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nir: Switch the indexing of block->live_in/out arrays.

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In nir-to-tgsi, I want to free temps storing SSA values when they go dead,
and NIR liveness has most of the information I need.  Hoever, when I reach
the end of a block, I need to free whatever temps were in liveout which
are dead at that point.  If liveout is indexed by live_index, then I don't
know the maximum live_index for iterating the live_out bitset, and I also
don't have a way to map that index back to the def->index that my temps
are stored under.

We can use the more typical def->index for these bitsets, which resolves
both of those problems.  The only cost is that ssa_undefs don't get merged
into a single bit in the bitfield, but there are generally 1-4 of them in
a shader and we don't track liveness for those anyway so splitting them
apart is fine.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6408>
This commit is contained in:
Eric Anholt
2020-07-23 12:29:02 -07:00
committed by Marge Bot
parent 5d2b2b59c4
commit 73d2c6cdce
3 changed files with 16 additions and 12 deletions
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2
src/compiler/nir/nir.c
View File

@@ -1847,6 +1847,8 @@ nir_index_ssa_defs(nir_function_impl *impl)
{
unsigned index = 0;
impl->valid_metadata &= ~nir_metadata_live_ssa_defs;
nir_foreach_block_unstructured(block, impl) {
nir_foreach_instr(instr, block)
nir_foreach_ssa_def(instr, index_ssa_def_cb, &index);

6
src/compiler/nir/nir.h
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@@ -768,7 +768,7 @@ typedef struct nir_ssa_def {
/** generic SSA definition index. */
unsigned index;
/** Index into the live_in and live_out bitfields */
/** Ordered SSA definition index used by nir_liveness. */
unsigned live_index;
/** Instruction which produces this SSA value. */
@@ -2603,7 +2603,9 @@ typedef struct nir_block {
*/
int16_t dom_pre_index, dom_post_index;
/* live in and out for this block; used for liveness analysis */
/* SSA def live in and out for this block; used for liveness analysis.
* Indexed by ssa_def->index
*/
BITSET_WORD *live_in;
BITSET_WORD *live_out;
} nir_block;

20
src/compiler/nir/nir_liveness.c
View File

@@ -96,7 +96,7 @@ set_src_live(nir_src *src, void *void_live)
if (src->ssa->live_index == 0)
return true; /* undefined variables are never live */
BITSET_SET(live, src->ssa->live_index);
BITSET_SET(live, src->ssa->index);
return true;
}
@@ -106,7 +106,7 @@ set_ssa_def_dead(nir_ssa_def *def, void *void_live)
{
BITSET_WORD *live = void_live;
BITSET_CLEAR(live, def->live_index);
BITSET_CLEAR(live, def->index);
return true;
}
@@ -160,7 +160,10 @@ propagate_across_edge(nir_block *pred, nir_block *succ,
void
nir_live_ssa_defs_impl(nir_function_impl *impl)
{
struct live_ssa_defs_state state;
struct live_ssa_defs_state state = {
.bitset_words = BITSET_WORDS(impl->ssa_alloc),
};
state.tmp_live = rzalloc_array(impl, BITSET_WORD, state.bitset_words),
/* We start at 1 because we reserve the index value of 0 for ssa_undef
* instructions. Those are never live, so their liveness information
@@ -174,12 +177,9 @@ nir_live_ssa_defs_impl(nir_function_impl *impl)
nir_block_worklist_init(&state.worklist, impl->num_blocks, NULL);
/* We now know how many unique ssa definitions we have and we can go
* ahead and allocate live_in and live_out sets and add all of the
* blocks to the worklist.
/* Allocate live_in and live_out sets and add all of the blocks to the
* worklist.
*/
state.bitset_words = BITSET_WORDS(state.num_ssa_defs);
state.tmp_live = rzalloc_array(impl, BITSET_WORD, state.bitset_words);
nir_foreach_block(block, impl) {
init_liveness_block(block, &state);
}
@@ -259,13 +259,13 @@ search_for_use_after_instr(nir_instr *start, nir_ssa_def *def)
static bool
nir_ssa_def_is_live_at(nir_ssa_def *def, nir_instr *instr)
{
if (BITSET_TEST(instr->block->live_out, def->live_index)) {
if (BITSET_TEST(instr->block->live_out, def->index)) {
/* Since def dominates instr, if def is in the liveout of the block,
* it's live at instr
*/
return true;
} else {
if (BITSET_TEST(instr->block->live_in, def->live_index) ||
if (BITSET_TEST(instr->block->live_in, def->index) ||
def->parent_instr->block == instr->block) {
/* In this case it is either live coming into instr's block or it
* is defined in the same block. In this case, we simply need to