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27 /** @file brw_fs_sel_peephole.cpp
29 * This file contains the opt_peephole_sel() optimization pass that replaces
30 * MOV instructions to the same destination in the "then" and "else" bodies of
31 * an if statement with SEL instructions.
34 /* Four MOVs seems to be pretty typical, so I picked the next power of two in
35 * the hopes that it would handle almost anything possible in a single
38 #define MAX_MOVS 8 /**< The maximum number of MOVs to attempt to match. */
43 * Scans forwards from an IF counting consecutive MOV instructions in the
44 * "then" and "else" blocks of the if statement.
46 * A pointer to the bblock_t following the IF is passed as the <then_block>
47 * argument. The function stores pointers to the MOV instructions in the
48 * <then_mov> and <else_mov> arrays.
50 * \return the minimum number of MOVs found in the two branches or zero if
55 * then_mov[0] = MOV g4, ...
56 * then_mov[1] = MOV g5, ...
57 * then_mov[2] = MOV g6, ...
59 * else_mov[0] = MOV g4, ...
60 * else_mov[1] = MOV g5, ...
61 * else_mov[2] = MOV g7, ...
66 count_movs_from_if(fs_inst
*then_mov
[MAX_MOVS
], fs_inst
*else_mov
[MAX_MOVS
],
67 bblock_t
*then_block
, bblock_t
*else_block
)
70 foreach_inst_in_block(fs_inst
, inst
, then_block
) {
71 if (then_movs
== MAX_MOVS
|| inst
->opcode
!= BRW_OPCODE_MOV
)
74 then_mov
[then_movs
] = inst
;
79 foreach_inst_in_block(fs_inst
, inst
, else_block
) {
80 if (else_movs
== MAX_MOVS
|| inst
->opcode
!= BRW_OPCODE_MOV
)
83 else_mov
[else_movs
] = inst
;
87 return MIN2(then_movs
, else_movs
);
91 * Try to replace IF/MOV+/ELSE/MOV+/ENDIF with SEL.
93 * Many GLSL shaders contain the following pattern:
95 * x = condition ? foo : bar
99 * if (...) a.xyzw = foo.xyzw;
100 * else a.xyzw = bar.xyzw;
102 * The compiler emits an ir_if tree for this, since each subexpression might be
103 * a complex tree that could have side-effects or short-circuit logic.
105 * However, the common case is to simply select one of two constants or
106 * variable values---which is exactly what SEL is for. In this case, the
107 * assembly looks like:
117 * where each pair of MOVs to a common destination and can be easily translated
120 * (+f0) SEL dst src0 src1
122 * If src0 is an immediate value, we promote it to a temporary GRF.
125 fs_visitor::opt_peephole_sel()
127 bool progress
= false;
129 foreach_block (block
, cfg
) {
130 /* IF instructions, by definition, can only be found at the ends of
133 fs_inst
*if_inst
= (fs_inst
*)block
->end();
134 if (if_inst
->opcode
!= BRW_OPCODE_IF
)
137 fs_inst
*else_mov
[MAX_MOVS
] = { NULL
};
138 fs_inst
*then_mov
[MAX_MOVS
] = { NULL
};
140 bblock_t
*then_block
= block
->next();
141 bblock_t
*else_block
= NULL
;
142 foreach_list_typed(bblock_link
, child
, link
, &block
->children
) {
143 if (child
->block
!= then_block
) {
144 if (child
->block
->prev()->end()->opcode
== BRW_OPCODE_ELSE
) {
145 else_block
= child
->block
;
150 if (else_block
== NULL
)
153 int movs
= count_movs_from_if(then_mov
, else_mov
, then_block
, else_block
);
158 /* Generate SEL instructions for pairs of MOVs to a common destination. */
159 for (int i
= 0; i
< movs
; i
++) {
160 if (!then_mov
[i
] || !else_mov
[i
])
163 /* Check that the MOVs are the right form. */
164 if (!then_mov
[i
]->dst
.equals(else_mov
[i
]->dst
) ||
165 then_mov
[i
]->exec_size
!= else_mov
[i
]->exec_size
||
166 then_mov
[i
]->group
!= else_mov
[i
]->group
||
167 then_mov
[i
]->force_writemask_all
!= else_mov
[i
]->force_writemask_all
||
168 then_mov
[i
]->is_partial_write() ||
169 else_mov
[i
]->is_partial_write() ||
170 then_mov
[i
]->conditional_mod
!= BRW_CONDITIONAL_NONE
||
171 else_mov
[i
]->conditional_mod
!= BRW_CONDITIONAL_NONE
) {
176 /* Check that source types for mov operations match. */
177 if (then_mov
[i
]->src
[0].type
!= else_mov
[i
]->src
[0].type
) {
186 for (int i
= 0; i
< movs
; i
++) {
187 const fs_builder ibld
= fs_builder(this, then_block
, then_mov
[i
])
190 if (then_mov
[i
]->src
[0].equals(else_mov
[i
]->src
[0])) {
191 ibld
.MOV(then_mov
[i
]->dst
, then_mov
[i
]->src
[0]);
193 /* Only the last source register can be a constant, so if the MOV
194 * in the "then" clause uses a constant, we need to put it in a
197 fs_reg
src0(then_mov
[i
]->src
[0]);
198 if (src0
.file
== IMM
) {
199 src0
= vgrf(glsl_type::float_type
);
200 src0
.type
= then_mov
[i
]->src
[0].type
;
201 ibld
.MOV(src0
, then_mov
[i
]->src
[0]);
204 set_predicate_inv(if_inst
->predicate
, if_inst
->predicate_inverse
,
205 ibld
.SEL(then_mov
[i
]->dst
, src0
,
206 else_mov
[i
]->src
[0]));
209 then_mov
[i
]->remove(then_block
);
210 else_mov
[i
]->remove(else_block
);
217 invalidate_live_intervals();