c++: Copy over DECL_DISREGARD_INLINE_LIMITS flag to inheriting ctors [PR114784]

c++: Copy over DECL_DISREGARD_INLINE_LIMITS flag to inheriting ctors [PR114784]

The following testcase is rejected with
error: inlining failed in call to 'always_inline' '...': call is unlikely and code size would grow
errors.  The problem is that starting with the r14-2149 change
we try to copy most of the attributes from the inherited to
inheriting ctor, but don't copy associated flags that decl_attributes
sets.

Now, the other clone_attrs user, cp/optimize.cc (maybe_clone_body)
copies over
      DECL_COMDAT (clone) = DECL_COMDAT (fn);
      DECL_WEAK (clone) = DECL_WEAK (fn);
      if (DECL_ONE_ONLY (fn))
        cgraph_node::get_create (clone)->set_comdat_group (cxx_comdat_group (clone));
      DECL_USE_TEMPLATE (clone) = DECL_USE_TEMPLATE (fn);
      DECL_EXTERNAL (clone) = DECL_EXTERNAL (fn);
      DECL_INTERFACE_KNOWN (clone) = DECL_INTERFACE_KNOWN (fn);
      DECL_NOT_REALLY_EXTERN (clone) = DECL_NOT_REALLY_EXTERN (fn);
      DECL_VISIBILITY (clone) = DECL_VISIBILITY (fn);
      DECL_VISIBILITY_SPECIFIED (clone) = DECL_VISIBILITY_SPECIFIED (fn);
      DECL_DLLIMPORT_P (clone) = DECL_DLLIMPORT_P (fn);
      DECL_DISREGARD_INLINE_LIMITS (clone) = DECL_DISREGARD_INLINE_LIMITS (fn);
The following patch just copies DECL_DISREGARD_INLINE_LIMITS to fix
this exact bug, not really sure which other flags should be copied
and which shouldn't.
Plus there are tons of other flags, some of which might need to be copied
too, some of which might not, perhaps in both places, like:
DECL_UNINLINABLE, maybe DECL_PRESERVE_P, TREE_USED, maybe
DECL_USER_ALIGN/DECL_ALIGN, maybe DECL_WEAK, maybe
DECL_NO_INSTRUMENT_FUNCTION_ENTRY_EXIT, DECL_NO_LIMIT_STACK.
TREE_READONLY, DECL_PURE_P, TREE_THIS_VOLATILE (for const, pure and
noreturn attributes) probably makes no sense, DECL_IS_RETURNS_TWICE neither
(returns_twice ctor?).  What about TREE_NOTHROW?
DECL_FUNCTION_SPECIFIC_OPTIMIZATION, DECL_FUNCTION_SPECIFIC_TARGET...

Anyway, another problem is that if inherited_ctor is a TEMPLATE_DECL, as
also can be seen in the using D<T>::D; case in the testcase, then
DECL_ATTRIBUTES (fn) = clone_attrs (DECL_ATTRIBUTES (inherited_ctor));
attempts to copy the attributes from the TEMPLATE_DECL which doesn't have
them.  The following patch copies them from STRIP_TEMPLATE (inherited_ctor)
which does.  E.g. DECL_DECLARED_CONSTEXPR_P works fine as the macro
itself uses STRIP_TEMPLATE too, but not 100% sure about other macros used
on inherited_ctor earlier.

2024-04-23  Jakub Jelinek  <jakub@redhat.com>

	PR c++/114784
	* method.cc (implicitly_declare_fn): Call clone_attrs
	on DECL_ATTRIBUTES on STRIP_TEMPLATE (inherited_ctor) rather than
	inherited_ctor.  Also copy DECL_DISREGARD_INLINE_LIMITS flag from it.

	* g++.dg/cpp0x/inh-ctor39.C: New test.