C++ frontend can not handle vector pointer constant parameter

[Sa Liu <SALIU at de dot ibm dot com>]

Hi all,

I have detected a bug in C++ frontend. 

When compiling a function with parameter of a pointer to a vector constant 
type, the compiler calls a recursive function and is not able to get out. 

Concretely, in gcc/cp/mangle.c file, in function write_type:

  if (write_CV_qualifiers_for_type (type) > 0)
    /* If TYPE was CV-qualified, we just wrote the qualifiers; now
       mangle the unqualified type.  The recursive call is needed here
       since both the qualified and unqualified types are substitution
       candidates.  */
    write_type (TYPE_MAIN_VARIANT (type));

But TYPE_MAIN_VARIANT (type) has been set as type itself in gcc/tree.c 
function make_node_stat:
   case tcc_type:
        ...
      TYPE_MAIN_VARIANT (t) = t;

Therefor the write_type function runs into a dead recursion.

I have a test case to show the incorrect behavior on Intel:

void bar(
    int __attribute__((vector_size(16))) * a,
    int __attribute__((vector_size(16))) * const b);

int instance(void)
{
   int __attribute__((vector_size(16))) a[1], b[1];

   bar(a, b);
}

The error also occurs on other machines supporting vector type. I suppose 
that some flags for the qualifier are not properly set. 
Does someone knowing frontend well could provide any help?

Thanks!
Sa