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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
) {
59 /* Instance ID, Vertex ID: Should have been removed at
62 if (inst
->src
[i
].index
== ~0)
65 uint32_t attr
= inst
->src
[i
].index
/ 4;
66 uint32_t offset
= inst
->src
[i
].index
% 4;
68 if (c
->vattr_sizes
[attr
] != offset
)
71 /* Can't get rid of the last VPM read, or the
72 * simulator (at least) throws an error.
74 uint32_t total_size
= 0;
75 for (uint32_t i
= 0; i
< ARRAY_SIZE(c
->vattr_sizes
); i
++)
76 total_size
+= c
->vattr_sizes
[i
];
86 can_write_to_null(struct v3d_compile
*c
, struct qinst
*inst
)
88 /* The SFU instructions must write to a physical register. */
89 if (c
->devinfo
->ver
>= 41 && v3d_qpu_uses_sfu(&inst
->qpu
))
96 vir_dce_flags(struct v3d_compile
*c
, struct qinst
*inst
)
100 "Removing flags write from: ");
101 vir_dump_inst(c
, inst
);
102 fprintf(stderr
, "\n");
105 assert(inst
->qpu
.type
== V3D_QPU_INSTR_TYPE_ALU
);
107 inst
->qpu
.flags
.apf
= V3D_QPU_PF_NONE
;
108 inst
->qpu
.flags
.mpf
= V3D_QPU_PF_NONE
;
109 inst
->qpu
.flags
.auf
= V3D_QPU_UF_NONE
;
110 inst
->qpu
.flags
.muf
= V3D_QPU_UF_NONE
;
114 vir_opt_dead_code(struct v3d_compile
*c
)
116 bool progress
= false;
117 bool *used
= calloc(c
->num_temps
, sizeof(bool));
119 /* Defuse the "are you removing the cursor?" assertion in the core.
120 * You'll need to set up a new cursor for any new instructions after
121 * doing DCE (which we would expect, anyway).
123 c
->cursor
.link
= NULL
;
125 vir_for_each_inst_inorder(inst
, c
) {
126 for (int i
= 0; i
< vir_get_nsrc(inst
); i
++) {
127 if (inst
->src
[i
].file
== QFILE_TEMP
)
128 used
[inst
->src
[i
].index
] = true;
132 vir_for_each_block(block
, c
) {
133 struct qinst
*last_flags_write
= NULL
;
135 vir_for_each_inst_safe(inst
, block
) {
136 /* If this instruction reads the flags, we can't
137 * remove the flags generation for it.
139 if (v3d_qpu_reads_flags(&inst
->qpu
))
140 last_flags_write
= NULL
;
142 if (inst
->dst
.file
!= QFILE_NULL
&&
143 !(inst
->dst
.file
== QFILE_TEMP
&&
144 !used
[inst
->dst
.index
])) {
148 if (vir_has_side_effects(c
, inst
))
151 if (v3d_qpu_writes_flags(&inst
->qpu
)) {
152 /* If we obscure a previous flags write,
155 if (last_flags_write
&&
156 (inst
->qpu
.flags
.apf
!= V3D_QPU_PF_NONE
||
157 inst
->qpu
.flags
.mpf
!= V3D_QPU_PF_NONE
)) {
158 vir_dce_flags(c
, last_flags_write
);
162 last_flags_write
= inst
;
165 if (v3d_qpu_writes_flags(&inst
->qpu
) ||
166 has_nonremovable_reads(c
, inst
)) {
167 /* If we can't remove the instruction, but we
168 * don't need its destination value, just
169 * remove the destination. The register
170 * allocator would trivially color it and it
171 * wouldn't cause any register pressure, but
172 * it's nicer to read the VIR code without
173 * unused destination regs.
175 if (inst
->dst
.file
== QFILE_TEMP
&&
176 can_write_to_null(c
, inst
)) {
179 "Removing dst from: ");
180 vir_dump_inst(c
, inst
);
181 fprintf(stderr
, "\n");
183 c
->defs
[inst
->dst
.index
] = NULL
;
184 inst
->dst
.file
= QFILE_NULL
;
190 for (int i
= 0; i
< vir_get_nsrc(inst
); i
++) {
191 if (inst
->src
[i
].file
!= QFILE_VPM
)
193 uint32_t attr
= inst
->src
[i
].index
/ 4;
194 uint32_t offset
= (inst
->src
[i
].index
% 4);
196 if (c
->vattr_sizes
[attr
] == offset
) {
198 c
->vattr_sizes
[attr
]--;
202 assert(inst
!= last_flags_write
);