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intel/fs: Don't let undefined values prevent copy propagation.

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This makes the dataflow propagation logic of the copy propagation pass
more intelligent in cases where the destination of a copy is known to
be undefined for some incoming CFG edges, building upon the
definedness information provided by the last patch.  Helps a few
programs, and avoids a handful shader-db regressions from the next
patch.

shader-db results on ILK:

  total instructions in shared programs: 6541547 -> 6541523 (-0.00%)
  instructions in affected programs: 360 -> 336 (-6.67%)
  helped: 8
  HURT: 0

  LOST:   0
  GAINED: 10

shader-db results on BDW:

  total instructions in shared programs: 8174323 -> 8173882 (-0.01%)
  instructions in affected programs: 7730 -> 7289 (-5.71%)
  helped: 5
  HURT: 2

  LOST:   0
  GAINED: 4

shader-db results on SKL:

  total instructions in shared programs: 8185669 -> 8184598 (-0.01%)
  instructions in affected programs: 10364 -> 9293 (-10.33%)
  helped: 5
  HURT: 2

  LOST:   0
  GAINED: 2

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
This commit is contained in:
Francisco Jerez 2017-10-23 13:47:10 -07:00
parent c3c1aa5aeb
commit 9355116bda
1 changed files with 47 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

50
src/intel/compiler/brw_fs_copy_propagation.cpp
View file

@ -36,9 +36,12 @@
#include "util/bitset.h"
#include "brw_fs.h"
#include "brw_fs_live_variables.h"
#include "brw_cfg.h"
#include "brw_eu.h"
using namespace brw;
namespace { /* avoid conflict with opt_copy_propagation_elements */
struct acp_entry : public exec_node {
fs_reg dst;
@ -77,12 +80,19 @@ struct block_data {
* course of this block.
*/
BITSET_WORD *kill;
/**
* Which entries in the fs_copy_prop_dataflow acp table are guaranteed to
* have a fully uninitialized destination at the end of this block.
*/
BITSET_WORD *undef;
};
class fs_copy_prop_dataflow
{
public:
fs_copy_prop_dataflow(void *mem_ctx, cfg_t *cfg,
const fs_live_variables *live,
exec_list *out_acp[ACP_HASH_SIZE]);
void setup_initial_values();
@ -92,6 +102,7 @@ public:
void *mem_ctx;
cfg_t *cfg;
const fs_live_variables *live;
acp_entry **acp;
int num_acp;
@ -102,8 +113,9 @@ public:
} /* anonymous namespace */
fs_copy_prop_dataflow::fs_copy_prop_dataflow(void *mem_ctx, cfg_t *cfg,
const fs_live_variables *live,
exec_list *out_acp[ACP_HASH_SIZE])
: mem_ctx(mem_ctx), cfg(cfg)
: mem_ctx(mem_ctx), cfg(cfg), live(live)
{
bd = rzalloc_array(mem_ctx, struct block_data, cfg->num_blocks);
@ -124,6 +136,7 @@ fs_copy_prop_dataflow::fs_copy_prop_dataflow(void *mem_ctx, cfg_t *cfg,
bd[block->num].liveout = rzalloc_array(bd, BITSET_WORD, bitset_words);
bd[block->num].copy = rzalloc_array(bd, BITSET_WORD, bitset_words);
bd[block->num].kill = rzalloc_array(bd, BITSET_WORD, bitset_words);
bd[block->num].undef = rzalloc_array(bd, BITSET_WORD, bitset_words);
for (int i = 0; i < ACP_HASH_SIZE; i++) {
foreach_in_list(acp_entry, entry, &out_acp[block->num][i]) {
@ -189,6 +202,18 @@ fs_copy_prop_dataflow::setup_initial_values()
}
}
}
/* Initialize the undef set. */
foreach_block (block, cfg) {
for (int i = 0; i < num_acp; i++) {
BITSET_SET(bd[block->num].undef, i);
for (unsigned off = 0; off < acp[i]->size_written; off += REG_SIZE) {
if (BITSET_TEST(live->block_data[block->num].defout,
live->var_from_reg(byte_offset(acp[i]->dst, off))))
BITSET_CLEAR(bd[block->num].undef, i);
}
}
}
}
/**
@ -229,13 +254,30 @@ fs_copy_prop_dataflow::run()
for (int i = 0; i < bitset_words; i++) {
const BITSET_WORD old_livein = bd[block->num].livein[i];
BITSET_WORD livein_from_any_block = 0;
bd[block->num].livein[i] = ~0u;
foreach_list_typed(bblock_link, parent_link, link, &block->parents) {
bblock_t *parent = parent_link->block;
bd[block->num].livein[i] &= bd[parent->num].liveout[i];
/* Consider ACP entries with a known-undefined destination to
* be available from the parent. This is valid because we're
* free to set the undefined variable equal to the source of
* the ACP entry without breaking the application's
* expectations, since the variable is undefined.
*/
bd[block->num].livein[i] &= (bd[parent->num].liveout[i] |
bd[parent->num].undef[i]);
livein_from_any_block |= bd[parent->num].liveout[i];
}
/* Limit to the set of ACP entries that can possibly be available
* at the start of the block, since propagating from a variable
* which is guaranteed to be undefined (rather than potentially
* undefined for some dynamic control-flow paths) doesn't seem
* particularly useful.
*/
bd[block->num].livein[i] &= livein_from_any_block;
if (old_livein != bd[block->num].livein[i])
progress = true;
}
@ -834,6 +876,8 @@ fs_visitor::opt_copy_propagation()
for (int i = 0; i < cfg->num_blocks; i++)
out_acp[i] = new exec_list [ACP_HASH_SIZE];
calculate_live_intervals();
/* First, walk through each block doing local copy propagation and getting
* the set of copies available at the end of the block.
*/
@ -843,7 +887,7 @@ fs_visitor::opt_copy_propagation()
}
/* Do dataflow analysis for those available copies. */
fs_copy_prop_dataflow dataflow(copy_prop_ctx, cfg, out_acp);
fs_copy_prop_dataflow dataflow(copy_prop_ctx, cfg, live_intervals, out_acp);
/* Next, re-run local copy propagation, this time with the set of copies
* provided by the dataflow analysis available at the start of a block.