Speed up psymbol reading by removing a copy

I noticed that cp_canonicalize_string and friends copy a
unique_xmalloc_ptr to a std::string.  However, this copy isn't
genuinely needed anywhere, and it serves to slow down DWARF psymbol
reading.

This patch removes the copy and updates the callers to adapt.

This speeds up the reader from 1.906 seconds (mean of 10 runs, of gdb
on a copy of itself) to 1.888 seconds (mean of 10 runs, on the same
copy as the first trial).

gdb/ChangeLog
2020-05-08  Tom Tromey  <tom@tromey.com>

	* symtab.h (class demangle_result_storage) <set_malloc_ptr>: New
	overload.
	<swap_string, m_string>: Remove.
	* symtab.c (demangle_for_lookup, completion_list_add_symbol):
	Update.
	* stabsread.c (define_symbol, read_type): Update.
	* linespec.c (find_linespec_symbols): Update.
	* gnu-v3-abi.c (gnuv3_get_typeid): Update.
	* dwarf2/read.c (dwarf2_canonicalize_name): Update.
	* dbxread.c (read_dbx_symtab): Update.
	* cp-support.h (cp_canonicalize_string_full)
	(cp_canonicalize_string, cp_canonicalize_string_no_typedefs):
	Return unique_xmalloc_ptr.
	* cp-support.c (inspect_type): Update.
	(cp_canonicalize_string_full): Return unique_xmalloc_ptr.
	(cp_canonicalize_string_no_typedefs, cp_canonicalize_string):
	Likewise.
	* c-typeprint.c (print_name_maybe_canonical): Update.
	* break-catch-throw.c (check_status_exception_catchpoint):
	Update.

1 files changed, 6 insertions, 6 deletions

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 652384c..ffd9707 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -1838,9 +1838,9 @@ demangle_for_lookup (const char *name, enum language lang,
 
       /* If we were given a non-mangled name, canonicalize it
 	 according to the language (so far only for C++).  */
-      std::string canon = cp_canonicalize_string (name);
-      if (!canon.empty ())
-	return storage.swap_string (canon);
+      gdb::unique_xmalloc_ptr<char> canon = cp_canonicalize_string (name);
+      if (canon != nullptr)
+	return storage.set_malloc_ptr (std::move (canon));
     }
   else if (lang == language_d)
     {
@@ -5349,10 +5349,10 @@ completion_list_add_symbol (completion_tracker &tracker,
       /* The call to canonicalize returns the empty string if the input
 	 string is already in canonical form, thanks to this we don't
 	 remove the symbol we just added above.  */
-      std::string str
+      gdb::unique_xmalloc_ptr<char> str
 	= cp_canonicalize_string_no_typedefs (sym->natural_name ());
-      if (!str.empty ())
-	tracker.remove_completion (str.c_str ());
+      if (str != nullptr)
+	tracker.remove_completion (str.get ());
     }
 }