Index: libcxx/include/__config
===================================================================
--- libcxx/include/__config
+++ libcxx/include/__config
@@ -315,6 +315,11 @@
 #  endif
 #endif // __sun__
 
+#if defined(_AIX) && !defined(__64BIT__)
+   // The size of wchar is 2 byte on 32-bit mode on AIX.
+#  define _LIBCPP_SHORT_WCHAR   1
+#endif
+
 #if defined(__OpenBSD__) || defined(__CloudABI__)
    // Certain architectures provide arc4random(). Prefer using
    // arc4random() over /dev/{u,}random to make it possible to obtain
Index: libcxx/src/locale.cpp
===================================================================
--- libcxx/src/locale.cpp
+++ libcxx/src/locale.cpp
@@ -3517,15 +3517,25 @@
 {
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
     const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+#if defined(_LIBCPP_SHORT_WCHAR)
+    return utf8_to_ucs2_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+#else
     return utf8_to_ucs4_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+#endif
 }
 
 int
 __codecvt_utf8<wchar_t>::do_max_length() const noexcept
 {
+#if defined(_LIBCPP_SHORT_WCHAR)
+    if (_Mode_ & consume_header)
+        return 6;
+    return 3;
+#else
     if (_Mode_ & consume_header)
         return 7;
     return 4;
+#endif
 }
 
 // __codecvt_utf8<char16_t>
@@ -3685,14 +3695,25 @@
     const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
     extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
 {
+#if defined(_LIBCPP_SHORT_WCHAR)
+    const uint16_t* _frm = reinterpret_cast<const uint16_t*>(frm);
+    const uint16_t* _frm_end = reinterpret_cast<const uint16_t*>(frm_end);
+    const uint16_t* _frm_nxt = _frm;
+#else
     const uint32_t* _frm = reinterpret_cast<const uint32_t*>(frm);
     const uint32_t* _frm_end = reinterpret_cast<const uint32_t*>(frm_end);
     const uint32_t* _frm_nxt = _frm;
+#endif
     uint8_t* _to = reinterpret_cast<uint8_t*>(to);
     uint8_t* _to_end = reinterpret_cast<uint8_t*>(to_end);
     uint8_t* _to_nxt = _to;
+#if defined(_LIBCPP_SHORT_WCHAR)
+    result r = ucs2_to_utf16be(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                               _Maxcode_, _Mode_);
+#else
     result r = ucs4_to_utf16be(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
                                _Maxcode_, _Mode_);
+#endif
     frm_nxt = frm + (_frm_nxt - _frm);
     to_nxt = to + (_to_nxt - _to);
     return r;
@@ -3706,11 +3727,19 @@
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
     const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
     const uint8_t* _frm_nxt = _frm;
+#if defined(_LIBCPP_SHORT_WCHAR)
+    uint16_t* _to = reinterpret_cast<uint16_t*>(to);
+    uint16_t* _to_end = reinterpret_cast<uint16_t*>(to_end);
+    uint16_t* _to_nxt = _to;
+    result r = utf16be_to_ucs2(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                               _Maxcode_, _Mode_);
+#else
     uint32_t* _to = reinterpret_cast<uint32_t*>(to);
     uint32_t* _to_end = reinterpret_cast<uint32_t*>(to_end);
     uint32_t* _to_nxt = _to;
     result r = utf16be_to_ucs4(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
                                _Maxcode_, _Mode_);
+#endif
     frm_nxt = frm + (_frm_nxt - _frm);
     to_nxt = to + (_to_nxt - _to);
     return r;
@@ -3742,15 +3771,25 @@
 {
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
     const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+#if defined(_LIBCPP_SHORT_WCHAR)
+    return utf16be_to_ucs2_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+#else
     return utf16be_to_ucs4_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+#endif
 }
 
 int
 __codecvt_utf16<wchar_t, false>::do_max_length() const noexcept
 {
+#if defined(_LIBCPP_SHORT_WCHAR)
+    if (_Mode_ & consume_header)
+        return 4;
+    return 2;
+#else
     if (_Mode_ & consume_header)
         return 6;
     return 4;
+#endif
 }
 
