2 * Copyright © 2012 Intel Corporation
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 * Eric Anholt <eric@anholt.net>
29 #include "brw_fs_live_variables.h"
33 #define MAX_INSTRUCTION (1 << 30)
35 /** @file brw_fs_live_variables.cpp
37 * Support for calculating liveness information about virtual GRFs.
39 * This produces a live interval for each whole virtual GRF. We could
40 * choose to expose per-component live intervals for VGRFs of size > 1,
41 * but we currently do not. It is easier for the consumers of this
42 * information to work with whole VGRFs.
44 * However, we internally track use/def information at the per-component
45 * (reg_offset) level for greater accuracy. Large VGRFs may be accessed
46 * piecemeal over many (possibly non-adjacent) instructions. In this case,
47 * examining a single instruction is insufficient to decide whether a whole
48 * VGRF is ultimately used or defined. Tracking individual components
49 * allows us to easily assemble this information.
51 * See Muchnick's Advanced Compiler Design and Implementation, section
56 fs_live_variables::setup_one_read(struct block_data
*bd
, fs_inst
*inst
,
57 int ip
, const fs_reg
®
)
59 int var
= var_from_reg(reg
);
60 assert(var
< num_vars
);
62 /* In most cases, a register can be written over safely by the
63 * same instruction that is its last use. For a single
64 * instruction, the sources are dereferenced before writing of the
65 * destination starts (naturally). This gets more complicated for
66 * simd16, because the instruction:
68 * add(16) g4<1>F g4<8,8,1>F g6<8,8,1>F
70 * is actually decoded in hardware as:
72 * add(8) g4<1>F g4<8,8,1>F g6<8,8,1>F
73 * add(8) g5<1>F g5<8,8,1>F g7<8,8,1>F
75 * Which is safe. However, if we have uniform accesses
76 * happening, we get into trouble:
78 * add(8) g4<1>F g4<0,1,0>F g6<8,8,1>F
79 * add(8) g5<1>F g4<0,1,0>F g7<8,8,1>F
81 * Now our destination for the first instruction overwrote the
82 * second instruction's src0, and we get garbage for those 8
83 * pixels. There's a similar issue for the pre-gen6
84 * pixel_x/pixel_y, which are registers of 16-bit values and thus
85 * would get stomped by the first decode as well.
88 if (inst
->exec_size
== 16 && (reg
.stride
== 0 ||
89 reg
.type
== BRW_REGISTER_TYPE_UW
||
90 reg
.type
== BRW_REGISTER_TYPE_W
||
91 reg
.type
== BRW_REGISTER_TYPE_UB
||
92 reg
.type
== BRW_REGISTER_TYPE_B
)) {
96 start
[var
] = MIN2(start
[var
], ip
);
97 end
[var
] = MAX2(end
[var
], end_ip
);
99 /* The use[] bitset marks when the block makes use of a variable (VGRF
100 * channel) without having completely defined that variable within the
103 if (!BITSET_TEST(bd
->def
, var
))
104 BITSET_SET(bd
->use
, var
);
108 fs_live_variables::setup_one_write(struct block_data
*bd
, fs_inst
*inst
,
109 int ip
, const fs_reg
®
)
111 int var
= var_from_reg(reg
);
112 assert(var
< num_vars
);
114 start
[var
] = MIN2(start
[var
], ip
);
115 end
[var
] = MAX2(end
[var
], ip
);
117 /* The def[] bitset marks when an initialization in a block completely
118 * screens off previous updates of that variable (VGRF channel).
120 if (inst
->dst
.file
== GRF
&& !inst
->is_partial_write()) {
121 if (!BITSET_TEST(bd
->use
, var
))
122 BITSET_SET(bd
->def
, var
);
127 * Sets up the use[] and def[] bitsets.
129 * The basic-block-level live variable analysis needs to know which
130 * variables get used before they're completely defined, and which
131 * variables are completely defined before they're used.
133 * These are tracked at the per-component level, rather than whole VGRFs.
