Index: lib/CodeGen/ABIInfo.h
===================================================================
--- lib/CodeGen/ABIInfo.h
+++ lib/CodeGen/ABIInfo.h
@@ -87,6 +87,8 @@
     virtual bool isHomogeneousAggregateSmallEnough(const Type *Base,
                                                    uint64_t Members) const;
 
+    virtual bool shouldSignExtUnsignedType(QualType Ty) const;
+
     bool isHomogeneousAggregate(QualType Ty, const Type *&Base,
                                 uint64_t &Members) const;
 
Index: lib/CodeGen/CGCall.cpp
===================================================================
--- lib/CodeGen/CGCall.cpp
+++ lib/CodeGen/CGCall.cpp
@@ -1588,8 +1588,12 @@
     case ABIArgInfo::Extend:
       if (ParamType->isSignedIntegerOrEnumerationType())
         Attrs.addAttribute(llvm::Attribute::SExt);
-      else if (ParamType->isUnsignedIntegerOrEnumerationType())
-        Attrs.addAttribute(llvm::Attribute::ZExt);
+      else if (ParamType->isUnsignedIntegerOrEnumerationType()) {
+        if(getTypes().getABIInfo().shouldSignExtUnsignedType(ParamType))
+          Attrs.addAttribute(llvm::Attribute::SExt);
+        else
+          Attrs.addAttribute(llvm::Attribute::ZExt);
+      }
       // FALL THROUGH
     case ABIArgInfo::Direct:
       if (ArgNo == 0 && FI.isChainCall())
Index: lib/CodeGen/TargetInfo.cpp
===================================================================
--- lib/CodeGen/TargetInfo.cpp
+++ lib/CodeGen/TargetInfo.cpp
@@ -108,6 +108,10 @@
   return false;
 }
 
+bool ABIInfo::shouldSignExtUnsignedType(QualType Ty) const {
+  return false;
+}
+
 void ABIArgInfo::dump() const {
   raw_ostream &OS = llvm::errs();
   OS << "(ABIArgInfo Kind=";
@@ -5544,6 +5548,7 @@
   void computeInfo(CGFunctionInfo &FI) const override;
   llvm::Value *EmitVAArg(llvm::Value *VAListAddr, QualType Ty,
                          CodeGenFunction &CGF) const override;
+  bool shouldSignExtUnsignedType(QualType Ty) const override;
 };
 
 class MIPSTargetCodeGenInfo : public TargetCodeGenInfo {
@@ -5846,6 +5851,16 @@
   return AddrTyped;
 }
 
+bool MipsABIInfo::shouldSignExtUnsignedType(QualType Ty) const {
+  int TySize = getContext().getTypeSize(Ty);
+  
+  // MIPS64 ABI requires unsigned 32 bit integers to be sign extended.
+  if(Ty->isUnsignedIntegerOrEnumerationType() && TySize == 32)
+    return true;
+  
+  return false;
+}
+
 bool
 MIPSTargetCodeGenInfo::initDwarfEHRegSizeTable(CodeGen::CodeGenFunction &CGF,
                                                llvm::Value *Address) const {
Index: test/CodeGen/atomics-inlining.c
===================================================================
--- test/CodeGen/atomics-inlining.c
+++ test/CodeGen/atomics-inlining.c
@@ -76,8 +76,8 @@
 // MIPS32: store atomic i32 {{.*}}, i32* @i1 seq_cst
 // MIPS32: call i64 @__atomic_load_8(i8* bitcast (i64* @ll1 to i8*)
 // MIPS32: call void @__atomic_store_8(i8* bitcast (i64* @ll1 to i8*), i64
-// MIPS32: call void @__atomic_load(i32 zeroext 100, i8* getelementptr inbounds ([100 x i8], [100 x i8]* @a1, i32 0, i32 0), i8* getelementptr inbounds ([100 x i8], [100 x i8]* @a2, i32 0, i32 0)
-// MIPS32: call void @__atomic_store(i32 zeroext 100, i8* getelementptr inbounds ([100 x i8], [100 x i8]* @a1, i32 0, i32 0), i8* getelementptr inbounds ([100 x i8], [100 x i8]* @a2, i32 0, i32 0)
+// MIPS32: call void @__atomic_load(i32 signext 100, i8* getelementptr inbounds ([100 x i8], [100 x i8]* @a1, i32 0, i32 0), i8* getelementptr inbounds ([100 x i8], [100 x i8]* @a2, i32 0, i32 0)
+// MIPS32: call void @__atomic_store(i32 signext 100, i8* getelementptr inbounds ([100 x i8], [100 x i8]* @a1, i32 0, i32 0), i8* getelementptr inbounds ([100 x i8], [100 x i8]* @a2, i32 0, i32 0)
 
