/*
* Copyright © 2013 Intel Corporation
*
* 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 "brw_fs.h"
#include "brw_cfg.h"
/** @file brw_fs_sel_peephole.cpp
*
* This file contains the opt_peephole_sel() optimization pass that replaces
* MOV instructions to the same destination in the "then" and "else" bodies of
* an if statement with SEL instructions.
*/
/* Four MOVs seems to be pretty typical, so I picked the next power of two in
* the hopes that it would handle almost anything possible in a single
* pass.
*/
#define MAX_MOVS 8 /**< The maximum number of MOVs to attempt to match. */
/**
* Scans forwards from an IF counting consecutive MOV instructions in the
* "then" and "else" blocks of the if statement.
*
* A pointer to the bblock_t following the IF is passed as the <then_block>
* argument. The function stores pointers to the MOV instructions in the
* <then_mov> and <else_mov> arrays.
*
* \return the minimum number of MOVs found in the two branches or zero if
* an error occurred.
*
* E.g.:
* IF ...
* then_mov[0] = MOV g4, ...
* then_mov[1] = MOV g5, ...
* then_mov[2] = MOV g6, ...
* ELSE ...
* else_mov[0] = MOV g4, ...
* else_mov[1] = MOV g5, ...
* else_mov[2] = MOV g7, ...
* ENDIF
* returns 3.
*/
static int
count_movs_from_if(fs_inst *then_mov[MAX_MOVS], fs_inst *else_mov[MAX_MOVS],
bblock_t *then_block, bblock_t *else_block)
{
int then_movs = 0;
foreach_inst_in_block(fs_inst, inst, then_block) {
if (then_movs == MAX_MOVS || inst->opcode != BRW_OPCODE_MOV)
break;
then_mov[then_movs] = inst;
then_movs++;
}
int else_movs = 0;
foreach_inst_in_block(fs_inst, inst, else_block) {
if (else_movs == MAX_MOVS || inst->opcode != BRW_OPCODE_MOV)
break;
else_mov[else_movs] = inst;
else_movs++;
}
return MIN2(then_movs, else_movs);
}
/**
* Try to replace IF/MOV+/ELSE/MOV+/ENDIF with SEL.
*
* Many GLSL shaders contain the following pattern:
*
* x = condition ? foo : bar
*
* or
*
* if (...) a.xyzw = foo.xyzw;
* else a.xyzw = bar.xyzw;
*
* The compiler emits an ir_if tree for this, since each subexpression might be
* a complex tree that could have side-effects or short-circuit logic.
*
* However, the common case is to simply select one of two constants or
* variable values---which is exactly what SEL is for. In this case, the
* assembly looks like:
*
* (+f0) IF
* MOV dst src0
* ...
* ELSE
* MOV dst src1
* ...
* ENDIF
*
* where each pair of MOVs to a common destination and can be easily translated
* into
*
* (+f0) SEL dst src0 src1
*
* If src0 is an immediate value, we promote it to a temporary GRF.
*/
bool
fs_visitor::opt_peephole_sel()
{
bool progress = false;
foreach_block (block, cfg) {
/* IF instructions, by definition, can only be found at the ends of
* basic blocks.
*/
fs_inst *if_inst = (fs_inst *)block->end();
if (if_inst->opcode != BRW_OPCODE_IF)
continue;
fs_inst *else_mov[MAX_MOVS] = { NULL };
fs_inst *then_mov[MAX_MOVS] = { NULL };
bblock_t *then_block = block->next();
bblock_t *else_block = NULL;
foreach_list_typed(bblock_link, child, link, &block->children) {
if (child->block != then_block) {
if (child->block->prev()->end()->opcode == BRW_OPCODE_ELSE) {
else_block = child->block;
}
break;
}
}
if (else_block == NULL)
continue;
int movs = count_movs_from_if(then_mov, else_mov, then_block, else_block);
if (movs == 0)
continue;
fs_inst *sel_inst[MAX_MOVS] = { NULL };
fs_inst *mov_imm_inst[MAX_MOVS] = { NULL };
enum brw_predicate predicate;
bool predicate_inverse;
if (devinfo->gen == 6 && if_inst->conditional_mod) {
/* For Sandybridge with IF with embedded comparison */
predicate = BRW_PREDICATE_NORMAL;
predicate_inverse = false;
} else {
/* Separate CMP and IF instructions */
predicate = if_inst->predicate;
predicate_inverse = if_inst->predicate_inverse;
}
/* Generate SEL instructions for pairs of MOVs to a common destination. */
for (int i = 0; i < movs; i++) {
if (!then_mov[i] || !else_mov[i])
break;
/* Check that the MOVs are the right form. */
if (!then_mov[i]->dst.equals(else_mov[i]->dst) ||
then_mov[i]->is_partial_write() ||
else_mov[i]->is_partial_write() ||
then_mov[i]->conditional_mod != BRW_CONDITIONAL_NONE ||
else_mov[i]->conditional_mod != BRW_CONDITIONAL_NONE) {
movs = i;
break;
}
/* Check that source types for mov operations match. */
if (then_mov[i]->src[0].type != else_mov[i]->src[0].type) {
movs = i;
break;
}
if (then_mov[i]->src[0].equals(else_mov[i]->src[0])) {
sel_inst[i] = MOV(then_mov[i]->dst, then_mov[i]->src[0]);
} else {
/* Only the last source register can be a constant, so if the MOV
* in the "then" clause uses a constant, we need to put it in a
* temporary.
*/
fs_reg src0(then_mov[i]->src[0]);
if (src0.file == IMM) {
src0 = vgrf(glsl_type::float_type);
src0.type = then_mov[i]->src[0].type;
mov_imm_inst[i] = MOV(src0, then_mov[i]->src[0]);
}
sel_inst[i] = SEL(then_mov[i]->dst, src0, else_mov[i]->src[0]);
sel_inst[i]->predicate = predicate;
sel_inst[i]->predicate_inverse = predicate_inverse;
}
}
if (movs == 0)
continue;
/* Emit a CMP if our IF used the embedded comparison */
if (devinfo->gen == 6 && if_inst->conditional_mod) {
fs_inst *cmp_inst = CMP(reg_null_d, if_inst->src[0], if_inst->src[1],
if_inst->conditional_mod);
if_inst->insert_before(block, cmp_inst);
}
for (int i = 0; i < movs; i++) {
if (mov_imm_inst[i])
if_inst->insert_before(block, mov_imm_inst[i]);
if_inst->insert_before(block, sel_inst[i]);
then_mov[i]->remove(then_block);
else_mov[i]->remove(else_block);
}
progress = true;
}
if (progress)
invalidate_live_intervals();
return progress;
}