Index: clang/lib/AST/Interp/InterpBuiltin.cpp
===================================================================
--- clang/lib/AST/Interp/InterpBuiltin.cpp
+++ clang/lib/AST/Interp/InterpBuiltin.cpp
@@ -186,6 +186,15 @@
   return true;
 }
 
+static bool interp__builtin_isfinite(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.isFinite()));
+  return true;
+}
+
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F) {
   InterpFrame *Frame = S.Current;
   APValue Dummy;
@@ -256,6 +265,11 @@
       return Ret<PT_Sint32>(S, OpPC, Dummy);
     break;
 
+  case Builtin::BI__builtin_isfinite:
+    if (interp__builtin_isfinite(S, OpPC, Frame, F))
+      return Ret<PT_Sint32>(S, OpPC, Dummy);
+    break;
+
   default:
     return false;
   }
Index: clang/test/AST/Interp/builtin-functions.cpp
===================================================================
--- clang/test/AST/Interp/builtin-functions.cpp
+++ clang/test/AST/Interp/builtin-functions.cpp
@@ -66,4 +66,7 @@
 namespace inf {
   static_assert(__builtin_isinf(__builtin_inf()), "");
   static_assert(!__builtin_isinf(1.0), "");
+
+  static_assert(__builtin_isfinite(1.0));
+  static_assert(!__builtin_isfinite(__builtin_inf()));
 }