diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 5ad69839f88..9e61921fc06 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2016-02-06  Richard Henderson  <rth@redhat.com>
+
+	PR c/69643
+	* tree.c (tree_nop_conversion_p): Do not strip casts into or
+	out of non-standard address spaces.
+
 2016-02-05  Jakub Jelinek  <jakub@redhat.com>
 
 	PR rtl-optimization/69691
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 61306d0fdd0..d8f088d1bd7 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2016-02-06  Richard HEnderson  <rth@redhat.com>
+
+	PR c/69643
+	* gcc.target/i386/addr-space-4.c: New.
+	* gcc.target/i386/addr-space-5.c: New.
+
 2016-02-05  Mikael Morin  <mikael@gcc.gnu.org>
 
 	PR fortran/66089
diff --git a/gcc/testsuite/gcc.target/i386/addr-space-4.c b/gcc/testsuite/gcc.target/i386/addr-space-4.c
new file mode 100644
index 00000000000..3e0966db69a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/addr-space-4.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+/* { dg-final { scan-assembler "gs:" } } */
+
+#define uintptr_t __SIZE_TYPE__
+
+struct S { int a, b, c; };
+
+extern struct S __seg_gs s;
+
+int foo (void)
+{
+  int r;
+  r = s.c;
+  return r;
+}
diff --git a/gcc/testsuite/gcc.target/i386/addr-space-5.c b/gcc/testsuite/gcc.target/i386/addr-space-5.c
new file mode 100644
index 00000000000..4f73f95aa3f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/addr-space-5.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+/* { dg-final { scan-assembler "gs:" } } */
+
+#define uintptr_t __SIZE_TYPE__
+
+struct S { int a, b, c; };
+
+extern struct S s;
+
+int ct_state3 (void)
+{
+  int r;
+  r = *((int __seg_gs *) (uintptr_t) &s.c);
+  return r;
+}
diff --git a/gcc/tree.c b/gcc/tree.c
index fa7646b14e1..07cb9d9765c 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -12219,6 +12219,23 @@ block_ultimate_origin (const_tree block)
 bool
 tree_nop_conversion_p (const_tree outer_type, const_tree inner_type)
 {
+  /* Do not strip casts into or out of differing address spaces.  */
+  if (POINTER_TYPE_P (outer_type)
+      && TYPE_ADDR_SPACE (TREE_TYPE (outer_type)) != ADDR_SPACE_GENERIC)
+    {
+      if (!POINTER_TYPE_P (inner_type)
+	  || (TYPE_ADDR_SPACE (TREE_TYPE (outer_type))
+	      != TYPE_ADDR_SPACE (TREE_TYPE (inner_type))))
+	return false;
+    }
+  else if (POINTER_TYPE_P (inner_type)
+	   && TYPE_ADDR_SPACE (TREE_TYPE (inner_type)) != ADDR_SPACE_GENERIC)
+    {
+      /* We already know that outer_type is not a pointer with
+	 a non-generic address space.  */
+      return false;
+    }
+
   /* Use precision rather then machine mode when we can, which gives
      the correct answer even for submode (bit-field) types.  */
   if ((INTEGRAL_TYPE_P (outer_type)