136 fs_live_variables::setup_def_use()
140 foreach_block (block
, cfg
) {
141 assert(ip
== block
->start_ip
);
143 assert(cfg
->blocks
[block
->num
- 1]->end_ip
== ip
- 1);
145 struct block_data
*bd
= &block_data
[block
->num
];
147 foreach_inst_in_block(fs_inst
, inst
, block
) {
148 /* Set use[] for this instruction */
149 for (unsigned int i
= 0; i
< inst
->sources
; i
++) {
150 fs_reg reg
= inst
->src
[i
];
155 for (int j
= 0; j
< inst
->regs_read(i
); j
++) {
156 setup_one_read(bd
, inst
, ip
, reg
);
160 if (inst
->reads_flag()) {
161 /* The vertical combination predicates read f0.0 and f0.1. */
162 if (inst
->predicate
== BRW_PREDICATE_ALIGN1_ANYV
||
163 inst
->predicate
== BRW_PREDICATE_ALIGN1_ALLV
) {
164 assert(inst
->flag_subreg
== 0);
165 if (!BITSET_TEST(bd
->flag_def
, 1)) {
166 BITSET_SET(bd
->flag_use
, 1);
169 if (!BITSET_TEST(bd
->flag_def
, inst
->flag_subreg
)) {
170 BITSET_SET(bd
->flag_use
, inst
->flag_subreg
);
174 /* Set def[] for this instruction */
175 if (inst
->dst
.file
== GRF
) {
176 fs_reg reg
= inst
->dst
;
177 for (int j
= 0; j
< inst
->regs_written
; j
++) {
178 setup_one_write(bd
, inst
, ip
, reg
);
182 if (inst
->writes_flag()) {
183 if (!BITSET_TEST(bd
->flag_use
, inst
->flag_subreg
)) {
184 BITSET_SET(bd
->flag_def
, inst
->flag_subreg
);
194 * The algorithm incrementally sets bits in liveout and livein,
195 * propagating it through control flow. It will eventually terminate
196 * because it only ever adds bits, and stops when no bits are added in
200 fs_live_variables::compute_live_variables()
207 foreach_block (block
, cfg
) {
208 struct block_data
*bd
= &block_data
[block
->num
];
211 for (int i
= 0; i
< bitset_words
; i
++) {
212 BITSET_WORD new_livein
= (bd
->use
[i
] |
215 if (new_livein
& ~bd
->livein
[i
]) {
216 bd
->livein
[i
] |= new_livein
;
220 BITSET_WORD new_livein
= (bd
->flag_use
[0] |
221 (bd
->flag_liveout
[0] &
223 if (new_livein
& ~bd
->flag_livein
[0]) {
224 bd
->flag_livein
[0] |= new_livein
;
229 foreach_list_typed(bblock_link
, child_link
, link
, &block
->children
) {
230 struct block_data
*child_bd
= &block_data
[child_link
->block
->num
];
232 for (int i
= 0; i
< bitset_words
; i
++) {
233 BITSET_WORD new_liveout
= (child_bd
->livein
[i
] &
236 bd
->liveout
[i
] |= new_liveout
;
240 BITSET_WORD new_liveout
= (child_bd
->flag_livein
[0] &
241 ~bd
->flag_liveout
[0]);
243 bd
->flag_liveout
[0] |= new_liveout
;
252 * Extend the start/end ranges for each variable to account for the
253 * new information calculated from control flow.
