[flang] Define IEEE_SCALB, IEEE_NEXT_AFTER, IEEE_NEXT_DOWN, IEEE_NEXT_UP

These functions were missing from the standard intrinsic module
IEEE_ARITHMETIC.  IEEE_SCALB is an alias for the standard intrinsic
function SCALE(), and the others are defined as new builtin intrinsic
functions.

Differential Revision: https://reviews.llvm.org/D111253

flang/lib/Evaluate/fold-real.cpp

@@ -144,6 +144,7 @@ Expr<Type<TypeCategory::Real, KIND>> FoldIntrinsicFunction(
   }
   // TODO: dim, dot_product, fraction, matmul,
   // modulo, nearest, norm2, rrspacing, scale,
+  // __builtin_next_after/down/up,
   // set_exponent, spacing, transfer,
   // bessel_jn (transformational) and bessel_yn (transformational)
   return Expr<T>{std::move(funcRef)};

flang/lib/Evaluate/intrinsics.cpp

@@ -690,7 +690,7 @@ static const IntrinsicInterface genericIntrinsicFunction[]{
         {{"a", ExtensibleDerived, Rank::anyOrAssumedRank},
             {"b", ExtensibleDerived, Rank::anyOrAssumedRank}},
         DefaultLogical, Rank::scalar, IntrinsicClass::inquiryFunction},
-    {"scale", {{"x", SameReal}, {"i", AnyInt}}, SameReal},
+    {"scale", {{"x", SameReal}, {"i", AnyInt}}, SameReal}, // == IEEE_SCALB()
     {"scan",
         {{"string", SameChar}, {"set", SameChar},
             {"back", AnyLogical, Rank::elemental, Optionality::optional},
@@ -791,6 +791,9 @@ static const IntrinsicInterface genericIntrinsicFunction[]{
             DefaultingKIND},
         KINDInt},
     {"__builtin_ieee_is_nan", {{"a", AnyFloating}}, DefaultLogical},
+    {"__builtin_ieee_next_after", {{"x", SameReal}, {"y", AnyReal}}, SameReal},
+    {"__builtin_ieee_next_down", {{"x", SameReal}}, SameReal},
+    {"__builtin_ieee_next_up", {{"x", SameReal}}, SameReal},
     {"__builtin_ieee_selected_real_kind", // alias for selected_real_kind
         {{"p", AnyInt, Rank::scalar},
             {"r", AnyInt, Rank::scalar, Optionality::optional},

flang/module/__fortran_builtins.f90

@@ -42,6 +42,9 @@ module __Fortran_builtins
   procedure(type(__builtin_c_ptr)) :: __builtin_c_loc
 
   intrinsic :: __builtin_ieee_is_nan
+  intrinsic :: __builtin_ieee_next_after, __builtin_ieee_next_down, &
+    __builtin_ieee_next_up
+  intrinsic :: scale ! for ieee_scalb
   intrinsic :: __builtin_ieee_selected_real_kind
   intrinsic :: __builtin_ieee_support_datatype, &
     __builtin_ieee_support_denormal, __builtin_ieee_support_divide, &

flang/module/ieee_arithmetic.f90

@@ -11,6 +11,10 @@ module ieee_arithmetic
 
   use __Fortran_builtins, only: &
     ieee_is_nan => __builtin_ieee_is_nan, &
+    ieee_next_after => __builtin_ieee_next_after, &
+    ieee_next_down => __builtin_ieee_next_down, &
+    ieee_next_up => __builtin_ieee_next_up, &
+    ieee_scalb => scale, &
     ieee_selected_real_kind => __builtin_ieee_selected_real_kind, &
     ieee_support_datatype => __builtin_ieee_support_datatype, &
     ieee_support_denormal => __builtin_ieee_support_denormal, &