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nak: Only insert barriers around ifs if they actually re-converge

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We don't care about patterns like

    loop {
        ...
        if (...) {
            break;
        } else {
            ...
        }
        ...
    }

In that case, we don't need to sync after the if because there's nothing
to re-converge.  Every path except one will end up breaking out of it
anyway.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26382>
This commit is contained in:
Faith Ekstrand 2023-10-25 22:03:30 -05:00 • committed by Marge Bot
parent 804201a3d7
commit 500955b6cb
1 changed files with 24 additions and 0 deletions
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24
src/nouveau/compiler/nak_nir_add_barriers.c
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@ -195,6 +195,27 @@ cf_node_imm_succ_is_sync(nir_cf_node *node)
}
}
static bool
block_is_merge(const nir_block *block)
{
/* If it's unreachable, there is no merge */
if (block->imm_dom == NULL)
return false;
unsigned num_preds = 0;
set_foreach(block->predecessors, entry) {
const nir_block *pred = entry->key;
/* We don't care about unreachable blocks */
if (pred->imm_dom == NULL)
continue;
num_preds++;
}
return num_preds > 1;
}
static void
add_barriers_cf_list(struct exec_list *cf_list,
struct add_barriers_state *state)
@ -213,6 +234,7 @@ add_barriers_cf_list(struct exec_list *cf_list,
nir_if *nif = nir_cf_node_as_if(node);
if (nif->condition.ssa->divergent &&
block_is_merge(nir_cf_node_as_block(nir_cf_node_next(node))) &&
!cf_node_imm_succ_is_sync(&nif->cf_node))
add_bar_cf_node(&nif->cf_node, state);
@ -243,6 +265,8 @@ static bool
nak_nir_add_barriers_impl(nir_function_impl *impl,
const struct nak_compiler *nak)
{
nir_metadata_require(impl, nir_metadata_dominance);
struct add_barriers_state state = {
.nak = nak,
.builder = nir_builder_create(impl),