 // MIPS64-LABEL: define void @test1
 // MIPS64: = load atomic i8, i8* @c1 seq_cst
Index: test/CodeGen/mips-unsigned-ext-var.c
===================================================================
--- test/CodeGen/mips-unsigned-ext-var.c
+++ test/CodeGen/mips-unsigned-ext-var.c
@@ -0,0 +1,22 @@
+// RUN: %clang -target mips64-unknown-linux -O2 -mabi=n64 -S -emit-llvm %s -o - | FileCheck %s -check-prefix=N64
+// RUN: %clang -target mips64-unknown-linux -O2 -mabi=n32 -S -emit-llvm %s -o - | FileCheck %s -check-prefix=N32
+// RUN: %clang -target mips-unknown-linux -O2 -mabi=o32 -S -emit-llvm %s -o - | FileCheck %s -check-prefix=O32 
+
+#include <stdarg.h>
+
+unsigned foo(int x, ...) {
+  va_list valist;
+  va_start(valist, x);
+  unsigned a;
+  a = va_arg(valist, unsigned);
+  return a;
+}
+
+void foo1() {
+  unsigned f = 0xffffffe0;
+  foo(1,f);
+}
+
+//N64: call i32 (i32, ...) @foo(i32 signext undef, i32 signext -32)
+//N32: call i32 (i32, ...) @foo(i32 signext undef, i32 signext -32)
+//O32: call i32 (i32, ...) @foo(i32 signext undef, i32 signext -32)
\ No newline at end of file
Index: test/CodeGen/mips-unsigned-extend.c
===================================================================
--- test/CodeGen/mips-unsigned-extend.c
+++ test/CodeGen/mips-unsigned-extend.c
@@ -0,0 +1,15 @@
+// RUN: %clang -target mips64-unknown-linux -O0 -mabi=n64 -S -emit-llvm %s -o - | FileCheck %s -check-prefix=N64
+// RUN: %clang -target mips64-unknown-linux -O0 -mabi=n32 -S -emit-llvm %s -o - | FileCheck %s -check-prefix=N32
+// RUN: %clang -target mips-unknown-linux -O0 -mabi=o32 -S -emit-llvm %s -o - | FileCheck %s -check-prefix=O32 
+
+void foo(unsigned a) {
+}
+
+void foo1() {
+  unsigned f = 0xffffffe0;
+  foo(f);
+}
+
+// N64: call void @foo(i32 signext %0)
+// N32: call void @foo(i32 signext %0)
+// O32: call void @foo(i32 signext %0)
\ No newline at end of file
Index: test/CodeGenCXX/mips-size_t-ptrdiff_t.cpp
===================================================================
--- test/CodeGenCXX/mips-size_t-ptrdiff_t.cpp
+++ test/CodeGenCXX/mips-size_t-ptrdiff_t.cpp
@@ -10,10 +10,10 @@
   return rv;
 }
 // O32-LABEL: define i32* @_Z10alloc_longv()
-// O32: call noalias i8* @_Znwj(i32 zeroext 4)
+// O32: call noalias i8* @_Znwj(i32 signext 4)
 
 // N32-LABEL: define i32* @_Z10alloc_longv()
-// N32: call noalias i8* @_Znwj(i32 zeroext 4)
+// N32: call noalias i8* @_Znwj(i32 signext 4)
 
 // N64-LABEL: define i64* @_Z10alloc_longv()
 // N64: call noalias i8* @_Znwm(i64 zeroext 8)
@@ -24,10 +24,10 @@
 }
 
 // O32-LABEL: define i32* @_Z16alloc_long_arrayv()
-// O32: call noalias i8* @_Znaj(i32 zeroext 8)
+// O32: call noalias i8* @_Znaj(i32 signext 8)
 
 // N32-LABEL: define i32* @_Z16alloc_long_arrayv()
-// N32: call noalias i8* @_Znaj(i32 zeroext 8)
+// N32: call noalias i8* @_Znaj(i32 signext 8)
 
 // N64-LABEL: define i64* @_Z16alloc_long_arrayv()
 // N64: call noalias i8* @_Znam(i64 zeroext 16)