 // __codecvt_utf16<wchar_t, true>
@@ -3760,14 +3799,25 @@
     const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
     extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
 {
+#if defined(_LIBCPP_SHORT_WCHAR)
+    const uint16_t* _frm = reinterpret_cast<const uint16_t*>(frm);
+    const uint16_t* _frm_end = reinterpret_cast<const uint16_t*>(frm_end);
+    const uint16_t* _frm_nxt = _frm;
+#else
     const uint32_t* _frm = reinterpret_cast<const uint32_t*>(frm);
     const uint32_t* _frm_end = reinterpret_cast<const uint32_t*>(frm_end);
     const uint32_t* _frm_nxt = _frm;
+#endif
     uint8_t* _to = reinterpret_cast<uint8_t*>(to);
     uint8_t* _to_end = reinterpret_cast<uint8_t*>(to_end);
     uint8_t* _to_nxt = _to;
+#if defined(_LIBCPP_SHORT_WCHAR)
+    result r = ucs2_to_utf16le(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                               _Maxcode_, _Mode_);
+#else
     result r = ucs4_to_utf16le(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
                                _Maxcode_, _Mode_);
+#endif
     frm_nxt = frm + (_frm_nxt - _frm);
     to_nxt = to + (_to_nxt - _to);
     return r;
@@ -3781,11 +3831,19 @@
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
     const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
     const uint8_t* _frm_nxt = _frm;
+#if defined(_LIBCPP_SHORT_WCHAR)
+    uint16_t* _to = reinterpret_cast<uint16_t*>(to);
+    uint16_t* _to_end = reinterpret_cast<uint16_t*>(to_end);
+    uint16_t* _to_nxt = _to;
+    result r = utf16le_to_ucs2(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                               _Maxcode_, _Mode_);
+#else
     uint32_t* _to = reinterpret_cast<uint32_t*>(to);
     uint32_t* _to_end = reinterpret_cast<uint32_t*>(to_end);
     uint32_t* _to_nxt = _to;
     result r = utf16le_to_ucs4(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
                                _Maxcode_, _Mode_);
+#endif
     frm_nxt = frm + (_frm_nxt - _frm);
     to_nxt = to + (_to_nxt - _to);
     return r;
@@ -3817,15 +3875,25 @@
 {
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
     const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+#if defined(_LIBCPP_SHORT_WCHAR)
+    return utf16le_to_ucs2_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+#else
     return utf16le_to_ucs4_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+#endif
 }
 
 int
 __codecvt_utf16<wchar_t, true>::do_max_length() const noexcept
 {
+#if defined(_LIBCPP_SHORT_WCHAR)
+    if (_Mode_ & consume_header)
+        return 4;
+    return 2;
+#else
     if (_Mode_ & consume_header)
         return 6;
     return 4;
+#endif
 }
 
 // __codecvt_utf16<char16_t, false>
@@ -4135,9 +4203,15 @@
     const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
     extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
 {
+#if defined(_LIBCPP_SHORT_WCHAR)
+    const uint16_t* _frm = reinterpret_cast<const uint16_t*>(frm);
+    const uint16_t* _frm_end = reinterpret_cast<const uint16_t*>(frm_end);
+    const uint16_t* _frm_nxt = _frm;
+#else
     const uint32_t* _frm = reinterpret_cast<const uint32_t*>(frm);
     const uint32_t* _frm_end = reinterpret_cast<const uint32_t*>(frm_end);
     const uint32_t* _frm_nxt = _frm;
+#endif
     uint8_t* _to = reinterpret_cast<uint8_t*>(to);
     uint8_t* _to_end = reinterpret_cast<uint8_t*>(to_end);
     uint8_t* _to_nxt = _to;
@@ -4156,9 +4230,15 @@
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
     const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
     const uint8_t* _frm_nxt = _frm;
+#if defined(_LIBCPP_SHORT_WCHAR)
+    uint16_t* _to = reinterpret_cast<uint16_t*>(to);
+    uint16_t* _to_end = reinterpret_cast<uint16_t*>(to_end);
+    uint16_t* _to_nxt = _to;
+#else
     uint32_t* _to = reinterpret_cast<uint32_t*>(to);
     uint32_t* _to_end = reinterpret_cast<uint32_t*>(to_end);
     uint32_t* _to_nxt = _to;
+#endif
     result r = utf8_to_utf16(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
                              _Maxcode_, _Mode_);
     frm_nxt = frm + (_frm_nxt - _frm);