Avoid copying in lookup_name_info

lookup_name_info always copies the name that is passed in.  However,
normally a copy is not needed.  This patch changes this class to avoid
copying.  This required changing the "name" method to return something
else; I chose a gdb::string_view, to avoid excessive calls to strlen
in the code using the lookup_name_info.  However, as this class does
not allow an arbitrary string_view, I've also added a c_str method
that guarantees a \0-terminated result -- a pedantic difference but
one that respects the string_view contract, IMO.

gdb/ChangeLog
2020-04-01  Tom Tromey  <tromey@adacore.com>

	* symtab.h (class lookup_name_info) <lookup_name_info>: Change
	"name" parameter to rvalue reference.  Initialize m_name_holder.
	<lookup_name_info>: New overloads.
	<name>: Return gdb::string_view.
	<c_str>: New method.
	<make_ignore_params>: Update.
	<search_name_hash>: Update.
	<language_lookup_name>: Return const char *.
	<m_name>: Change type.
	* symtab.c (demangle_for_lookup_info::demangle_for_lookup_info)
	(demangle_for_lookup_info::demangle_for_lookup_info): Update.
	(lookup_name_info::match_any): Update.
	* psymtab.c (match_partial_symbol, lookup_partial_symbol):
	Update.
	* minsyms.c (linkage_name_str): Update.
	* language.c (default_symbol_name_matcher): Update.
	* dwarf2/read.c (mapped_index_base::find_name_components_bounds):
	Update.
	* ada-lang.c (ada_fold_name): Change parameter to string_view.
	(ada_lookup_name_info::ada_lookup_name_info): Update.
	(literal_symbol_name_matcher): Update.

1 files changed, 42 insertions, 13 deletions

diff --git a/gdb/symtab.h b/gdb/symtab.h
index 18be5d5..77f60e6 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -185,29 +185,58 @@ private:
 class lookup_name_info final
 {
  public:
-  /* Create a new object.  */
-  lookup_name_info (std::string name,
+  /* We delete this overload so that the callers are required to
+     explicitly handle the lifetime of the name.  */
+  lookup_name_info (std::string &&name,
+		    symbol_name_match_type match_type,
+		    bool completion_mode = false,
+		    bool ignore_parameters = false) = delete;
+
+  /* This overload requires that NAME have a lifetime at least as long
+     as the lifetime of this object.  */
+  lookup_name_info (const std::string &name,
+		    symbol_name_match_type match_type,
+		    bool completion_mode = false,
+		    bool ignore_parameters = false)
+    : m_match_type (match_type),
+      m_completion_mode (completion_mode),
+      m_ignore_parameters (ignore_parameters),
+      m_name (name)
+  {}
+
+  /* This overload requires that NAME have a lifetime at least as long
+     as the lifetime of this object.  */
+  lookup_name_info (const char *name,
 		    symbol_name_match_type match_type,
 		    bool completion_mode = false,
 		    bool ignore_parameters = false)
     : m_match_type (match_type),
       m_completion_mode (completion_mode),
       m_ignore_parameters (ignore_parameters),
-      m_name (std::move (name))
+      m_name (name)
   {}
 
   /* Getters.  See description of each corresponding field.  */
   symbol_name_match_type match_type () const { return m_match_type; }
   bool completion_mode () const { return m_completion_mode; }
-  const std::string &name () const { return m_name; }
+  gdb::string_view name () const { return m_name; }
   const bool ignore_parameters () const { return m_ignore_parameters; }
 
+  /* Like the "name" method but guarantees that the returned string is
+     \0-terminated.  */
+  const char *c_str () const
+  {
+    /* Actually this is always guaranteed due to how the class is
+       constructed.  */
+    return m_name.data ();
+  }
+
   /* Return a version of this lookup name that is usable with
      comparisons against symbols have no parameter info, such as
      psymbols and GDB index symbols.  */
   lookup_name_info make_ignore_params () const
   {
-    return lookup_name_info (m_name, m_match_type, m_completion_mode,
+    return lookup_name_info (c_str (), m_match_type, m_completion_mode,
 			     true /* ignore params */);
   }
 
@@ -218,27 +247,27 @@ class lookup_name_info final
     if (!m_demangled_hashes_p[lang])
       {
 	m_demangled_hashes[lang]
-	  = ::search_name_hash (lang, language_lookup_name (lang).c_str ());
+	  = ::search_name_hash (lang, language_lookup_name (lang));
 	m_demangled_hashes_p[lang] = true;
       }
     return m_demangled_hashes[lang];
   }
 
   /* Get the search name for searches in language LANG.  */
-  const std::string &language_lookup_name (language lang) const
+  const char *language_lookup_name (language lang) const
   {
     switch (lang)
       {
       case language_ada:
-	return ada ().lookup_name ();
+	return ada ().lookup_name ().c_str ();
       case language_cplus:
-	return cplus ().lookup_name ();
+	return cplus ().lookup_name ().c_str ();
       case language_d:
-	return d ().lookup_name ();
+	return d ().lookup_name ().c_str ();
       case language_go:
-	return go ().lookup_name ();
+	return go ().lookup_name ().c_str ();
       default:
-	return m_name;
+	return m_name.data ();
       }
   }
 
@@ -287,7 +316,7 @@ private:
   symbol_name_match_type m_match_type;
   bool m_completion_mode;
   bool m_ignore_parameters;
-  std::string m_name;
+  gdb::string_view m_name;
 
   /* Language-specific info.  These fields are filled lazily the first
      time a lookup is done in the corresponding language.  They're