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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
||
69 /* Only an AND.NZ can be propagated. Many AND.Z instructions are
70 * generated (for ir_unop_not in fs_visitor::emit_bool_to_cond_code).
71 * Propagating those would require inverting the condition on the CMP.
72 * This changes both the flag value and the register destination of the
73 * CMP. That result may be used elsewhere, so we can't change its value
76 if (inst
->opcode
== BRW_OPCODE_AND
&&
77 !(inst
->src
[1].is_one() &&
78 inst
->conditional_mod
== BRW_CONDITIONAL_NZ
&&
79 !inst
->src
[0].negate
))
82 if (inst
->opcode
== BRW_OPCODE_CMP
&& !inst
->src
[1].is_zero())
85 if (inst
->opcode
== BRW_OPCODE_MOV
&&
86 inst
->conditional_mod
!= BRW_CONDITIONAL_NZ
)
89 bool read_flag
= false;
90 foreach_inst_in_block_reverse_starting_from(fs_inst
, scan_inst
, inst
) {
91 if (scan_inst
->overwrites_reg(inst
->src
[0])) {
92 if (scan_inst
->is_partial_write() ||
93 scan_inst
->dst
.reg_offset
!= inst
->src
[0].reg_offset
||
94 scan_inst
->exec_size
!= inst
->exec_size
)
97 /* CMP's result is the same regardless of dest type. */
98 if (inst
->conditional_mod
== BRW_CONDITIONAL_NZ
&&
99 scan_inst
->opcode
== BRW_OPCODE_CMP
&&
100 (inst
->dst
.type
== BRW_REGISTER_TYPE_D
||
101 inst
->dst
.type
== BRW_REGISTER_TYPE_UD
)) {
107 /* If the AND wasn't handled by the previous case, it isn't safe
110 if (inst
->opcode
== BRW_OPCODE_AND
)
113 /* Comparisons operate differently for ints and floats */
114 if (scan_inst
->dst
.type
!= inst
->dst
.type
&&
115 (scan_inst
->dst
.type
== BRW_REGISTER_TYPE_F
||
116 inst
->dst
.type
== BRW_REGISTER_TYPE_F
))
119 /* If the instruction generating inst's source also wrote the
120 * flag, and inst is doing a simple .nz comparison, then inst
121 * is redundant - the appropriate value is already in the flag
122 * register. Delete inst.
124 if (inst
->conditional_mod
== BRW_CONDITIONAL_NZ
&&
125 !inst
->src
[0].negate
&&
126 scan_inst
->flags_written()) {
132 /* The conditional mod of the CMP/CMPN instructions behaves
133 * specially because the flag output is not calculated from the
134 * result of the instruction, but the other way around, which
135 * means that even if the condmod to propagate and the condmod
136 * from the CMP instruction are the same they will in general give
137 * different results because they are evaluated based on different
140 if (scan_inst
->opcode
== BRW_OPCODE_CMP
||
141 scan_inst
->opcode
== BRW_OPCODE_CMPN
)
144 /* Otherwise, try propagating the conditional. */
145 enum brw_conditional_mod cond
=
146 inst
->src
[0].negate
? brw_swap_cmod(inst
->conditional_mod
)
147 : inst
->conditional_mod
;
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
);
170 fs_visitor::opt_cmod_propagation()
172 bool progress
= false;
174 foreach_block_reverse(block
, cfg
) {
175 progress
= opt_cmod_propagation_local(devinfo
, block
) || progress
;
179 invalidate_live_intervals();