Mesa (master): nir/validate: Explain why we don't use nir_foreach_block
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Mon Nov 2 23:32:29 UTC 2020
Module: Mesa
Branch: master
Commit: 78a420ce46716bf788b4a6bfc85ae226e0c6c804
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=78a420ce46716bf788b4a6bfc85ae226e0c6c804
Author: Jason Ekstrand <jason at jlekstrand.net>
Date: Mon Nov 2 14:28:01 2020 -0600
nir/validate: Explain why we don't use nir_foreach_block
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz at gmail.com>
Reviewed-by: Eric Anholt <eric at anholt.net>
Reviewed-by: Rob Clark <robdclark at chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7409>
---
src/compiler/nir/nir_validate.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/src/compiler/nir/nir_validate.c b/src/compiler/nir/nir_validate.c
index a4bc1aba8e3..83d7e846c7b 100644
--- a/src/compiler/nir/nir_validate.c
+++ b/src/compiler/nir/nir_validate.c
@@ -949,6 +949,25 @@ validate_phi_srcs(nir_block *block, nir_block *succ, validate_state *state)
static void
collect_blocks(struct exec_list *cf_list, validate_state *state)
{
+ /* We walk the blocks manually here rather than using nir_foreach_block for
+ * a few reasons:
+ *
+ * 1. nir_foreach_block() doesn't work properly for unstructured NIR and
+ * we need to be able to handle all forms of NIR here.
+ *
+ * 2. We want to call exec_list_validate() on every linked list in the IR
+ * which means we need to touch every linked and just walking blocks
+ * with nir_foreach_block() would make that difficult. In particular,
+ * we want to validate each list before the first time we walk it so
+ * that we catch broken lists in exec_list_validate() instead of
+ * getting stuck in a hard-to-debug infinite loop in the validator.
+ *
+ * 3. nir_foreach_block() depends on several invariants of the CF node
+ * hierarchy which nir_validate_shader() is responsible for verifying.
+ * If we used nir_foreach_block() in nir_validate_shader(), we could
+ * end up blowing up on a bad list walk instead of throwing the much
+ * easier to debug validation error.
+ */
exec_list_validate(cf_list);
foreach_list_typed(nir_cf_node, node, node, cf_list) {
switch (node->type) {
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