Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -3256,18 +3256,24 @@
 class X86_64TargetInfo : public X86TargetInfo {
 public:
   X86_64TargetInfo(const llvm::Triple &Triple) : X86TargetInfo(Triple) {
-    LongWidth = LongAlign = PointerWidth = PointerAlign = 64;
+    const bool IsX32{getTriple().getEnvironment() == llvm::Triple::GNUX32};
+    LongWidth = LongAlign = PointerWidth = PointerAlign = IsX32 ? 32 : 64;
     LongDoubleWidth = 128;
     LongDoubleAlign = 128;
     LargeArrayMinWidth = 128;
     LargeArrayAlign = 128;
     SuitableAlign = 128;
-    IntMaxType = SignedLong;
-    UIntMaxType = UnsignedLong;
-    Int64Type = SignedLong;
+    SizeType    = IsX32 ? UnsignedInt      : UnsignedLong;
+    PtrDiffType = IsX32 ? SignedInt        : SignedLong;
+    IntPtrType  = IsX32 ? SignedInt        : SignedLong;
+    IntMaxType  = IsX32 ? SignedLongLong   : SignedLong;
+    UIntMaxType = IsX32 ? UnsignedLongLong : UnsignedLong;
+    Int64Type   = IsX32 ? SignedLongLong   : SignedLong;
     RegParmMax = 6;
 
-    DescriptionString = "e-m:e-i64:64-f80:128-n8:16:32:64-S128";
+    DescriptionString = (IsX32)
+                            ? "e-m:e-" "p:32:32-" "i64:64-f80:128-n8:16:32:64-S128"
+                            : "e-m:e-"            "i64:64-f80:128-n8:16:32:64-S128";
 
     // Use fpret only for long double.
     RealTypeUsesObjCFPRet = (1 << TargetInfo::LongDouble);
Index: lib/Driver/ToolChains.cpp
===================================================================
--- lib/Driver/ToolChains.cpp
+++ lib/Driver/ToolChains.cpp
@@ -1341,8 +1341,9 @@
     "x86_64-linux-gnu", "x86_64-unknown-linux-gnu", "x86_64-pc-linux-gnu",
     "x86_64-redhat-linux6E", "x86_64-redhat-linux", "x86_64-suse-linux",
     "x86_64-manbo-linux-gnu", "x86_64-linux-gnu", "x86_64-slackware-linux",
-    "x86_64-linux-android"
+    "x86_64-linux-android", "x86_64-unknown-linux"
   };
+  static const char *const X32LibDirs[] = { "/libx32" };
   static const char *const X86LibDirs[] = { "/lib32", "/lib" };
   static const char *const X86Triples[] = {
     "i686-linux-gnu", "i686-pc-linux-gnu", "i486-linux-gnu", "i386-linux-gnu",
@@ -1445,10 +1446,19 @@
                    X86_64LibDirs + llvm::array_lengthof(X86_64LibDirs));
     TripleAliases.append(X86_64Triples,
                          X86_64Triples + llvm::array_lengthof(X86_64Triples));
-    BiarchLibDirs.append(X86LibDirs,
-                         X86LibDirs + llvm::array_lengthof(X86LibDirs));
-    BiarchTripleAliases.append(X86Triples,
-                               X86Triples + llvm::array_lengthof(X86Triples));
+    // x32 is always available when x86_64 is available, so adding it as secondary
+    // arch with x86_64 triples
+    if (TargetTriple.getEnvironment() == llvm::Triple::GNUX32) {
+      BiarchLibDirs.append(X32LibDirs,
+                           X32LibDirs + llvm::array_lengthof(X32LibDirs));
+      BiarchTripleAliases.append(X86_64Triples,
+                                 X86_64Triples + llvm::array_lengthof(X86_64Triples));
+    } else {
+      BiarchLibDirs.append(X86LibDirs,
+                           X86LibDirs + llvm::array_lengthof(X86LibDirs));
+      BiarchTripleAliases.append(X86Triples,
+                                 X86Triples + llvm::array_lengthof(X86Triples));
+    }
     break;
   case llvm::Triple::x86:
     LibDirs.append(X86LibDirs, X86LibDirs + llvm::array_lengthof(X86LibDirs));
@@ -1935,47 +1945,64 @@
   Multilib Alt64 = Multilib()
     .gccSuffix("/64")
     .includeSuffix("/64")
-    .flag("-m32").flag("+m64");
+    .flag("-m32").flag("+m64").flag("-mx32");
   Multilib Alt32 = Multilib()
     .gccSuffix("/32")
     .includeSuffix("/32")
-    .flag("+m32").flag("-m64");
+    .flag("+m32").flag("-m64").flag("-mx32");
+  Multilib Altx32 = Multilib()
+    .gccSuffix("/x32")
+    .includeSuffix("/x32")
+    .flag("-m32").flag("-m64").flag("+mx32");
 
