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/CodeGen/WinEHPrepare.cpp b/llvm/lib/CodeGen/WinEHPrepare.cpp
index a71f657..baca410 100644
--- a/llvm/lib/CodeGen/WinEHPrepare.cpp
+++ b/llvm/lib/CodeGen/WinEHPrepare.cpp
@@ -733,7 +733,7 @@ void WinEHPrepare::demotePHIsOnFunclets(Function &F,
 
   for (auto *PN : PHINodes) {
     // There may be lingering uses on other EH PHIs being removed
-    PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+    PN->replaceAllUsesWith(PoisonValue::get(PN->getType()));
     PN->eraseFromParent();
   }
 }