===================================================================
@@ -213,7 +213,9 @@ DEF_RTL_EXPR(ASM_OPERANDS, "asm_operands
*/
DEF_RTL_EXPR(UNSPEC, "unspec", "Ei", RTX_EXTRA)
-/* Similar, but a volatile operation and one which may trap. */
+/* Similar, but a volatile operation and one which may trap. Moreover, it's
a
+ full optimization barrier, i.e. no instructions may be moved and no
register
+ (hard or pseudo) or memory equivalences may be used across it. */
DEF_RTL_EXPR(UNSPEC_VOLATILE, "unspec_volatile", "Ei", RTX_EXTRA)