   FilterNonExistent NonExistent(Path);
 
-  // Decide whether the default multilib is 32bit, correcting for
-  // when the default multilib and the alternate appear backwards
-  bool DefaultIs32Bit;
+  // Determine default multilib from: 32, 64, x32
+  // Also handle cases such as 64 on 32, 32 on 64, etc.
+  enum { UNKNOWN, WANT32, WANT64, WANTX32 } Want = UNKNOWN;
+  const bool isX32 {TargetTriple.getEnvironment() == llvm::Triple::GNUX32};
   if (TargetTriple.isArch32Bit() && !NonExistent(Alt32))
-    DefaultIs32Bit = false;
-  else if (TargetTriple.isArch64Bit() && !NonExistent(Alt64))
-    DefaultIs32Bit = true;
+    Want = WANT64;
+  else if (TargetTriple.isArch64Bit() && isX32 && !NonExistent(Altx32))
+    Want = WANT64;
+  else if (TargetTriple.isArch64Bit() && !isX32 && !NonExistent(Alt64))
+    Want = WANT32;
   else {
-    if (NeedsBiarchSuffix)
-      DefaultIs32Bit = TargetTriple.isArch64Bit();
+    if (TargetTriple.isArch32Bit())
+      Want = NeedsBiarchSuffix ? WANT64 : WANT32;
+    else if (isX32)
+      Want = NeedsBiarchSuffix ? WANT64 : WANTX32;
     else
-      DefaultIs32Bit = TargetTriple.isArch32Bit();
+      Want = NeedsBiarchSuffix ? WANT32 : WANT64;
   }
 
-  if (DefaultIs32Bit)
-    Default.flag("+m32").flag("-m64");
+  if (Want == WANT32)
+    Default.flag("+m32").flag("-m64").flag("-mx32");
+  else if (Want == WANT64)
+    Default.flag("-m32").flag("+m64").flag("-mx32");
+  else if (Want == WANTX32)
+    Default.flag("-m32").flag("-m64").flag("+mx32");
   else
-    Default.flag("-m32").flag("+m64");
+    return false;
 
   Result.Multilibs.push_back(Default);
   Result.Multilibs.push_back(Alt64);
   Result.Multilibs.push_back(Alt32);
+  Result.Multilibs.push_back(Altx32);
 
   Result.Multilibs.FilterOut(NonExistent);
 
   Multilib::flags_list Flags;
-  addMultilibFlag(TargetTriple.isArch64Bit(), "m64", Flags);
+  addMultilibFlag(TargetTriple.isArch64Bit() && !isX32, "m64", Flags);
   addMultilibFlag(TargetTriple.isArch32Bit(), "m32", Flags);
+  addMultilibFlag(TargetTriple.isArch64Bit() && isX32, "mx32", Flags);
 
   if (!Result.Multilibs.select(Flags, Result.SelectedMultilib))
     return false;
 
