[clang][Interp] Implement __builtin_isinf

[cor3ntin]

LGTM

clang/lib/AST/Interp/Floating.h

public:
   bool isSigned() const { return true; }
   bool isNegative() const { return F.isNegative(); }
   bool isPositive() const { return !F.isNegative(); }
   bool isZero() const { return F.isZero(); }
   bool isNonZero() const { return F.isNonZero(); }
   bool isMin() const { return F.isSmallest(); }
   bool isMinusOne() const { return F.isExactlyValue(-1.0); }
   bool isNan() const { return F.isNaN(); }
+  bool isInf() const { return F.isInfinity(); }
   bool isFinite() const { return F.isFinite(); }
 
   ComparisonCategoryResult compare(const Floating &RHS) const {
     return Compare(F, RHS.F);
   }
 
   static APFloat::opStatus fromIntegral(APSInt Val,
                                         const llvm::fltSemantics &Sem,

clang/lib/AST/Interp/InterpBuiltin.cpp

static bool interp__builtin_isnan(InterpState &S, CodePtr OpPC,
   // doesn't have any parameters. Wait for a pattern to emerge and maybe
   // refactor this into a different function that checks things are valid.
   const Floating &Arg = S.Stk.peek<Floating>();
 
   S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Arg.isNan()));
   return true;
 }
 
+static bool interp__builtin_isinf(InterpState &S, CodePtr OpPC,
+                                  const InterpFrame *Frame, const Function *F,
+                                  bool CheckSign) {
+  const Floating &Arg = S.Stk.peek<Floating>();
+  bool IsInf = Arg.isInf();
+
+  if (CheckSign)
+    S.Stk.push<Integral<32, true>>(
+        Integral<32, true>::from(IsInf ? (Arg.isNegative() ? -1 : 1) : 0));
+  else
+    S.Stk.push<Integral<32, true>>(Integral<32, true>::from(Arg.isInf()));
+  return true;
+}
+
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F) {
   InterpFrame *Frame = S.Current;
   APValue Dummy;
 
   switch (F->getBuiltinID()) {
   case Builtin::BI__builtin_is_constant_evaluated:
     S.Stk.push<Boolean>(Boolean::from(S.inConstantContext()));
     return Ret<PT_Bool>(S, OpPC, Dummy);
if (interp__builtin_fmin(S, OpPC, Frame, 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;
 
+  case Builtin::BI__builtin_isinf:
+    if (interp__builtin_isinf(S, OpPC, Frame, F, /*Sign=*/false))
+      return Ret<PT_Sint32>(S, OpPC, Dummy);
+    break;
+
+  case Builtin::BI__builtin_isinf_sign:
+    if (interp__builtin_isinf(S, OpPC, Frame, F, /*Sign=*/true))
+      return Ret<PT_Sint32>(S, OpPC, Dummy);
+    break;
+
   default:
     return false;
   }
 
   return false;
 }
 
 } // namespace interp
 } // namespace clang

clang/test/AST/Interp/builtin-functions.cpp

static_assert(foo() == 1); // ref-error {{not an integral constant expression}} \
                              // expected-error {{not an integral constant expression}} \
                              // expected-note {{in call to}}
 #endif
 
 
   constexpr float Nan2 = __builtin_nans([](){return "0xAE98";}()); // ref-error {{must be initialized by a constant expression}}
 
 }
+
+namespace inf {
+  static_assert(__builtin_isinf(__builtin_inf()), "");
+  static_assert(!__builtin_isinf(1.0), "");
+}