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, 10 insertions, 8 deletions

diff --git a/gdb/language.c b/gdb/language.c
index 76efc49..ac74c7f 100644
--- a/gdb/language.c
+++ b/gdb/language.c
@@ -652,21 +652,23 @@ language_class_name_from_physname (const struct language_defn *lang,
   return NULL;
 }
 
-/* Return non-zero if TYPE should be passed (and returned) by
-   reference at the language level.  */
-int
+/* Return information about whether TYPE should be passed
+   (and returned) by reference at the language level.  */
+
+struct language_pass_by_ref_info
 language_pass_by_reference (struct type *type)
 {
   return current_language->la_pass_by_reference (type);
 }
 
-/* Return zero; by default, types are passed by value at the language
-   level.  The target ABI may pass or return some structs by reference
-   independent of this.  */
-int
+/* Return a default struct that provides pass-by-reference information
+   about the given TYPE.  Languages should update the default values
+   as appropriate.  */
+
+struct language_pass_by_ref_info
 default_pass_by_reference (struct type *type)
 {
-  return 0;
+  return {};
 }
 
 /* Return the default string containing the list of characters