-  if (Result.SelectedMultilib == Alt64 || Result.SelectedMultilib == Alt32)
+  if (Result.SelectedMultilib == Alt64 ||
+      Result.SelectedMultilib == Alt32 ||
+      Result.SelectedMultilib == Altx32)
     Result.BiarchSibling = Default;
 
   return true;
@@ -2889,7 +2916,9 @@
       return "i386-linux-gnu";
     return TargetTriple.str();
   case llvm::Triple::x86_64:
-    if (llvm::sys::fs::exists(SysRoot + "/lib/x86_64-linux-gnu"))
+    // We don't want this for x32, otherwise it will match x86_64 libs
+    if (TargetTriple.getEnvironment() != llvm::Triple::GNUX32 &&
+        llvm::sys::fs::exists(SysRoot + "/lib/x86_64-linux-gnu"))
       return "x86_64-linux-gnu";
     return TargetTriple.str();
   case llvm::Triple::arm64:
@@ -2953,6 +2982,10 @@
       Triple.getArch() == llvm::Triple::ppc)
     return "lib32";
 
+  if (Triple.getArch() == llvm::Triple::x86_64 &&
+      Triple.getEnvironment() == llvm::Triple::GNUX32)
+    return "libx32";
+
   return Triple.isArch32Bit() ? "lib" : "lib64";
 }
 
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -6741,7 +6741,10 @@
   if (getToolChain().getArch() == llvm::Triple::x86) {
     CmdArgs.push_back("--32");
   } else if (getToolChain().getArch() == llvm::Triple::x86_64) {
-    CmdArgs.push_back("--64");
+    if (getToolChain().getTriple().getEnvironment() == llvm::Triple::GNUX32)
+      CmdArgs.push_back("--x32");
+    else
+      CmdArgs.push_back("--64");
   } else if (getToolChain().getArch() == llvm::Triple::ppc) {
     CmdArgs.push_back("-a32");
     CmdArgs.push_back("-mppc");
@@ -6938,6 +6941,9 @@
     return "/lib64/ld64.so.2";
   else if (ToolChain.getArch() == llvm::Triple::sparcv9)
     return "/lib64/ld-linux.so.2";
+  else if (ToolChain.getArch() == llvm::Triple::x86_64 &&
+           ToolChain.getTriple().getEnvironment() == llvm::Triple::GNUX32)
+    return "/libx32/ld-linux-x32.so.2";
   else
     return "/lib64/ld-linux-x86-64.so.2";
 }
@@ -7048,6 +7054,9 @@
   }
   else if (ToolChain.getArch() == llvm::Triple::systemz)
     CmdArgs.push_back("elf64_s390");
+  else if (ToolChain.getArch() == llvm::Triple::x86_64 &&
+           ToolChain.getTriple().getEnvironment() == llvm::Triple::GNUX32)
+    CmdArgs.push_back("elf32_x86_64");
   else
     CmdArgs.push_back("elf_x86_64");
 
Index: test/Driver/cross-linux.c
===================================================================
--- test/Driver/cross-linux.c
+++ test/Driver/cross-linux.c
@@ -16,6 +16,14 @@
 //
 // RUN: %clang -### -o %t %s 2>&1 -no-integrated-as \
 // RUN:   --gcc-toolchain=%S/Inputs/basic_cross_linux_tree/usr \
+// RUN:   --target=x86_64-unknown-linux-gnux32 \
+// RUN:   | FileCheck --check-prefix=CHECK-X32 %s
+// CHECK-X32: "-cc1" "-triple" "x86_64-unknown-linux-gnux32"
+// CHECK-X32: "{{.*}}/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.0/../../../../x86_64-unknown-linux-gnu/bin{{/|\\}}as" "--x32"
+// CHECK-X32: "{{.*}}/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.0/../../../../x86_64-unknown-linux-gnu/bin{{/|\\}}ld" {{.*}} "-m" "elf32_x86_64"
+//
+// RUN: %clang -### -o %t %s 2>&1 -no-integrated-as \
+// RUN:   --gcc-toolchain=%S/Inputs/basic_cross_linux_tree/usr \
 // RUN:   --target=x86_64-unknown-linux-gnu -m32 \
 // RUN:   | FileCheck --check-prefix=CHECK-I386 %s
 //
Index: test/Driver/dyld-prefix.c
===================================================================
--- test/Driver/dyld-prefix.c
+++ test/Driver/dyld-prefix.c
@@ -7,3 +7,6 @@
 
