Precompute hash value for symbol_set_names

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:

2019-11-27  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.

Change-Id: I044449e7eb60cffc1c43efd3412f2b485bd9faac

4 files changed, 42 insertions, 6 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 0816e73..c278a77 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2019-11-27  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.
+
 2019-11-27  Kevin Buettner  <kevinb@redhat.com>
 
 	* dwarf2read.c (inherit_abstract_dies): Ensure that delayed
diff --git a/gdb/minsyms.c b/gdb/minsyms.c
index 03a1932..141c3d2 100644
--- a/gdb/minsyms.c
+++ b/gdb/minsyms.c
@@ -1258,6 +1258,16 @@ clear_minimal_symbol_hash_tables (struct objfile *objfile)
     }
 }
 
+/* This struct is used to store values we compute for msymbols on the
+   background threads but don't need to keep around long term.  */
+struct computed_hash_values
+{
+  /* Length of the linkage_name of the symbol.  */
+  size_t name_length;
+  /* Hash code (using fast_hash) of the linkage_name.  */
+  hashval_t mangled_name_hash;
+};
+
 /* Build (or rebuild) the minimal symbol hash tables.  This is necessary
    after compacting or sorting the table since the entries move around
    thus causing the internal minimal_symbol pointers to become jumbled.  */
@@ -1370,6 +1380,8 @@ minimal_symbol_reader::install ()
       std::mutex demangled_mutex;
 #endif
 
+      std::vector<computed_hash_values> hash_values (mcount);
+
       msymbols = m_objfile->per_bfd->msymbols.get ();
       gdb::parallel_for_each
 	(&msymbols[0], &msymbols[mcount],
@@ -1377,6 +1389,8 @@ minimal_symbol_reader::install ()
 	 {
 	   for (minimal_symbol *msym = start; msym < end; ++msym)
 	     {
+	       size_t idx = msym - msymbols;
+	       hash_values[idx].name_length = strlen (msym->name);
 	       if (!msym->name_set)
 		 {
 		   /* This will be freed later, by symbol_set_names.  */
@@ -1386,6 +1400,9 @@ minimal_symbol_reader::install ()
 		     (msym, demangled_name,
 		      &m_objfile->per_bfd->storage_obstack);
 		   msym->name_set = 1;
+
+		   hash_values[idx].mangled_name_hash
+		     = fast_hash (msym->name, hash_values[idx].name_length);
 		 }
 	     }
 	   {
@@ -1396,8 +1413,14 @@ minimal_symbol_reader::install ()
 #endif
 	     for (minimal_symbol *msym = start; msym < end; ++msym)
 	       {
-		 symbol_set_names (msym, msym->name, false,
-				   m_objfile->per_bfd);
+		 size_t idx = msym - msymbols;
+		 symbol_set_names
+		   (msym,
+		    gdb::string_view(msym->name,
+				     hash_values[idx].name_length),
+		    false,
+		    m_objfile->per_bfd,
+		    hash_values[idx].mangled_name_hash);
 	       }
 	   }
 	 });
diff --git a/gdb/symtab.c b/gdb/symtab.c
index 8f46321..894a323 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -836,7 +836,8 @@ symbol_find_demangled_name (struct general_symbol_info *gsymbol,
 void
 symbol_set_names (struct general_symbol_info *gsymbol,
 		  gdb::string_view linkage_name, bool copy_name,
-		  struct objfile_per_bfd_storage *per_bfd)
+		  struct objfile_per_bfd_storage *per_bfd,
+		  gdb::optional<hashval_t> hash)
 {
   struct demangled_name_entry **slot;
 
@@ -864,9 +865,11 @@ symbol_set_names (struct general_symbol_info *gsymbol,
     create_demangled_names_hash (per_bfd);
 
   struct demangled_name_entry entry (linkage_name);
+  if (!hash.has_value ())
+    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 7a51456..4cfdf06 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -553,7 +553,9 @@ extern char *symbol_find_demangled_name (struct general_symbol_info *gsymbol,
 		    (objfile)->per_bfd)
 extern void symbol_set_names (struct general_symbol_info *symbol,
 			      gdb::string_view linkage_name, bool copy_name,
-			      struct objfile_per_bfd_storage *per_bfd);
+			      struct objfile_per_bfd_storage *per_bfd,
+			      gdb::optional<hashval_t> hash
+			        = gdb::optional<hashval_t> ());
 
 /* Return true if NAME matches the "search" name of SYMBOL, according
    to the symbol's language.  */