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, 8 insertions, 6 deletions

diff --git a/gdb/gnu-v3-abi.c b/gdb/gnu-v3-abi.c
index 7055843..83deed5 100644
--- a/gdb/gnu-v3-abi.c
+++ b/gdb/gnu-v3-abi.c
@@ -1090,7 +1090,8 @@ gnuv3_get_typeid (struct value *value)
   struct type *type;
   struct gdbarch *gdbarch;
   struct value *result;
-  std::string type_name, canonical;
+  std::string type_name;
+  gdb::unique_xmalloc_ptr<char> canonical;
 
   /* We have to handle values a bit trickily here, to allow this code
      to work properly with non_lvalue values that are really just
@@ -1118,8 +1119,9 @@ gnuv3_get_typeid (struct value *value)
      uses.  E.g., GDB tends to use "const char *" as a type name, but
      the demangler uses "char const *".  */
   canonical = cp_canonicalize_string (type_name.c_str ());
-  if (!canonical.empty ())
-    type_name = canonical;
+  const char *name = (canonical == nullptr
+		      ? type_name.c_str ()
+		      : canonical.get ());
 
   typeinfo_type = gnuv3_get_typeid_type (gdbarch);
 
@@ -1135,19 +1137,19 @@ gnuv3_get_typeid (struct value *value)
       vtable = gnuv3_get_vtable (gdbarch, type, address);
       if (vtable == NULL)
 	error (_("cannot find typeinfo for object of type '%s'"),
-	       type_name.c_str ());
+	       name);
       typeinfo_value = value_field (vtable, vtable_field_type_info);
       result = value_ind (value_cast (make_pointer_type (typeinfo_type, NULL),
 				      typeinfo_value));
     }
   else
     {
-      std::string sym_name = std::string ("typeinfo for ") + type_name;
+      std::string sym_name = std::string ("typeinfo for ") + name;
       bound_minimal_symbol minsym
 	= lookup_minimal_symbol (sym_name.c_str (), NULL, NULL);
 
       if (minsym.minsym == NULL)
-	error (_("could not find typeinfo symbol for '%s'"), type_name.c_str ());
+	error (_("could not find typeinfo symbol for '%s'"), name);
 
       result = value_at_lazy (typeinfo_type, BMSYMBOL_VALUE_ADDRESS (minsym));
     }