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/*
* Copyright (C) 2018 Alyssa Rosenzweig
* Copyright (C) 2019 Collabora, Ltd.
*
* 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 "compiler.h"
#include "util/u_memory.h"
#include "midgard_ops.h"
/* SIMD-aware dead code elimination. Perform liveness analysis step-by-step,
* removing dead components. If an instruction ends up with a zero mask, the
* instruction in total is dead and should be removed. */
static bool
can_cull_mask(compiler_context *ctx, midgard_instruction *ins)
{
if (ins->dest >= ctx->temp_count)
return false;
if (ins->type == TAG_LOAD_STORE_4)
if (load_store_opcode_props[ins->load_store.op].props & LDST_SPECIAL_MASK)
return false;
return true;
}
static bool
can_dce(midgard_instruction *ins)
{
if (ins->mask)
return false;
if (ins->compact_branch)
return false;
if (ins->type == TAG_LOAD_STORE_4)
if (load_store_opcode_props[ins->load_store.op].props & LDST_SIDE_FX)
return false;
if (ins->type == TAG_TEXTURE_4)
if (ins->texture.op == TEXTURE_OP_BARRIER)
return false;
return true;
}
static bool
midgard_opt_dead_code_eliminate_block(compiler_context *ctx, midgard_block *block)
{
bool progress = false;
uint16_t *live = mem_dup(block->base.live_out, ctx->temp_count * sizeof(uint16_t));
mir_foreach_instr_in_block_rev(block, ins) {
if (can_cull_mask(ctx, ins)) {
unsigned type_size = nir_alu_type_get_type_size(ins->dest_type);
unsigned oldmask = ins->mask;
unsigned rounded = mir_round_bytemask_up(live[ins->dest], type_size);
unsigned cmask = mir_from_bytemask(rounded, type_size);
ins->mask &= cmask;
progress |= (ins->mask != oldmask);
}
mir_liveness_ins_update(live, ins, ctx->temp_count);
}
mir_foreach_instr_in_block_safe(block, ins) {
if (can_dce(ins)) {
mir_remove_instruction(ins);
progress = true;
}
}
free(live);
return progress;
}
bool
midgard_opt_dead_code_eliminate(compiler_context *ctx)
{
/* We track liveness. In fact, it's ok if we assume more things are
* live than they actually are, that just reduces the effectiveness of
* this iterations lightly. And DCE has the effect of strictly reducing
* liveness, so we can run DCE across all blocks while only computing
* liveness at the beginning. */
mir_invalidate_liveness(ctx);
mir_compute_liveness(ctx);
bool progress = false;
mir_foreach_block(ctx, block) {
progress |= midgard_opt_dead_code_eliminate_block(ctx, (midgard_block *) block);
}
return progress;
}
/* Removes dead moves, that is, moves with a destination overwritten before
* being read. Normally handled implicitly as part of DCE, but this has to run
* after the out-of-SSA pass */
bool
midgard_opt_dead_move_eliminate(compiler_context *ctx, midgard_block *block)
{
bool progress = false;
mir_foreach_instr_in_block_safe(block, ins) {
if (ins->type != TAG_ALU_4) continue;
if (ins->compact_branch) continue;
if (!OP_IS_MOVE(ins->alu.op)) continue;
/* Check if it's overwritten in this block before being read */
bool overwritten = false;
mir_foreach_instr_in_block_from(block, q, mir_next_op(ins)) {
/* Check if used */
if (mir_has_arg(q, ins->dest))
break;
/* Check if overwritten */
if (q->dest == ins->dest) {
/* Special case to vec4; component tracking is
* harder */
overwritten = (q->mask == 0xF);
break;
}
}
if (overwritten) {
mir_remove_instruction(ins);
progress = true;
}
}
return progress;
}
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