pending/1262: [RFA] performance improvement of lookup_partial_symtab

[Jerome Guitton <guitton at act-europe dot fr>]

>Number:         1262
>Category:       pending
>Synopsis:       [RFA]  performance improvement of lookup_partial_symtab
>Confidential:   yes
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          change-request
>Submitter-Id:   unknown
>Arrival-Date:   Thu Jun 26 17:38:01 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     
>Release:        
>Organization:
>Environment:
>Description:
 Hello,
 
 Debugging an executable build with more than 3000 source files, it
 can take several seconds to GDB to output some source file information.
 A reproducer can be generated with the following script (It generated an
 Ada program):
 
 ---
 
 rm main.adb
 rm -rf many_files
 mkdir many_files
 for i in 0 1 2 3 ; do
    for j in 0 1 2 3 4 5 6 7 8 9 ; do
       for k in 0 1 2 3 4 5 6 7 8 9 ; do
          for l in 0 1 2 3 4 5 6 7 8 9 ; do
 echo "with Pack_${i}${j}${k}${l}_Test;" >> main.adb
 echo "package Pack_${i}$j${k}${l}_Test is" \
 	>> many_files/pack_${i}${j}${k}${l}_test.ads
 echo "   pragma Pure;" \
 	>> many_files/pack_${i}${j}${k}${l}_test.ads
 echo "   Var_${i}$j${k}${l}_Test : constant String := \"${i}${j}${k}${l}\";" \
 	>> many_files/pack_${i}${j}${k}${l}_test.ads
 echo "end Pack_${i}$j${k}${l}_Test;" \
 	>> many_files/pack_${i}${j}${k}${l}_test.ads
          done
       done
    done
 done
 echo "procedure Main is" >> main.adb
 echo "begin" >> main.adb
 echo "   null;" >> main.adb
 echo "end Main;" >> main.adb
 
 ---
 
 Compiling with GNAT 3.16a, and debugging with gdb 5.3:
 
 
 (gdb) l /home/guitton/bug/C411-003/many_files/pack_0001_test.ads:2
 
 [after several seconds:]
 
 1       package Pack_0001_Test is
 2          pragma Pure;
 3          Var_0001_Test : constant String := "0001";
 4       end Pack_0001_Test;
 (gdb)
 
 The culprit is lookup_partial_symtab, that may do a call
 to source_full_path_of for every file referenced. I suggest trying
 to avoid as much as possible this function call by doing some preliminary
 testing: if the basenames are not equal, no need to fetch the
 fullname and make the fullname comparison. With this modification
 GDB reacts almost instantly. 
 
 I have tested this patch against the testsuite on linux; no regression
 appeared. There seems to be no test using an absolute path, I can
 also propose one.
 
 Joel Brobecker volunteered to commit this path if/when it is approved.
 
 
 2003-05-26  J. Guitton <guitton@gnat.com>
 
         * symtab.c (lookup_partial_symbol): To improve the performance,
         try to avoid as much as possible to call source_full_path_of,
 	by doing some preliminary testing.
 
 Index: symtab.c
 ===================================================================
 RCS file: /cvs/src/src/gdb/symtab.c,v
 retrieving revision 1.109
 diff -c -r1.109 symtab.c
 *** symtab.c	20 May 2003 01:55:17 -0000	1.109
 --- symtab.c	10 Jun 2003 13:22:43 -0000
 ***************
 *** 273,280 ****
         }
   
       /* If the user gave us an absolute path, try to find the file in
 !        this symtab and use its absolute path.  */
 !     if (full_path != NULL)
         {
   	if (pst->fullname == NULL)
   	  source_full_path_of (pst->filename, &pst->fullname);
 --- 273,283 ----
         }
   
       /* If the user gave us an absolute path, try to find the file in
 !        this symtab and use its absolute path.  However, if the
 !        base names are different, the two files are different and there
 !        is no need to do a full comparison.  */
 !     if (full_path != NULL &&
 ! 	strcmp (lbasename (full_path), lbasename (pst->filename)) == 0)
         {
   	if (pst->fullname == NULL)
   	  source_full_path_of (pst->filename, &pst->fullname);
 ***************
 *** 285,291 ****
   	  }
         }
   
 !     if (real_path != NULL)
         {
           char *rp = NULL;
   	if (pst->fullname == NULL)
 --- 288,295 ----
   	  }
         }
   
 !     if (real_path != NULL &&
 ! 	strcmp (lbasename (real_path), lbasename (pst->filename)) == 0)
         {
           char *rp = NULL;
   	if (pst->fullname == NULL)
 
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