2 * Copyright © 2015 Connor Abbott
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
24 * Connor Abbott (cwabbott0@gmail.com)
31 * This is a pass for removing phi nodes that look like:
32 * a = phi(b, b, b, ...)
34 * Note that we can't ignore undef sources here, or else we may create a
35 * situation where the definition of b isn't dominated by its uses. We're
36 * allowed to do this since the definition of b must dominate all of the
37 * phi node's predecessors, which means it must dominate the phi node as well
38 * as all of the phi node's uses. In essence, the phi node acts as a copy
39 * instruction. b can't be another phi node in the same block, since the only
40 * time when phi nodes can source other phi nodes defined in the same block is
41 * at the loop header, and in that case one of the sources of the phi has to
42 * be from before the loop and that source can't be b.
46 remove_phis_block(nir_block
*block
, void *state
)
48 bool *progress
= state
;
50 nir_foreach_instr_safe(block
, instr
) {
51 if (instr
->type
!= nir_instr_type_phi
)
54 nir_phi_instr
*phi
= nir_instr_as_phi(instr
);
56 nir_ssa_def
*def
= NULL
;
57 bool srcs_same
= true;
59 nir_foreach_phi_src(phi
, src
) {
60 assert(src
->src
.is_ssa
);
62 /* For phi nodes at the beginning of loops, we may encounter some
63 * sources from backedges that point back to the destination of the
64 * same phi, i.e. something like:
68 * We can safely ignore these sources, since if all of the normal
69 * sources point to the same definition, then that definition must
70 * still dominate the phi node, and the phi will still always take
71 * the value of that definition.
73 if (src
->src
.ssa
== &phi
->dest
.ssa
)
79 if (src
->src
.ssa
!= def
) {
89 /* We must have found at least one definition, since there must be at
90 * least one forward edge.
94 assert(phi
->dest
.is_ssa
);
95 nir_ssa_def_rewrite_uses(&phi
->dest
.ssa
, nir_src_for_ssa(def
));
96 nir_instr_remove(instr
);
105 remove_phis_impl(nir_function_impl
*impl
)
107 bool progress
= false;
109 nir_foreach_block(impl
, remove_phis_block
, &progress
);
112 nir_metadata_preserve(impl
, nir_metadata_block_index
|
113 nir_metadata_dominance
);
120 nir_opt_remove_phis(nir_shader
*shader
)
122 bool progress
= false;
124 nir_foreach_function(shader
, function
)
126 progress
= remove_phis_impl(function
->impl
) || progress
;