2 * Copyright (C) 2018-2019 Alyssa Rosenzweig <alyssa@rosenzweig.io>
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 FROM,
20 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
24 /* mir_is_live_after performs liveness analysis on the MIR, used primarily
25 * as part of register allocation. TODO: Algorithmic improvements for
26 * compiler performance (this is the worst algorithm possible -- see
27 * backlog with Connor on IRC) */
30 #include "util/u_memory.h"
32 /* Routines for liveness analysis */
35 liveness_gen(uint8_t *live
, unsigned node
, unsigned max
, unsigned mask
)
44 liveness_kill(uint8_t *live
, unsigned node
, unsigned max
, unsigned mask
)
52 /* Updates live_in for a single instruction */
55 mir_liveness_ins_update(uint8_t *live
, midgard_instruction
*ins
, unsigned max
)
57 /* live_in[s] = GEN[s] + (live_out[s] - KILL[s]) */
59 liveness_kill(live
, ins
->dest
, max
, ins
->mask
);
61 mir_foreach_src(ins
, src
) {
62 unsigned node
= ins
->src
[src
];
63 unsigned mask
= mir_mask_of_read_components(ins
, node
);
65 liveness_gen(live
, node
, max
, mask
);
69 /* live_out[s] = sum { p in succ[s] } ( live_in[p] ) */
72 liveness_block_live_out(compiler_context
*ctx
, midgard_block
*blk
)
74 mir_foreach_successor(blk
, succ
) {
75 for (unsigned i
= 0; i
< ctx
->temp_count
; ++i
)
76 blk
->live_out
[i
] |= succ
->live_in
[i
];
80 /* Liveness analysis is a backwards-may dataflow analysis pass. Within a block,
81 * we compute live_out from live_in. The intrablock pass is linear-time. It
82 * returns whether progress was made. */
85 liveness_block_update(compiler_context
*ctx
, midgard_block
*blk
)
87 bool progress
= false;
89 liveness_block_live_out(ctx
, blk
);
91 uint8_t *live
= mem_dup(blk
->live_out
, ctx
->temp_count
);
93 mir_foreach_instr_in_block_rev(blk
, ins
)
94 mir_liveness_ins_update(live
, ins
, ctx
->temp_count
);
96 /* To figure out progress, diff live_in */
98 for (unsigned i
= 0; (i
< ctx
->temp_count
) && !progress
; ++i
)
99 progress
|= (blk
->live_in
[i
] != live
[i
]);
107 /* Globally, liveness analysis uses a fixed-point algorithm based on a
108 * worklist. We initialize a work list with the exit block. We iterate the work
109 * list to compute live_in from live_out for each block on the work list,
110 * adding the predecessors of the block to the work list if we made progress.
114 mir_compute_liveness(compiler_context
*ctx
)
116 /* If we already have fresh liveness, nothing to do */
117 if (ctx
->metadata
& MIDGARD_METADATA_LIVENESS
)
120 /* List of midgard_block */
121 struct set
*work_list
= _mesa_set_create(ctx
,
123 _mesa_key_pointer_equal
);
127 mir_foreach_block(ctx
, block
) {
128 block
->live_in
= calloc(ctx
->temp_count
, 1);
129 block
->live_out
= calloc(ctx
->temp_count
, 1);
132 /* Initialize the work list with the exit block */
133 struct set_entry
*cur
;
135 midgard_block
*exit
= mir_exit_block(ctx
);
136 cur
= _mesa_set_add(work_list
, exit
);
138 /* Iterate the work list */
141 /* Pop off a block */
142 midgard_block
*blk
= (struct midgard_block
*) cur
->key
;
143 _mesa_set_remove(work_list
, cur
);
145 /* Update its liveness information */
146 bool progress
= liveness_block_update(ctx
, blk
);
148 /* If we made progress, we need to process the predecessors */
150 if (progress
|| (blk
== exit
)) {
151 mir_foreach_predecessor(blk
, pred
)
152 _mesa_set_add(work_list
, pred
);
154 } while((cur
= _mesa_set_next_entry(work_list
, NULL
)) != NULL
);
156 /* Liveness is now valid */
157 ctx
->metadata
|= MIDGARD_METADATA_LIVENESS
;
160 /* Once liveness data is no longer valid, call this */
163 mir_invalidate_liveness(compiler_context
*ctx
)
165 /* If we didn't already compute liveness, there's nothing to do */
166 if (!(ctx
->metadata
& MIDGARD_METADATA_LIVENESS
))
169 /* It's now invalid regardless */
170 ctx
->metadata
&= ~MIDGARD_METADATA_LIVENESS
;
172 mir_foreach_block(ctx
, block
) {
174 free(block
->live_in
);
177 free(block
->live_out
);
179 block
->live_in
= NULL
;
180 block
->live_out
= NULL
;
184 /* Determine if a variable is live in the successors of a block */
186 is_live_after_successors(compiler_context
*ctx
, midgard_block
*bl
, int src
)
188 for (unsigned i
= 0; i
< bl
->nr_successors
; ++i
) {
189 midgard_block
*succ
= bl
->successors
[i
];
191 /* If we already visited, the value we're seeking
192 * isn't down this path (or we would have short
195 if (succ
->visited
) continue;
197 /* Otherwise (it's visited *now*), check the block */
199 succ
->visited
= true;
201 /* Within this block, check if it's overwritten first */
202 unsigned overwritten_mask
= 0;
204 mir_foreach_instr_in_block(succ
, ins
) {
205 /* Did we read any components that we haven't overwritten yet? */
206 if (mir_mask_of_read_components(ins
, src
) & ~overwritten_mask
)
209 /* If written-before-use, we're gone */
211 if (ins
->dest
== src
)
212 overwritten_mask
|= ins
->mask
;
215 /* ...and also, check *its* successors */
216 if (is_live_after_successors(ctx
, succ
, src
))
221 /* Welp. We're really not live. */
227 mir_is_live_after(compiler_context
*ctx
, midgard_block
*block
, midgard_instruction
*start
, int src
)
229 assert(ctx
->metadata
& MIDGARD_METADATA_LIVENESS
);
231 /* Check the rest of the block for liveness */
233 mir_foreach_instr_in_block_from(block
, ins
, mir_next_op(start
)) {
234 if (mir_has_arg(ins
, src
))
238 /* Check the rest of the blocks for liveness recursively */
240 bool succ
= is_live_after_successors(ctx
, block
, src
);
242 mir_foreach_block(ctx
, block
) {
243 block
->visited
= false;