diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b4e12f3646f..cbd6f4b0e61 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2003-12-27  Zdenek Dvorak  <rakdver@atrey.karlin.mff.cuni.cz>
+
+	PR opt/13159
+	* cfgloopanal.c (mark_irreducible_loops): Fix the strongly connected
+	components detection.
+	* loop-unswitch.c (unswitch_loop): Preserve simple preheaders.
+
 2003-12-27  Bernardo Innocenti  <bernie@develer.com>
 
 	* config/m68k/uclinux.h (LIB_SPEC): Add elf2flt magic required for
diff --git a/gcc/cfgloopanal.c b/gcc/cfgloopanal.c
index 3d6e69ef48d..74cebe00919 100644
--- a/gcc/cfgloopanal.c
+++ b/gcc/cfgloopanal.c
@@ -1247,7 +1247,7 @@ mark_irreducible_loops (struct loops *loops)
 	           : e->dest->index + 1;
           if (closed[sidx])
 	    {
-	      if (!closed[mri[sidx]])
+	      if (mri[sidx] != -1 && !closed[mri[sidx]])
 		{
 		  if (mr[sidx] < mr[idx])
 		    {
diff --git a/gcc/loop-unswitch.c b/gcc/loop-unswitch.c
index f276b7307a4..25728c2bf62 100644
--- a/gcc/loop-unswitch.c
+++ b/gcc/loop-unswitch.c
@@ -402,5 +402,9 @@ unswitch_loop (struct loops *loops, struct loop *loop, basic_block unswitch_on)
   fix_loop_placement (loop);
   fix_loop_placement (nloop);
 
+  /* Preserve the simple loop preheaders.  */
+  loop_split_edge_with (loop_preheader_edge (loop), NULL_RTX, loops);
+  loop_split_edge_with (loop_preheader_edge (nloop), NULL_RTX, loops);
+
   return nloop;
 }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index e0086f471e9..b124d130981 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2003-12-27  Zdenek Dvorak  <rakdver@atrey.karlin.mff.cuni.cz>
+
+	* gcc.c-torture/compile/20031227-1.c: New test.
+
 2003-12-23  Mark Mitchell  <mark@codesourcery.com>
 
 	* g++.dg/bprob/bprob.exp: Load target-supports.exp
diff --git a/gcc/testsuite/gcc.c-torture/compile/20031227-1.c b/gcc/testsuite/gcc.c-torture/compile/20031227-1.c
new file mode 100644
index 00000000000..41597bd18e6
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/20031227-1.c
@@ -0,0 +1,17 @@
+/* PR opt/13159 -- test unswitching a loop multiple times.  */
+
+void
+foo (void)
+{
+  long j, k, p, g;
+
+  while (p)
+    {
+      while (k < 0 && j < 0)
+	;
+      if (g)
+	;
+      else if (g)
+	;      
+    }
+}