diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -5426,8 +5426,8 @@
 
   ErrorUnsupported(E, "builtin function");
 
-  // Unknown builtin, for now just dump it out and return undef.
-  return GetUndefRValue(E->getType());
+  // Unknown builtin, for now just dump it out and return poison.
+  return GetPoisonRValue(E->getType());
 }
 
 static Value *EmitTargetArchBuiltinExpr(CodeGenFunction *CGF,
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -5520,7 +5520,7 @@
     EnsureInsertPoint();
 
     // Return a reasonable RValue.
-    return GetUndefRValue(RetTy);
+    return GetPoisonRValue(RetTy);
   }
 
   // If this is a musttail call, return immediately. We do not branch to the
@@ -5538,7 +5538,7 @@
       Builder.CreateRet(CI);
     Builder.ClearInsertionPoint();
     EnsureInsertPoint();
-    return GetUndefRValue(RetTy);
+    return GetPoisonRValue(RetTy);
   }
 
   // Perform the swifterror writeback.
@@ -5595,7 +5595,7 @@
     case ABIArgInfo::Ignore:
       // If we are ignoring an argument that had a result, make sure to
       // construct the appropriate return value for our caller.
-      return GetUndefRValue(RetTy);
+      return GetPoisonRValue(RetTy);
 
     case ABIArgInfo::Extend:
     case ABIArgInfo::Direct: {
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -1169,7 +1169,7 @@
   return Builder.CreateICmpNE(V, llvm::Constant::getNullValue(V->getType()));
 }
 
-RValue CodeGenFunction::GetUndefRValue(QualType Ty) {
+RValue CodeGenFunction::GetPoisonRValue(QualType Ty) {
   if (Ty->isVoidType())
     return RValue::get(nullptr);
 
@@ -1177,7 +1177,7 @@
   case TEK_Complex: {
     llvm::Type *EltTy =
       ConvertType(Ty->castAs<ComplexType>()->getElementType());
-    llvm::Value *U = llvm::UndefValue::get(EltTy);
+    llvm::Value *U = llvm::PoisonValue::get(EltTy);
     return RValue::getComplex(std::make_pair(U, U));
   }
 
@@ -1190,7 +1190,7 @@
   }
 
   case TEK_Scalar:
-    return RValue::get(llvm::UndefValue::get(ConvertType(Ty)));
+    return RValue::get(llvm::PoisonValue::get(ConvertType(Ty)));
   }
   llvm_unreachable("bad evaluation kind");
 }
@@ -1198,7 +1198,7 @@
 RValue CodeGenFunction::EmitUnsupportedRValue(const Expr *E,
                                               const char *Name) {
   ErrorUnsupported(E, Name);
-  return GetUndefRValue(E->getType());
+  return GetPoisonRValue(E->getType());
 }
 
 LValue CodeGenFunction::EmitUnsupportedLValue(const Expr *E,
@@ -1207,7 +1207,7 @@
   llvm::Type *ElTy = ConvertType(E->getType());
   llvm::Type *Ty = llvm::PointerType::getUnqual(ElTy);
   return MakeAddrLValue(
-      Address(llvm::UndefValue::get(Ty), ElTy, CharUnits::One()), E->getType());
+      Address(llvm::PoisonValue::get(Ty), ElTy, CharUnits::One()), E->getType());
 }
 
 bool CodeGenFunction::IsWrappedCXXThis(const Expr *Obj) {
diff --git a/clang/lib/CodeGen/CGExprComplex.cpp b/clang/lib/CodeGen/CGExprComplex.cpp
--- a/clang/lib/CodeGen/CGExprComplex.cpp
+++ b/clang/lib/CodeGen/CGExprComplex.cpp
@@ -419,7 +419,7 @@
   CGF.ErrorUnsupported(E, "complex expression");
   llvm::Type *EltTy =
     CGF.ConvertType(getComplexType(E->getType())->getElementType());
-  llvm::Value *U = llvm::UndefValue::get(EltTy);
+  llvm::Value *U = llvm::PoisonValue::get(EltTy);
   return ComplexPairTy(U, U);
 }
 
