diff --git a/gcc/df-scan.cc b/gcc/df-scan.cc
index 5df70e957516b4ca5c81d18902ea88c267ac4c50..9b2375d561bcd96173fe2bfa45ea55567e81dc9a 100644
--- a/gcc/df-scan.cc
+++ b/gcc/df-scan.cc
@@ -1769,13 +1769,15 @@ df_insn_change_bb (rtx_insn *insn, basic_block new_bb)
   if (!INSN_P (insn))
     return;
 
-  df_set_bb_dirty (new_bb);
+  if (!DEBUG_INSN_P (insn))
+    df_set_bb_dirty (new_bb);
   if (old_bb)
     {
       if (dump_file)
 	fprintf (dump_file, "  from %d to %d\n",
 		 old_bb->index, new_bb->index);
-      df_set_bb_dirty (old_bb);
+      if (!DEBUG_INSN_P (insn))
+	df_set_bb_dirty (old_bb);
     }
   else
     if (dump_file)
diff --git a/gcc/testsuite/gcc.dg/pr104459.c b/gcc/testsuite/gcc.dg/pr104459.c
new file mode 100644
index 0000000000000000000000000000000000000000..de8a643d9e218f1c4dbb53d59727bee1267b8f51
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104459.c
@@ -0,0 +1,38 @@
+/* PR rtl-optimization/104459 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -funswitch-loops -fno-tree-dce -fcompare-debug -w" } */
+
+void
+foo (int x, int y)
+{
+  unsigned int a;
+
+  for (;;)
+    {
+      short int *p = (short int *) &x;
+      unsigned int q = 0;
+
+      a /= 2;
+      if (a)
+	{
+	  q -= y;
+	  while (q)
+	    ;
+	}
+
+      if (x)
+	{
+	  for (q = 0; q != 1; q += 2)
+	    {
+	      unsigned int n;
+
+	      n = *p ? 0 : q;
+	      y += n < 1;
+
+	      n = a || *p;
+	      if (n % x == 0)
+		y /= x;
+	    }
+	}
+    }
+}