256 fs_live_variables::compute_start_end()
258 foreach_block (block
, cfg
) {
259 struct block_data
*bd
= &block_data
[block
->num
];
261 for (int i
= 0; i
< num_vars
; i
++) {
262 if (BITSET_TEST(bd
->livein
, i
)) {
263 start
[i
] = MIN2(start
[i
], block
->start_ip
);
264 end
[i
] = MAX2(end
[i
], block
->start_ip
);
267 if (BITSET_TEST(bd
->liveout
, i
)) {
268 start
[i
] = MIN2(start
[i
], block
->end_ip
);
269 end
[i
] = MAX2(end
[i
], block
->end_ip
);
276 fs_live_variables::fs_live_variables(fs_visitor
*v
, const cfg_t
*cfg
)
279 mem_ctx
= ralloc_context(NULL
);
281 num_vgrfs
= v
->alloc
.count
;
283 var_from_vgrf
= rzalloc_array(mem_ctx
, int, num_vgrfs
);
284 for (int i
= 0; i
< num_vgrfs
; i
++) {
285 var_from_vgrf
[i
] = num_vars
;
286 num_vars
+= v
->alloc
.sizes
[i
];
289 vgrf_from_var
= rzalloc_array(mem_ctx
, int, num_vars
);
290 for (int i
= 0; i
< num_vgrfs
; i
++) {
291 for (unsigned j
= 0; j
< v
->alloc
.sizes
[i
]; j
++) {
292 vgrf_from_var
[var_from_vgrf
[i
] + j
] = i
;
296 start
= ralloc_array(mem_ctx
, int, num_vars
);
297 end
= rzalloc_array(mem_ctx
, int, num_vars
);
298 for (int i
= 0; i
< num_vars
; i
++) {
299 start
[i
] = MAX_INSTRUCTION
;
303 block_data
= rzalloc_array(mem_ctx
, struct block_data
, cfg
->num_blocks
);
305 bitset_words
= BITSET_WORDS(num_vars
);
306 for (int i
= 0; i
< cfg
->num_blocks
; i
++) {
307 block_data
[i
].def
= rzalloc_array(mem_ctx
, BITSET_WORD
, bitset_words
);
308 block_data
[i
].use
= rzalloc_array(mem_ctx
, BITSET_WORD
, bitset_words
);
309 block_data
[i
].livein
= rzalloc_array(mem_ctx
, BITSET_WORD
, bitset_words
);
310 block_data
[i
].liveout
= rzalloc_array(mem_ctx
, BITSET_WORD
, bitset_words
);
312 block_data
[i
].flag_def
[0] = 0;
313 block_data
[i
].flag_use
[0] = 0;
314 block_data
[i
].flag_livein
[0] = 0;
315 block_data
[i
].flag_liveout
[0] = 0;
319 compute_live_variables();
323 fs_live_variables::~fs_live_variables()
325 ralloc_free(mem_ctx
);
329 fs_visitor::invalidate_live_intervals()
331 ralloc_free(live_intervals
);
332 live_intervals
= NULL
;
336 * Compute the live intervals for each virtual GRF.
338 * This uses the per-component use/def data, but combines it to produce
339 * information about whole VGRFs.
342 fs_visitor::calculate_live_intervals()
344 if (this->live_intervals
)
347 int num_vgrfs
= this->alloc
.count
;
348 ralloc_free(this->virtual_grf_start
);
349 ralloc_free(this->virtual_grf_end
);
350 virtual_grf_start
= ralloc_array(mem_ctx
, int, num_vgrfs
);
351 virtual_grf_end
= ralloc_array(mem_ctx
, int, num_vgrfs
);
353 for (int i
= 0; i
< num_vgrfs
; i
++) {
354 virtual_grf_start
[i
] = MAX_INSTRUCTION
;
355 virtual_grf_end
[i
] = -1;
358 this->live_intervals
= new(mem_ctx
) fs_live_variables(this, cfg
);
360 /* Merge the per-component live ranges to whole VGRF live ranges. */
361 for (int i
= 0; i
< live_intervals
->num_vars
; i
++) {
362 int vgrf
= live_intervals
->vgrf_from_var
[i
];
363 virtual_grf_start
[vgrf
] = MIN2(virtual_grf_start
[vgrf
],
364 live_intervals
->start
[i
]);
365 virtual_grf_end
[vgrf
] = MAX2(virtual_grf_end
[vgrf
],
366 live_intervals
->end
[i
]);
371 fs_live_variables::vars_interfere(int a
, int b
)
373 return !(end
[b
] <= start
[a
] ||
378 fs_visitor::virtual_grf_interferes(int a
, int b
)
380 return !(virtual_grf_end
[a
] <= virtual_grf_start
[b
] ||
381 virtual_grf_end
[b
] <= virtual_grf_start
[a
]);