553,8 @@ bool nir_opt_dead_cf(nir_shader *shader);
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bool nir_opt_gcm(nir_shader *shader, bool value_number);
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bool nir_opt_loop_unroll(nir_shader *shader, nir_variable_mode indirect_mask);
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bool nir_opt_peephole_select(nir_shader *shader, unsigned limit);
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bool nir_opt_remove_phis(nir_shader *shader);
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575
src/compiler/nir/nir_opt_loop_unroll.c
Normal file
575
src/compiler/nir/nir_opt_loop_unroll.c
Normal file
@@ -0,0 +1,575 @@
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/*
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* Copyright © 2016 Intel Corporation
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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* DEALINGS IN THE SOFTWARE.
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*/
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#include "nir.h"
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#include "nir_builder.h"
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#include "nir_control_flow.h"
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#include "nir_loop_analyze.h"
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/* Prepare this loop for unrolling by first converting to lcssa and then
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* converting the phis from the loops first block and the block that follows
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* the loop into regs. Partially converting out of SSA allows us to unroll
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* the loop without having to keep track of and update phis along the way
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* which gets tricky and doesn't add much value over conveting to regs.
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*
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* The loop may have a continue instruction at the end of the loop which does
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* nothing. Once we're out of SSA, we can safely delete it so we don't have
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* to deal with it later.
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*/
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static void
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loop_prepare_for_unroll(nir_loop *loop)
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{
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nir_convert_loop_to_lcssa(loop);
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nir_lower_phis_to_regs_block(nir_loop_first_block(loop));
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nir_block *block_after_loop =
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nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node));
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nir_lower_phis_to_regs_block(block_after_loop);
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nir_instr *last_instr = nir_block_last_instr(nir_loop_last_block(loop));
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if (last_instr && last_instr->type == nir_instr_type_jump) {
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assert(nir_instr_as_jump(last_instr)->type == nir_jump_continue);
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nir_instr_remove(last_instr);
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}
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}
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static void
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get_first_blocks_in_terminator(nir_loop_terminator *term,
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nir_block **first_break_block,
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nir_block **first_continue_block)
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{
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if (term->continue_from_then) {
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*first_continue_block = nir_if_first_then_block(term->nif);
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*first_break_block = nir_if_first_else_block(term->nif);
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} else {
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*first_continue_block = nir_if_first_else_block(term->nif);
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*first_break_block = nir_if_first_then_block(term->nif);
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}
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}
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/**
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* Unroll a loop where we know exactly how many iterations there are and there
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* is only a single exit point. Note here we can unroll loops with multiple
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* theoretical exits that only have a single terminating exit that we always
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* know is the "real" exit.
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*
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* loop {
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* ...instrs...
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* }
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*
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* And the iteration count is 3, the output will be:
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*
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* ...instrs... ...instrs... ...instrs...
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*/
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static void
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simple_unroll(nir_loop *loop)
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{
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nir_loop_terminator *limiting_term = loop->info->limiting_terminator;
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assert(nir_is_trivial_loop_if(limiting_term->nif,
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limiting_term->break_block));
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loop_prepare_for_unroll(loop);
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/* Skip over loop terminator and get the loop body. */
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list_for_each_entry(nir_loop_terminator, terminator,
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&loop->info->loop_terminator_list,
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loop_terminator_link) {
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/* Remove all but the limiting terminator as we know the other exit
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* conditions can never be met. Note we need to extract any instructions
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* in the continue from branch and insert then into the loop body before
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* removing it.
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*/
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if (terminator->nif != limiting_term->nif) {
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nir_block *first_break_block;
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nir_block *first_continue_block;
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get_first_blocks_in_terminator(terminator, &first_break_block,
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&first_continue_block);
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assert(nir_is_trivial_loop_if(terminator->nif,
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terminator->break_block));
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nir_cf_list continue_from_lst;
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nir_cf_extract(&continue_from_lst,
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nir_before_block(first_continue_block),
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nir_after_block(terminator->continue_from_block));
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nir_cf_reinsert(&continue_from_lst,
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nir_after_cf_node(&terminator->nif->cf_node));
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nir_cf_node_remove(&terminator->nif->cf_node);
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}
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}
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nir_block *first_break_block;
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nir_block *first_continue_block;
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get_first_blocks_in_terminator(limiting_term, &first_break_block,
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&first_continue_block);
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/* Pluck out the loop header */
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nir_block *header_blk = nir_loop_first_block(loop);
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nir_cf_list lp_header;
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nir_cf_extract(&lp_header, nir_before_block(header_blk),
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nir_before_cf_node(&limiting_term->nif->cf_node));
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/* Add the continue from block of the limiting terminator to the loop body
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*/
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nir_cf_list continue_from_lst;
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nir_cf_extract(&continue_from_lst, nir_before_block(first_continue_block),
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nir_after_block(limiting_term->continue_from_block));
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nir_cf_reinsert(&continue_from_lst,
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nir_after_cf_node(&limiting_term->nif->cf_node));
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/* Pluck out the loop body */
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nir_cf_list loop_body;
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nir_cf_extract(&loop_body, nir_after_cf_node(&limiting_term->nif->cf_node),
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nir_after_block(nir_loop_last_block(loop)));
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struct hash_table *remap_table =
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_mesa_hash_table_create(NULL, _mesa_hash_pointer,
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_mesa_key_pointer_equal);
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/* Clone the loop header */
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nir_cf_list cloned_header;
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nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent,
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remap_table);
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/* Insert cloned loop header before the loop */
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nir_cf_reinsert(&cloned_header, nir_before_cf_node(&loop->cf_node));
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/* Temp list to store the cloned loop body as we unroll */
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nir_cf_list unrolled_lp_body;
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/* Clone loop header and append to the loop body */
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for (unsigned i = 0; i < loop->info->trip_count; i++) {
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/* Clone loop body */
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nir_cf_list_clone(&unrolled_lp_body, &loop_body, loop->cf_node.parent,
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remap_table);
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/* Insert unrolled loop body before the loop */
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nir_cf_reinsert(&unrolled_lp_body, nir_before_cf_node(&loop->cf_node));
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/* Clone loop header */
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nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent,
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remap_table);
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/* Insert loop header after loop body */
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nir_cf_reinsert(&cloned_header, nir_before_cf_node(&loop->cf_node));
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}
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/* Remove the break from the loop terminator and add instructions from
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* the break block after the unrolled loop.
