Index: llvm/trunk/lib/Support/SpecialCaseList.cpp
===================================================================
--- llvm/trunk/lib/Support/SpecialCaseList.cpp
+++ llvm/trunk/lib/Support/SpecialCaseList.cpp
@@ -28,6 +28,11 @@
 
 bool SpecialCaseList::Matcher::insert(std::string Regexp,
                                       std::string &REError) {
+  if (Regexp.empty()) {
+    REError = "Supplied regexp was blank";
+    return false;
+  }
+
   if (Regex::isLiteralERE(Regexp)) {
     Strings.insert(Regexp);
     return true;
Index: llvm/trunk/unittests/Support/SpecialCaseListTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/SpecialCaseListTest.cpp
+++ llvm/trunk/unittests/Support/SpecialCaseListTest.cpp
@@ -67,6 +67,9 @@
 
   EXPECT_EQ(makeSpecialCaseList("[[]", Error), nullptr);
   EXPECT_TRUE(((StringRef)Error).startswith("malformed regex for section [: "));
+
+  EXPECT_EQ(makeSpecialCaseList("src:=", Error), nullptr);
+  EXPECT_TRUE(((StringRef)Error).endswith("Supplied regexp was blank"));
 }
 
 TEST_F(SpecialCaseListTest, Section) {