diff --git a/clang/lib/AST/Interp/InterpBuiltin.cpp b/clang/lib/AST/Interp/InterpBuiltin.cpp
index 9cf206ecc212ad..4384ace6b6be5e 100644
--- a/clang/lib/AST/Interp/InterpBuiltin.cpp
+++ b/clang/lib/AST/Interp/InterpBuiltin.cpp
@@ -34,6 +34,19 @@ PrimType getIntPrimType(const InterpState &S) {
   llvm_unreachable("Int isn't 16 or 32 bit?");
 }
 
+PrimType getLongPrimType(const InterpState &S) {
+  const TargetInfo &TI = S.getCtx().getTargetInfo();
+  unsigned LongWidth = TI.getLongWidth();
+
+  if (LongWidth == 64)
+    return PT_Sint64;
+  else if (LongWidth == 32)
+    return PT_Sint32;
+  else if (LongWidth == 16)
+    return PT_Sint16;
+  llvm_unreachable("long isn't 16, 32 or 64 bit?");
+}
+
 /// Peek an integer value from the stack into an APSInt.
 static APSInt peekToAPSInt(InterpStack &Stk, PrimType T, size_t Offset = 0) {
   if (Offset == 0)
@@ -110,6 +123,19 @@ static void pushAPSInt(InterpState &S, const APSInt &Val) {
   }
 }
 
+/// Pushes \p Val to the stack, as a target-dependent 'long'.
+static void pushLong(InterpState &S, int64_t Val) {
+  PrimType LongType = getLongPrimType(S);
+  if (LongType == PT_Sint64)
+    S.Stk.push<Integral<64, true>>(Integral<64, true>::from(Val));
+  else if (LongType == PT_Sint32)
+    S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Val));
+  else if (LongType == PT_Sint16)
+    S.Stk.push<Integral<16, true>>(Integral<16, true>::from(Val));
+  else
+    llvm_unreachable("Long isn't 16, 32 or 64 bit?");
+}
+
 static void pushSizeT(InterpState &S, uint64_t Val) {
   const TargetInfo &TI = S.getCtx().getTargetInfo();
   unsigned SizeTWidth = TI.getTypeWidth(TI.getSizeType());
@@ -533,6 +559,26 @@ static bool interp__builtin_classify_type(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+// __builtin_expect(long, long)
+// __builtin_expect_with_probability(long, long, double)
+static bool interp__builtin_expect(InterpState &S, CodePtr OpPC,
+                                   const InterpFrame *Frame,
+                                   const Function *Func, const CallExpr *Call) {
+  // The return value is simply the value of the first parameter.
+  // We ignore the probability.
+  unsigned NumArgs = Call->getNumArgs();
+  assert(NumArgs == 2 || NumArgs == 3);
+
+  PrimType ArgT = *S.getContext().classify(Call->getArg(0)->getType());
+  unsigned Offset = align(primSize(getLongPrimType(S))) * 2;
+  if (NumArgs == 3)
+    Offset += align(primSize(PT_Float));
+
+  APSInt Val = peekToAPSInt(S.Stk, ArgT, Offset);
+  pushLong(S, Val.getSExtValue());
+  return true;
+}
+
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
                       const CallExpr *Call) {
   InterpFrame *Frame = S.Current;
@@ -702,6 +748,12 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
       return false;
     break;
 
+  case Builtin::BI__builtin_expect:
+  case Builtin::BI__builtin_expect_with_probability:
+    if (!interp__builtin_expect(S, OpPC, Frame, F, Call))
+      return false;
+    break;
+
   default:
     return false;
   }
diff --git a/clang/test/AST/Interp/builtin-functions.cpp b/clang/test/AST/Interp/builtin-functions.cpp
index 0726dab37cb4eb..35a1f9a75092a0 100644
--- a/clang/test/AST/Interp/builtin-functions.cpp
+++ b/clang/test/AST/Interp/builtin-functions.cpp
@@ -331,3 +331,11 @@ namespace bitreverse {
   char bitreverse3[__builtin_bitreverse32(0x12345678) == 0x1E6A2C48 ? 1 : -1];
   char bitreverse4[__builtin_bitreverse64(0x0123456789ABCDEFULL) == 0xF7B3D591E6A2C480 ? 1 : -1];
 }
+
+namespace expect {
+  constexpr int a() {
+    return 12;
+  }
+  static_assert(__builtin_expect(a(),1) == 12, "");
+  static_assert(__builtin_expect_with_probability(a(), 1, 1.0) == 12, "");
+}
diff --git a/clang/test/Sema/builtin-expect-with-probability.cpp b/clang/test/Sema/builtin-expect-with-probability.cpp
index 2b72c7b27ae93e..c55cde84b25483 100644
--- a/clang/test/Sema/builtin-expect-with-probability.cpp
+++ b/clang/test/Sema/builtin-expect-with-probability.cpp
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fsyntax-only -verify -fexperimental-new-constant-interpreter %s
 
 __attribute__((noreturn)) extern void bar();