 // RUN: %clang -target x86_64-unknown-linux --dyld-prefix /foo -### %t.o 2>&1 | FileCheck --check-prefix=CHECK-64 %s
 // CHECK-64: "-dynamic-linker" "/foo/lib64/ld-linux-x86-64.so.2"
+
+// RUN: %clang -target x86_64-unknown-linux-gnux32 --dyld-prefix /foo -### %t.o 2>&1 | FileCheck --check-prefix=CHECK-X32 %s
+// CHECK-X32: "-dynamic-linker" "/foo/libx32/ld-linux-x32.so.2"
Index: test/Driver/linux-header-search.cpp
===================================================================
--- test/Driver/linux-header-search.cpp
+++ test/Driver/linux-header-search.cpp
@@ -55,6 +55,22 @@
 // CHECK-UBUNTU-13-04: "-internal-externc-isystem" "[[SYSROOT]]/usr/include"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
+// RUN:     -target x86_64-unknown-linux-gnux32 \
+// RUN:     --sysroot=%S/Inputs/ubuntu_14.04_multiarch_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-UBUNTU-14-04 %s
+// CHECK-UBUNTU-14-04: "{{[^"]*}}clang{{[^"]*}}" "-cc1"
+// CHECK-UBUNTU-14-04: "-isysroot" "[[SYSROOT:[^"]+]]"
+// CHECK-UBUNTU-14-04: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8"
+// CHECK-UBUNTU-14-04: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/x86_64-linux-gnu/x32"
+// CHECK-UBUNTU-14-04: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/backward"
+// CHECK-UBUNTU-14-04: "-internal-isystem" "[[SYSROOT]]/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/x86_64-linux-gnu/c++/4.8/x32"
+// CHECK-UBUNTU-14-04: "-internal-isystem" "[[SYSROOT]]/usr/local/include"
+// CHECK-UBUNTU-14-04: "-internal-isystem" "{{.*}}{{/|\\\\}}lib{{(64|x32)?}}{{/|\\\\}}clang{{/|\\\\}}{{[0-9]\.[0-9]\.[0-9]}}{{/|\\\\}}include"
+// CHECK-UBUNTU-14-04: "-internal-externc-isystem" "[[SYSROOT]]/usr/include/x86_64-linux-gnu"
+// CHECK-UBUNTU-14-04: "-internal-externc-isystem" "[[SYSROOT]]/include"
+// CHECK-UBUNTU-14-04: "-internal-externc-isystem" "[[SYSROOT]]/usr/include"
+///
+// RUN: %clang -no-canonical-prefixes %s -### -fsyntax-only 2>&1 \
 // RUN:     -target arm-linux-gnueabihf \
 // RUN:     --sysroot=%S/Inputs/ubuntu_13.04_multiarch_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-UBUNTU-13-04-CROSS %s
Index: test/Driver/linux-ld.c
===================================================================
--- test/Driver/linux-ld.c
+++ test/Driver/linux-ld.c
@@ -34,6 +34,19 @@
 // CHECK-LD-64: "-lgcc" "--as-needed" "-lgcc_s" "--no-as-needed"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     --target=x86_64-unknown-linux-gnux32 \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-LD-X32 %s
+// CHECK-LD-X32-NOT: warning:
+// CHECK-LD-X32: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
+// CHECK-LD-X32: "--eh-frame-hdr"
+// CHECK-LD-X32: "-m" "elf32_x86_64"
+// CHECK-LD-X32: "-dynamic-linker"
+// CHECK-LD-X32: "-lgcc" "--as-needed" "-lgcc_s" "--no-as-needed"
+// CHECK-LD-X32: "-lc"
+// CHECK-LD-X32: "-lgcc" "--as-needed" "-lgcc_s" "--no-as-needed"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     --target=x86_64-unknown-linux \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:     --rtlib=compiler-rt \
@@ -186,6 +199,23 @@
 // CHECK-64-TO-32: "-L[[SYSROOT]]/usr/lib"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     --target=x86_64-unknown-linux-gnux32 \
