Merge pull request swiftlang#9882 from eeckstein/fix-demangler-hang

Author: swift-ci

lib/Demangling/Demangler.cpp

@@ -442,6 +442,10 @@ NodePointer Demangler::demangleMultiSubstitutions() {
   int RepeatCount = -1;
   while (true) {
     char c = nextChar();
+    if (c == 0) {
+      // End of text.
+      return nullptr;
+    }
     if (isLowerLetter(c)) {
       // It's a substitution with an index < 26.
       NodePointer Nd = pushMultiSubstitutions(RepeatCount, c - 'a');

test/Demangle/Inputs/manglings.txt

@@ -256,4 +256,5 @@ _T08_ElementQzSbs5Error_pIxxdzo_ABSbsAC_pIxidzo_s26RangeReplaceableCollectionRzA
 _T0Ix_IyB_Tr ---> {T:} reabstraction thunk from @callee_owned () -> () to @callee_unowned @convention(block) () -> ()
 _T0Rml ---> _T0Rml
 _T0Tk ---> _T0Tk
+_T0A8 ---> _T0A8