infcall, c++: allow more info to be computed for pass-by-reference values

In C++, call-by-value arguments that cannot be trivially copied are
implicitly passed by reference.  When making an infcall, GDB needs to
find out if an argument is pass-by-reference or not, so that the
correct semantics can be followed.  This patch enriches the
information computed by the language ops for pass-by-reference
arguments.  Instead of a plain binary result, the computed information
now includes whether the argument is

  - copy constructible
  - destructible
  - trivially copyable
  - trivially copy constructible
  - trivially destructible

This information is stored in a struct named 'language_pass_by_ref_info'.

This patch paves the way for GDB's infcall mechanism to call the copy
ctor and the destructor of a pass-by-ref argument appropriately.

gdb/ChangeLog:
2019-12-20  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* language.h (struct language_pass_by_ref_info): New struct.
	(struct language_defn)<la_pass_by_reference>: Change the signature
	to return a language_pass_by_ref_info instead of an int.
	(language_pass_by_reference): Ditto.
	(default_pass_by_reference): Ditto.
	Adjust the users listed below.
	* arch-utils.c (default_return_in_first_hidden_param_p):
	Update.
	* cp-abi.c (cp_pass_by_reference): Update.
	* cp-abi.h (cp_pass_by_reference): Update declaration.
	(struct cp_abi_ops)<pass_by_reference>: Update.
	* gnu-v3-abi.c (gnuv3_pass_by_reference): Update.
	* infcall.c (call_function_by_hand_dummy): Update.
	* language.c (language_pass_by_reference): Update.
	(default_pass_by_reference): Update.
	* tic6x-tdep.c (tic6x_return_value): Update.

Change-Id: Ib1c1f87f2490a5737c469f7b7185ddc7f6a164cb

1 files changed, 2 insertions, 1 deletions

diff --git a/gdb/infcall.c b/gdb/infcall.c
index 5553fc9..f3664d5 100644
--- a/gdb/infcall.c
+++ b/gdb/infcall.c
@@ -1020,7 +1020,8 @@ call_function_by_hand_dummy (struct value *function,
       args[i] = value_arg_coerce (gdbarch, args[i],
 				  param_type, prototyped);
 
-      if (param_type != NULL && language_pass_by_reference (param_type))
+      if (param_type != NULL
+	  && !(language_pass_by_reference (param_type).trivially_copyable))
 	args[i] = value_addr (args[i]);
     }