Vector subscription, register storage class

[Artem Shinkarov]

Hi,

I'm working on the vector subscription patch in terms of GSoC 2010 project.
The patch basically does the following, if we have a vector subscription like:

#define vector __attribute__((vector_size(16)))
vector int a;
a[1] = 10;

then the code "a[1] = 10" is transformed into the code "*((int *)a + 1) = 10".


The problem however is, when we have a register-declared variable like:
register vector int a = {1,2,3,4};

It should be addressable, but register keyword disallows it. To solve
this problem I modify c-decl.c:start_decl like this:
Index: c-decl.c
===================================================================
--- c-decl.c    (revision 160230)
+++ c-decl.c    (working copy)
@@ -4071,6 +4071,11 @@
        }
     }

+  /* Vectors need to be addressable for subscripting to work,
+     so drop the qualifier.  */
+  if (TREE_CODE (TREE_TYPE (decl)) == VECTOR_TYPE)
+    C_DECL_REGISTER (decl) = 0;
+
   if (TREE_CODE (decl) == FUNCTION_DECL
       && DECL_DECLARED_INLINE_P (decl)
       && DECL_UNINLINABLE (decl)

Which allows now to subscript register-declared variables.


But still I have an example that does not work:
struct vec_s {
   vector short member;
};

int main () {
   register struct vec_s v2;
   v2.member[2] = 4;
   return 0;
}

The question is should it work at all? And what would be the optimal
way to implement it?



-- 
Thank you,
Artem Shinkarov