[PATCH] gdb: remove unneeded switch_to_thread from thr_try_catch_cmd

[Andrew Burgess]

I spotted that every time thr_try_catch_cmd is called GDB has already
switched to the required thread.  The call to switch_to_thread at the
head of thr_try_catch_cmd is therefore redundant.

This commit replaces the call to switch_to_thread with an assertion
that we already have the required thread selected.

I also extended the header comment on thr_try_catch_cmd to make it
clearer when this function could throw an exception.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* thread.c (thr_try_catch_cmd): Replace swith_to_thread with an
	assert.  Extend the header comment.
---
 gdb/ChangeLog | 5 +++++
 gdb/thread.c  | 7 ++++---
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/gdb/thread.c b/gdb/thread.c
index 899c2116470..82107067217 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -1466,15 +1466,16 @@ tp_array_compar_descending (const thread_info_ref &a, const thread_info_ref &b)
   return (a->per_inf_num > b->per_inf_num);
 }
 
-/* Switch to thread THR and execute CMD.
+/* Assuming that THR is the current thread, execute CMD.
    FLAGS.QUIET controls the printing of the thread information.
-   FLAGS.CONT and FLAGS.SILENT control how to handle errors.  */
+   FLAGS.CONT and FLAGS.SILENT control how to handle errors.  Can throw an
+   exception if !FLAGS.SILENT and !FLAGS.CONT and CMD fails.  */
 
 static void
 thr_try_catch_cmd (thread_info *thr, const char *cmd, int from_tty,
 		   const qcs_flags &flags)
 {
-  switch_to_thread (thr);
+  gdb_assert (is_current_thread (thr));
 
   /* The thread header is computed before running the command since
      the command can change the inferior, which is not permitted
-- 
2.25.4