[review] Create a correctly-sized demangled names hashtable

Christian Biesinger (Code Review)
2019-11-18T23:14:42Z

Create a correctly-sized demangled names hashtable

If we have a minsym count, we know the demangled names hashtable will
be at least that big. So use that count to create it, so we don't
have to resize/rehash it as much.

This is a 6% improvement in minsym loading time.

2019-11-18 Christian Biesinger <cbiesinger@google.com>

* symtab.c (create_demangled_names_hash): Use per_bfd->
minimal_symbol_count as the initial size, if greater than
our default size.

Change-Id: I1f074d38e1d90af58705ec852f90c84cc034cd2e
---
M gdb/symtab.c
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 3502827..e4da065 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -769,10 +769,17 @@
/* Choose 256 as the starting size of the hash table, somewhat arbitrarily.
The hash table code will round this up to the next prime number.
Choosing a much larger table size wastes memory, and saves only about
- 1% in symbol reading. */
+ 1% in symbol reading. However, if the minsym count is already
+ initialized (e.g. because symbol name setting was deferred to
+ a background thread) we can initialize the hashtable with that
+ count, because we will almost certainly have at least that
+ many entries. If we have a nonzero number but less than 256,
+ we still stay with 256 to have some space for psymbols, etc. */
+
+ int count = std::max (per_bfd->minimal_symbol_count, 256);

per_bfd->demangled_names_hash.reset (htab_create_alloc
- (256, hash_demangled_name_entry, eq_demangled_name_entry,
+ (count, hash_demangled_name_entry, eq_demangled_name_entry,
free_demangled_name_entry, xcalloc, xfree));
}

--
Gerrit-Project: binutils-gdb
Gerrit-Branch: master
Gerrit-Change-Id: I1f074d38e1d90af58705ec852f90c84cc034cd2e
Gerrit-Change-Number: 686
Gerrit-PatchSet: 1
Gerrit-Owner: Christian Biesinger <cbiesinger@google.com>
Gerrit-MessageType: newchange