MDEV-21133: Introduce memmove_aligned()

Both variants of the InnoDB page directory are aligned to the entry size
(16 bits). Inform the compiler about it.

Author: dr-m

include/m_string.h

@@ -210,6 +210,13 @@ inline void *memcpy_aligned(void *dest, const void *src, size_t n)
                 MY_ASSUME_ALIGNED(src, Alignment), n);
 }
 template <size_t Alignment>
+inline void *memmove_aligned(void *dest, const void *src, size_t n)
+{
+  static_assert(Alignment && !(Alignment & (Alignment - 1)), "power of 2");
+  return memmove(MY_ASSUME_ALIGNED(dest, Alignment),
+                 MY_ASSUME_ALIGNED(src, Alignment), n);
+}
+template <size_t Alignment>
 inline int memcmp_aligned(const void *s1, const void *s2, size_t n)
 {
   static_assert(Alignment && !(Alignment & (Alignment - 1)), "power of 2");

storage/innobase/page/page0cur.cc

@@ -1273,7 +1273,8 @@ static void page_dir_split_slot(page_t* page, page_zip_des_t* page_zip,
 	const ulint n_slots = page_dir_get_n_slots(page);
 	page_dir_set_n_slots(page, page_zip, n_slots + 1);
 	page_dir_slot_t* last_slot = page_dir_get_nth_slot(page, n_slots);
-	memmove(last_slot, last_slot + PAGE_DIR_SLOT_SIZE, slot - last_slot);
+	memmove_aligned<2>(last_slot, last_slot + PAGE_DIR_SLOT_SIZE,
+			   slot - last_slot);
 
 	/* 3. We store the appropriate values to the new slot. */
 
@@ -1327,8 +1328,8 @@ static void page_dir_balance_slot(page_t* page, page_zip_des_t* page_zip,
 		/* Shift the slots */
 		page_dir_slot_t* last_slot = page_dir_get_nth_slot(
 			page, n_slots - 1);
-		memmove(last_slot + PAGE_DIR_SLOT_SIZE, last_slot,
-			slot - last_slot);
+		memmove_aligned<2>(last_slot + PAGE_DIR_SLOT_SIZE, last_slot,
+				   slot - last_slot);
 		mach_write_to_2(last_slot, 0);
 		page_dir_set_n_slots(page, page_zip, n_slots - 1);
 		return;

storage/innobase/page/page0zip.cc

@@ -4430,8 +4430,8 @@ page_zip_dir_insert(
 	}
 
 	/* Shift the dense directory to allocate place for rec. */
-	memmove(slot_free - PAGE_ZIP_DIR_SLOT_SIZE, slot_free,
-		ulint(slot_rec - slot_free));
+	memmove_aligned<2>(slot_free - PAGE_ZIP_DIR_SLOT_SIZE, slot_free,
+			   ulint(slot_rec - slot_free));
 
 	/* Write the entry for the inserted record.
 	The "owned" and "deleted" flags must be zero. */
@@ -4489,9 +4489,8 @@ page_zip_dir_delete(
 	}
 
 	if (UNIV_LIKELY(slot_rec > slot_free)) {
-		memmove(slot_free + PAGE_ZIP_DIR_SLOT_SIZE,
-			slot_free,
-			ulint(slot_rec - slot_free));
+		memmove_aligned<2>(slot_free + PAGE_ZIP_DIR_SLOT_SIZE,
+				   slot_free, ulint(slot_rec - slot_free));
 	}
 
 	/* Write the entry for the deleted record.
@@ -4585,7 +4584,8 @@ page_zip_dir_add_slot(
 
 	/* Move the uncompressed area backwards to make space
 	for one directory slot. */
-	memmove(stored - PAGE_ZIP_DIR_SLOT_SIZE, stored, ulint(dir - stored));
+	memmove_aligned<2>(stored - PAGE_ZIP_DIR_SLOT_SIZE, stored,
+			   ulint(dir - stored));
 }
 
 /***********************************************************//**