fix bug in SourceColumnMap::startOfPreviousColumn

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@167360 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Frontend/TextDiagnostic.cpp

@@ -298,7 +298,7 @@ struct SourceColumnMap {
   /// \brief Map from a byte index to the previous byte which starts a column.
   int startOfPreviousColumn(int N) const {
     assert(0 < N && N < static_cast<int>(m_columnToByte.size()));
-    while (byteToColumn(N--) == -1) {}
+    while (byteToColumn(--N) == -1) {}
     return N;
   }
 

test/Misc/wrong-encoding2.c

@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fsyntax-only -fmessage-length 100 %s 2>&1 | FileCheck -strict-whitespace %s
+// REQUIRES: asserts
+
+int main() {
+    "É#x#p)6Ò)ѽŠ$ûž>U êhÑüÃö|Ÿ থϻgŸY|`?ò;;Æ¿VjÇ\\ù€‡ûݪW9úТ:ÌŠO EøÛ<C3B8>y?SKªy¦¹‡Øài&n";
+}
+
+// CHECK-NOT:Assertion