Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -5724,32 +5724,44 @@
 public:
   Mips64TargetInfoBase(const llvm::Triple &Triple)
       : MipsTargetInfoBase(Triple, "n64", "mips64r2") {
-    LongWidth = LongAlign = 64;
-    PointerWidth = PointerAlign = 64;
     LongDoubleWidth = LongDoubleAlign = 128;
     LongDoubleFormat = &llvm::APFloat::IEEEquad;
     if (getTriple().getOS() == llvm::Triple::FreeBSD) {
       LongDoubleWidth = LongDoubleAlign = 64;
       LongDoubleFormat = &llvm::APFloat::IEEEdouble;
     }
+    setN64ABITypes();
     SuitableAlign = 128;
     MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
   }
+
+  void setN64ABITypes() {
+    LongWidth = LongAlign = 64;
+    PointerWidth = PointerAlign = 64;
+    SizeType = UnsignedLong;
+    PtrDiffType = SignedLong;
+  }
+
+  void setN32ABITypes() {
+    LongWidth = LongAlign = 32;
+    PointerWidth = PointerAlign = 32;
+    SizeType = UnsignedInt;
+    PtrDiffType = SignedInt;
+  }
+
   bool setABI(const std::string &Name) override {
     if (Name == "n32") {
-      LongWidth = LongAlign = 32;
-      PointerWidth = PointerAlign = 32;
-      ABI = Name;
-      return true;
-    } else if (Name == "n64") {
+      setN32ABITypes();
       ABI = Name;
       return true;
-    } else if (Name == "64") {
+    } else if (Name == "n64" || Name == "64") {
+      setN64ABITypes();
       ABI = "n64";
       return true;
     } else
       return false;
   }
+
   void getTargetDefines(const LangOptions &Opts,
                         MacroBuilder &Builder) const override {
     MipsTargetInfoBase::getTargetDefines(Opts, Builder);
Index: test/CodeGenCXX/mips-size_t-ptrdiff_t.cpp
===================================================================
--- /dev/null
+++ test/CodeGenCXX/mips-size_t-ptrdiff_t.cpp
@@ -0,0 +1,49 @@
+// RUN: %clang_cc1 -x c++ -emit-llvm -triple=mips-unknown-linux-gnu < %s | FileCheck --check-prefix=O32 %s
+// RUN: %clang_cc1 -x c++ -emit-llvm -triple=mips64-unknown-linux-gnu -target-abi n32 < %s | FileCheck --check-prefix=N32 %s
+// RUN: %clang_cc1 -x c++ -emit-llvm -triple=mips64-unknown-linux-gnu -target-abi 64 < %s | FileCheck --check-prefix=N64 %s
+
+// Test that the size_t is correct for the ABI. It's not sufficient to be the
+// correct size, it must be the same type for correct name mangling.
+
+long *alloc_long() {
+  long *rv = new long; // size_t is implicit in the new operator
+  return rv;
+}
+// O32-LABEL: define i32* @_Z10alloc_longv()
+// O32: call noalias i8* @_Znwj(i32 4)
+
+// N32-LABEL: define i32* @_Z10alloc_longv()
+// N32: call noalias i8* @_Znwj(i32 4)
+
+// N64-LABEL: define i64* @_Z10alloc_longv()
+// N64: call noalias i8* @_Znwm(i64 8)
+
+long *alloc_long_array() {
+  long *rv = new long[2];
+  return rv;
+}
+
+// O32-LABEL: define i32* @_Z16alloc_long_arrayv()
+// O32: call noalias i8* @_Znaj(i32 8)
+
+// N32-LABEL: define i32* @_Z16alloc_long_arrayv()
+// N32: call noalias i8* @_Znaj(i32 8)
+
+// N64-LABEL: define i64* @_Z16alloc_long_arrayv()
+// N64: call noalias i8* @_Znam(i64 16)
+
+#include <stddef.h>
+
+void size_t_arg(size_t a) {
+}
+
+// O32-LABEL: _Z10size_t_argj
+// N32-LABEL: _Z10size_t_argj
+// N64-LABEL: _Z10size_t_argm
+
+void ptrdiff_t_arg(ptrdiff_t a) {
+}
+
+// O32-LABEL: _Z13ptrdiff_t_argi
+// N32-LABEL: _Z13ptrdiff_t_argi
+// N64-LABEL: _Z13ptrdiff_t_argl