[patch] Atomic alignment override.

[Andrew MacLeod <amacleod at redhat dot com>]

I'd like to check in this code from the C11 branch so that it is present 
in 4.9.

Its adds a target hook which can be used to override the default 
alignment of an atomic type when used with C11's _Atomic qualifier. 
There are a couple of ports which have stricter alignment requirements 
for an atomic operation than the natural alignment of the integral type. 
   Today they are just broken with no real facility to repair it.

If this hook is not utilized by a port, the code is transparent and 
should therefore be harmless in the code base.  It will enable the ports 
that care to experiment with changing alignment and see if their current 
problems can be resolved for C11....  and then we can look to push that 
into C++11 atomic templates somehow.  It will also allow them to flush 
out any remaining problems that show up with the fundamental base code 
which enables it that went in as part of C11.

Bootstraps on x86-64 and currently running regression tests. Assuming 
everything passes, OK for mainline?

I wont actually check it in until HP reports back that it actually is 
useful to him, I just want to submit it before stage 1 ends :-).

Andrew

	
	* hooks.h (hook_uint_mode_0): Add Prototype.
	* hooks.c (hook_uint_mode_0): New default function.
	* target.def (atomic_align_for_mode): New target hook.
	* tree.c (build_atomic_base): Add alignment override parameter.
	(build_common_tree_nodes): Use atomic alignment override.
	* doc/tm.texi.in (TARGET_ATOMIC_ALIGN_FOR_MODE): Define.
	* doc/tm.texi (TARGET_ATOMIC_ALIGN_FOR_MODE): Add description.


Index: hooks.h
===================================================================
*** hooks.h	(revision 205220)
--- hooks.h	(working copy)
*************** extern tree hook_tree_tree_tree_tree_3rd
*** 92,97 ****
--- 92,98 ----
  extern tree hook_tree_tree_int_treep_bool_null (tree, int, tree *, bool);
  
  extern unsigned hook_uint_void_0 (void);
+ extern unsigned int hook_uint_mode_0 (enum machine_mode);
  
  extern bool default_can_output_mi_thunk_no_vcall (const_tree, HOST_WIDE_INT,
  						  HOST_WIDE_INT, const_tree);
Index: hooks.c
===================================================================
*** hooks.c	(revision 205220)
--- hooks.c	(working copy)
*************** hook_rtx_tree_int_null (tree a ATTRIBUTE
*** 358,363 ****
--- 358,370 ----
    return NULL;
  }
  
+ /* Generic hook that takes a machine mode and returns an unsigned int 0.  */
+ unsigned int
+ hook_uint_mode_0 (enum machine_mode m ATTRIBUTE_UNUSED)
+ {
+   return 0;
+ }
+ 
  /* Generic hook that takes three trees and returns the last one as is.  */
  tree
  hook_tree_tree_tree_tree_3rd_identity (tree a ATTRIBUTE_UNUSED,
Index: target.def
===================================================================
*** target.def	(revision 205220)
--- target.def	(working copy)
*************** DEFHOOKPOD
*** 5297,5302 ****
--- 5297,5313 ----
   @code{bool} @code{true}.",
   unsigned char, 1)
  
+ /* Return an unsigned int representing the alignment (in bits) of the atomic
+    type which maps to machine MODE.  This allows alignment to be overridden
+    as needed.  */
+ DEFHOOK
+ (atomic_align_for_mode,
+ "If defined, this function returns an appropriate alignment in bits for an\
+  atomic object of machine_mode @var{mode}.  If 0 is returned then the\
+  default alignment for the specified mode is used. ",
+  unsigned int, (enum machine_mode mode),
+  hook_uint_mode_0)
+ 
  DEFHOOK
  (atomic_assign_expand_fenv,
  "ISO C11 requires atomic compound assignments that may raise floating-point\
Index: tree.c
===================================================================
*** tree.c	(revision 205220)
--- tree.c	(working copy)
*************** make_or_reuse_accum_type (unsigned size,
*** 9547,9556 ****
     during initialization of data types to create the 5 basic atomic
     types. The generic build_variant_type function requires these to
     already be set up in order to function properly, so cannot be
!    called from there.  */
  
  static tree
! build_atomic_base (tree type)
  {
    tree t;
  
--- 9547,9557 ----
     during initialization of data types to create the 5 basic atomic
     types. The generic build_variant_type function requires these to
     already be set up in order to function properly, so cannot be
!    called from there.  If ALIGN is non-zero, then ensure alignment is
!    overridden to this value.  */
  
  static tree
! build_atomic_base (tree type, unsigned int align)
  {
    tree t;
  
