bounds checking and optimization

[Bruce Carneal]

The following code auto vectorizes nicely, as you'd hope:

     void abc(const(int)[] a, const(int)[] b, int[] c) @nogc 
nothrow pure @trusted {
         const bound = c.length;
         (a.length == bound) || assert(0);
         (b.length == bound) || assert(0);
         foreach(i; 0..bound)
             c.ptr[i] = a.ptr[i] + b.ptr[i];
     }

If you drop the .ptr suffixes the bounds checks are elided, 
correctly, but the code is not auto vectorized.

Similarly, if you drop the .ptr suffixes and compile @safe, the 
bounds checks are elided but the code is not auto vectorized.

It would be great if known-within-bound indexing could yield fast 
code without requiring either .ptr or @trusted.  IOW, I'm hoping 
for faster safe code.  Is that easily achieved in cases like the 
above or is it quite hard?