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, 6 insertions, 4 deletions

diff --git a/gdb/cp-abi.h b/gdb/cp-abi.h
index 3cbf19c..cc77e0b 100644
--- a/gdb/cp-abi.h
+++ b/gdb/cp-abi.h
@@ -207,9 +207,11 @@ extern std::string cplus_typename_from_type_info (struct value *value);
 CORE_ADDR cplus_skip_trampoline (struct frame_info *frame,
 				 CORE_ADDR stop_pc);
 
-/* Return non-zero if an argument of type TYPE should be passed by
-   reference instead of value.  */
-extern int cp_pass_by_reference (struct type *type);
+/* Return a struct that provides pass-by-reference information
+   about the given TYPE.  */
+
+extern struct language_pass_by_ref_info cp_pass_by_reference
+  (struct type *type);
 
 struct cp_abi_ops
 {
@@ -246,7 +248,7 @@ struct cp_abi_ops
   struct type *(*get_type_from_type_info) (struct value *value);
   std::string (*get_typename_from_type_info) (struct value *value);
   CORE_ADDR (*skip_trampoline) (struct frame_info *, CORE_ADDR);
-  int (*pass_by_reference) (struct type *type);
+  struct language_pass_by_ref_info (*pass_by_reference) (struct type *type);
 };