2015-05-01 07:38:17 +01:00
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/*
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* Copyright © 2014 Connor Abbott
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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 DEALINGS
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* IN THE SOFTWARE.
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*
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* Authors:
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* Connor Abbott (cwabbott0@gmail.com)
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*
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*/
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#include "nir.h"
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#include "nir_control_flow.h"
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/*
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2015-05-08 19:42:14 +01:00
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* This file implements an optimization that deletes statically
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* unreachable/dead code. In NIR, one way this can happen if if an if
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* statement has a constant condition:
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2015-05-01 07:38:17 +01:00
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*
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* if (true) {
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* ...
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* }
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*
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* We delete the if statement and paste the contents of the always-executed
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* branch into the surrounding control flow, possibly removing more code if
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* the branch had a jump at the end.
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2015-05-08 06:44:24 +01:00
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*
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2015-05-08 19:42:14 +01:00
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* Another way is that control flow can end in a jump so that code after it
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2015-05-08 06:44:24 +01:00
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* never gets executed. In particular, this can happen after optimizing
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* something like:
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*
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* if (true) {
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* ...
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* break;
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* }
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* ...
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*
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* We also consider the case where both branches of an if end in a jump, e.g.:
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*
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* if (...) {
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* break;
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* } else {
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* continue;
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* }
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* ...
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*
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2015-05-08 19:42:14 +01:00
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* Finally, we also handle removing useless loops, i.e. loops with no side
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* effects and without any definitions that are used elsewhere. This case is a
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* little different from the first two in that the code is actually run (it
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* just never does anything), but there are similar issues with needing to
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* be careful with restarting after deleting the cf_node (see dead_cf_list())
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* so this is a convenient place to remove them.
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2015-05-01 07:38:17 +01:00
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*/
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static void
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remove_after_cf_node(nir_cf_node *node)
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{
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nir_cf_node *end = node;
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while (!nir_cf_node_is_last(end))
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end = nir_cf_node_next(end);
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nir_cf_list list;
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nir_cf_extract(&list, nir_after_cf_node(node), nir_after_cf_node(end));
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nir_cf_delete(&list);
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}
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static void
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opt_constant_if(nir_if *if_stmt, bool condition)
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{
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/* First, we need to remove any phi nodes after the if by rewriting uses to
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* point to the correct source.
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*/
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nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&if_stmt->cf_node));
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nir_block *last_block =
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nir_cf_node_as_block(condition ? nir_if_last_then_node(if_stmt)
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: nir_if_last_else_node(if_stmt));
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2016-04-27 02:34:19 +01:00
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nir_foreach_instr_safe(instr, after) {
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2015-05-01 07:38:17 +01:00
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if (instr->type != nir_instr_type_phi)
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break;
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nir_phi_instr *phi = nir_instr_as_phi(instr);
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nir_ssa_def *def = NULL;
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2016-04-27 04:16:21 +01:00
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nir_foreach_phi_src(phi_src, phi) {
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2015-05-01 07:38:17 +01:00
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if (phi_src->pred != last_block)
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continue;
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assert(phi_src->src.is_ssa);
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def = phi_src->src.ssa;
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}
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assert(def);
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assert(phi->dest.is_ssa);
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2015-09-09 21:24:35 +01:00
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nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(def));
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2015-05-01 07:38:17 +01:00
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nir_instr_remove(instr);
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}
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/* The control flow list we're about to paste in may include a jump at the
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* end, and in that case we have to delete the rest of the control flow
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* list after the if since it's unreachable and the validator will balk if
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* we don't.
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*/
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if (!exec_list_is_empty(&last_block->instr_list)) {
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nir_instr *last_instr = nir_block_last_instr(last_block);
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if (last_instr->type == nir_instr_type_jump)
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remove_after_cf_node(&if_stmt->cf_node);
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}
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/* Finally, actually paste in the then or else branch and delete the if. */
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struct exec_list *cf_list = condition ? &if_stmt->then_list
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: &if_stmt->else_list;
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nir_cf_list list;
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nir_cf_extract(&list, nir_before_cf_list(cf_list),
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nir_after_cf_list(cf_list));
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nir_cf_reinsert(&list, nir_after_cf_node(&if_stmt->cf_node));
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nir_cf_node_remove(&if_stmt->cf_node);
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}
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2015-05-08 19:42:14 +01:00
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static bool
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2016-04-12 19:43:16 +01:00
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cf_node_has_side_effects(nir_cf_node *node)
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2015-05-08 19:42:14 +01:00
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{
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2016-04-12 19:43:16 +01:00
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nir_foreach_block_in_cf_node(block, node) {
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2016-04-27 02:34:19 +01:00
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nir_foreach_instr(instr, block) {
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2016-04-12 19:43:16 +01:00
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if (instr->type == nir_instr_type_call)
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return true;
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2015-05-08 19:42:14 +01:00
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2016-04-12 19:43:16 +01:00
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/* Return instructions can cause us to skip over other side-effecting
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* instructions after the loop, so consider them to have side effects
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* here.
