Optimize/eliminate bounds checking

TODO: do better at it by tracking min/max values of integers. The
following straightforward code doesn't have its bounds checks removed:

    for _, n := range slice {
        println(n)
    }

src/runtime/interface.go

@@ -44,6 +44,7 @@ var (
 
 // Get the function pointer for the method on the interface.
 // This is a compiler intrinsic.
+//go:nobounds
 func interfaceMethod(itf _interface, method uint16) *uint8 {
 	// This function doesn't do bounds checking as the supplied method must be
 	// in the list of signatures. The compiler will only emit