*************** build_atomic_base (tree type)
*** 9561,9566 ****
--- 9562,9570 ----
    t = build_variant_type_copy (type);
    set_type_quals (t, TYPE_QUAL_ATOMIC);
  
+   if (align)
+     TYPE_ALIGN (t) = align;
+ 
    return t;
  }
  
*************** build_common_tree_nodes (bool signed_cha
*** 9648,9660 ****
  
    /* Don't call build_qualified type for atomics.  That routine does
       special processing for atomics, and until they are initialized
!      it's better not to make that call.  */
! 
!   atomicQI_type_node = build_atomic_base (unsigned_intQI_type_node);
!   atomicHI_type_node = build_atomic_base (unsigned_intHI_type_node);
!   atomicSI_type_node = build_atomic_base (unsigned_intSI_type_node);
!   atomicDI_type_node = build_atomic_base (unsigned_intDI_type_node);
!   atomicTI_type_node = build_atomic_base (unsigned_intTI_type_node);
  
    access_public_node = get_identifier ("public");
    access_protected_node = get_identifier ("protected");
--- 9652,9669 ----
  
    /* Don't call build_qualified type for atomics.  That routine does
       special processing for atomics, and until they are initialized
!      it's better not to make that call.
!      
!      Check to see if there is a target override for atomic types.  */
! 
! #define SET_ATOMIC_TYPE_NODE(TYPE, MODE, DEFAULT) 		\
!  (TYPE) = build_atomic_base (DEFAULT, targetm.atomic_align_for_mode (MODE));
! 
!   SET_ATOMIC_TYPE_NODE (atomicQI_type_node, QImode, unsigned_intQI_type_node);
!   SET_ATOMIC_TYPE_NODE (atomicHI_type_node, HImode, unsigned_intHI_type_node);
!   SET_ATOMIC_TYPE_NODE (atomicSI_type_node, SImode, unsigned_intSI_type_node);
!   SET_ATOMIC_TYPE_NODE (atomicDI_type_node, DImode, unsigned_intDI_type_node);
!   SET_ATOMIC_TYPE_NODE (atomicTI_type_node, TImode, unsigned_intTI_type_node);
  
    access_public_node = get_identifier ("public");
    access_protected_node = get_identifier ("protected");
Index: doc/tm.texi.in
===================================================================
*** doc/tm.texi.in	(revision 205220)
--- doc/tm.texi.in	(working copy)
*************** and the associated definitions of those
*** 8407,8410 ****
--- 8407,8412 ----
  
  @hook TARGET_HAS_IFUNC_P
  
+ @hook TARGET_ATOMIC_ALIGN_FOR_MODE
+ 
  @hook TARGET_ATOMIC_ASSIGN_EXPAND_FENV
Index: doc/tm.texi
===================================================================
*** doc/tm.texi	(revision 205220)
--- doc/tm.texi	(working copy)
*************** The support includes the assembler, link
*** 11500,11505 ****
--- 11500,11509 ----
  The default value of this hook is based on target's libc.
  @end deftypefn
  
+ @deftypefn {Target Hook} {unsigned int} TARGET_ATOMIC_ALIGN_FOR_MODE (enum machine_mode @var{mode})
+ If defined, this function returns an appropriate alignment in bits for an atomic object of machine_mode @var{mode}.  If 0 is returned then the default alignment for the specified mode is used. 
+ @end deftypefn
+ 
  @deftypefn {Target Hook} void TARGET_ATOMIC_ASSIGN_EXPAND_FENV (tree *@var{hold}, tree *@var{clear}, tree *@var{update})
  ISO C11 requires atomic compound assignments that may raise floating-point exceptions to raise exceptions corresponding to the arithmetic operation whose result was successfully stored in a compare-and-exchange sequence.  This requires code equivalent to calls to @code{feholdexcept}, @code{feclearexcept} and @code{feupdateenv} to be generated at appropriate points in the compare-and-exchange sequence.  This hook should set @code{*@var{hold}} to an expression equivalent to the call to @code{feholdexcept}, @code{*@var{clear}} to an expression equivalent to the call to @code{feclearexcept} and @code{*@var{update}} to an expression equivalent to the call to @code{feupdateenv}.  The three expressions are @code{NULL_TREE} on entry to the hook and may be left as @code{NULL_TREE} if no code is required in a particular place.  The default implementation leaves all three expressions as @code{NULL_TREE}.  The @code{__atomic_feraiseexcept} function from @code{libatomic} may be of use as part of the code generated in @code{*@var{update}}.
  @end deftypefn