diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index decdd7111fe..7617d4acc9c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2016-03-29  Richard Henderson  <rth@redhat.com>
+
+	PR middle-end/70355
+	* lower-subreg.c (simplify_subreg_concatn): Reject paradoxical
+	subregs.
+
 2016-03-29  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/70424
diff --git a/gcc/lower-subreg.c b/gcc/lower-subreg.c
index 5432d0597c5..f7b3ac4170e 100644
--- a/gcc/lower-subreg.c
+++ b/gcc/lower-subreg.c
@@ -614,7 +614,8 @@ simplify_subreg_concatn (machine_mode outermode, rtx op,
 
   innermode = GET_MODE (op);
   gcc_assert (byte < GET_MODE_SIZE (innermode));
-  gcc_assert (GET_MODE_SIZE (outermode) <= GET_MODE_SIZE (innermode));
+  if (GET_MODE_SIZE (outermode) > GET_MODE_SIZE (innermode))
+    return NULL_RTX;
 
   inner_size = GET_MODE_SIZE (innermode) / XVECLEN (op, 0);
   part = XVECEXP (op, 0, byte / inner_size);
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr70355.c b/gcc/testsuite/gcc.c-torture/compile/pr70355.c
new file mode 100644
index 00000000000..474942715f8
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr70355.c
@@ -0,0 +1,14 @@
+/* { dg-require-effective-target int128 } */
+/* { dg-additional-options "-g" } */
+
+typedef unsigned __int128 v2ti __attribute__ ((vector_size (32)));
+
+unsigned
+foo (unsigned i, v2ti v)
+{
+  do {
+    i--;
+    v %= ~v;
+  } while (i);
+  return v[0] + v[1];
+}
diff --git a/gcc/testsuite/gcc.target/i386/pr70355.c b/gcc/testsuite/gcc.target/i386/pr70355.c
new file mode 100644
index 00000000000..b55f6fc5260
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr70355.c
@@ -0,0 +1,14 @@
+/* { dg-require-effective-target int128 } */
+/* { dg-options "-O2 -fno-tree-ter -funroll-loops -mavx512f -g" } */
+
+typedef unsigned __int128 v2ti __attribute__ ((vector_size (32)));
+
+unsigned
+foo (unsigned i, v2ti v)
+{
+  do {
+    i--;
+    v %= ~v;
+  } while (i);
+  return v[0] + v[1];
+}