[binutils-gdb] Optimize the performance of the group_setup function.

[Nick Clifton <nickc at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=564e11c9a9d9570b233b38cd995f1b4eb7c757e8

commit 564e11c9a9d9570b233b38cd995f1b4eb7c757e8
Author: Jens Widell <jl@opera.com>
Date:   Fri Jan 12 13:16:17 2018 +0000

    Optimize the performance of the group_setup function.
    
    When processing a section that is a member of a group, the group
    that contains it is looked up using a linear search. The resulting
    O(n^2) complexity causes significant performance issues when
    dealing with object files with very many groups.
    
    By remembering the index of the last found group and restarting
    the next search from that index, the search instead becomes O(n)
    in common cases.
    
    	* elf.c (setup_group): Optimize search for group by remembering
    	last found group and restarting search at that index.
    	* elf-bfd.h (struct elf_obj_tdata): Add group_search_offset field.

Diff:
---
 bfd/ChangeLog |  6 ++++++
 bfd/elf-bfd.h |  4 ++++
 bfd/elf.c     | 11 ++++++++---
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 19364c0..cc54b53 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,9 @@
+2018-01-12  Jens Widell  <jl@opera.com>
+
+	* elf.c (setup_group): Optimize search for group by remembering
+	last found group and restarting search at that index.
+	* elf-bfd.h (struct elf_obj_tdata): Add group_search_offset field.
+
 2018-01-12  Gunther Nikl  <gnikl@users.sourceforge.net>
 
 	* aoutx.h (aout_link_check_ar_symbols): Remove default and handle
diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index 9c9b0c7..b580dc2 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -1909,6 +1909,10 @@ struct elf_obj_tdata
   Elf_Internal_Shdr **group_sect_ptr;
   int num_group;
 
+  /* Index into group_sect_ptr, updated by setup_group when finding a
+     section's group.  Used to optimize subsequent group searches.  */
+  unsigned int group_search_offset;
+
   unsigned int symtab_section, dynsymtab_section;
   unsigned int dynversym_section, dynverdef_section, dynverref_section;
 
diff --git a/bfd/elf.c b/bfd/elf.c
index 1d0eefd..90aef09 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -737,10 +737,14 @@ setup_group (bfd *abfd, Elf_Internal_Shdr *hdr, asection *newsect)
 
   if (num_group != (unsigned) -1)
     {
-      unsigned int i;
+      unsigned int search_offset = elf_tdata (abfd)->group_search_offset;
+      unsigned int j;
 
-      for (i = 0; i < num_group; i++)
+      for (j = 0; j < num_group; j++)
 	{
+	  /* Begin search from previous found group.  */
+	  unsigned i = (j + search_offset) % num_group;
+
 	  Elf_Internal_Shdr *shdr = elf_tdata (abfd)->group_sect_ptr[i];
 	  Elf_Internal_Group *idx;
 	  bfd_size_type n_elt;
@@ -803,7 +807,8 @@ setup_group (bfd *abfd, Elf_Internal_Shdr *hdr, asection *newsect)
 		if (shdr->bfd_section != NULL)
 		  elf_next_in_group (shdr->bfd_section) = newsect;
 
-		i = num_group - 1;
+		elf_tdata (abfd)->group_search_offset = i;
+		j = num_group - 1;
 		break;
 	      }
 	}