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11 * The above copyright notice and this permission notice (including the next
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16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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25 #include "nir_builder.h"
27 /** @file nir_opt_conditional_discard.c
29 * Handles optimization of lowering of
30 * - if (cond) discard to discard_if(cond) and
31 * - if (cond) demote to demote_if(cond)
35 nir_opt_conditional_discard_block(nir_builder
*b
, nir_block
*block
)
37 if (nir_cf_node_is_first(&block
->cf_node
))
40 nir_cf_node
*prev_node
= nir_cf_node_prev(&block
->cf_node
);
41 if (prev_node
->type
!= nir_cf_node_if
)
44 nir_if
*if_stmt
= nir_cf_node_as_if(prev_node
);
45 nir_block
*then_block
= nir_if_first_then_block(if_stmt
);
46 nir_block
*else_block
= nir_if_first_else_block(if_stmt
);
48 /* check there is only one else block and it is empty */
49 if (nir_if_last_else_block(if_stmt
) != else_block
)
51 if (!exec_list_is_empty(&else_block
->instr_list
))
54 /* check there is only one then block and it has only one instruction in it */
55 if (nir_if_last_then_block(if_stmt
) != then_block
)
57 if (exec_list_is_empty(&then_block
->instr_list
))
59 if (exec_list_length(&then_block
->instr_list
) > 1)
62 * make sure no subsequent phi nodes point at this if.
64 nir_block
*after
= nir_cf_node_as_block(nir_cf_node_next(&if_stmt
->cf_node
));
65 nir_foreach_instr_safe(instr
, after
) {
66 if (instr
->type
!= nir_instr_type_phi
)
68 nir_phi_instr
*phi
= nir_instr_as_phi(instr
);
70 nir_foreach_phi_src(phi_src
, phi
) {
71 if (phi_src
->pred
== then_block
||
72 phi_src
->pred
== else_block
)
77 /* Get the first instruction in the then block and confirm it is
78 * a discard or a demote instruction.
80 nir_instr
*instr
= nir_block_first_instr(then_block
);
81 if (instr
->type
!= nir_instr_type_intrinsic
)
84 nir_intrinsic_instr
*intrin
= nir_instr_as_intrinsic(instr
);
85 nir_intrinsic_op op
= intrin
->intrinsic
;
86 assert(if_stmt
->condition
.is_ssa
);
87 nir_ssa_def
*cond
= if_stmt
->condition
.ssa
;
88 b
->cursor
= nir_before_cf_node(prev_node
);
90 switch (intrin
->intrinsic
) {
91 case nir_intrinsic_discard
:
92 op
= nir_intrinsic_discard_if
;
94 case nir_intrinsic_demote
:
95 op
= nir_intrinsic_demote_if
;
97 case nir_intrinsic_discard_if
:
98 case nir_intrinsic_demote_if
:
99 assert(intrin
->src
[0].is_ssa
);
100 cond
= nir_iand(b
, cond
, intrin
->src
[0].ssa
);
106 nir_intrinsic_instr
*discard_if
=
107 nir_intrinsic_instr_create(b
->shader
, op
);
108 discard_if
->src
[0] = nir_src_for_ssa(cond
);
110 nir_instr_insert_before_cf(prev_node
, &discard_if
->instr
);
111 nir_instr_remove(&intrin
->instr
);
112 nir_cf_node_remove(&if_stmt
->cf_node
);
118 nir_opt_conditional_discard(nir_shader
*shader
)
120 bool progress
= false;
124 nir_foreach_function(function
, shader
) {
125 if (function
->impl
) {
126 nir_builder_init(&builder
, function
->impl
);
128 bool impl_progress
= false;
129 nir_foreach_block_safe(block
, function
->impl
) {
130 if (nir_opt_conditional_discard_block(&builder
, block
))
131 impl_progress
= true;
135 nir_metadata_preserve(function
->impl
, nir_metadata_none
);
138 nir_metadata_preserve(function
->impl
, nir_metadata_all
);