arm: Fix up arm_override_options_after_change [PR96939]

arm: Fix up arm_override_options_after_change [PR96939]

As mentioned in the PR, the testcase fails to link, because when set_cfun is
being called on the crc function, arm_override_options_after_change is
called from set_cfun -> invoke_set_current_function_hook:
      /* Change optimization options if needed.  */
      if (optimization_current_node != opts)
        {
          optimization_current_node = opts;
          cl_optimization_restore (&global_options, TREE_OPTIMIZATION (opts));
        }
and at that point target_option_default_node actually matches even the
current state of options, so this means armv7 (or whatever) arch is set as
arm_active_target, then
      targetm.set_current_function (fndecl);
is called later in that function, which because the crc function's
DECL_FUNCTION_SPECIFIC_TARGET is different from the current one will do:
  cl_target_option_restore (&global_options, TREE_TARGET_OPTION (new_tree));
which calls arm_option_restore and sets arm_active_target to armv8-a+crc
(so far so good).
Later arm_set_current_function calls:
  save_restore_target_globals (new_tree);
which in this case calls:
      /* Call target_reinit and save the state for TARGET_GLOBALS.  */
      TREE_TARGET_GLOBALS (new_tree) = save_target_globals_default_opts ();
which because optimization_current_node != optimization_default_node
(the testcase is LTO, so all functions have their
DECL_FUNCTION_SPECIFIC_TARGET and TREE_OPTIMIZATION nodes) will call:
      cl_optimization_restore
        (&global_options,
         TREE_OPTIMIZATION (optimization_default_node));
and
      cl_optimization_restore (&global_options,
                               TREE_OPTIMIZATION (opts));
The problem is that these call arm_override_options_after_change again,
and that one uses the target_option_default_node as what to set the
arm_active_target to (i.e. back to armv7 or whatever, but not to the
armv8-a+crc that should be the active target for the crc function).
That means we then error on the builtin call in that function.

Now, the targetm.override_options_after_change hook is called always at the
end of cl_optimization_restore, i.e. when we change the Optimization marked
generic options.  So it seems unnecessary to call arm_configure_build_target
at that point (nothing it depends on changed), and additionally incorrect
(because it uses the target_option_default_node, rather than the current
set of options; we'd need to revert
https://gcc.gnu.org/legacy-ml/gcc-patches/2016-12/msg01390.html
otherwise so that it works again with global_options otherwise).
The options that arm_configure_build_target cares about will change only
during option parsing (which is where it is called already), or during
arm_set_current_function, where it is done during the
cl_target_option_restore.
Now, arm_override_options_after_change_1 wants to adjust the
str_align_functions, which depends on the current Optimization options (e.g.
optimize_size and flag_align_options and str_align_functions) as well as
the target options target_flags, so IMHO needs to be called both
when the Optimization options (possibly) change, i.e. from
the targetm.override_options_after_change hook, and from when the target
options change (set_current_function hook).

2020-09-10  Jakub Jelinek  <jakub@redhat.com>

	PR target/96939
	* config/arm/arm.c (arm_override_options_after_change): Don't call
	arm_configure_build_target here.
	(arm_set_current_function): Call arm_override_options_after_change_1
	at the end.

	* gcc.target/arm/lto/pr96939_0.c: New test.
	* gcc.target/arm/lto/pr96939_1.c: New file.