Merge pull request #13474 from ethereum/add-note-about-peephole-optimizer

Add note about peephole optimizer in docs

docs/internals/optimizer.rst

@@ -26,6 +26,10 @@ One can use ``solc --ir-optimized --optimize`` to produce an
 optimized Yul IR for a Solidity source. Similarly, one can use ``solc --strict-assembly --optimize``
 for a stand-alone Yul mode.
 
+.. note::
+    The `peephole optimizer <https://en.wikipedia.org/wiki/Peephole_optimization>`_ and the inliner are always
+    enabled by default and can only be turned off via the :ref:`Standard JSON <compiler-api>`.
+
 You can find more details on both optimizer modules and their optimization steps below.
 
 Benefits of Optimizing Solidity Code