diff --git a/clang/lib/AST/Interp/Function.cpp b/clang/lib/AST/Interp/Function.cpp
index e409002171c4b..75312999d23d6 100644
--- a/clang/lib/AST/Interp/Function.cpp
+++ b/clang/lib/AST/Interp/Function.cpp
@@ -7,11 +7,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "Function.h"
-#include "Opcode.h"
 #include "Program.h"
+#include "Opcode.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
-#include "clang/Basic/Builtins.h"
 
 using namespace clang;
 using namespace clang::interp;
@@ -48,9 +47,3 @@ bool Function::isVirtual() const {
     return M->isVirtual();
   return false;
 }
-
-bool Function::needsRuntimeArgPop(const ASTContext &Ctx) const {
-  if (!isBuiltin())
-    return false;
-  return Ctx.BuiltinInfo.hasCustomTypechecking(getBuiltinID());
-}
diff --git a/clang/lib/AST/Interp/Function.h b/clang/lib/AST/Interp/Function.h
index 5444c9f59cda7..644d4cd53b1e1 100644
--- a/clang/lib/AST/Interp/Function.h
+++ b/clang/lib/AST/Interp/Function.h
@@ -171,12 +171,6 @@ class Function final {
 
   unsigned getBuiltinID() const { return F->getBuiltinID(); }
 
-  bool isBuiltin() const { return F->getBuiltinID() != 0; }
-
-  /// Does this function need its arguments to be classified at runtime
-  /// rather than at bytecode-compile-time?
-  bool needsRuntimeArgPop(const ASTContext &Ctx) const;
-
   unsigned getNumParams() const { return ParamTypes.size(); }
 
   unsigned getParamOffset(unsigned ParamIndex) const {
diff --git a/clang/lib/AST/Interp/Interp.cpp b/clang/lib/AST/Interp/Interp.cpp
index e006c196f6ed4..b891306e6aa40 100644
--- a/clang/lib/AST/Interp/Interp.cpp
+++ b/clang/lib/AST/Interp/Interp.cpp
@@ -122,18 +122,6 @@ static bool CheckGlobal(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
 namespace clang {
 namespace interp {
 
-bool popBuiltinArgs(InterpState &S, CodePtr OpPC) {
-  assert(S.Current && S.Current->getFunction()->needsRuntimeArgPop(S.getCtx()));
-  const Expr *E = S.Current->getExpr(OpPC);
-  assert(isa<CallExpr>(E));
-  const CallExpr *CE = cast<CallExpr>(E);
-  for (const auto *A : llvm::reverse(CE->arguments())) {
-    PrimType Ty = S.getContext().classify(A->getType()).value_or(PT_Ptr);
-    TYPE_SWITCH(Ty, S.Stk.discard<T>());
-  }
-  return true;
-}
-
 bool CheckExtern(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
   if (!Ptr.isExtern())
     return true;
diff --git a/clang/lib/AST/Interp/Interp.h b/clang/lib/AST/Interp/Interp.h
index 4da5985e3b3d6..9eae79ba5d1e7 100644
--- a/clang/lib/AST/Interp/Interp.h
+++ b/clang/lib/AST/Interp/Interp.h
@@ -181,9 +181,6 @@ enum class ArithOp { Add, Sub };
 // Returning values
 //===----------------------------------------------------------------------===//
 
-/// Pop arguments of builtins defined as func-name(...).
-bool popBuiltinArgs(InterpState &S, CodePtr OpPC);
-
 template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool Ret(InterpState &S, CodePtr &PC, APValue &Result) {
   const T &Ret = S.Stk.pop<T>();
@@ -200,16 +197,8 @@ bool Ret(InterpState &S, CodePtr &PC, APValue &Result) {
   }
 
   assert(S.Current->getFrameOffset() == S.Stk.size() && "Invalid frame");
-  if (!S.checkingPotentialConstantExpression() || S.Current->Caller) {
-    // Certain builtin functions are declared as func-name(...), so the
-    // parameters are checked in Sema and only available through the CallExpr.
-    // The interp::Function we create for them has 0 parameters, so we need to
-    // remove them from the stack by checking the CallExpr.
-    if (S.Current && S.Current->getFunction()->needsRuntimeArgPop(S.getCtx()))
-      popBuiltinArgs(S, PC);
-    else
-      S.Current->popArgs();
-  }
+  if (!S.checkingPotentialConstantExpression() || S.Current->Caller)
+    S.Current->popArgs();
 
   if (InterpFrame *Caller = S.Current->Caller) {
     PC = S.Current->getRetPC();
diff --git a/clang/lib/AST/Interp/InterpBuiltin.cpp b/clang/lib/AST/Interp/InterpBuiltin.cpp
index 01c41339bba8c..b023d09df4878 100644
--- a/clang/lib/AST/Interp/InterpBuiltin.cpp
+++ b/clang/lib/AST/Interp/InterpBuiltin.cpp
@@ -162,17 +162,6 @@ static bool interp__builtin_fmin(InterpState &S, CodePtr OpPC,
   return true;
 }
 
-/// Defined as __builtin_isnan(...), to accommodate the fact that it can
-/// take a float, double, long double, etc.
-/// But for us, that's all a Floating anyway.
-static bool interp__builtin_isnan(InterpState &S, CodePtr OpPC,
-                                  const InterpFrame *Frame, const Function *F) {
-  const Floating &Arg = S.Stk.peek<Floating>();
-
-  S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Arg.isNan()));
-  return true;
-}
-
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F) {
   InterpFrame *Frame = S.Current;
   APValue Dummy;
@@ -234,11 +223,6 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F) {
       return Ret<PT_Float>(S, OpPC, Dummy);
     break;
 
-  case Builtin::BI__builtin_isnan:
-    if (interp__builtin_isnan(S, OpPC, Frame, F))
-      return Ret<PT_Sint32>(S, OpPC, Dummy);
-    break;
-
   default:
     return false;
   }
diff --git a/clang/test/Sema/constant-builtins-fmin.cpp b/clang/test/Sema/constant-builtins-fmin.cpp
index 8c80f7550666e..bf3e81e21e617 100644
--- a/clang/test/Sema/constant-builtins-fmin.cpp
+++ b/clang/test/Sema/constant-builtins-fmin.cpp
@@ -1,5 +1,4 @@
 // RUN: %clang_cc1 -std=c++17 -fsyntax-only -verify %s
-// RUN: %clang_cc1 -std=c++17 -fsyntax-only -verify -fexperimental-new-constant-interpreter %s
 // expected-no-diagnostics
 
 constexpr double NaN = __builtin_nan("");