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*/
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2015-05-08 19:42:14 +01:00
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2016-04-12 19:43:16 +01:00
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if (instr->type == nir_instr_type_jump &&
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nir_instr_as_jump(instr)->type == nir_jump_return)
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return true;
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2015-05-08 19:42:14 +01:00
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2016-04-12 19:43:16 +01:00
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if (instr->type != nir_instr_type_intrinsic)
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continue;
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2015-05-08 19:42:14 +01:00
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2016-04-12 19:43:16 +01:00
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nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
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if (!nir_intrinsic_infos[intrin->intrinsic].flags &
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NIR_INTRINSIC_CAN_ELIMINATE)
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return true;
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}
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2015-05-08 19:42:14 +01:00
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}
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2016-04-12 19:43:16 +01:00
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return false;
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2015-05-08 19:42:14 +01:00
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}
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static bool
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def_not_live_out(nir_ssa_def *def, void *state)
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{
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nir_block *after = state;
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return !BITSET_TEST(after->live_in, def->live_index);
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}
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/*
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* Test if a loop is dead. A loop is dead if:
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*
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* 1) It has no side effects (i.e. intrinsics which could possibly affect the
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* state of the program aside from producing an SSA value, indicated by a lack
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* of NIR_INTRINSIC_CAN_ELIMINATE).
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*
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* 2) It has no phi nodes after it, since those indicate values inside the
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* loop being used after the loop.
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*
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* 3) If there are no phi nodes after the loop, then the only way a value
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* defined inside the loop can be used outside the loop is if its definition
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* dominates the block after the loop. If none of the definitions that
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* dominate the loop exit are used outside the loop, then the loop is dead
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* and it can be deleted.
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*/
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static bool
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loop_is_dead(nir_loop *loop)
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{
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nir_block *before = nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
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nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node));
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if (!exec_list_is_empty(&after->instr_list) &&
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nir_block_first_instr(after)->type == nir_instr_type_phi)
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return false;
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2016-04-12 19:43:16 +01:00
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if (cf_node_has_side_effects(&loop->cf_node))
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2015-05-08 19:42:14 +01:00
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return false;
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2015-09-19 12:40:07 +01:00
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nir_function_impl *impl = nir_cf_node_get_function(&loop->cf_node);
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2015-11-04 01:15:24 +00:00
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nir_metadata_require(impl, nir_metadata_live_ssa_defs |
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2015-09-19 12:40:07 +01:00
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nir_metadata_dominance);
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2015-05-08 19:42:14 +01:00
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for (nir_block *cur = after->imm_dom; cur != before; cur = cur->imm_dom) {
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2016-04-27 02:34:19 +01:00
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nir_foreach_instr(instr, cur) {
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2015-05-08 19:42:14 +01:00
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if (!nir_foreach_ssa_def(instr, def_not_live_out, after))
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return false;
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}
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}
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return true;
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}
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2015-05-01 07:38:17 +01:00
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static bool
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2015-05-08 06:44:24 +01:00
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dead_cf_block(nir_block *block)
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2015-05-01 07:38:17 +01:00
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{
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nir_if *following_if = nir_block_get_following_if(block);
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2015-05-08 19:42:14 +01:00
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if (following_if) {
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nir_const_value *const_value =
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nir_src_as_const_value(following_if->condition);
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if (!const_value)
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return false;
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2015-05-01 07:38:17 +01:00
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2016-03-16 11:11:34 +00:00
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opt_constant_if(following_if, const_value->u32[0] != 0);
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2015-05-08 19:42:14 +01:00
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return true;
