[llvm] [Assignment Tracking] Change placeholder from `undef` to `poison` (PR #119760)

[Nuno Lopes via llvm-commits]

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@@ -223,12 +223,12 @@ void DbgAssignIntrinsic::setAddress(Value *V) {
 void DbgAssignIntrinsic::setKillAddress() {
   if (isKillAddress())
     return;
-  setAddress(UndefValue::get(getAddress()->getType()));
+  setAddress(PoisonValue::get(getAddress()->getType()));
 }
 
 bool DbgAssignIntrinsic::isKillAddress() const {
   Value *Addr = getAddress();
-  return !Addr || isa<UndefValue>(Addr);
+  return !Addr || isa<PoisonValue>(Addr);
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nunoplopes wrote:

don't change this one yet for compatibility with older IR.

https://github.com/llvm/llvm-project/pull/119760