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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 opt_cmod_propagation_local(const gen_device_info
*devinfo
, bblock_t
*block
)
54 bool progress
= false;
55 int ip
= block
->end_ip
+ 1;
57 foreach_inst_in_block_reverse_safe(fs_inst
, inst
, block
) {
60 if ((inst
->opcode
!= BRW_OPCODE_AND
&&
61 inst
->opcode
!= BRW_OPCODE_CMP
&&
62 inst
->opcode
!= BRW_OPCODE_MOV
) ||
63 inst
->predicate
!= BRW_PREDICATE_NONE
||
64 !inst
->dst
.is_null() ||
65 (inst
->src
[0].file
!= VGRF
&& inst
->src
[0].file
!= ATTR
&&
66 inst
->src
[0].file
!= UNIFORM
) ||
70 /* Only an AND.NZ can be propagated. Many AND.Z instructions are
71 * generated (for ir_unop_not in fs_visitor::emit_bool_to_cond_code).
72 * Propagating those would require inverting the condition on the CMP.
73 * This changes both the flag value and the register destination of the
74 * CMP. That result may be used elsewhere, so we can't change its value
77 if (inst
->opcode
== BRW_OPCODE_AND
&&
78 !(inst
->src
[1].is_one() &&
79 inst
->conditional_mod
== BRW_CONDITIONAL_NZ
&&
80 !inst
->src
[0].negate
))
83 if (inst
->opcode
== BRW_OPCODE_CMP
&& !inst
->src
[1].is_zero())
86 if (inst
->opcode
== BRW_OPCODE_MOV
&&
87 inst
->conditional_mod
!= BRW_CONDITIONAL_NZ
)
90 bool read_flag
= false;
91 foreach_inst_in_block_reverse_starting_from(fs_inst
, scan_inst
, inst
) {
92 if (regions_overlap(scan_inst
->dst
, scan_inst
->size_written
,
93 inst
->src
[0], inst
->size_read(0))) {
94 if (scan_inst
->is_partial_write() ||
95 scan_inst
->dst
.offset
!= inst
->src
[0].offset
||
96 scan_inst
->exec_size
!= inst
->exec_size
)
99 /* CMP's result is the same regardless of dest type. */
100 if (inst
->conditional_mod
== BRW_CONDITIONAL_NZ
&&
101 scan_inst
->opcode
== BRW_OPCODE_CMP
&&
102 (inst
->dst
.type
== BRW_REGISTER_TYPE_D
||
103 inst
->dst
.type
== BRW_REGISTER_TYPE_UD
)) {
109 /* If the AND wasn't handled by the previous case, it isn't safe
112 if (inst
->opcode
== BRW_OPCODE_AND
)
115 /* Comparisons operate differently for ints and floats */
116 if (scan_inst
->dst
.type
!= inst
->dst
.type
&&
117 (scan_inst
->dst
.type
== BRW_REGISTER_TYPE_F
||
118 inst
->dst
.type
== BRW_REGISTER_TYPE_F
))
121 /* If the instruction generating inst's source also wrote the
122 * flag, and inst is doing a simple .nz comparison, then inst
123 * is redundant - the appropriate value is already in the flag
124 * register. Delete inst.
126 if (inst
->conditional_mod
== BRW_CONDITIONAL_NZ
&&
127 !inst
->src
[0].negate
&&
128 scan_inst
->flags_written()) {
134 /* The conditional mod of the CMP/CMPN instructions behaves
135 * specially because the flag output is not calculated from the
136 * result of the instruction, but the other way around, which
137 * means that even if the condmod to propagate and the condmod
138 * from the CMP instruction are the same they will in general give
139 * different results because they are evaluated based on different
142 if (scan_inst
->opcode
== BRW_OPCODE_CMP
||
143 scan_inst
->opcode
== BRW_OPCODE_CMPN
)
146 /* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
148 * * Note that the [post condition signal] bits generated at
149 * the output of a compute are before the .sat.
151 if (scan_inst
->saturate
)
154 /* From the Sky Lake PRM, Vol 2a, "Multiply":
156 * "When multiplying integer data types, if one of the sources
157 * is a DW, the resulting full precision data is stored in
158 * the accumulator. However, if the destination data type is
159 * either W or DW, the low bits of the result are written to
160 * the destination register and the remaining high bits are
161 * discarded. This results in undefined Overflow and Sign
162 * flags. Therefore, conditional modifiers and saturation
163 * (.sat) cannot be used in this case."
165 * We just disallow cmod propagation on all integer multiplies.
167 if (!brw_reg_type_is_floating_point(scan_inst
->dst
.type
) &&
168 scan_inst
->opcode
== BRW_OPCODE_MUL
)
171 /* Otherwise, try propagating the conditional. */
172 enum brw_conditional_mod cond
=
173 inst
->src
[0].negate
? brw_swap_cmod(inst
->conditional_mod
)
174 : inst
->conditional_mod
;
176 if (scan_inst
->can_do_cmod() &&
177 ((!read_flag
&& scan_inst
->conditional_mod
== BRW_CONDITIONAL_NONE
) ||
178 scan_inst
->conditional_mod
== cond
)) {
179 scan_inst
->conditional_mod
= cond
;
186 if (scan_inst
->flags_written())
189 read_flag
= read_flag
|| scan_inst
->flags_read(devinfo
);
197 fs_visitor::opt_cmod_propagation()
199 bool progress
= false;
201 foreach_block_reverse(block
, cfg
) {
202 progress
= opt_cmod_propagation_local(devinfo
, block
) || progress
;
206 invalidate_live_intervals();