217 lines
7.1 KiB
C
217 lines
7.1 KiB
C
/*
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* Copyright (c) 2019 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, sub license,
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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
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* next paragraph) shall be included in all copies or substantial portions
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* of the 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 NON-INFRINGEMENT. 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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*/
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#include "gpir.h"
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/* Here we perform a few optimizations that can't currently be done in NIR:
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*
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* - Optimize the result of a conditional break/continue. In NIR something
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* like:
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*
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* loop {
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* ...
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* if (cond)
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* continue;
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*
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* would get lowered to:
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*
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* block_0:
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* ...
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* block_1:
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* branch_cond !cond block_3
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* block_2:
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* branch_uncond block_0
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* block_3:
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* ...
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*
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* We recognize the conditional branch skipping over the unconditional
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* branch, and turn it into:
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*
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* block_0:
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* ...
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* block_1:
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* branch_cond cond block_0
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* block_2:
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* block_3:
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* ...
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*
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* - Optimize away nots of comparisons as produced by lowering ifs to
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* branches, and nots of nots produced by the above optimization.
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*
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* - DCE
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*/
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static void
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optimize_branches(gpir_compiler *comp)
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{
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list_for_each_entry(gpir_block, block, &comp->block_list, list) {
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/* Look for a block with a single unconditional branch. */
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if (!list_is_singular(&block->node_list))
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continue;
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gpir_node *node = list_first_entry(&block->node_list, gpir_node, list);
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if (node->op != gpir_op_branch_uncond)
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continue;
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gpir_block *target = gpir_node_to_branch(node)->dest;
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/* Find the previous block */
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if (block->list.prev == &comp->block_list)
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continue;
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gpir_block *prev_block = list_entry(block->list.prev, gpir_block, list);
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if (list_is_empty(&prev_block->node_list))
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continue;
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/* Previous block must end with a conditional branch */
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gpir_node *prev_block_last =
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list_last_entry(&prev_block->node_list, gpir_node, list);
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if (prev_block_last->op != gpir_op_branch_cond)
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continue;
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/* That branch must branch to the block after this */
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gpir_branch_node *prev_branch = gpir_node_to_branch(prev_block_last);
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gpir_block *prev_target = prev_branch->dest;
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if (&prev_target->list != block->list.next)
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continue;
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/* Hooray! Invert the conditional branch and change the target */
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gpir_alu_node *cond = gpir_node_create(prev_block, gpir_op_not);
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cond->children[0] = prev_branch->cond;
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cond->num_child = 1;
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gpir_node_add_dep(&cond->node, cond->children[0], GPIR_DEP_INPUT);
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list_addtail(&cond->node.list, &prev_block_last->list);
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gpir_node_insert_child(prev_block_last, prev_branch->cond, &cond->node);
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prev_branch->dest = target;
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prev_block->successors[1] = target;
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/* Delete the branch */
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list_del(&node->list);
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block->successors[0] = list_entry(block->list.next, gpir_block, list);
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}
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}
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static void
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optimize_not(gpir_compiler *comp)
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{
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list_for_each_entry(gpir_block, block, &comp->block_list, list) {
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list_for_each_entry_rev(gpir_node, node, &block->node_list, list) {
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if (node->op != gpir_op_not)
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continue;
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gpir_alu_node *alu = gpir_node_to_alu(node);
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gpir_node *replace = NULL;
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if (alu->children[0]->op == gpir_op_not) {
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/* (not (not a)) -> a */
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gpir_alu_node *child = gpir_node_to_alu(alu->children[0]);
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replace = child->children[0];
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} else if (alu->children[0]->op == gpir_op_ge ||
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alu->children[0]->op == gpir_op_lt) {
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/* (not (ge a, b)) -> (lt a, b) and
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* (not (lt a, b)) -> (ge a, b)
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*/
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gpir_alu_node *child = gpir_node_to_alu(alu->children[0]);
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gpir_op op = alu->children[0]->op == gpir_op_ge ?
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gpir_op_lt : gpir_op_ge;
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gpir_alu_node *new = gpir_node_create(block, op);
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new->children[0] = child->children[0];
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new->children[1] = child->children[1];
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new->num_child = 2;
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gpir_node_add_dep(&new->node, new->children[0], GPIR_DEP_INPUT);
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gpir_node_add_dep(&new->node, new->children[1], GPIR_DEP_INPUT);
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list_addtail(&new->node.list, &alu->children[0]->list);
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replace = &new->node;
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}
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if (replace) {
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gpir_node_replace_succ(replace, node);
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}
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}
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}
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}
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/* Does what it says. In addition to removing unused nodes from the not
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* optimization above, we need this to remove unused load_const nodes which
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* were created from store_output intrinsics in NIR, since we ignore the
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* offset.
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*/
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static void
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dead_code_eliminate(gpir_compiler *comp)
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{
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list_for_each_entry(gpir_block, block, &comp->block_list, list) {
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list_for_each_entry_safe_rev(gpir_node, node, &block->node_list, list) {
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if (node->type != gpir_node_type_store &&
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node->type != gpir_node_type_branch &&
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list_is_empty(&node->succ_list)) {
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gpir_node_delete(node);
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}
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}
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}
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/* Kill all the writes to regs that are never read. All the known
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* instances of these are coming from the cycle-breaking register
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* created in out-of-SSA. See resolve_parallel_copy() in nir_from_ssa.c
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* Since we kill redundant movs when we translate nir into gpir, it
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* results in this reg being written, but never read.
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*/
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BITSET_WORD *regs = rzalloc_array(comp, BITSET_WORD, comp->cur_reg);
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list_for_each_entry(gpir_block, block, &comp->block_list, list) {
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list_for_each_entry(gpir_node, node, &block->node_list, list) {
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if (node->op != gpir_op_load_reg)
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continue;
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gpir_load_node *load = gpir_node_to_load(node);
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BITSET_SET(regs, load->reg->index);
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}
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}
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list_for_each_entry(gpir_block, block, &comp->block_list, list) {
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list_for_each_entry_safe(gpir_node, node, &block->node_list, list) {
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if (node->op != gpir_op_store_reg)
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continue;
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gpir_store_node *store = gpir_node_to_store(node);
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if (!BITSET_TEST(regs, store->reg->index))
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gpir_node_delete(node);
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}
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}
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ralloc_free(regs);
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}
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bool
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gpir_optimize(gpir_compiler *comp)
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{
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optimize_branches(comp);
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optimize_not(comp);
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dead_code_eliminate(comp);
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gpir_debug("after optimization\n");
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gpir_node_print_prog_seq(comp);
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return true;
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}
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