[clang] fix out of bounds access in an empty string when lexing a _Pragma with missing string token

The lexer can attempt to lex a _Pragma and crash with an out of bounds string access when it's
lexing a _Pragma whose string token is an invalid buffer, e.g. when a module header file from which the macro
expansion for that token was deleted from the file system.

Differential Revision: https://reviews.llvm.org/D116052

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Frontend/PrintPreprocessedOutput.cpp b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
index 1d0022b..e2fc862 100644
--- a/clang/lib/Frontend/PrintPreprocessedOutput.cpp
+++ b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
@@ -189,7 +189,8 @@ public:
   bool MoveToLine(const Token &Tok, bool RequireStartOfLine) {
     PresumedLoc PLoc = SM.getPresumedLoc(Tok.getLocation());
     unsigned TargetLine = PLoc.isValid() ? PLoc.getLine() : CurLine;
-    bool IsFirstInFile = Tok.isAtStartOfLine() && PLoc.getLine() == 1;
+    bool IsFirstInFile =
+        Tok.isAtStartOfLine() && PLoc.isValid() && PLoc.getLine() == 1;
     return MoveToLine(TargetLine, RequireStartOfLine) || IsFirstInFile;
   }