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28 /** @file brw_fs_cmod_propagation.cpp
30 * Implements a pass that propagates the conditional modifier from a CMP x 0.0
31 * instruction into the instruction that generated x. For instance, in this
34 * add(8) g70<1>F g69<8,8,1>F 4096F
35 * cmp.ge.f0(8) null g70<8,8,1>F 0F
37 * we can do the comparison as part of the ADD instruction directly:
39 * add.ge.f0(8) g70<1>F g69<8,8,1>F 4096F
41 * If there had been a use of the flag register and another CMP using g70
43 * add.ge.f0(8) g70<1>F g69<8,8,1>F 4096F
44 * (+f0) sel(8) g71<F> g72<8,8,1>F g73<8,8,1>F
45 * cmp.ge.f0(8) null g70<8,8,1>F 0F
47 * we can recognize that the CMP is generating the flag value that already
48 * exists and therefore remove the instruction.
52 cmod_propagate_cmp_to_add(const gen_device_info
*devinfo
, bblock_t
*block
,
55 bool read_flag
= false;
57 foreach_inst_in_block_reverse_starting_from(fs_inst
, scan_inst
, inst
) {
58 if (scan_inst
->opcode
== BRW_OPCODE_ADD
&&
59 !scan_inst
->is_partial_write() &&
60 scan_inst
->exec_size
== inst
->exec_size
) {
63 /* A CMP is basically a subtraction. The result of the
64 * subtraction must be the same as the result of the addition.
65 * This means that one of the operands must be negated. So (a +
66 * b) vs (a == -b) or (a + -b) vs (a == b).
68 if ((inst
->src
[0].equals(scan_inst
->src
[0]) &&
69 inst
->src
[1].negative_equals(scan_inst
->src
[1])) ||
70 (inst
->src
[0].equals(scan_inst
->src
[1]) &&
71 inst
->src
[1].negative_equals(scan_inst
->src
[0]))) {
73 } else if ((inst
->src
[0].negative_equals(scan_inst
->src
[0]) &&
74 inst
->src
[1].equals(scan_inst
->src
[1])) ||
75 (inst
->src
[0].negative_equals(scan_inst
->src
[1]) &&
76 inst
->src
[1].equals(scan_inst
->src
[0]))) {
82 /* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
84 * * Note that the [post condition signal] bits generated at
85 * the output of a compute are before the .sat.
87 * So we don't have to bail if scan_inst has saturate.
89 /* Otherwise, try propagating the conditional. */
90 const enum brw_conditional_mod cond
=
91 negate
? brw_swap_cmod(inst
->conditional_mod
)
92 : inst
->conditional_mod
;
94 if (scan_inst
->can_do_cmod() &&
95 ((!read_flag
&& scan_inst
->conditional_mod
== BRW_CONDITIONAL_NONE
) ||
96 scan_inst
->conditional_mod
== cond
)) {
97 scan_inst
->conditional_mod
= cond
;
105 if (scan_inst
->flags_written())
108 read_flag
= read_flag
|| scan_inst
->flags_read(devinfo
);
115 * Propagate conditional modifiers from NOT instructions
117 * Attempt to convert sequences like
119 * or(8) g78<8,8,1> g76<8,8,1>UD g77<8,8,1>UD
121 * not.nz.f0(8) null g78<8,8,1>UD
125 * or.z.f0(8) g78<8,8,1> g76<8,8,1>UD g77<8,8,1>UD
128 cmod_propagate_not(const gen_device_info
*devinfo
, bblock_t
*block
,
131 const enum brw_conditional_mod cond
= brw_negate_cmod(inst
->conditional_mod
);
132 bool read_flag
= false;
134 if (cond
!= BRW_CONDITIONAL_Z
&& cond
!= BRW_CONDITIONAL_NZ
)
137 foreach_inst_in_block_reverse_starting_from(fs_inst
, scan_inst
, inst
) {
138 if (regions_overlap(scan_inst
->dst
, scan_inst
->size_written
,
139 inst
->src
[0], inst
->size_read(0))) {
140 if (scan_inst
->opcode
!= BRW_OPCODE_OR
&&
141 scan_inst
->opcode
!= BRW_OPCODE_AND
)
144 if (scan_inst
->is_partial_write() ||
145 scan_inst
->dst
.offset
!= inst
->src
[0].offset
||
146 scan_inst
->exec_size
!= inst
->exec_size
)
149 if (scan_inst
->can_do_cmod() &&
150 ((!read_flag
&& scan_inst
->conditional_mod
== BRW_CONDITIONAL_NONE
) ||
151 scan_inst
->conditional_mod
== cond
)) {
152 scan_inst
->conditional_mod
= cond
;
159 if (scan_inst
->flags_written())
162 read_flag
= read_flag
|| scan_inst
->flags_read(devinfo
);
169 opt_cmod_propagation_local(const gen_device_info
*devinfo
, bblock_t
*block
)
171 bool progress
= false;
172 int ip
= block
->end_ip
+ 1;
174 foreach_inst_in_block_reverse_safe(fs_inst
, inst
, block
) {
177 if ((inst
->opcode
!= BRW_OPCODE_AND
&&
178 inst
->opcode
!= BRW_OPCODE_CMP
&&
179 inst
->opcode
!= BRW_OPCODE_MOV
&&
180 inst
->opcode
!= BRW_OPCODE_NOT
) ||
181 inst
->predicate
!= BRW_PREDICATE_NONE
||
182 !inst
->dst
.is_null() ||
183 (inst
->src
[0].file
!= VGRF
&& inst
->src
[0].file
!= ATTR
&&
184 inst
->src
[0].file
!= UNIFORM
))
187 /* An ABS source modifier can only be handled when processing a compare
188 * with a value other than zero.
