--- /dev/null
+/*
+ * 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 fs_inst* for IF is passed as the <if_inst> 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],
+ fs_inst *if_inst, fs_inst *else_inst)
+{
+ fs_inst *m = if_inst;
+
+ assert(m->opcode == BRW_OPCODE_IF);
+ m = (fs_inst *) m->next;
+
+ int then_movs = 0;
+ while (then_movs < MAX_MOVS && m->opcode == BRW_OPCODE_MOV) {
+ then_mov[then_movs] = m;
+ m = (fs_inst *) m->next;
+ then_movs++;
+ }
+
+ m = (fs_inst *) else_inst->next;
+
+ int else_movs = 0;
+ while (else_movs < MAX_MOVS && m->opcode == BRW_OPCODE_MOV) {
+ else_mov[else_movs] = m;
+ m = (fs_inst *) m->next;
+ 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;
+
+ cfg_t cfg(&instructions);
+
+ for (int b = 0; b < cfg.num_blocks; b++) {
+ bblock_t *block = cfg.blocks[b];
+
+ /* 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;
+
+ if (!block->else_inst)
+ continue;
+
+ fs_inst *else_inst = (fs_inst *) block->else_inst;
+ assert(else_inst->opcode == BRW_OPCODE_ELSE);
+
+ fs_inst *else_mov[MAX_MOVS] = { NULL };
+ fs_inst *then_mov[MAX_MOVS] = { NULL };
+ bool malformed_mov_found = false;
+
+ int movs = count_movs_from_if(then_mov, else_mov, if_inst, else_inst);
+
+ if (movs == 0)
+ continue;
+
+ fs_inst *sel_inst[MAX_MOVS] = { NULL };
+ fs_inst *mov_imm_inst[MAX_MOVS] = { NULL };
+
+ /* 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()) {
+ malformed_mov_found = true;
+ break;
+ }
+
+ /* 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 = fs_reg(this, 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]);
+
+ if (brw->gen == 6 && if_inst->conditional_mod) {
+ /* For Sandybridge with IF with embedded comparison */
+ sel_inst[i]->predicate = BRW_PREDICATE_NORMAL;
+ } else {
+ /* Separate CMP and IF instructions */
+ sel_inst[i]->predicate = if_inst->predicate;
+ sel_inst[i]->predicate_inverse = if_inst->predicate_inverse;
+ }
+ }
+
+ if (malformed_mov_found)
+ continue;
+
+ /* Emit a CMP if our IF used the embedded comparison */
+ if (brw->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(cmp_inst);
+ }
+
+ for (int i = 0; i < movs; i++) {
+ if (mov_imm_inst[i])
+ if_inst->insert_before(mov_imm_inst[i]);
+ if_inst->insert_before(sel_inst[i]);
+
+ then_mov[i]->remove();
+ else_mov[i]->remove();
+ }
+
+ progress = true;
+ }
+
+ if (progress)
+ invalidate_live_intervals();
+
+ return progress;
+}
projects / mesa.git / commitdiff