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mesa/src/broadcom/compiler/vir_opt_dead_code.c

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/*
* Copyright © 2014 Broadcom
*
* 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.
*/
/**
* @file v3d_opt_dead_code.c
*
* This is a simple dead code eliminator for SSA values in VIR.
*
* It walks all the instructions finding what temps are used, then walks again
* to remove instructions writing unused temps.
*
* This is an inefficient implementation if you have long chains of
* instructions where the entire chain is dead, but we expect those to have
* been eliminated at the NIR level, and here we're just cleaning up small
* problems produced by NIR->VIR.
*/
#include "v3d_compiler.h"
static bool debug;
static void
dce(struct v3d_compile *c, struct qinst *inst)
{
if (debug) {
fprintf(stderr, "Removing: ");
vir_dump_inst(c, inst);
fprintf(stderr, "\n");
}
assert(!v3d_qpu_writes_flags(&inst->qpu));
vir_remove_instruction(c, inst);
}
static bool
has_nonremovable_reads(struct v3d_compile *c, struct qinst *inst)
{
for (int i = 0; i < vir_get_nsrc(inst); i++) {
if (inst->src[i].file == QFILE_VPM)
return true;
}
return false;
}
static bool
can_write_to_null(struct v3d_compile *c, struct qinst *inst)
{
/* The SFU instructions must write to a physical register. */
if (c->devinfo->ver >= 41 && v3d_qpu_uses_sfu(&inst->qpu))
return false;
return true;
}
static void
vir_dce_flags(struct v3d_compile *c, struct qinst *inst)
{
if (debug) {
fprintf(stderr,
"Removing flags write from: ");
vir_dump_inst(c, inst);
fprintf(stderr, "\n");
}
assert(inst->qpu.type == V3D_QPU_INSTR_TYPE_ALU);
inst->qpu.flags.apf = V3D_QPU_PF_NONE;
inst->qpu.flags.mpf = V3D_QPU_PF_NONE;
inst->qpu.flags.auf = V3D_QPU_UF_NONE;
inst->qpu.flags.muf = V3D_QPU_UF_NONE;
}
static bool
check_last_ldunifa(struct v3d_compile *c,
struct qinst *inst,
struct qblock *block)
{
if (!inst->qpu.sig.ldunifa && !inst->qpu.sig.ldunifarf)
return false;
list_for_each_entry_from(struct qinst, scan_inst, inst->link.next,
&block->instructions, link) {
/* If we find a new write to unifa, then this was the last
* ldunifa in its sequence and is safe to remove.
*/
if (scan_inst->dst.file == QFILE_MAGIC &&
scan_inst->dst.index == V3D_QPU_WADDR_UNIFA) {
return true;
}
/* If we find another ldunifa in the same sequence then we
* can't remove it.
*/
if (scan_inst->qpu.sig.ldunifa || scan_inst->qpu.sig.ldunifarf)
return false;
}
return true;
}
static bool
check_first_ldunifa(struct v3d_compile *c,
struct qinst *inst,
struct qblock *block,
struct qinst **unifa)
{
if (!inst->qpu.sig.ldunifa && !inst->qpu.sig.ldunifarf)
return false;
list_for_each_entry_from_rev(struct qinst, scan_inst, inst->link.prev,
&block->instructions, link) {
/* If we find a write to unifa, then this was the first
* ldunifa in its sequence and is safe to remove.
*/
if (scan_inst->dst.file == QFILE_MAGIC &&
scan_inst->dst.index == V3D_QPU_WADDR_UNIFA) {
*unifa = scan_inst;
return true;
}
/* If we find another ldunifa in the same sequence then we
* can't remove it.
