From cc2f268d14eafcf446c3f26d031a40f823b787fc Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@polymtl.ca>
Date: Sun, 16 Mar 2025 22:38:22 -0400
Subject: gdb/dwarf: use gdb::unordered_set for seen_names
Direct replacement of an htab with a gdb::unordered_set.
Using a large test program, I see a small but consistent performance
improvement. The "file" command time goes on average from 7.88 to 7.73
seconds (~2%). To give a rough estimate of the scale of the test
program, the 8 seen_names hash tables (one for each worker thread) had
between 173846 and 866961 entries.
Change-Id: I0157cbd04bb55338bb1fcefd2690aeef52fe3afe
Approved-By: Tom Tromey <tom@tromey.com>
---
gdb/dwarf2/cooked-index.c | 64 ++++++++++++++++++++++++++++-------------------
1 file changed, 38 insertions(+), 26 deletions(-)
(limited to 'gdb')
diff --git a/gdb/dwarf2/cooked-index.c b/gdb/dwarf2/cooked-index.c
index 866a07c..13f0540 100644
--- a/gdb/dwarf2/cooked-index.c
+++ b/gdb/dwarf2/cooked-index.c
@@ -390,30 +390,41 @@ cooked_index_shard::handle_gnat_encoded_entry
entry->canonical = m_names.insert (tail);
}
+/* Hash a cooked index entry by name pointer value.
+
+ We can use pointer equality here because names come from .debug_str, which
+ will normally be unique-ified by the linker. Also, duplicates are relatively
+ harmless -- they just mean a bit of extra memory is used. */
+
+struct cooked_index_entry_name_ptr_hash
+{
+ using is_avalanching = void;
+
+ std::uint64_t operator () (const cooked_index_entry *entry) const noexcept
+ {
+ return ankerl::unordered_dense::hash<const char *> () (entry->name);
+ }
+};
+
+/* Compare cooked index entries by name pointer value. */
+
+struct cooked_index_entry_name_ptr_eq
+{
+ bool operator () (const cooked_index_entry *a,
+ const cooked_index_entry *b) const noexcept
+ {
+ return a->name == b->name;
+ }
+};
+
/* See cooked-index.h. */
void
cooked_index_shard::finalize (const parent_map_map *parent_maps)
{
- auto hash_name_ptr = [] (const void *p)
- {
- const cooked_index_entry *entry = (const cooked_index_entry *) p;
- return htab_hash_pointer (entry->name);
- };
-
- auto eq_name_ptr = [] (const void *a, const void *b) -> int
- {
- const cooked_index_entry *ea = (const cooked_index_entry *) a;
- const cooked_index_entry *eb = (const cooked_index_entry *) b;
- return ea->name == eb->name;
- };
-
- /* We can use pointer equality here because names come from
- .debug_str, which will normally be unique-ified by the linker.
- Also, duplicates are relatively harmless -- they just mean a bit
- of extra memory is used. */
- htab_up seen_names (htab_create_alloc (10, hash_name_ptr, eq_name_ptr,
- nullptr, xcalloc, xfree));
+ gdb::unordered_set<const cooked_index_entry *,
+ cooked_index_entry_name_ptr_hash,
+ cooked_index_entry_name_ptr_eq> seen_names;
auto hash_entry = [] (const void *e)
{
@@ -494,10 +505,12 @@ cooked_index_shard::finalize (const parent_map_map *parent_maps)
}
else if (entry->lang == language_cplus || entry->lang == language_c)
{
- void **slot = htab_find_slot (seen_names.get (), entry,
- INSERT);
- if (*slot == nullptr)
+ auto [it, inserted] = seen_names.insert (entry);
+
+ if (inserted)
{
+ /* No entry with that name was present, compute the canonical
+ name. */
gdb::unique_xmalloc_ptr<char> canon_name
= (entry->lang == language_cplus
? cp_canonicalize_string (entry->name)
@@ -506,13 +519,12 @@ cooked_index_shard::finalize (const parent_map_map *parent_maps)
entry->canonical = entry->name;
else
entry->canonical = m_names.insert (std::move (canon_name));
- *slot = entry;
}
else
{
- const cooked_index_entry *other
- = (const cooked_index_entry *) *slot;
- entry->canonical = other->canonical;
+ /* An entry with that name was present, re-use its canonical
+ name. */
+ entry->canonical = (*it)->canonical;
}
}
else
--
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