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authorJason Ekstrand <[email protected]>2017-01-17 18:38:35 -0800
committerMarge Bot <[email protected]>2020-04-20 03:46:29 +0000
commit4d083b52c04745d18d8f5446be5805077fa2c51a (patch)
treee81d14171feb7f373bee69bf0d1dd56043226b63 /src/compiler
parent425558bfd595ed3a7a049ad0f47a46b8b3c4691e (diff)
nir/dominance: Better handle unreachable blocks
v2: Fix minor comments (Ken) Reviewed-by: Kenneth Graunke <[email protected]> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4636>
Diffstat (limited to 'src/compiler')
-rw-r--r--src/compiler/nir/nir.h9
-rw-r--r--src/compiler/nir/nir_dominance.c37
2 files changed, 38 insertions, 8 deletions
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index b9a5637e68e..105e09347b5 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2406,13 +2406,20 @@ typedef struct nir_block {
* dom_pre_index and dom_post_index for this block, which makes testing if
* a given block is dominated by another block an O(1) operation.
*/
- unsigned dom_pre_index, dom_post_index;
+ int16_t dom_pre_index, dom_post_index;
/* live in and out for this block; used for liveness analysis */
BITSET_WORD *live_in;
BITSET_WORD *live_out;
} nir_block;
+static inline bool
+nir_block_is_reachable(nir_block *b)
+{
+ /* See also nir_block_dominates */
+ return b->dom_post_index != -1;
+}
+
static inline nir_instr *
nir_block_first_instr(nir_block *block)
{
diff --git a/src/compiler/nir/nir_dominance.c b/src/compiler/nir/nir_dominance.c
index 8369c28984d..192d3305801 100644
--- a/src/compiler/nir/nir_dominance.c
+++ b/src/compiler/nir/nir_dominance.c
@@ -42,6 +42,10 @@ init_block(nir_block *block, nir_function_impl *impl)
block->imm_dom = NULL;
block->num_dom_children = 0;
+ /* See nir_block_dominates */
+ block->dom_pre_index = INT16_MAX;
+ block->dom_post_index = -1;
+
set_foreach(block->dom_frontier, entry) {
_mesa_set_remove(block->dom_frontier, entry);
}
@@ -201,18 +205,25 @@ nir_calc_dominance(nir_shader *shader)
}
}
+static nir_block *
+block_return_if_reachable(nir_block *b)
+{
+ return (b && nir_block_is_reachable(b)) ? b : NULL;
+}
+
/**
- * Computes the least common anscestor of two blocks. If one of the blocks
- * is null, the other block is returned.
+ * Computes the least common ancestor of two blocks. If one of the blocks
+ * is null or unreachable, the other block is returned or NULL if it's
+ * unreachable.
*/
nir_block *
nir_dominance_lca(nir_block *b1, nir_block *b2)
{
- if (b1 == NULL)
- return b2;
+ if (b1 == NULL || !nir_block_is_reachable(b1))
+ return block_return_if_reachable(b2);
- if (b2 == NULL)
- return b1;
+ if (b2 == NULL || !nir_block_is_reachable(b2))
+ return block_return_if_reachable(b1);
assert(nir_cf_node_get_function(&b1->cf_node) ==
nir_cf_node_get_function(&b2->cf_node));
@@ -224,7 +235,15 @@ nir_dominance_lca(nir_block *b1, nir_block *b2)
}
/**
- * Returns true if parent dominates child
+ * Returns true if parent dominates child according to the following
+ * definition:
+ *
+ * "The block A dominates the block B if every path from the start block
+ * to block B passes through A."
+ *
+ * This means, in particular, that any unreachable block is dominated by every
+ * other block and an unreachable block does not dominate anything except
+ * another unreachable block.
*/
bool
nir_block_dominates(nir_block *parent, nir_block *child)
@@ -235,6 +254,10 @@ nir_block_dominates(nir_block *parent, nir_block *child)
assert(nir_cf_node_get_function(&parent->cf_node)->valid_metadata &
nir_metadata_dominance);
+ /* If a block is unreachable, then nir_block::dom_pre_index == INT16_MAX
+ * and nir_block::dom_post_index == -1. This allows us to trivially handle
+ * unreachable blocks here with zero extra work.
+ */
return child->dom_pre_index >= parent->dom_pre_index &&
child->dom_post_index <= parent->dom_post_index;
}