fix Issue 13138 add peek/poke to core.bitop

src/core/bitop.d

@@ -213,6 +213,60 @@ version (DigitalMars) version (AnyX86) @system // not pure
 }
 
 
+/*************************************
+ * Read/write value from/to the memory location indicated by ptr.
+ *
+ * These functions are recognized by the compiler, and calls to them are guaranteed
+ * to not be removed (as dead assignment elimination or presumed to have no effect)
+ * or reordered in the same thread.
+ *
+ * These reordering guarantees are only made with regards to other
+ * operations done through these functions; the compiler is free to reorder regular
+ * loads/stores with regards to loads/stores done through these functions.
+ *
+ * This is useful when dealing with memory-mapped I/O (MMIO) where a store can
+ * have an effect other than just writing a value, or where sequential loads
+ * with no intervening stores can retrieve
+ * different values from the same location due to external stores to the location.
+ *
+ * These functions will, when possible, do the load/store as a single operation. In
+ * general, this is possible when the size of the operation is less than or equal to
+ * $(D (void*).sizeof), although some targets may support larger operations. If the
+ * load/store cannot be done as a single operation, multiple smaller operations will be used.
+ *
+ * These are not to be conflated with atomic operations. They do not guarantee any
+ * atomicity. This may be provided by coincidence as a result of the instructions
+ * used on the target, but this should not be relied on for portable programs.
+ * Further, no memory fences are implied by these functions.
+ * They should not be used for communication between threads.
+ * They may be used to guarantee a write or read cycle occurs at a specified address.
+ */
+
+ubyte  volatileLoad(ubyte * ptr);
+ushort volatileLoad(ushort* ptr);  /// ditto
+uint   volatileLoad(uint  * ptr);  /// ditto
+ulong  volatileLoad(ulong * ptr);  /// ditto
+
+void volatileStore(ubyte * ptr, ubyte  value);   /// ditto
+void volatileStore(ushort* ptr, ushort value);   /// ditto
+void volatileStore(uint  * ptr, uint   value);   /// ditto
+void volatileStore(ulong * ptr, ulong  value);   /// ditto
+
+@system unittest
+{
+    alias TT(T...) = T;
+
+    foreach (T; TT!(ubyte, ushort, uint, ulong))
+    {
+        T u;
+        T* p = &u;
+        volatileStore(p, 1);
+        T r = volatileLoad(p);
+        assert(r == u);
+    }
+}
+
+
 /**
  *  Calculates the number of set bits in a 32-bit integer.
  */