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[Ada] Leverage 6.2(12) to restrict parameter aliasing


The 6.2(12) paragraph reads:

"If one name  denotes a part of a formal parameter, and a second name  denotes 
a part of a distinct formal parameter or an object that is not part of a 
formal parameter, then the two names are considered distinct access paths. If 
an object is of a type for which the parameter passing mechanism is not 
specified, then it is a bounded error to assign to the object via one access 
path, and then read the value of the object via a distinct access path, unless 
the first access path denotes a part of a formal parameter that no longer 
exists at the point of the second access (due to leaving the corresponding 
callable construct). The possible consequences are that Program_Error is 
raised, or the newly assigned value is read, or some old value of the object 
is read. "

We leverage it to consider that parameters passed by reference at the sole 
decision of the compiler are restrict-qualified in the C sense.

Tested on i586-suse-linux, applied on the mainline.


2011-12-11  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc-interface/decl.c (gnat_to_gnu_param): Set the restrict qualifier
	on references built for parameters which aren't specifically by-ref.


-- 
Eric Botcazou
Index: gcc-interface/decl.c
===================================================================
--- gcc-interface/decl.c	(revision 182201)
+++ gcc-interface/decl.c	(working copy)
@@ -5518,7 +5518,15 @@ gnat_to_gnu_param (Entity_Id gnat_param,
 		   || (!foreign
 		       && default_pass_by_ref (gnu_param_type)))))
     {
+      /* We take advantage of 6.2(12) by considering that references built for
+	 parameters whose type isn't by-ref and for which the mechanism hasn't
+	 been forced to by-ref are restrict-qualified in the C sense.  */
+      bool restrict_p
+	= !TREE_ADDRESSABLE (gnu_param_type) && mech != By_Reference;
       gnu_param_type = build_reference_type (gnu_param_type);
+      if (restrict_p)
+	gnu_param_type
+	  = build_qualified_type (gnu_param_type, TYPE_QUAL_RESTRICT);
       by_ref = true;
 
       /* In some ABIs, e.g. SPARC 32-bit, fat pointer types are themselves

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