re PR libfortran/38199 (missed optimization: I/O performance)

2014-03-12  Jerry DeLisle  <jvdelisle@gcc.gnu>

	PR libfortran/38199
	* io/read.c (read_decimal): Quickly skip spaces to avoid calls
	to next_char.
	* io/unit.c (is_trim_ok): New helper function to check various
	conditions to see if its OK to trim the internal unit string.
	(get_internal_unit): Use LEN_TRIM to shorten selected internal
	unit strings for optimizing READ. Enable this optimization for
	formatted READ.
	* io/list_read.c (finish_list_read): Don't call eat_line for
	internal units.

From-SVN: r208528

1 files changed, 48 insertions, 21 deletions

diff --git a/libgfortran/io/unit.c b/libgfortran/io/unit.c
index 901d66f..e522195 100644
--- a/libgfortran/io/unit.c
+++ b/libgfortran/io/unit.c
@@ -375,6 +375,38 @@ find_or_create_unit (int n)
 }
 
 
+/* Helper function to check rank, stride, format string, and namelist.
+   This is used for optimization. You can't trim out blanks or shorten
+   the string if trailing spaces are significant.  */
+static bool
+is_trim_ok (st_parameter_dt *dtp)
+{
+  /* Check rank and stride.  */
+  if (dtp->internal_unit_desc
+      && (GFC_DESCRIPTOR_RANK (dtp->internal_unit_desc) > 1
+	  || GFC_DESCRIPTOR_STRIDE(dtp->internal_unit_desc, 0) != 1))
+    return false;
+  /* Format strings can not have 'BZ' or '/'.  */
+  if (dtp->common.flags & IOPARM_DT_HAS_FORMAT)
+    {
+      char *p = dtp->format;
+      off_t i;
+      if (dtp->common.flags & IOPARM_DT_HAS_BLANK)
+	return false;
+      for (i = 0; i < dtp->format_len; i++)
+	{
+	  if (p[i] == '/') return false;
+	  if (p[i] == 'b' || p[i] == 'B')
+	    if (p[i+1] == 'z' || p[i+1] == 'Z')
+	      return false;
+	}
+    }
+  if (dtp->u.p.ionml) /* A namelist.  */
+    return false;
+  return true;
+}
+
+
 gfc_unit *
 get_internal_unit (st_parameter_dt *dtp)
 {
@@ -402,6 +434,22 @@ get_internal_unit (st_parameter_dt *dtp)
      some other file I/O unit.  */
   iunit->unit_number = -1;
 
+  /* As an optimization, adjust the unit record length to not
+     include trailing blanks. This will not work under certain conditions
+     where trailing blanks have significance.  */
+  if (dtp->u.p.mode == READING && is_trim_ok (dtp))
+    {
+      int len;
+      if (dtp->common.unit == 0)
+	  len = string_len_trim (dtp->internal_unit_len,
+						   dtp->internal_unit);
+      else
+	  len = string_len_trim_char4 (dtp->internal_unit_len,
+			      (const gfc_char4_t*) dtp->internal_unit);
+      dtp->internal_unit_len = len; 
+      iunit->recl = dtp->internal_unit_len;
+    }
+
   /* Set up the looping specification from the array descriptor, if any.  */
 
   if (is_array_io (dtp))
@@ -414,27 +462,6 @@ get_internal_unit (st_parameter_dt *dtp)
 
       start_record *= iunit->recl;
     }
-  else
-    {
-      /* If we are not processing an array, adjust the unit record length not
-	 to include trailing blanks for list-formatted reads.  */
-      if (dtp->u.p.mode == READING && !(dtp->common.flags & IOPARM_DT_HAS_FORMAT))
-	{
-	  if (dtp->common.unit == 0)
-	    {
-	      dtp->internal_unit_len =
-		string_len_trim (dtp->internal_unit_len, dtp->internal_unit);
-	      iunit->recl = dtp->internal_unit_len;
-	    }
-	  else
-	    {
-	      dtp->internal_unit_len =
-		string_len_trim_char4 (dtp->internal_unit_len,
-				       (const gfc_char4_t*) dtp->internal_unit);
-	      iunit->recl = dtp->internal_unit_len;
-	    }
-	}
-    }
 
   /* Set initial values for unit parameters.  */
   if (dtp->common.unit)