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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_opt_dead_code(struct v3d_compile
*c
)
98 bool progress
= false;
99 bool *used
= calloc(c
->num_temps
, sizeof(bool));
101 /* Defuse the "are you removing the cursor?" assertion in the core.
102 * You'll need to set up a new cursor for any new instructions after
103 * doing DCE (which we would expect, anyway).
105 c
->cursor
.link
= NULL
;
107 vir_for_each_inst_inorder(inst
, c
) {
108 for (int i
= 0; i
< vir_get_nsrc(inst
); i
++) {
109 if (inst
->src
[i
].file
== QFILE_TEMP
)
110 used
[inst
->src
[i
].index
] = true;
114 vir_for_each_block(block
, c
) {
115 vir_for_each_inst_safe(inst
, block
) {
116 if (inst
->dst
.file
!= QFILE_NULL
&&
117 !(inst
->dst
.file
== QFILE_TEMP
&&
118 !used
[inst
->dst
.index
])) {
122 if (vir_has_side_effects(c
, inst
))
125 if (inst
->qpu
.flags
.apf
!= V3D_QPU_PF_NONE
||
126 inst
->qpu
.flags
.mpf
!= V3D_QPU_PF_NONE
||
127 inst
->qpu
.flags
.auf
!= V3D_QPU_UF_NONE
||
128 inst
->qpu
.flags
.muf
!= V3D_QPU_UF_NONE
||
129 has_nonremovable_reads(c
, inst
)) {
130 /* If we can't remove the instruction, but we
131 * don't need its destination value, just
132 * remove the destination. The register
133 * allocator would trivially color it and it
134 * wouldn't cause any register pressure, but
135 * it's nicer to read the VIR code without
136 * unused destination regs.
138 if (inst
->dst
.file
== QFILE_TEMP
&&
139 can_write_to_null(c
, inst
)) {
142 "Removing dst from: ");
143 vir_dump_inst(c
, inst
);
144 fprintf(stderr
, "\n");
146 c
->defs
[inst
->dst
.index
] = NULL
;
147 inst
->dst
.file
= QFILE_NULL
;
153 for (int i
= 0; i
< vir_get_nsrc(inst
); i
++) {
154 if (inst
->src
[i
].file
!= QFILE_VPM
)
156 uint32_t attr
= inst
->src
[i
].index
/ 4;
157 uint32_t offset
= (inst
->src
[i
].index
% 4);
159 if (c
->vattr_sizes
[attr
] == offset
) {
161 c
->vattr_sizes
[attr
]--;