Simplify IO_CACHE by removing current_pos and end_pos as self-references

These self references were previously used to avoid having to check the
IO_CACHE's type. However, a benchmark shows that on x86 5930k stock,
the type comparison is marginally faster than the double pointer dereference.
For 40 billion my_b_tell calls, the difference is .1 seconds in favor of performing the
type check. (Basically there is no measurable difference)

To prevent bugs from copying the structure using the equals(=) operator,
and having to do the bookkeeping manually, remove these "convenience"
variables.

include/my_sys.h

@@ -422,14 +422,6 @@ typedef struct st_io_cache		/* Used when cacheing files */
   /* The non-inclusive boundary of the valid write area */
   uchar *write_end;
 
-  /*
-    Current_pos and current_end are convenience variables used by
-    my_b_tell() and other routines that need to know the current offset
-    current_pos points to &write_pos, and current_end to &write_end in a
-    WRITE_CACHE, and &read_pos and &read_end respectively otherwise
-  */
-  uchar  **current_pos, **current_end;
-
   /*
     The lock is for append buffer used in SEQ_READ_APPEND cache
     need mutex copying from append buffer to read buffer.
@@ -584,7 +576,11 @@ static inline size_t my_b_fill(IO_CACHE *info)
 
 static inline my_off_t my_b_tell(const IO_CACHE *info)
 {
-  return info->pos_in_file + (*info->current_pos - info->request_pos);
+  if (info->type == WRITE_CACHE) {
+    return info->pos_in_file + (info->write_pos - info->request_pos);
+
+  }
+  return info->pos_in_file + (info->read_pos - info->request_pos);
 }
 
 static inline my_off_t my_b_write_tell(const IO_CACHE *info)
@@ -609,7 +605,10 @@ static inline my_off_t my_b_get_pos_in_file(const IO_CACHE *info)
 
 static inline size_t my_b_bytes_in_cache(const IO_CACHE *info)
 {
-  return *info->current_end - *info->current_pos;
+  if (info->type == WRITE_CACHE) {
+    return info->write_end - info->write_pos;
+  }
+  return info->read_end - info->read_pos;
 }
 
 int      my_b_copy_to_file(IO_CACHE *cache, FILE *file);
@@ -803,7 +802,6 @@ extern int init_io_cache(IO_CACHE *info,File file,size_t cachesize,
 extern my_bool reinit_io_cache(IO_CACHE *info,enum cache_type type,
 			       my_off_t seek_offset, my_bool use_async_io,
 			       my_bool clear_cache);
-extern void setup_io_cache(IO_CACHE* info);
 extern void init_io_cache_share(IO_CACHE *read_cache, IO_CACHE_SHARE *cshare,
                                 IO_CACHE *write_cache, uint num_threads);
 

mysys/mf_iocache.c

@@ -74,34 +74,6 @@ int (*_my_b_encr_read)(IO_CACHE *info,uchar *Buffer,size_t Count)= 0;
 int (*_my_b_encr_write)(IO_CACHE *info,const uchar *Buffer,size_t Count)= 0;
 
 
-/*
-  Setup internal pointers inside IO_CACHE
-
-  SYNOPSIS
-    setup_io_cache()
-    info		IO_CACHE handler
-
-  NOTES
-    This is called on automatically on init or reinit of IO_CACHE
-    It must be called externally if one moves or copies an IO_CACHE
-    object.
-*/
-
-void setup_io_cache(IO_CACHE* info)
-{
-  /* Ensure that my_b_tell() and my_b_bytes_in_cache works */
-  if (info->type == WRITE_CACHE)
-  {
-    info->current_pos= &info->write_pos;
-    info->current_end= &info->write_end;
-  }
-  else
-  {
-    info->current_pos= &info->read_pos;
-    info->current_end= &info->read_end;
-  }
-}
-
 
 static void
 init_functions(IO_CACHE* info)
@@ -148,8 +120,6 @@ init_functions(IO_CACHE* info)
     DBUG_ASSERT(0);
     break;
   }
-
-  setup_io_cache(info);
 }
 
 
@@ -360,12 +330,7 @@ int init_slave_io_cache(IO_CACHE *master, IO_CACHE *slave)
   memcpy(slave->buffer, master->buffer, master->buffer_length);
   slave->read_pos= slave->buffer + (master->read_pos - master->buffer);
   slave->read_end= slave->buffer + (master->read_end - master->buffer);
-
-  DBUG_ASSERT(master->current_pos == &master->read_pos);
-  slave->current_pos= &slave->read_pos;
-  DBUG_ASSERT(master->current_end == &master->read_end);
-  slave->current_end= &slave->read_end;
-
+
   if (master->next_file_user)
   {
     IO_CACHE *p;
@@ -924,8 +889,6 @@ void init_io_cache_share(IO_CACHE *read_cache, IO_CACHE_SHARE *cshare,
 
   read_cache->share=         cshare;
   read_cache->read_function= _my_b_cache_read_r;
-  read_cache->current_pos=   NULL;
-  read_cache->current_end=   NULL;
 
   if (write_cache)
   {

sql/filesort.cc

@@ -1483,16 +1483,13 @@ int merge_many_buff(Sort_param *param, uchar *sort_buffer,
     if (flush_io_cache(to_file))
       break;					/* purecov: inspected */
     temp=from_file; from_file=to_file; to_file=temp;
-    setup_io_cache(from_file);
-    setup_io_cache(to_file);
     *maxbuffer= (uint) (lastbuff-buffpek)-1;
   }
 cleanup:
   close_cached_file(to_file);			// This holds old result
   if (to_file == t_file)
   {
     *t_file=t_file2;				// Copy result file
-    setup_io_cache(t_file);
   }
 
   DBUG_RETURN(*maxbuffer >= MERGEBUFF2);	/* Return 1 if interrupted */

storage/maria/ma_sort.c

@@ -896,8 +896,6 @@ static int merge_many_buff(MARIA_SORT_PARAM *info, ha_keys keys,
   {
     DBUG_ASSERT(t_file2.type == WRITE_CACHE);
     *t_file=t_file2;                            /* Copy result file */
-    t_file->current_pos= &t_file->write_pos;
-    t_file->current_end= &t_file->write_end;
   }
 
   DBUG_RETURN(*maxbuffer >= MERGEBUFF2);        /* Return 1 if interrupted */

storage/myisam/sort.c

@@ -844,8 +844,6 @@ static int merge_many_buff(MI_SORT_PARAM *info, ha_keys keys,
   {
     DBUG_ASSERT(t_file2.type == WRITE_CACHE);
     *t_file=t_file2;                            /* Copy result file */
-    t_file->current_pos= &t_file->write_pos;
-    t_file->current_end= &t_file->write_end;
   }
 
   DBUG_RETURN(*maxbuffer >= MERGEBUFF2);        /* Return 1 if interrupted */

unittest/sql/mf_iocache-t.cc

@@ -93,7 +93,7 @@ IO_CACHE info;
 #define CACHE_SIZE 16384
 
 #define INFO_TAIL ", pos_in_file = %llu, pos_in_mem = %lu", \
-    info.pos_in_file, (ulong) (*info.current_pos - info.request_pos)
+    info.pos_in_file, (ulong) ((info.type == READ_CACHE ? info.read_pos : info.write_pos) - info.request_pos)
 
 #define FILL 0x5A