190 if (inst
->src
[0].abs
&&
191 (inst
->opcode
!= BRW_OPCODE_CMP
|| inst
->src
[1].is_zero()))
194 /* Only an AND.NZ can be propagated. Many AND.Z instructions are
195 * generated (for ir_unop_not in fs_visitor::emit_bool_to_cond_code).
196 * Propagating those would require inverting the condition on the CMP.
197 * This changes both the flag value and the register destination of the
198 * CMP. That result may be used elsewhere, so we can't change its value
201 if (inst
->opcode
== BRW_OPCODE_AND
&&
202 !(inst
->src
[1].is_one() &&
203 inst
->conditional_mod
== BRW_CONDITIONAL_NZ
&&
204 !inst
->src
[0].negate
))
207 if (inst
->opcode
== BRW_OPCODE_MOV
&&
208 inst
->conditional_mod
!= BRW_CONDITIONAL_NZ
)
211 /* A CMP with a second source of zero can match with anything. A CMP
212 * with a second source that is not zero can only match with an ADD
215 if (inst
->opcode
== BRW_OPCODE_CMP
&& !inst
->src
[1].is_zero()) {
216 progress
= cmod_propagate_cmp_to_add(devinfo
, block
, inst
) || progress
;
220 if (inst
->opcode
== BRW_OPCODE_NOT
) {
221 progress
= cmod_propagate_not(devinfo
, block
, inst
) || progress
;
225 bool read_flag
= false;
226 foreach_inst_in_block_reverse_starting_from(fs_inst
, scan_inst
, inst
) {
227 if (regions_overlap(scan_inst
->dst
, scan_inst
->size_written
,
228 inst
->src
[0], inst
->size_read(0))) {
229 if (scan_inst
->is_partial_write() ||
230 scan_inst
->dst
.offset
!= inst
->src
[0].offset
||
231 scan_inst
->exec_size
!= inst
->exec_size
)
234 /* CMP's result is the same regardless of dest type. */
235 if (inst
->conditional_mod
== BRW_CONDITIONAL_NZ
&&
236 scan_inst
->opcode
== BRW_OPCODE_CMP
&&
237 (inst
->dst
.type
== BRW_REGISTER_TYPE_D
||
238 inst
->dst
.type
== BRW_REGISTER_TYPE_UD
)) {
244 /* If the AND wasn't handled by the previous case, it isn't safe
247 if (inst
->opcode
== BRW_OPCODE_AND
)
250 /* Comparisons operate differently for ints and floats */
251 if (scan_inst
->dst
.type
!= inst
->dst
.type
&&
252 (scan_inst
->dst
.type
== BRW_REGISTER_TYPE_F
||
253 inst
->dst
.type
== BRW_REGISTER_TYPE_F
))
256 /* If the instruction generating inst's source also wrote the
257 * flag, and inst is doing a simple .nz comparison, then inst
258 * is redundant - the appropriate value is already in the flag
259 * register. Delete inst.
261 if (inst
->conditional_mod
== BRW_CONDITIONAL_NZ
&&
262 !inst
->src
[0].negate
&&
263 scan_inst
->flags_written()) {
269 /* The conditional mod of the CMP/CMPN instructions behaves
270 * specially because the flag output is not calculated from the
271 * result of the instruction, but the other way around, which
272 * means that even if the condmod to propagate and the condmod
273 * from the CMP instruction are the same they will in general give
274 * different results because they are evaluated based on different
277 if (scan_inst
->opcode
== BRW_OPCODE_CMP
||
278 scan_inst
->opcode
== BRW_OPCODE_CMPN
)
281 /* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
283 * * Note that the [post condition signal] bits generated at
284 * the output of a compute are before the .sat.
286 if (scan_inst
->saturate
)
289 /* From the Sky Lake PRM, Vol 2a, "Multiply":
291 * "When multiplying integer data types, if one of the sources
292 * is a DW, the resulting full precision data is stored in
293 * the accumulator. However, if the destination data type is
294 * either W or DW, the low bits of the result are written to
295 * the destination register and the remaining high bits are
296 * discarded. This results in undefined Overflow and Sign
297 * flags. Therefore, conditional modifiers and saturation
298 * (.sat) cannot be used in this case."
300 * We just disallow cmod propagation on all integer multiplies.
302 if (!brw_reg_type_is_floating_point(scan_inst
->dst
.type
) &&
303 scan_inst
->opcode
== BRW_OPCODE_MUL
)
306 /* Otherwise, try propagating the conditional. */
307 enum brw_conditional_mod cond
=
308 inst
->src
[0].negate
? brw_swap_cmod(inst
->conditional_mod
)
309 : inst
->conditional_mod
;
311 if (scan_inst
->can_do_cmod() &&
312 ((!read_flag
&& scan_inst
->conditional_mod
== BRW_CONDITIONAL_NONE
) ||
313 scan_inst
->conditional_mod
== cond
)) {
314 scan_inst
->conditional_mod
= cond
;
321 if (scan_inst
->flags_written())
324 read_flag
= read_flag
|| scan_inst
->flags_read(devinfo
);
332 fs_visitor::opt_cmod_propagation()
334 bool progress
= false;
336 foreach_block_reverse(block
, cfg
) {
337 progress
= opt_cmod_propagation_local(devinfo
, block
) || progress
;
341 invalidate_live_intervals();