Introduce long_const_operation

This adds class long_const_operation, which holds a scalar constant.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* expop.h (class long_const_operation): New.
	* ax-gdb.c (long_const_operation::do_generate_ax): New method.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2021-03-08  Tom Tromey  <tom@tromey.com>
+
+	* expop.h (class long_const_operation): New.
+	* ax-gdb.c (long_const_operation::do_generate_ax): New method.
+
 2021-03-08  Tom Tromey  <tom@tromey.com>
 
 	* expop.h (class scope_operation): New.

gdb/ax-gdb.c

@@ -2314,6 +2314,16 @@ scope_operation::do_generate_ax (struct expression *exp,
     error (_("There is no field named %s"), name.c_str ());
 }
 
+void
+long_const_operation::do_generate_ax (struct expression *exp,
+				      struct agent_expr *ax,
+				      struct axs_value *value,
+				      struct type *cast_type)
+{
+  gen_int_literal (ax, value, std::get<1> (m_storage),
+		   std::get<0> (m_storage));
+}
+
 }
 
 /* This handles the middle-to-right-side of code generation for binary

gdb/expop.h

@@ -451,6 +451,36 @@ protected:
     override;
 };
 
+class long_const_operation
+  : public tuple_holding_operation<struct type *, LONGEST>
+{
+public:
+
+  using tuple_holding_operation::tuple_holding_operation;
+
+  value *evaluate (struct type *expect_type,
+		   struct expression *exp,
+		   enum noside noside) override
+  {
+    return value_from_longest (std::get<0> (m_storage),
+			       std::get<1> (m_storage));
+  }
+
+  enum exp_opcode opcode () const override
+  { return OP_LONG; }
+
+  bool constant_p () const override
+  { return true; }
+
+protected:
+
+  void do_generate_ax (struct expression *exp,
+		       struct agent_expr *ax,
+		       struct axs_value *value,
+		       struct type *cast_type)
+    override;
+};
+
 } /* namespace expr */
 
 #endif /* EXPOP_H */