Documentation nit

Author: oli-obk

src/librustc_mir/interpret/operand.rs

@@ -582,7 +582,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 // The reason we use `const_eval_raw` everywhere else is to prevent cycles during
                 // validation, because validation automatically reads through any references, thus
                 // potentially requiring the current static to be evaluated again. This is not a
-                // problem here, because we need an operand and operands are always reads.
+                // problem here, because we are building an operand which means an actual read is
+                // happening.
                 // FIXME(oli-obk): eliminate all the `const_eval_raw` usages when we get rid of
                 // `StaticKind` once and for all.
                 return self.const_eval(GlobalId { instance, promoted: None });