+// RUN:     --sysroot=%S/Inputs/multilib_64bit_linux_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-X32 %s
+// CHECK-X32: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
+// CHECK-X32: "{{.*}}/usr/lib/gcc/x86_64-unknown-linux/4.6.0/x32{{/|\\\\}}crtbegin.o"
+// CHECK-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-unknown-linux/4.6.0/x32"
+// CHECK-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-unknown-linux/4.6.0/../../../../x86_64-unknown-linux/lib/../libx32"
+// CHECK-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-unknown-linux/4.6.0/../../../../libx32"
+// CHECK-X32: "-L[[SYSROOT]]/lib/../libx32"
+// CHECK-X32: "-L[[SYSROOT]]/usr/lib/../libx32"
+// CHECK-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-unknown-linux/4.6.0"
+// CHECK-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-unknown-linux/4.6.0/../../../../x86_64-unknown-linux/lib"
+// CHECK-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-unknown-linux/4.6.0/../../.."
+// CHECK-X32: "-L[[SYSROOT]]/lib"
+// CHECK-X32: "-L[[SYSROOT]]/usr/lib"
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     --target=x86_64-unknown-linux -m32 \
 // RUN:     --gcc-toolchain=%S/Inputs/multilib_64bit_linux_tree/usr \
 // RUN:     --sysroot=%S/Inputs/multilib_32bit_linux_tree \
@@ -364,6 +394,26 @@
 // CHECK-UBUNTU-14-04-PPC64LE: "{{.*}}/usr/lib/gcc/powerpc64le-linux-gnu/4.8{{/|\\\\}}crtend.o"
 // CHECK-UBUNTU-14-04-PPC64LE: "{{.*}}/usr/lib/gcc/powerpc64le-linux-gnu/4.8/../../../powerpc64le-linux-gnu{{/|\\\\}}crtn.o"
 //
+// Check Ubuntu 14.04 on x32.
+// "/usr/lib/gcc/x86_64-linux-gnu/4.8/x32/crtend.o" "/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../libx32/crtn.o"
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     --target=x86_64-unknown-linux-gnux32 \
+// RUN:     --sysroot=%S/Inputs/ubuntu_14.04_multiarch_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-UBUNTU-14-04-X32 %s
+// CHECK-UBUNTU-14-04-X32: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
+// CHECK-UBUNTU-14-04-X32: "{{.*}}/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../libx32{{/|\\\\}}crt1.o"
+// CHECK-UBUNTU-14-04-X32: "{{.*}}/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../libx32{{/|\\\\}}crti.o"
+// CHECK-UBUNTU-14-04-X32: "{{.*}}/usr/lib/gcc/x86_64-linux-gnu/4.8/x32{{/|\\\\}}crtbegin.o"
+// CHECK-UBUNTU-14-04-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-linux-gnu/4.8/x32"
+// CHECK-UBUNTU-14-04-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../libx32"
+// CHECK-UBUNTU-14-04-X32: "-L[[SYSROOT]]/lib/../libx32"
+// CHECK-UBUNTU-14-04-X32: "-L[[SYSROOT]]/usr/lib/../libx32"
+// CHECK-UBUNTU-14-04-X32: "-L[[SYSROOT]]/usr/lib/x86_64-linux-gnu/../../libx32"
+// CHECK-UBUNTU-14-04-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-linux-gnu/4.8"
+// CHECK-UBUNTU-14-04-X32: "-L[[SYSROOT]]/usr/lib/gcc/x86_64-linux-gnu/4.8/../../.."
+// CHECK-UBUNTU-14-04-X32: "{{.*}}/usr/lib/gcc/x86_64-linux-gnu/4.8/x32{{/|\\\\}}crtend.o"
+// CHECK-UBUNTU-14-04-X32: "{{.*}}/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../libx32{{/|\\\\}}crtn.o"
+//
 // Check fedora 18 on arm.
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     --target=armv7-unknown-linux-gnueabihf \