diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 976bbb4..5da4da2 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -7545,6 +7545,18 @@ ix86_promote_function_mode (const_tree type,
enum machine_mode mode,
 					for_return);
 }

+/* Return true if a structure, union or array with MODE containing FIELD
+   should be accessed using BLKmode.  */
+
+static bool
+ix86_member_type_forces_blk (const_tree field, enum machine_mode mode)
+{
+  /* Union with XFmode must be in BLKmode.  */
+  return (mode == XFmode
+	  && (TREE_CODE (DECL_FIELD_CONTEXT (field)) == UNION_TYPE
+	      || TREE_CODE (DECL_FIELD_CONTEXT (field)) == QUAL_UNION_TYPE));
+}
+
 rtx
 ix86_libcall_value (enum machine_mode mode)
 {
@@ -40725,6 +40737,9 @@ ix86_memmodel_check (unsigned HOST_WIDE_INT val)
 #undef TARGET_PROMOTE_FUNCTION_MODE
 #define TARGET_PROMOTE_FUNCTION_MODE ix86_promote_function_mode

+#undef TARGET_MEMBER_TYPE_FORCES_BLK
+#define TARGET_MEMBER_TYPE_FORCES_BLK ix86_member_type_forces_blk
+
 #undef TARGET_SECONDARY_RELOAD
 #define TARGET_SECONDARY_RELOAD ix86_secondary_reload

diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
index 5ff82ab..11f79e3 100644
--- a/gcc/config/i386/i386.h
+++ b/gcc/config/i386/i386.h
@@ -1816,6 +1816,10 @@ do {							\
 #define BRANCH_COST(speed_p, predictable_p) \
   (!(speed_p) ? 2 : (predictable_p) ? 0 : ix86_branch_cost)

+/* An integer expression for the size in bits of the largest integer machine
+   mode that should actually be used.  We allow pairs of registers.  */
+#define MAX_FIXED_MODE_SIZE GET_MODE_BITSIZE (TARGET_64BIT ? TImode : DImode)
+
 /* Define this macro as a C expression which is nonzero if accessing
    less than a word of memory (i.e. a `char' or a `short') is no
    faster than accessing a word of memory, i.e., if such access
diff --git a/gcc/testsuite/gcc.target/i386/pr20020-1.c
b/gcc/testsuite/gcc.target/i386/pr20020-1.c
new file mode 100644
index 0000000..3f10970
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr20020-1.c
@@ -0,0 +1,26 @@
+/* Check that 128-bit struct's are represented as TImode values.  */
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2 -fdump-rtl-expand" } */
+
+struct shared_ptr_struct
+{
+  unsigned long long phase:48;
+  unsigned short thread:16;
+  union
+    {
+      void *addr;
+      unsigned long long pad;
+    };
+};
+typedef struct shared_ptr_struct sptr_t;
+
+sptr_t S;
+
+sptr_t
+sptr_result (void)
+{
+  return S;
+}
+/* { dg-final { scan-rtl-dump "\\\(set \\\(reg:TI \[0-9\]* \\\[
<retval> \\\]\\\)" "expand" } } */
+/* { dg-final { scan-rtl-dump "\\\(set \\\(reg/i:TI 0 ax\\\)" "expand" } } */
+/* { dg-final { cleanup-rtl-dump "expand" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr20020-2.c
b/gcc/testsuite/gcc.target/i386/pr20020-2.c
new file mode 100644
index 0000000..e8c5b3d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr20020-2.c
@@ -0,0 +1,24 @@
+/* Check that 128-bit struct's are represented as TImode values.  */
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2 -fdump-rtl-expand" } */
+
+struct shared_ptr_struct
+{
+  unsigned long long phase:48;
+  unsigned short thread:16;
+  union
+    {
+      void *addr;
+      unsigned long long pad;
+    };
+};
+typedef struct shared_ptr_struct sptr_t;
+
+void
+copy_sptr (sptr_t *dest, sptr_t src)
+{
+  *dest = src;
+}
+
+/* { dg-final { scan-rtl-dump "\\\(set \\\(reg:TI \[0-9\]*" "expand" } } */
+/* { dg-final { cleanup-rtl-dump "expand" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr20020-3.c
b/gcc/testsuite/gcc.target/i386/pr20020-3.c
new file mode 100644
index 0000000..b1cc926
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr20020-3.c
@@ -0,0 +1,27 @@
+/* Check that 128-bit struct's are represented as TImode values.  */
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2 -fdump-rtl-expand" } */
+
+struct shared_ptr_struct
+{
+  unsigned long long phase:48;
+  unsigned short thread:16;
+  union
+    {
+      void *addr;
+      unsigned long long pad;
+    };
+};
+typedef struct shared_ptr_struct sptr_t;
+
+sptr_t sptr_1, sptr_2;
+
+void
+copy_sptr (void)
+{
+  sptr_1 = sptr_2;
+}
+
+/* { dg-final { scan-rtl-dump "\\\(set \\\(reg:TI \[0-9\]*" "expand" } } */
+/* { dg-final { scan-rtl-dump "\\\(set \\\(mem/c:TI" "expand" } } */
+/* { dg-final { cleanup-rtl-dump "expand" } } */