Index: llvm/trunk/lib/Support/Regex.cpp
===================================================================
--- llvm/trunk/lib/Support/Regex.cpp
+++ llvm/trunk/lib/Support/Regex.cpp
@@ -19,6 +19,8 @@
 #include <string>
 using namespace llvm;
 
+Regex::Regex() : error(REG_BADPAT), preg(nullptr) {}
+
 Regex::Regex(StringRef regex, unsigned Flags) {
   unsigned flags = 0;
   preg = new llvm_regex();
Index: llvm/trunk/unittests/Support/RegexTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/RegexTest.cpp
+++ llvm/trunk/unittests/Support/RegexTest.cpp
@@ -153,4 +153,13 @@
   EXPECT_TRUE(r2.match("916"));
 }
 
+TEST_F(RegexTest, NoArgConstructor) {
+  std::string Error;
+  Regex r1;
+  EXPECT_FALSE(r1.isValid(Error));
+  EXPECT_EQ("invalid regular expression", Error);
+  r1 = Regex("abc");
+  EXPECT_TRUE(r1.isValid(Error));
+}
+
 }