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*/
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nir_instr *break_instr = nir_block_last_instr(limiting_term->break_block);
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nir_instr_remove(break_instr);
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nir_cf_list break_list;
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nir_cf_extract(&break_list, nir_before_block(first_break_block),
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nir_after_block(limiting_term->break_block));
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/* Clone so things get properly remapped */
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nir_cf_list cloned_break_list;
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nir_cf_list_clone(&cloned_break_list, &break_list, loop->cf_node.parent,
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remap_table);
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nir_cf_reinsert(&cloned_break_list, nir_before_cf_node(&loop->cf_node));
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/* Remove the loop */
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nir_cf_node_remove(&loop->cf_node);
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/* Delete the original loop body, break block & header */
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nir_cf_delete(&lp_header);
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nir_cf_delete(&loop_body);
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nir_cf_delete(&break_list);
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_mesa_hash_table_destroy(remap_table, NULL);
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}
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static void
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move_cf_list_into_loop_term(nir_cf_list *lst, nir_loop_terminator *term)
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{
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/* Move the rest of the loop inside the continue-from-block */
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nir_cf_reinsert(lst, nir_after_block(term->continue_from_block));
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/* Remove the break */
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nir_instr_remove(nir_block_last_instr(term->break_block));
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}
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static nir_cursor
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get_complex_unroll_insert_location(nir_cf_node *node, bool continue_from_then)
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{
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if (node->type == nir_cf_node_loop) {
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return nir_before_cf_node(node);
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} else {
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nir_if *if_stmt = nir_cf_node_as_if(node);
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if (continue_from_then) {
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return nir_after_block(nir_if_last_then_block(if_stmt));
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} else {
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return nir_after_block(nir_if_last_else_block(if_stmt));
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}
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}
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}
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/**
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* Unroll a loop with two exists when the trip count of one of the exits is
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* unknown. If continue_from_then is true, the loop is repeated only when the
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* "then" branch of the if is taken; otherwise it is repeated only
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* when the "else" branch of the if is taken.
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*
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* For example, if the input is:
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*
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* loop {
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* ...phis/condition...
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* if condition {
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* ...then instructions...
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* } else {
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* ...continue instructions...
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* break
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* }
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* ...body...
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* }
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*
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* And the iteration count is 3, and unlimit_term->continue_from_then is true,
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* then the output will be:
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*
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* ...condition...
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* if condition {
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* ...then instructions...
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* ...body...
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* if condition {
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* ...then instructions...
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* ...body...
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* if condition {
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* ...then instructions...
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* ...body...
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* } else {
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* ...continue instructions...
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* }
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* } else {
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* ...continue instructions...
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* }
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* } else {
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* ...continue instructions...
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* }
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*/
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static void
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complex_unroll(nir_loop *loop, nir_loop_terminator *unlimit_term,
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bool limiting_term_second)
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{
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assert(nir_is_trivial_loop_if(unlimit_term->nif,
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unlimit_term->break_block));
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nir_loop_terminator *limiting_term = loop->info->limiting_terminator;
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assert(nir_is_trivial_loop_if(limiting_term->nif,
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limiting_term->break_block));
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loop_prepare_for_unroll(loop);
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nir_block *header_blk = nir_loop_first_block(loop);
|
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|
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nir_cf_list lp_header;
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nir_cf_list limit_break_list;
|
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unsigned num_times_to_clone;
|
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if (limiting_term_second) {
|
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/* Pluck out the loop header */
|
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nir_cf_extract(&lp_header, nir_before_block(header_blk),
|
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nir_before_cf_node(&unlimit_term->nif->cf_node));
|
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|
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/* We need some special handling when its the second terminator causing
|
||||
* us to exit the loop for example:
|
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*
|
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* for (int i = 0; i < uniform_lp_count; i++) {
|
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* colour = vec4(0.0, 1.0, 0.0, 1.0);
|
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*
|
||||
* if (i == 1) {
|
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* break;
|
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* }
|
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* ... any further code is unreachable after i == 1 ...
|
||||
* }
|
||||
*/
|
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nir_cf_list after_lt;
|
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nir_if *limit_if = limiting_term->nif;
|
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nir_cf_extract(&after_lt, nir_after_cf_node(&limit_if->cf_node),
|
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nir_after_block(nir_loop_last_block(loop)));
|
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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.
|
||||
*/
|
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num_times_to_clone = loop->info->trip_count + 1;
|
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} else {
|
||||
/* Pluck out the loop header */
|
||||
nir_cf_extract(&lp_header, nir_before_block(header_blk),
|
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nir_before_cf_node(&limiting_term->nif->cf_node));
|
||||
|
||||
nir_block *first_break_block;
|
||||
nir_block *first_continue_block;
|
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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);
|
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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;
|
||||
}
|
||||
Reference in New Issue
Block a user