This is the common infrastructure part.  As explained in the initial message, 
nothing is activated unless both the language and the target opt in.


2016-07-04  Eric Botcazou  <ebotcazou@adacore.com>

	PR ada/37139
	PR ada/67205
	* common.opt (-ftrampolines): New option.
	* doc/invoke.texi (Code Gen Options): Document it.
	* doc/tm.texi.in (Trampolines): AddTARGET_CUSTOM_FUNCTION_DESCRIPTORS
	* doc/tm.texi: Regenerate.
	* builtins.def: Add init_descriptor and adjust_descriptor.
	* builtins.c (expand_builtin_init_trampoline): Do not issue a warning
	on platforms with descriptors.
	(expand_builtin_init_descriptor): New function.
	(expand_builtin_adjust_descriptor): Likewise.
	(expand_builtin) <BUILT_IN_INIT_DESCRIPTOR>: New case.
	<BUILT_IN_ADJUST_DESCRIPTOR>: Likewise.
	* calls.c (prepare_call_address): Remove SIBCALLP parameter and add
	FLAGS parameter.  Deal with indirect calls by descriptor and adjust.
	Set STATIC_CHAIN_REG_P on the static chain register, if any.
	(call_expr_flags): Set ECF_BY_DESCRIPTOR for calls by descriptor.
	(expand_call): Likewise.  Move around call to prepare_call_address
	and pass all flags to it.
	* cfgexpand.c (expand_call_stmt): Reinstate CALL_EXPR_BY_DESCRIPTOR.
	* gimple.h (enum gf_mask): New GF_CALL_BY_DESCRIPTOR value.
	(gimple_call_set_by_descriptor): New setter.
	(gimple_call_by_descriptor_p): New getter.
	* gimple.c (gimple_build_call_from_tree): SetCALL_EXPR_BY_DESCRIPTOR.
	(gimple_call_flags): Deal with GF_CALL_BY_DESCRIPTOR.
	* langhooks.h (struct lang_hooks): Add custom_function_descriptors.
	* langhooks-def.h (LANG_HOOKS_CUSTOM_FUNCTION_DESCRIPTORS): Define.
	(LANG_HOOKS_INITIALIZER): Add LANG_HOOKS_CUSTOM_FUNCTION_DESCRIPTORS.
	* rtl.h (STATIC_CHAIN_REG_P): New macro.
	* rtlanal.c (find_first_parameter_load): Skip static chain registers.
	* target.def (custom_function_descriptors): New POD hook.
	* tree.h (FUNC_ADDR_BY_DESCRIPTOR): New flag on ADDR_EXPR.
	(CALL_EXPR_BY_DESCRIPTOR): New flag on CALL_EXPR.
	* tree-core.h (ECF_BY_DESCRIPTOR): New mask.
	Document FUNC_ADDR_BY_DESCRIPTOR and CALL_EXPR_BY_DESCRIPTOR.
	* tree.c (make_node_stat) <tcc_declaration>: Use FUNCTION_ALIGNMENT.
	(build_common_builtin_nodes): Initialize init_descriptor and
	adjust_descriptor.
	* tree-nested.c: Include target.h.
	(struct nesting_info): Add 'any_descr_created' field.
	(get_descriptor_type): New function.
	(lookup_element_for_decl): New function extracted from...
	(create_field_for_decl): Likewise.
	(lookup_tramp_for_decl): ...here.  Adjust.
	(lookup_descr_for_decl): New function.
	(convert_tramp_reference_op): Deal with descriptors.
	(build_init_call_stmt): New function extracted from...
	(finalize_nesting_tree_1): ...here.  Adjust and deal withdescriptors.
	* defaults.h (FUNCTION_ALIGNMENT): Define.
	(TRAMPOLINE_ALIGNMENT): Set to above instead of FUNCTION_BOUNDARY.

-- 
Eric Botcazou