_Assume_bounds_cast added with checked array type

[kyleheadley]

The icecast benchmarks includes a few copies of this error:

md5.c:122:112: error: expected _Array_ptr type
          MD5Transform(_Assume_bounds_cast<uint32_t _Checked[4]>(ctx->buf, ...),...);
                                           ^

According to the spec, _Assume_bounds_cast must use a checked pointer type (_Ptr,_Array_ptr, or _Nt_array_ptr).

In this case, both MD5Transform and ctx->buf use identical uint32_t buf[4] types in the source. I assume ctx could not be verified, hence the cast.

We probably need a new code path for sized arrays, if it doesn't already exist.

[john-h-kastner]

Here's a concrete example:

void test(int a[1]) {}
void caller() {
  int *b = 1;
  test(b);
}

The call becomes test(_Assume_bounds_cast<int _Checked[1]>(b, bounds(unknown)));. The target type of the cast should instead be _Array_ptr<int>. This cast would be valid because the checked array type int _Checked[1] in a function parameter decays to a checked array pointer type _Array_ptr<int>.