[PATCH] Speed up psymbol reading by removing a copy

[Tom Tromey]

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
2020-04-04  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.
---
 gdb/ChangeLog           | 23 +++++++++++++++++++++++
 gdb/break-catch-throw.c |  2 +-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/gdb/break-catch-throw.c b/gdb/break-catch-throw.c
index 7c684de40b6..59293c4e570 100644
--- a/gdb/break-catch-throw.c
+++ b/gdb/break-catch-throw.c
@@ -148,7 +148,6 @@ check_status_exception_catchpoint (struct bpstats *bs)
   struct exception_catchpoint *self
     = (struct exception_catchpoint *) bs->breakpoint_at;
   std::string type_name;
-  gdb::unique_xmalloc_ptr<char> canon;
 
   bkpt_breakpoint_ops.check_status (bs);
   if (bs->stop == 0)
@@ -158,6 +157,7 @@ check_status_exception_catchpoint (struct bpstats *bs)
     return;
 
   const char *name = nullptr;
+  gdb::unique_xmalloc_ptr<char> canon;
   try
     {
       struct value *typeinfo_arg;
-- 
2.17.2