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}
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2015-05-01 07:38:17 +01:00
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2015-05-08 19:42:14 +01:00
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nir_loop *following_loop = nir_block_get_following_loop(block);
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if (!following_loop)
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return false;
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2015-05-01 07:38:17 +01:00
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2015-05-08 19:42:14 +01:00
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if (!loop_is_dead(following_loop))
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return false;
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nir_cf_node_remove(&following_loop->cf_node);
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2015-05-01 07:38:17 +01:00
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return true;
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}
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static bool
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2015-05-08 06:44:24 +01:00
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ends_in_jump(nir_block *block)
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{
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if (exec_list_is_empty(&block->instr_list))
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return false;
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nir_instr *instr = nir_block_last_instr(block);
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return instr->type == nir_instr_type_jump;
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}
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static bool
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dead_cf_list(struct exec_list *list, bool *list_ends_in_jump)
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2015-05-01 07:38:17 +01:00
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{
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bool progress = false;
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2015-05-08 06:44:24 +01:00
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*list_ends_in_jump = false;
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nir_cf_node *prev = NULL;
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foreach_list_typed(nir_cf_node, cur, node, list) {
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switch (cur->type) {
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case nir_cf_node_block: {
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nir_block *block = nir_cf_node_as_block(cur);
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if (dead_cf_block(block)) {
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2015-05-08 19:42:14 +01:00
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/* We just deleted the if or loop after this block, so we may have
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2015-05-08 06:44:24 +01:00
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* deleted the block before or after it -- which one is an
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* implementation detail. Therefore, to recover the place we were
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* at, we have to use the previous cf_node.
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*/
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if (prev) {
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cur = nir_cf_node_next(prev);
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} else {
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cur = exec_node_data(nir_cf_node, exec_list_get_head(list),
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node);
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}
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block = nir_cf_node_as_block(cur);
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progress = true;
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}
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if (ends_in_jump(block)) {
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*list_ends_in_jump = true;
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if (!exec_node_is_tail_sentinel(cur->node.next)) {
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remove_after_cf_node(cur);
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return true;
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}
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}
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break;
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}
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case nir_cf_node_if: {
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nir_if *if_stmt = nir_cf_node_as_if(cur);
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bool then_ends_in_jump, else_ends_in_jump;
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progress |= dead_cf_list(&if_stmt->then_list, &then_ends_in_jump);
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progress |= dead_cf_list(&if_stmt->else_list, &else_ends_in_jump);
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if (then_ends_in_jump && else_ends_in_jump) {
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*list_ends_in_jump = true;
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nir_block *next = nir_cf_node_as_block(nir_cf_node_next(cur));
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if (!exec_list_is_empty(&next->instr_list) ||
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!exec_node_is_tail_sentinel(next->cf_node.node.next)) {
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remove_after_cf_node(cur);
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return true;
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}
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}
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break;
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}
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case nir_cf_node_loop: {
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nir_loop *loop = nir_cf_node_as_loop(cur);
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bool dummy;
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progress |= dead_cf_list(&loop->body, &dummy);
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break;
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}
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default:
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unreachable("unknown cf node type");
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}
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prev = cur;
|
|
|
|
}
|
|
|
|
|
|
|
|
return progress;
|
|
|
|
}
|
|
|
|
|
|
|
|
static bool
|
|
|
|
opt_dead_cf_impl(nir_function_impl *impl)
|
|
|
|
{
|
|
|
|
bool dummy;
|
|
|
|
bool progress = dead_cf_list(&impl->body, &dummy);
|
2015-05-01 07:38:17 +01:00
|
|
|
|
|
|
|
if (progress)
|
|
|
|
nir_metadata_preserve(impl, nir_metadata_none);
|
|
|
|
|
|
|
|
return progress;
|
|
|
|
}
|
|
|
|
|
|
|
|
bool
|
|
|
|
nir_opt_dead_cf(nir_shader *shader)
|
|
|
|
{
|
|
|
|
bool progress = false;
|
|
|
|
|
2015-12-26 18:00:47 +00:00
|
|
|
nir_foreach_function(shader, function)
|
|
|
|
if (function->impl)
|
|
|
|
progress |= opt_dead_cf_impl(function->impl);
|
2015-05-01 07:38:17 +01:00
|
|
|
|
|
|
|
return progress;
|
|
|
|
}
|