Use PoisonValue instead of UndefValue when RAUWing unreachable code [NFC]

Replacing the following instances of UndefValue with PoisonValue, where the UndefValue is used as an arbitrary value:

- llvm/lib/CodeGen/WinEHPrepare.cpp
`demotePHIsOnFunclets`: RAUW arbitrary value for lingering uses of removed PHI nodes

 - llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
`FoldSingleEntryPHINodes`: Removes a self-referential single entry phi node.

 - llvm/lib/Transforms/Utils/CallGraphUpdater.cpp
`finalize`: Remove all references to removed functions.

- llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
`cleanup`: the result is not used then the inserted instructions are removed.

 - llvm/tools/bugpoint/CrashDebugger.cpp
`TestInts`:  the program is cloned and instructions are removed to narrow down source of crash.

Differential Revision: https://reviews.llvm.org/D133640

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 9ab8014..746fe79 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -149,7 +149,7 @@ bool llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
     if (PN->getIncomingValue(0) != PN)
       PN->replaceAllUsesWith(PN->getIncomingValue(0));
     else
-      PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+      PN->replaceAllUsesWith(PoisonValue::get(PN->getType()));
 
     if (MemDep)
       MemDep->removeInstruction(PN);  // Memdep updates AA itself.