Re: [patch,libfortran] [4.7/4.8/4.9 Regression] PR38199 missed optimization: I/O performance

[Jerry DeLisle <jvdelisle at charter dot net>]

On 03/09/2014 05:39 PM, Jerry DeLisle wrote:
> Hi all,
> 
> This final patch does two things.
> 
> First:  In read.c it implements a simple space skipping scheme in read_decimal
> where I found a lot of repeated next_char calls happening. This gives a pretty
> good boost in performance and is applicable in general for reading integers.
> 
> Second: I have taken Thomas idea of using LEN_TRIM in unit.c revised it to work
> on formatted READ.  I tried to document the code with comments.  There are
> certain conditions for which one can not shorten the string length for internal
> units. For arrays of characters you can not do this for strings more than rank 1
> and stride 1. Also, you can not do this any time a BLANK='zero' is being used. I
> also skip the optimization if there is any BLANK= specified in the READ. Thats
> conservative.  I could also test for BLANK='NULL' in the DTP structure. I will
> probably do that later.
> 
> I have added a helper function which tests for the BZ within a format string
> when a format string is present.  I also check to see if the UNIT has had the
> BLANK status set.  The optimization is skipped for these conditions.
> 
Updated patch to resolve issue found during NIST tests.

Regression tested and NIST tested.

OK for trunk?

Regards,

Jerry

Index: read.c
===================================================================
--- read.c	(revision 208303)
+++ read.c	(working copy)
@@ -677,7 +677,13 @@ read_decimal (st_parameter_dt *dtp, const fnode *f
 	
       if (c == ' ')
         {
-	  if (dtp->u.p.blank_status == BLANK_NULL) continue;
+	  if (dtp->u.p.blank_status == BLANK_NULL)
+	    {
+	      /* Skip spaces.  */
+	      for ( ; w > 0; p++, w--)
+		if (*p != ' ') break; 
+	      continue;
+	    }
 	  if (dtp->u.p.blank_status == BLANK_ZERO) c = '0';
         }
         
Index: unit.c
===================================================================
--- unit.c	(revision 208303)
+++ unit.c	(working copy)
@@ -375,6 +375,38 @@ find_or_create_unit (int n)
 }
 
 
+/* Helper function to test conditions in format string. This
+   is used for optimization. You can't trim out blanks or shorten the
+   string if blank length is 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 +434,30 @@ 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 = 0;
+      if (dtp->common.unit == 0)
+	{
+	  len = string_len_trim (dtp->internal_unit_len,
+				     dtp->internal_unit);
+	  if (len > 0)
+	    dtp->internal_unit_len = len; 
+	  iunit->recl = dtp->internal_unit_len;
+	}
+      else
+	{
+	  len = string_len_trim_char4 (dtp->internal_unit_len,
+			      (const gfc_char4_t*) dtp->internal_unit);
+	  if (len > 0)
+	    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 +470,6 @@ 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)