*/
if (scan_inst->qpu.sig.ldunifa || scan_inst->qpu.sig.ldunifarf)
return false;
}
unreachable("could not find starting unifa for ldunifa sequence");
}
static bool
increment_unifa_address(struct v3d_compile *c, struct qinst *unifa)
{
if (unifa->qpu.type == V3D_QPU_INSTR_TYPE_ALU &&
unifa->qpu.alu.mul.op == V3D_QPU_M_MOV) {
c->cursor = vir_after_inst(unifa);
struct qreg unifa_reg = vir_reg(QFILE_MAGIC, V3D_QPU_WADDR_UNIFA);
vir_ADD_dest(c, unifa_reg, unifa->src[0], vir_uniform_ui(c, 4u));
vir_remove_instruction(c, unifa);
return true;
}
if (unifa->qpu.type == V3D_QPU_INSTR_TYPE_ALU &&
unifa->qpu.alu.add.op == V3D_QPU_A_ADD) {
c->cursor = vir_after_inst(unifa);
struct qreg unifa_reg = vir_reg(QFILE_MAGIC, V3D_QPU_WADDR_UNIFA);
struct qreg tmp =
vir_ADD(c, unifa->src[1], vir_uniform_ui(c, 4u));
vir_ADD_dest(c, unifa_reg, unifa->src[0], tmp);
vir_remove_instruction(c, unifa);
return true;
}
return false;
}
bool
vir_opt_dead_code(struct v3d_compile *c)
{
bool progress = false;
bool *used = calloc(c->num_temps, sizeof(bool));
/* Defuse the "are you removing the cursor?" assertion in the core.
* You'll need to set up a new cursor for any new instructions after
* doing DCE (which we would expect, anyway).
*/
c->cursor.link = NULL;
vir_for_each_inst_inorder(inst, c) {
for (int i = 0; i < vir_get_nsrc(inst); i++) {
if (inst->src[i].file == QFILE_TEMP)
used[inst->src[i].index] = true;
}
}
vir_for_each_block(block, c) {
struct qinst *last_flags_write = NULL;
c->cur_block = block;
vir_for_each_inst_safe(inst, block) {
/* If this instruction reads the flags, we can't
* remove the flags generation for it.
*/
if (v3d_qpu_reads_flags(&inst->qpu))
last_flags_write = NULL;
if (inst->dst.file != QFILE_NULL &&
!(inst->dst.file == QFILE_TEMP &&
!used[inst->dst.index])) {
continue;
}
const bool is_ldunifa = inst->qpu.sig.ldunifa ||
inst->qpu.sig.ldunifarf;
if (vir_has_side_effects(c, inst) && !is_ldunifa)
continue;
bool is_first_ldunifa = false;
bool is_last_ldunifa = false;
struct qinst *unifa = NULL;
if (is_ldunifa) {
is_last_ldunifa =
check_last_ldunifa(c, inst, block);
is_first_ldunifa =
check_first_ldunifa(c, inst, block, &unifa);
}
if (v3d_qpu_writes_flags(&inst->qpu)) {
/* If we obscure a previous flags write,
* drop it.
*/
if (last_flags_write &&
(inst->qpu.flags.apf != V3D_QPU_PF_NONE ||
inst->qpu.flags.mpf != V3D_QPU_PF_NONE)) {
vir_dce_flags(c, last_flags_write);
progress = true;
}
last_flags_write = inst;
}
if (v3d_qpu_writes_flags(&inst->qpu) ||
has_nonremovable_reads(c, inst) ||
(is_ldunifa && !is_first_ldunifa && !is_last_ldunifa)) {
/* If we can't remove the instruction, but we
* don't need its destination value, just
* remove the destination. The register
* allocator would trivially color it and it
* wouldn't cause any register pressure, but
* it's nicer to read the VIR code without
* unused destination regs.
*/
if (inst->dst.file == QFILE_TEMP &&
can_write_to_null(c, inst)) {
if (debug) {
fprintf(stderr,
"Removing dst from: ");
vir_dump_inst(c, inst);
fprintf(stderr, "\n");
}
c->defs[inst->dst.index] = NULL;
inst->dst.file = QFILE_NULL;
progress = true;
}
continue;
}
/* If we are removing the first ldunifa in a sequence
* we need to update the unifa address.
*/
if (is_first_ldunifa) {
assert(unifa);
if (!increment_unifa_address(c, unifa))
continue;
}
assert(inst != last_flags_write);
dce(c, inst);
progress = true;
continue;
}
}
free(used);
return progress;
}
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