@@ -1274,7 +1274,7 @@
     CGF.ErrorUnsupported(E, "complex va_arg expression");
     llvm::Type *EltTy =
       CGF.ConvertType(E->getType()->castAs<ComplexType>()->getElementType());
-    llvm::Value *U = llvm::UndefValue::get(EltTy);
+    llvm::Value *U = llvm::PoisonValue::get(EltTy);
     return ComplexPairTy(U, U);
   }
 
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -1624,7 +1624,7 @@
   CGF.ErrorUnsupported(E, "scalar expression");
   if (E->getType()->isVoidType())
     return nullptr;
-  return llvm::UndefValue::get(CGF.ConvertType(E->getType()));
+  return llvm::PoisonValue::get(CGF.ConvertType(E->getType()));
 }
 
 Value *
@@ -4906,7 +4906,7 @@
   // If EmitVAArg fails, emit an error.
   if (!ArgPtr.isValid()) {
     CGF.ErrorUnsupported(VE, "va_arg expression");
-    return llvm::UndefValue::get(ArgTy);
+    return llvm::PoisonValue::get(ArgTy);
   }
 
   // FIXME Volatility.
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -3740,8 +3740,8 @@
   /// Create a check that a scalar RValue is non-null.
   llvm::Value *EmitNonNullRValueCheck(RValue RV, QualType T);
 
-  /// GetUndefRValue - Get an appropriate 'undef' rvalue for the given type.
-  RValue GetUndefRValue(QualType Ty);
+  /// GetPoisonRValue - Get an appropriate 'poison' rvalue for the given type.
+  RValue GetPoisonRValue(QualType Ty);
 
   /// EmitUnsupportedRValue - Emit a dummy r-value using the type of E
   /// and issue an ErrorUnsupported style diagnostic (using the
diff --git a/libcxxabi/test/test_demangle.pass.cpp b/libcxxabi/test/test_demangle.pass.cpp
--- a/libcxxabi/test/test_demangle.pass.cpp
+++ b/libcxxabi/test/test_demangle.pass.cpp
@@ -3169,7 +3169,7 @@
     {"_ZN5clang7CodeGen15CodeGenFunction9EmitCheckEPN4llvm5ValueEj", "clang::CodeGen::CodeGenFunction::EmitCheck(llvm::Value*, unsigned int)"},
     {"_ZN5clang7CodeGen15CodeGenFunction9getTrapBBEv", "clang::CodeGen::CodeGenFunction::getTrapBB()"},
     {"_ZN5clang7CodeGen15CodeGenFunction24EmitComplexPrePostIncDecEPKNS_13UnaryOperatorENS0_6LValueEbb", "clang::CodeGen::CodeGenFunction::EmitComplexPrePostIncDec(clang::UnaryOperator const*, clang::CodeGen::LValue, bool, bool)"},
-    {"_ZN5clang7CodeGen15CodeGenFunction14GetUndefRValueENS_8QualTypeE", "clang::CodeGen::CodeGenFunction::GetUndefRValue(clang::QualType)"},
+    {"_ZN5clang7CodeGen15CodeGenFunction14GetPoisonRValueENS_8QualTypeE", "clang::CodeGen::CodeGenFunction::GetPoisonRValue(clang::QualType)"},
     {"_ZN5clang7CodeGen15CodeGenFunction21EmitUnsupportedRValueEPKNS_4ExprEPKc", "clang::CodeGen::CodeGenFunction::EmitUnsupportedRValue(clang::Expr const*, char const*)"},
     {"_ZN5clang7CodeGen15CodeGenFunction21EmitUnsupportedLValueEPKNS_4ExprEPKc", "clang::CodeGen::CodeGenFunction::EmitUnsupportedLValue(clang::Expr const*, char const*)"},
     {"_ZN5clang7CodeGen15CodeGenFunction17EmitCheckedLValueEPKNS_4ExprE", "clang::CodeGen::CodeGenFunction::EmitCheckedLValue(clang::Expr const*)"},