[flang-commits] [flang] 1def98d - [flang] Avoid forming a reference from null pointer (#84787)

[via flang-commits]

Author: Krzysztof Parzyszek
Date: 2024-03-11T14:35:31-05:00
New Revision: 1def98d9f2eb2ae39e774369693e6f2f74551b7f

URL: https://github.com/llvm/llvm-project/commit/1def98d9f2eb2ae39e774369693e6f2f74551b7f
DIFF: https://github.com/llvm/llvm-project/commit/1def98d9f2eb2ae39e774369693e6f2f74551b7f.diff

LOG: [flang] Avoid forming a reference from null pointer (#84787)

Doing so is an undefined behavior.

This was detected by the undefined behavior sanitizer.

Added: 
    

Modified: 
    flang/lib/Parser/token-sequence.cpp

Removed: 
    


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diff  --git a/flang/lib/Parser/token-sequence.cpp b/flang/lib/Parser/token-sequence.cpp
index c5a630c471d16e..799d13a423660c 100644
--- a/flang/lib/Parser/token-sequence.cpp
+++ b/flang/lib/Parser/token-sequence.cpp
@@ -136,7 +136,10 @@ void TokenSequence::Put(
 }
 
 void TokenSequence::Put(const CharBlock &t, Provenance provenance) {
-  Put(&t[0], t.size(), provenance);
+  // Avoid t[0] if t is empty: it would create a reference to nullptr,
+  // which is UB.
+  const char *addr{t.size() ? &t[0] : nullptr};
+  Put(addr, t.size(), provenance);
 }
 
 void TokenSequence::Put(const std::string &s, Provenance provenance) {