[PATCH v2 2/2] Precompute hash value for symbol_set_names

["Christian Biesinger via gdb-patches" <gdb-patches@sourceware.org>]

We can also compute the hash for the mangled name on a background
thread so make this function even faster (about a 7% speedup).

gdb/ChangeLog:

2019-10-03  Christian Biesinger  <cbiesinger@google.com>

	* minsyms.c (minimal_symbol_reader::install): Also compute the hash
	of the mangled name on the background thread.
	* symtab.c (symbol_set_names): Allow passing in the hash of the
	linkage_name.
	* symtab.h (symbol_set_names): Likewise.
---
 gdb/minsyms.c | 12 +++++++++++-
 gdb/symtab.c  |  8 +++++---
 gdb/symtab.h  |  7 +++++--
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/gdb/minsyms.c b/gdb/minsyms.c
index 95ca9f6c93..b60381a0c9 100644
--- a/gdb/minsyms.c
+++ b/gdb/minsyms.c
@@ -1342,6 +1342,11 @@ minimal_symbol_reader::install ()
       std::mutex demangled_mutex;
 #endif
 
+      struct computed_hash_values {
+	hashval_t mangled_name_hash;
+      };
+      std::vector<computed_hash_values> hash_values (mcount);
+
       msymbols = m_objfile->per_bfd->msymbols.get ();
       gdb::parallel_for_each
 	(&msymbols[0], &msymbols[mcount],
@@ -1361,6 +1366,9 @@ minimal_symbol_reader::install ()
 		   symbol_set_demangled_name (msym, demangled_name,
 					      &m_objfile->per_bfd->storage_obstack);
 		   msym->name_set = 1;
+
+		   size_t idx = msym - msymbols;
+		   hash_values[idx].mangled_name_hash = htab_hash_string (msym->name);
 		 }
 	     }
 	   {
@@ -1371,9 +1379,11 @@ minimal_symbol_reader::install ()
 #endif
 	     for (minimal_symbol *msym = start; msym < end; ++msym)
 	       {
+		 size_t idx = msym - msymbols;
 		 symbol_set_names (msym, msym->name,
 				   strlen (msym->name), 0,
-				   m_objfile->per_bfd);
+				   m_objfile->per_bfd,
+				   hash_values[idx].mangled_name_hash);
 	       }
 	   }
 	 });
diff --git a/gdb/symtab.c b/gdb/symtab.c
index 47da5cf4e8..40cc34b205 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -808,7 +808,7 @@ symbol_find_demangled_name (struct general_symbol_info *gsymbol,
 void
 symbol_set_names (struct general_symbol_info *gsymbol,
 		  const char *linkage_name, int len, bool copy_name,
-		  struct objfile_per_bfd_storage *per_bfd)
+		  struct objfile_per_bfd_storage *per_bfd, hashval_t hash)
 {
   struct demangled_name_entry **slot;
   /* A 0-terminated copy of the linkage name.  */
@@ -854,9 +854,11 @@ symbol_set_names (struct general_symbol_info *gsymbol,
     create_demangled_names_hash (per_bfd);
 
   entry.mangled = linkage_name_copy;
+  if (hash == 0)
+    hash = hash_demangled_name_entry (&entry);
   slot = ((struct demangled_name_entry **)
-          htab_find_slot (per_bfd->demangled_names_hash.get (),
-      		    &entry, INSERT));
+          htab_find_slot_with_hash (per_bfd->demangled_names_hash.get (),
+				    &entry, hash, INSERT));
 
   /* If this name is not in the hash table, add it.  */
   if (*slot == NULL
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 17903df92d..2814f401fe 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -502,13 +502,16 @@ extern char *symbol_find_demangled_name (struct general_symbol_info *gsymbol,
   (symbol)->ginfo.name = (linkage_name)
 
 /* Set the linkage and natural names of a symbol, by demangling
-   the linkage name.  */
+   the linkage name.  Optionally, HASH can be set to the value
+   of htab_hash_string (linkage_name) (if nullterminated), to
+   speed up this function.  */
 #define SYMBOL_SET_NAMES(symbol,linkage_name,len,copy_name,objfile)	\
   symbol_set_names (&(symbol)->ginfo, linkage_name, len, copy_name, \
 		    (objfile)->per_bfd)
 extern void symbol_set_names (struct general_symbol_info *symbol,
 			      const char *linkage_name, int len, bool copy_name,
-			      struct objfile_per_bfd_storage *per_bfd);
+			      struct objfile_per_bfd_storage *per_bfd,
+			      hashval_t hash = 0);
 
 /* Now come lots of name accessor macros.  Short version as to when to
    use which: Use SYMBOL_NATURAL_NAME to refer to the name of the
-- 
2.23.0.444.g18eeb5a265-goog