[LLParser] Use poison instead of undef when cleaning up forward refs

Author: nikic

llvm/lib/AsmParser/LLParser.cpp

@@ -3546,15 +3546,15 @@ LLParser::PerFunctionState::~PerFunctionState() {
     if (isa<BasicBlock>(P.second.first))
       continue;
     P.second.first->replaceAllUsesWith(
-        UndefValue::get(P.second.first->getType()));
+        PoisonValue::get(P.second.first->getType()));
     P.second.first->deleteValue();
   }
 
   for (const auto &P : ForwardRefValIDs) {
     if (isa<BasicBlock>(P.second.first))
       continue;
     P.second.first->replaceAllUsesWith(
-        UndefValue::get(P.second.first->getType()));
+        PoisonValue::get(P.second.first->getType()));
     P.second.first->deleteValue();
   }
 }