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25 * @file v3d_opt_dead_code.c
27 * This is a simple dead code eliminator for SSA values in VIR.
29 * It walks all the instructions finding what temps are used, then walks again
30 * to remove instructions writing unused temps.
32 * This is an inefficient implementation if you have long chains of
33 * instructions where the entire chain is dead, but we expect those to have
34 * been eliminated at the NIR level, and here we're just cleaning up small
35 * problems produced by NIR->VIR.
38 #include "v3d_compiler.h"
43 dce(struct v3d_compile
*c
, struct qinst
*inst
)
46 fprintf(stderr
, "Removing: ");
47 vir_dump_inst(c
, inst
);
48 fprintf(stderr
, "\n");
50 assert(!v3d_qpu_writes_flags(&inst
->qpu
));
51 vir_remove_instruction(c
, inst
);
55 has_nonremovable_reads(struct v3d_compile
*c
, struct qinst
*inst
)
57 for (int i
= 0; i
< vir_get_nsrc(inst
); i
++) {
58 if (inst
->src
[i
].file
== QFILE_VPM
)
66 can_write_to_null(struct v3d_compile
*c
, struct qinst
*inst
)
68 /* The SFU instructions must write to a physical register. */
69 if (c
->devinfo
->ver
>= 41 && v3d_qpu_uses_sfu(&inst
->qpu
))
76 vir_dce_flags(struct v3d_compile
*c
, struct qinst
*inst
)
80 "Removing flags write from: ");
81 vir_dump_inst(c
, inst
);
82 fprintf(stderr
, "\n");
85 assert(inst
->qpu
.type
== V3D_QPU_INSTR_TYPE_ALU
);
87 inst
->qpu
.flags
.apf
= V3D_QPU_PF_NONE
;
88 inst
->qpu
.flags
.mpf
= V3D_QPU_PF_NONE
;
89 inst
->qpu
.flags
.auf
= V3D_QPU_UF_NONE
;
90 inst
->qpu
.flags
.muf
= V3D_QPU_UF_NONE
;
94 vir_opt_dead_code(struct v3d_compile
*c
)
96 bool progress
= false;
97 bool *used
= calloc(c
->num_temps
, sizeof(bool));
99 /* Defuse the "are you removing the cursor?" assertion in the core.
100 * You'll need to set up a new cursor for any new instructions after
101 * doing DCE (which we would expect, anyway).
103 c
->cursor
.link
= NULL
;
105 vir_for_each_inst_inorder(inst
, c
) {
106 for (int i
= 0; i
< vir_get_nsrc(inst
); i
++) {
107 if (inst
->src
[i
].file
== QFILE_TEMP
)
108 used
[inst
->src
[i
].index
] = true;
112 vir_for_each_block(block
, c
) {
113 struct qinst
*last_flags_write
= NULL
;
115 vir_for_each_inst_safe(inst
, block
) {
116 /* If this instruction reads the flags, we can't
117 * remove the flags generation for it.
119 if (v3d_qpu_reads_flags(&inst
->qpu
))
120 last_flags_write
= NULL
;
122 if (inst
->dst
.file
!= QFILE_NULL
&&
123 !(inst
->dst
.file
== QFILE_TEMP
&&
124 !used
[inst
->dst
.index
])) {
128 if (vir_has_side_effects(c
, inst
))
131 if (v3d_qpu_writes_flags(&inst
->qpu
)) {
132 /* If we obscure a previous flags write,
135 if (last_flags_write
&&
136 (inst
->qpu
.flags
.apf
!= V3D_QPU_PF_NONE
||
137 inst
->qpu
.flags
.mpf
!= V3D_QPU_PF_NONE
)) {
138 vir_dce_flags(c
, last_flags_write
);
142 last_flags_write
= inst
;
145 if (v3d_qpu_writes_flags(&inst
->qpu
) ||
146 has_nonremovable_reads(c
, inst
)) {
147 /* If we can't remove the instruction, but we
148 * don't need its destination value, just
149 * remove the destination. The register
150 * allocator would trivially color it and it
151 * wouldn't cause any register pressure, but
152 * it's nicer to read the VIR code without
153 * unused destination regs.
155 if (inst
->dst
.file
== QFILE_TEMP
&&
156 can_write_to_null(c
, inst
)) {
159 "Removing dst from: ");
160 vir_dump_inst(c
, inst
);
161 fprintf(stderr
, "\n");
163 c
->defs
[inst
->dst
.index
] = NULL
;
164 inst
->dst
.file
= QFILE_NULL
;
170 assert(inst
!= last_flags_write
);