Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -5513,6 +5513,8 @@
     if (RegNo == 1) return 5;
     return -1;
   }
+
+  bool isCLZForZeroUndef() const override { return false; }
 };
 
 const Builtin::Info MipsTargetInfoBase::BuiltinInfo[] = {
Index: test/CodeGen/mips-count-builtins.c
===================================================================
--- /dev/null
+++ test/CodeGen/mips-count-builtins.c
@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 %s -triple mips-unknown-linux-gnu -emit-llvm -o - | FileCheck %s
+//
+// Test that the ctlz and cttz builtins are defined for zero.
+// Based on count-builtin.c
+
+int leading, trailing, pop;
+
+void test_i16(short P) {
+  leading = __builtin_clzs(P);
+  trailing = __builtin_ctzs(P);
+
+// CHECK: @test_i16
+// CHECK: call i16 @llvm.ctlz.i16(i16 {{.*}}, i1 false)
+// CHECK: call i16 @llvm.cttz.i16(i16 {{.*}}, i1 false)
+}
+
+void test_i32(int P) {
+  leading = __builtin_clz(P);
+  trailing = __builtin_ctz(P);
+
+// CHECK: @test_i32
+// CHECK: call i32 @llvm.ctlz.i32(i32 {{.*}}, i1 false)
+// CHECK: call i32 @llvm.cttz.i32(i32 {{.*}}, i1 false)
+}
+
+void test_i64(float P) {
+  leading = __builtin_clzll(P);
+  trailing = __builtin_ctzll(P);
+// CHECK: @test_i64
+// CHECK: call i64 @llvm.ctlz.i64(i64 {{.*}}, i1 false)
+// CHECK: call i64 @llvm.cttz.i64(i64 {{.*}}, i1 false)
+}