diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 346b366f04d..bdb4d26f94b 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2013-01-03  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/55838
+	* loop-iv.c (iv_number_of_iterations): Call lowpart_subreg on
+	iv0.step, iv1.step and step.
+
 2013-01-03  Jakub Jelinek  <jakub@redhat.com>
 	    Marc Glisse  <marc.glisse@inria.fr>
 
diff --git a/gcc/loop-iv.c b/gcc/loop-iv.c
index 50b75362a97..d089fbf7cea 100644
--- a/gcc/loop-iv.c
+++ b/gcc/loop-iv.c
@@ -1,5 +1,5 @@
 /* Rtl-level induction variable analysis.
-   Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010
+   Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013
    Free Software Foundation, Inc.
 
 This file is part of GCC.
@@ -2406,6 +2406,9 @@ iv_number_of_iterations (struct loop *loop, rtx insn, rtx condition,
       iv1.step = const0_rtx;
     }
 
+  iv0.step = lowpart_subreg (mode, iv0.step, comp_mode);
+  iv1.step = lowpart_subreg (mode, iv1.step, comp_mode);
+
   /* This is either infinite loop or the one that ends immediately, depending
      on initial values.  Unswitching should remove this kind of conditions.  */
   if (iv0.step == const0_rtx && iv1.step == const0_rtx)
@@ -2516,6 +2519,7 @@ iv_number_of_iterations (struct loop *loop, rtx insn, rtx condition,
 	step = simplify_gen_unary (NEG, comp_mode, iv1.step, comp_mode);
       else
 	step = iv0.step;
+      step = lowpart_subreg (mode, step, comp_mode);
       delta = simplify_gen_binary (MINUS, comp_mode, iv1.base, iv0.base);
       delta = lowpart_subreg (mode, delta, comp_mode);
       delta = simplify_gen_binary (UMOD, mode, delta, step);
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 12f1688c447..37244533de0 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2013-01-03  Jakub Jelinek  <jakub@redhat.com>
 
+	PR rtl-optimization/55838
+	* gcc.dg/pr55838.c: New test.
+
 	PR tree-optimization/55832
 	* gcc.c-torture/compile/pr55832.c: New test.
 
diff --git a/gcc/testsuite/gcc.dg/pr55838.c b/gcc/testsuite/gcc.dg/pr55838.c
new file mode 100644
index 00000000000..d2d6e142ba2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr55838.c
@@ -0,0 +1,13 @@
+/* PR rtl-optimization/55838 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -funroll-loops" } */
+
+int a;
+unsigned char c;
+
+void
+f (void)
+{
+  while (c++ < 2)
+    c = a += 129;
+}