Index: cfe/trunk/include/clang/Basic/TargetInfo.h
===================================================================
--- cfe/trunk/include/clang/Basic/TargetInfo.h
+++ cfe/trunk/include/clang/Basic/TargetInfo.h
@@ -358,7 +358,7 @@
 
   /// \brief Determine whether the __int128 type is supported on this target.
   virtual bool hasInt128Type() const {
-    return getPointerWidth(0) >= 64;
+    return (getPointerWidth(0) >= 64) || getTargetOpts().ForceEnableInt128;
   } // FIXME
 
   /// \brief Determine whether the __float128 type is supported on this target.
Index: cfe/trunk/include/clang/Basic/TargetOptions.h
===================================================================
--- cfe/trunk/include/clang/Basic/TargetOptions.h
+++ cfe/trunk/include/clang/Basic/TargetOptions.h
@@ -60,6 +60,9 @@
   /// \brief The list of OpenCL extensions to enable or disable, as written on
   /// the command line.
   std::vector<std::string> OpenCLExtensionsAsWritten;
+
+  /// \brief If given, enables support for __int128_t and __uint128_t types.
+  bool ForceEnableInt128;
 };
 
 }  // end namespace clang
Index: cfe/trunk/include/clang/Driver/Options.td
===================================================================
--- cfe/trunk/include/clang/Driver/Options.td
+++ cfe/trunk/include/clang/Driver/Options.td
@@ -849,6 +849,12 @@
 def fjump_tables : Flag<["-"], "fjump-tables">, Group<f_Group>;
 def fno_jump_tables : Flag<["-"], "fno-jump-tables">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Do not use jump tables for lowering switches">;
+def fforce_enable_int128 : Flag<["-"], "fforce-enable-int128">,
+  Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Enable support for int128_t type">;
+def fno_force_enable_int128 : Flag<["-"], "fno-force-enable-int128">,
+  Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Disable support for int128_t type">;
 
 // Begin sanitizer flags. These should all be core options exposed in all driver
 // modes.
Index: cfe/trunk/lib/Basic/Targets/Mips.h
===================================================================
--- cfe/trunk/lib/Basic/Targets/Mips.h
+++ cfe/trunk/lib/Basic/Targets/Mips.h
@@ -392,7 +392,9 @@
     return llvm::makeArrayRef(NewABIRegAliases);
   }
 
-  bool hasInt128Type() const override { return ABI == "n32" || ABI == "n64"; }
+  bool hasInt128Type() const override {
+    return (ABI == "n32" || ABI == "n64") || getTargetOpts().ForceEnableInt128;
+  }
 
   bool validateTarget(DiagnosticsEngine &Diags) const override;
 };
Index: cfe/trunk/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- cfe/trunk/lib/Driver/ToolChains/Clang.cpp
+++ cfe/trunk/lib/Driver/ToolChains/Clang.cpp
@@ -4750,6 +4750,12 @@
     }
   }
 
+  if (Arg *A = Args.getLastArg(options::OPT_fforce_enable_int128,
+                               options::OPT_fno_force_enable_int128)) {
+    if (A->getOption().matches(options::OPT_fforce_enable_int128))
+      CmdArgs.push_back("-fforce-enable-int128");
+  }
+
   // Finally add the compile command to the compilation.
   if (Args.hasArg(options::OPT__SLASH_fallback) &&
       Output.getType() == types::TY_Object &&
Index: cfe/trunk/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- cfe/trunk/lib/Frontend/CompilerInvocation.cpp
+++ cfe/trunk/lib/Frontend/CompilerInvocation.cpp
@@ -2781,6 +2781,7 @@
   if (Opts.Triple.empty())
     Opts.Triple = llvm::sys::getDefaultTargetTriple();
   Opts.OpenCLExtensionsAsWritten = Args.getAllArgValues(OPT_cl_ext_EQ);
+  Opts.ForceEnableInt128 = Args.hasArg(OPT_fforce_enable_int128);
 }
 
 bool CompilerInvocation::CreateFromArgs(CompilerInvocation &Res,
Index: cfe/trunk/test/CodeGen/riscv32-abi.c
===================================================================
--- cfe/trunk/test/CodeGen/riscv32-abi.c
+++ cfe/trunk/test/CodeGen/riscv32-abi.c
@@ -1,4 +1,6 @@
 // RUN: %clang_cc1 -triple riscv32 -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple riscv32 -emit-llvm -fforce-enable-int128 %s -o - \
+// RUN: | FileCheck %s -check-prefixes=CHECK,CHECK-FORCEINT128
 
 #include <stddef.h>
 #include <stdint.h>
@@ -24,6 +26,11 @@
 // CHECK-LABEL: define i64 @f_scalar_4(i64 %x)
 int64_t f_scalar_4(int64_t x) { return x; }
 
+#ifdef __SIZEOF_INT128__
+// CHECK-FORCEINT128-LABEL: define i128 @f_scalar_5(i128 %x)
+__int128_t f_scalar_5(__int128_t x) { return x; }
+#endif
+
 // CHECK-LABEL: define float @f_fp_scalar_1(float %x)
 float f_fp_scalar_1(float x) { return x; }
 
Index: cfe/trunk/test/Driver/types.c
===================================================================
--- cfe/trunk/test/Driver/types.c
+++ cfe/trunk/test/Driver/types.c
@@ -0,0 +1,18 @@
+// Check whether __int128_t and __uint128_t are supported.
+
+// RUN: not %clang -c --target=riscv32-unknown-linux-gnu -fsyntax-only %s \
+// RUN: 2>&1 | FileCheck %s
+
+// RUN: %clang -c --target=riscv32-unknown-linux-gnu -fsyntax-only %s \
+// RUN: -fno-force-enable-int128 -fforce-enable-int128
+
+// RUN: not %clang -c --target=riscv32-unknown-linux-gnu -fsyntax-only %s \
+// RUN: -fforce-enable-int128 -fno-force-enable-int128
+
+void a() {
+  __int128_t s;
+  __uint128_t t;
+}
+
+// CHECK: error: use of undeclared identifier '__int128_t'
+// CHECK: error: use of undeclared identifier '__uint128_t'
Index: cfe/trunk/test/Preprocessor/init.c
===================================================================
--- cfe/trunk/test/Preprocessor/init.c
+++ cfe/trunk/test/Preprocessor/init.c
@@ -10007,6 +10007,9 @@
 // RUN:   | FileCheck -match-full-lines -check-prefix=RISCV32 %s
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=riscv32-unknown-linux < /dev/null \
 // RUN:   | FileCheck -match-full-lines -check-prefixes=RISCV32,RISCV32-LINUX %s
+// RUN: %clang_cc1 -E -dM -ffreestanding -triple=riscv32 \
+// RUN: -fforce-enable-int128 < /dev/null | FileCheck -match-full-lines \
+// RUN: -check-prefixes=RISCV32,RISCV32-INT128 %s
 // RISCV32: #define _ILP32 1
 // RISCV32: #define __ATOMIC_ACQUIRE 2
 // RISCV32: #define __ATOMIC_ACQ_REL 4
@@ -10136,6 +10139,7 @@
 // RISCV32: #define __SIG_ATOMIC_WIDTH__ 32
 // RISCV32: #define __SIZEOF_DOUBLE__ 8
 // RISCV32: #define __SIZEOF_FLOAT__ 4
+// RISCV32-INT128: #define __SIZEOF_INT128__ 16
 // RISCV32: #define __SIZEOF_INT__ 4
 // RISCV32: #define __SIZEOF_LONG_DOUBLE__ 16
 // RISCV32: #define __SIZEOF_LONG_LONG__ 8