[flang] Work around a gcc-7.2 specific build bug by recoding with a better approach

Original-commit: flang-compiler/f18@bc2b4015b0
Reviewed-on: https://github.com/flang-compiler/f18/pull/785

flang/lib/evaluate/check-expression.cc

@@ -28,9 +28,9 @@ namespace Fortran::evaluate {
 // able to fold it (yet) into a known constant value; specifically,
 // the expression may reference derived type kind parameters whose values
 // are not yet known.
-class IsConstantExprHelper : public AllTraverse<IsConstantExprHelper> {
+class IsConstantExprHelper : public AllTraverse<IsConstantExprHelper, true> {
 public:
-  using Base = AllTraverse<IsConstantExprHelper>;
+  using Base = AllTraverse<IsConstantExprHelper, true>;
   IsConstantExprHelper() : Base{*this} {}
   using Base::operator();
 
@@ -76,8 +76,8 @@ template bool IsConstantExpr(const Expr<SomeInteger> &);
 // This code determines whether an expression is allowable as the static
 // data address used to initialize a pointer with "=> x".  See C765.
 struct IsInitialDataTargetHelper
-  : public AllTraverse<IsInitialDataTargetHelper> {
-  using Base = AllTraverse<IsInitialDataTargetHelper>;
+  : public AllTraverse<IsInitialDataTargetHelper, true> {
+  using Base = AllTraverse<IsInitialDataTargetHelper, true>;
   using Base::operator();
   explicit IsInitialDataTargetHelper(parser::ContextualMessages &m)
     : Base{*this}, messages_{m} {}

flang/lib/evaluate/tools.cc

@@ -660,33 +660,20 @@ bool IsProcedurePointer(const Expr<SomeType> &expr) {
 }
 
 // IsNullPointer()
-static bool IsNullPointer(const ProcedureRef &call) {
-  auto *intrinsic{call.proc().GetSpecificIntrinsic()};
-  return intrinsic &&
-      intrinsic->characteristics.value().attrs.test(
-          characteristics::Procedure::Attr::NullPointer);
-}
-template<TypeCategory CAT, int KIND>
-bool IsNullPointer(const Expr<Type<CAT, KIND>> &expr) {
-  const auto *call{std::get_if<FunctionRef<Type<CAT, KIND>>>(&expr.u)};
-  return call && IsNullPointer(*call);
-}
-template<TypeCategory CAT> bool IsNullPointer(const Expr<SomeKind<CAT>> &expr) {
-  return std::visit([](const auto &x) { return IsNullPointer(x); }, expr.u);
-}
-bool IsNullPointer(const Expr<SomeDerived> &expr) {
-  const auto *call{std::get_if<FunctionRef<SomeDerived>>(&expr.u)};
-  return call && IsNullPointer(*call);
-}
+struct IsNullPointerHelper : public AllTraverse<IsNullPointerHelper, false> {
+  using Base = AllTraverse<IsNullPointerHelper, false>;
+  IsNullPointerHelper() : Base(*this) {}
+  using Base::operator();
+  bool operator()(const ProcedureRef &call) const {
+    auto *intrinsic{call.proc().GetSpecificIntrinsic()};
+    return intrinsic &&
+        intrinsic->characteristics.value().attrs.test(
+            characteristics::Procedure::Attr::NullPointer);
+  }
+  bool operator()(const NullPointer &) const { return true; }
+};
 bool IsNullPointer(const Expr<SomeType> &expr) {
-  return std::visit(
-      common::visitors{
-          [](const NullPointer &) { return true; },
-          [](const BOZLiteralConstant &) { return false; },
-          [](const ProcedureDesignator &) { return false; },
-          [](const auto &x) { return IsNullPointer(x); },
-      },
-      expr.u);
+  return IsNullPointerHelper{}(expr);
 }
 
 // GetLastTarget()

flang/lib/evaluate/traverse.h

@@ -247,11 +247,12 @@ private:
 
 // For validity checks across an expression: if any operator() result is
 // false, so is the overall result.
-template<typename Visitor, typename Base = Traverse<Visitor, bool>>
+template<typename Visitor, bool DefaultValue,
+    typename Base = Traverse<Visitor, bool>>
 struct AllTraverse : public Base {
   AllTraverse(Visitor &v) : Base{v} {}
   using Base::operator();
-  static bool Default() { return true; }
+  static bool Default() { return DefaultValue; }
   static bool Combine(bool x, bool y) { return x && y; }
 };
 

flang/test/evaluate/CMakeLists.txt

@@ -64,6 +64,7 @@ add_executable(integer-test
 target_link_libraries(integer-test
   FortranEvaluateTesting
   FortranEvaluate
+  FortranSemantics
 )
 
 add_executable(intrinsics-test
@@ -85,6 +86,8 @@ add_executable(logical-test
 
 target_link_libraries(logical-test
   FortranEvaluateTesting
+  FortranEvaluate
+  FortranSemantics
 )
 
 # GCC -fno-exceptions breaks the fenv.h interfaces needed to capture