[Bug c/69037] New: arrays of constants as function arguments misinterpreted

[arigo at tunes dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69037

            Bug ID: 69037
           Summary: arrays of constants as function arguments
                    misinterpreted
           Product: gcc
           Version: 5.3.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arigo at tunes dot org
  Target Milestone: ---

The following occurs in `gcc_5_branch` but not in the 5.3.0 release tag.

The C front-end misinterprets arrays of constants which are passed as function
arguments.  Example:

    typedef const int array_t[3];
    int allocate_with_allocator(array_t ar)
    {
        int a = ar[0];
        int b = ar[1];
        return a + b;
    }

This produces two warnings on the lines defining `int a` and `int b`
("initialization makes integer from pointer without a cast") and outputs bogus
code (tested with `gcc -S -O2` on x86-64):

        leal    12(%rdi,%rdi), %eax
        ret

Note that it works fine if we remove "const" from the example above.  In that
case, or on previous versions of gcc (up to and including 5.3.0), the code is
compiled without warning to:

        movl    4(%rdi), %eax
        addl    (%rdi), %eax
        ret

Fwiw, this error is consistent with the argument "ar" being mistakenly
considered to be of type "array_t *" instead of "array_t".