* calls.c (expand_call): Try to do a tail call for thunks at -O0 too.
	* cgraph.h (struct cgraph_thunk_info): Add indirect_offset.
	(cgraph_node::create_thunk): Add indirect_offset parameter.
	(thunk_adjust): Likewise.
	* cgraph.c (cgraph_node::create_thunk): Add indirect_offset parameter
	and initialize the corresponding field with it.
	(cgraph_node::dump): Dump indirect_offset field.
	* cgraphclones.c (duplicate_thunk_for_node): Deal with indirect_offset.
	* cgraphunit.c (cgraph_node::analyze): Be prepared for external thunks.
	(thunk_adjust): Add indirect_offset parameter and deal with it.
	(cgraph_node::expand_thunk): Deal with the indirect_offset field and
	pass it to thunk_adjust.  Do not call the target hook if it's non-zero
	or if the thunk is external or local.  Fix formatting.  Do not chain
	the RESULT_DECL to BLOCK_VARS.  Pass the static chain to the target,
	if any, in the GIMPLE representation.
	* ipa-icf.c (sem_function::equals_wpa): Deal with indirect_offset.
	* lto-cgraph.c (lto_output_node): Write indirect_offset field.
	(input_node): Read indirect_offset field.
	* tree-inline.c (expand_call_inline): Pass indirect_offset field in the
	call to thunk_adjust.
	* tree-nested.c (struct nesting_info): Add thunk_p field.
	(create_nesting_tree): Set it.
	(convert_all_function_calls): Copy static chain from targets to thunks.
	(finalize_nesting_tree_1): Return early for thunks.
	(unnest_nesting_tree_1): Do not finalize thunks.
	(gimplify_all_functions): Do not gimplify thunks.
cp/
	* method.c (use_thunk): Adjust call to cgraph_node::create_thunk.
ada/
	* gcc-interface/decl.c (is_cplusplus_method): Do not require C++
	convention on Interfaces.
	* gcc-interface/trans.c (Subprogram_Body_to_gnu): Try to create a
	bona-fide thunk and hand it over to the middle-end.
	(get_controlling_type): New function.
	(use_alias_for_thunk_p): Likewise.
	(thunk_labelno): New static variable.
	(make_covariant_thunk): New function.
	(maybe_make_gnu_thunk): Likewise.
	* gcc-interface/utils.c (finish_subprog_decl): Set DECL_CONTEXT of the
	result DECL here instead of...
	(end_subprog_body): ...here.

Co-Authored-By: Pierre-Marie de Rodat <derodat@adacore.com>

From-SVN: r264701