[Ada] Add new pragmas Linker_Constructor/Destructor

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on mainline.

These are two new pragmas that are modeled on the homonym (minus Linker_)
attributes in C/C++.  A procedure to which pragma Linker_Constructor is
applied will be treated as an initialization routine by the linker, that
is to say it will be invoked before the entry point of the executable is
called (or immediately after the shared library is loaded if the procedure
is linked in a shared library).  Symmetrically, a procedure to which pragma
Linker_Destructor is applied will be treated as a finalization routine by
the linker, that is to say it will be invoked after the entry point of the
executable has exited (or immediately before the shared library is unloaded
if the procedure is linked in a shared library).
They are used to implement enhanced auto-initialization of shared Stand
Alone Libraries and make it possible to use Zero-Cost exceptions in the
initialization procedure of the libraries.

At the same time, perform the following clean up: Generate renamings instead
of 'References in Remove_Side_Effects when it is valid to do so (non-volatile
objects, except function calls), independently of whether Variable_Ref is false
or true, on the grounds that renamings and 'References have the same
semantics with regard to the constraint conveyed by Variable_Ref. The
idea being to avoid as much as possible confronting Gigi with 'References
to unaddressable objects, which are very tricky to deal with.

2005-07-04  Eric Botcazou  <ebotcazou@adacore.com>

	* decl.c (prepend_attributes) <Pragma_Linker_Constructor>: New case.
	<Pragma_Linker_Destructor>: Likewise.

	* einfo.ads (Has_Gigi_Rep_Item): Document Pragma_Linker_Constructor and
	Pragma_Linker_Destructor.

	* gigi.h (attr_type): Add ATTR_LINK_CONSTRUCTOR and
	ATTR_LINK_DESTRUCTOR.
	(static_ctors, static_dtors): New variables.

	* misc.c (gnat_expand_body): Output current function as constructor
	and destructor if requested.

	* par-prag.adb: Add processing for pragma Linker_Constructor and
	Linker_Destructor.

	* sem_prag.adb (Find_Unique_Parameterless_Procedure): New function
	extracted from Check_Interrupt_Or_Attach_Handler.
	(Check_Interrupt_Or_Attach_Handler): Invoke it.
	Implement pragma Linker_Constructor and Linker_Destructor with the
	help of Find_Unique_Parameterless_Procedure.
	Replace Name_Alias with Name_Target for pragma Linker_Alias.

	* snames.h, snames.ads, snames.adb: 
	Add Name_Linker_Constructor and Name_Linker_Destructor.
	Add Pragma_Linker_Constructor and Pragma_Linker_Destructor.
	* snames.adb: Remove Name_Alias.

	* trans.c: Include cgraph.h.
	(build_global_cdtor): New function.
	(Compilation_Unit_to_gnu): Build global constructor and destructor if
	needed.
	(tree_transform) <N_Identifier>: Substitute renaming of view-conversions
	of objects too.
	(addressable_p) <COMPONENT_REF>: Unconditionally test
	DECL_NONADDRESSABLE_P on STRICT_ALIGNMENT platforms.

	* utils.c (process_attributes) <ATTR_LINK_ALIAS>: Do not assemble the
	variable if it is external.

	(static_ctors, static_dtors): New global variables.
	(process_attributes) <ATTR_LINK_CONSTRUCTOR>: New case.
	<ATTR_LINK_DESTRUCTOR>: Likewise.
	(end_subprog_body): Chain function as constructor and destructor
	if requested.

	* exp_util.adb (Force_Evaluation): Unconditionally invoke
	Remove_Side_Effects with Variable_Ref set to true.
	(Remove_Side_Effects): Handle scalar types first. Use a renaming
	for non-scalar types even if Variable_Ref is true and for class-wide
	expressions.

Attachment: difs.6
Description: Text document