[expr.ass] Clarify that assignment always modifies

Author: eisenwave

source/expressions.tex

@@ -7310,6 +7310,10 @@
 In simple assignment (\tcode{=}), the object referred to by the left operand
 is modified\iref{defns.access}
 by replacing its value with the result of the right operand.
+\begin{note}
+The object is modified even if the value of the right operand
+compares equal\iref{expr.eq} to the object's old value.
+\end{note}
 
 \pnum
 \indextext{assignment!conversion by}%