From: Tom Tromey Date: Sun, 9 Mar 2025 16:14:34 +0000 (-0600) Subject: Add string cache and use it in cooked index X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=2609ee6f193505ec96552a9c33ecdea679242114;p=thirdparty%2Fbinutils-gdb.git Add string cache and use it in cooked index The cooked index needs to allocate names in some cases -- when canonicalizing or when synthesizing Ada package names. This process currently uses a vector of unique_ptrs to manage the memory. Another series I'm writing adds another spot where this allocation must be done, and examining the result showed that certain names were allocated multiple times. To clean this up, this patch introduces a string cache object and changes the cooked indexer to use it. I considered using bcache here, but bcache doesn't work as nicely with string_view -- because bcache is fundamentally memory-based, a temporary copy of the contents must be made to ensure that bcache can see the trailing \0. Furthermore, writing a custom class lets us avoid another copy when canonicalizing C++ names. Approved-By: Simon Marchi --- diff --git a/gdb/dwarf2/cooked-index.c b/gdb/dwarf2/cooked-index.c index 457ea44cc23..866a07ce8a0 100644 --- a/gdb/dwarf2/cooked-index.c +++ b/gdb/dwarf2/cooked-index.c @@ -374,13 +374,11 @@ cooked_index_shard::handle_gnat_encoded_entry cooked_index_entry *last = (cooked_index_entry *) *slot; if (last == nullptr || last->per_cu != entry->per_cu) { - gdb::unique_xmalloc_ptr new_name - = make_unique_xstrndup (name.data (), name.length ()); + const char *new_name = m_names.insert (name); last = create (entry->die_offset, DW_TAG_module, - IS_SYNTHESIZED, language_ada, new_name.get (), parent, + IS_SYNTHESIZED, language_ada, new_name, parent, entry->per_cu); last->canonical = last->name; - m_names.push_back (std::move (new_name)); new_entries.push_back (last); *slot = last; } @@ -389,9 +387,7 @@ cooked_index_shard::handle_gnat_encoded_entry } entry->set_parent (parent); - auto new_canon = make_unique_xstrndup (tail.data (), tail.length ()); - entry->canonical = new_canon.get (); - m_names.push_back (std::move (new_canon)); + entry->canonical = m_names.insert (tail); } /* See cooked-index.h. */ @@ -509,10 +505,7 @@ cooked_index_shard::finalize (const parent_map_map *parent_maps) if (canon_name == nullptr) entry->canonical = entry->name; else - { - entry->canonical = canon_name.get (); - m_names.push_back (std::move (canon_name)); - } + entry->canonical = m_names.insert (std::move (canon_name)); *slot = entry; } else @@ -532,7 +525,6 @@ cooked_index_shard::finalize (const parent_map_map *parent_maps) m_entries.insert (m_entries.end (), new_gnat_entries.begin (), new_gnat_entries.end ()); - m_names.shrink_to_fit (); m_entries.shrink_to_fit (); std::sort (m_entries.begin (), m_entries.end (), [] (const cooked_index_entry *a, const cooked_index_entry *b) diff --git a/gdb/dwarf2/cooked-index.h b/gdb/dwarf2/cooked-index.h index 4c35d5b65dd..02f4512213a 100644 --- a/gdb/dwarf2/cooked-index.h +++ b/gdb/dwarf2/cooked-index.h @@ -32,6 +32,7 @@ #include "dwarf2/read.h" #include "dwarf2/parent-map.h" #include "gdbsupport/range-chain.h" +#include "gdbsupport/string-set.h" #include "complaints.h" #if CXX_STD_THREAD @@ -381,7 +382,7 @@ private: /* The addrmap. This maps address ranges to dwarf2_per_cu objects. */ addrmap_fixed *m_addrmap = nullptr; /* Storage for canonical names. */ - std::vector> m_names; + gdb::string_set m_names; }; using cooked_index_shard_up = std::unique_ptr; diff --git a/gdbsupport/string-set.h b/gdbsupport/string-set.h new file mode 100644 index 00000000000..c2507454650 --- /dev/null +++ b/gdbsupport/string-set.h @@ -0,0 +1,129 @@ +/* String-interning set + + Copyright (C) 2025 Free Software Foundation, Inc. + + This file is part of GDB. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +#ifndef GDBSUPPORT_STRING_SET_H +#define GDBSUPPORT_STRING_SET_H + +#include "gdbsupport/unordered_set.h" +#include + +namespace gdb +{ + +/* This is a string-interning set. It manages storage for strings, + ensuring that just a single copy of a given string is kept. The + underlying C string will remain valid for the lifetime of this + object. */ + +class string_set +{ +public: + + /* Insert STR into this set. Returns a pointer to the interned + string. */ + const char *insert (const char *str) + { + /* We need to take the length to hash the string anyway, so it's + convenient to just wrap it here. */ + return insert (std::string_view (str)); + } + + /* An overload accepting a string view. */ + const char *insert (std::string_view str) + { + return m_set.insert (str).first->get (); + } + + /* An overload that takes ownership of the string. */ + const char *insert (gdb::unique_xmalloc_ptr str) + { + return m_set.insert (local_string (std::move (str))).first->get (); + } + +private: + + /* The type of string we store. Note that we do not store + std::string here to avoid the small-string optimization + invalidating a pointer on rehash. */ + struct local_string + { + explicit local_string (std::string_view str) + : contents (xstrndup (str.data (), str.size ())), + len (str.size ()) + { } + + explicit local_string (gdb::unique_xmalloc_ptr str) + : contents (std::move (str)), + len (strlen (contents.get ())) + { } + + const char *get () const + { return contents.get (); } + + std::string_view as_view () const + { return std::string_view (contents.get (), len); } + + /* \0-terminated string contents. */ + gdb::unique_xmalloc_ptr contents; + /* Length of the string. */ + size_t len; + }; + + /* Equality object for the set. */ + struct str_eq + { + using is_transparent = void; + + bool operator() (std::string_view lhs, const local_string &rhs) + const noexcept + { + return lhs == rhs.as_view (); + } + + bool operator() (const local_string &lhs, const local_string &rhs) + const noexcept + { + return (*this) (lhs.as_view (), rhs); + } + }; + + /* Hash object for the set. */ + struct str_hash + { + using is_transparent = void; + using is_avalanching = void; + + bool operator() (const local_string &rhs) const noexcept + { + return (*this) (rhs.as_view ()); + } + + bool operator() (std::string_view rhs) const noexcept + { + return ankerl::unordered_dense::hash () (rhs); + } + }; + + /* The strings. */ + gdb::unordered_set m_set; +}; + +} + +#endif /* GDBSUPPORT_STRING_SET_H */