Introduce class operation

This patch introduces class operation, the new base class for all
expression operations.

In the new approach, an operation is simply a class that presents a
certain interface.  Operations own their operands, and management is
done via unique_ptr.

The operation interface is largely ad hoc, based on the evolution of
expression handling in GDB.  Parts (for example,
evaluate_with_coercion) are probably redundant; however I took this
approach to try to avoid mixing different kinds of refactorings.

In some specific situations, rather than add a generic method across
the entire operation class hierarchy, I chose instead to use
dynamic_cast and specialized methods on certain concrete subclasses.
This will appear in some subsequent patches.

One goal of this work is to avoid the kinds of easy-to-make errors
that affected the old implementation.  To this end, some helper
subclasses are also added here.  These helpers automate the
implementation of the 'dump', 'uses_objfile', and 'constant_p'
methods.  Nearly every concrete operation that is subsequently added
will use these facilities.  (Note that the 'dump' implementation is
only outlined here, the body appears in the next patch.)

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

	* expression.h (expr::operation): New class.
	(expr::make_operation): New function.
	(expr::operation_up): New typedef.
	* expop.h: New file.
	* eval.c (operation::evaluate_for_cast)
	(operation::evaluate_for_address, operation::evaluate_for_sizeof):
	New methods.
	* ax-gdb.c (operation::generate_ax): New method.

1 files changed, 315 insertions, 0 deletions

diff --git a/gdb/expop.h b/gdb/expop.h
new file mode 100644
index 0000000..861e3c2
--- /dev/null
+++ b/gdb/expop.h
@@ -0,0 +1,315 @@
+/* Definitions for expressions in GDB
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef EXPOP_H
+#define EXPOP_H
+
+#include "block.h"
+#include "c-lang.h"
+#include "cp-abi.h"
+#include "expression.h"
+#include "objfiles.h"
+#include "gdbsupport/traits.h"
+#include "gdbsupport/enum-flags.h"
+
+struct agent_expr;
+struct axs_value;
+
+namespace expr
+{
+
+/* The check_objfile overloads are used to check whether a particular
+   component of some operation references an objfile.  The passed-in
+   objfile will never be a debug objfile.  */
+
+/* See if EXP_OBJFILE matches OBJFILE.  */
+static inline bool
+check_objfile (struct objfile *exp_objfile, struct objfile *objfile)
+{
+  if (exp_objfile->separate_debug_objfile_backlink)
+    exp_objfile = exp_objfile->separate_debug_objfile_backlink;
+  return exp_objfile == objfile;
+}
+
+static inline bool 
+check_objfile (struct type *type, struct objfile *objfile)
+{
+  struct objfile *ty_objfile = type->objfile_owner ();
+  if (ty_objfile != nullptr)
+    return check_objfile (ty_objfile, objfile);
+  return false;
+}
+
+static inline bool 
+check_objfile (struct symbol *sym, struct objfile *objfile)
+{
+  return check_objfile (symbol_objfile (sym), objfile);
+}
+
+static inline bool 
+check_objfile (const struct block *block, struct objfile *objfile)
+{
+  return check_objfile (block_objfile (block), objfile);
+}
+
+static inline bool
+check_objfile (minimal_symbol *minsym, struct objfile *objfile)
+{
+  /* This may seem strange but minsyms are only used with an objfile
+     as well.  */
+  return false;
+}
+
+static inline bool
+check_objfile (internalvar *ivar, struct objfile *objfile)
+{
+  return false;
+}
+
+static inline bool
+check_objfile (const std::string &str, struct objfile *objfile)
+{
+  return false;
+}
+
+static inline bool 
+check_objfile (const operation_up &op, struct objfile *objfile)
+{
+  return op->uses_objfile (objfile);
+}
+
+static inline bool
+check_objfile (enum exp_opcode val, struct objfile *objfile)
+{
+  return false;
+}
+
+static inline bool
+check_objfile (ULONGEST val, struct objfile *objfile)
+{
+  return false;
+}
+
+template<typename T>
+static inline bool
+check_objfile (enum_flags<T> val, struct objfile *objfile)
+{
+  return false;
+}
+
+template<typename T>
+static inline bool 
+check_objfile (const std::vector<T> &collection, struct objfile *objfile)
+{
+  for (const auto &item : collection)
+    {
+      if (check_objfile (item, objfile))
+	return true;
+    }
+  return false;
+}
+
+template<typename S, typename T>
+static inline bool 
+check_objfile (const std::pair<S, T> &item, struct objfile *objfile)
+{
+  return (check_objfile (item.first, objfile)
+	  || check_objfile (item.second, objfile));
+}
+
+/* Base class for most concrete operations.  This class holds data,
+   specified via template parameters, and supplies generic
+   implementations of the 'dump' and 'uses_objfile' methods.  */
+template<typename... Arg>
+class tuple_holding_operation : public operation
+{
+public:
+
+  explicit tuple_holding_operation (Arg... args)
+    : m_storage (std::forward<Arg> (args)...)
+  {
+  }
+
+  DISABLE_COPY_AND_ASSIGN (tuple_holding_operation);
+
+  bool uses_objfile (struct objfile *objfile) const override
+  {
+    return do_check_objfile<0, Arg...> (objfile, m_storage);
+  }
+
+  void dump (struct ui_file *stream, int depth) const override
+  {
+    do_dump<0, Arg...> (stream, depth, m_storage);
+  }
+
+protected:
+
+  /* Storage for the data.  */
+  std::tuple<Arg...> m_storage;
+
+private:
+
+  /* do_dump does the work of dumping the data.  */
+  template<int I, typename... T>
+  typename std::enable_if<I == sizeof... (T), void>::type
+  do_dump (struct ui_file *stream, int depth, const std::tuple<T...> &value)
+    const
+  {
+  }
+
+  template<int I, typename... T>
+  typename std::enable_if<I < sizeof... (T), void>::type
+  do_dump (struct ui_file *stream, int depth, const std::tuple<T...> &value)
+    const
+  {
+    do_dump<I + 1, T...> (stream, depth, value);
+  }
+
+  /* do_check_objfile does the work of checking whether this object
+     refers to OBJFILE.  */
+  template<int I, typename... T>
+  typename std::enable_if<I == sizeof... (T), bool>::type
+  do_check_objfile (struct objfile *objfile, const std::tuple<T...> &value)
+    const
+  {
+    return false;
+  }
+
+  template<int I, typename... T>
+  typename std::enable_if<I < sizeof... (T), bool>::type
+  do_check_objfile (struct objfile *objfile, const std::tuple<T...> &value)
+    const
+  {
+    if (check_objfile (std::get<I> (value), objfile))
+      return true;
+    return do_check_objfile<I + 1, T...> (objfile, value);
+  }
+};
+
+/* The check_constant overloads are used to decide whether a given
+   concrete operation is a constant.  This is done by checking the
+   operands.  */
+
+static inline bool
+check_constant (const operation_up &item)
+{
+  return item->constant_p ();
+}
+
+static inline bool
+check_constant (struct minimal_symbol *msym)
+{
+  return false;
+}
+
+static inline bool
+check_constant (struct type *type)
+{
+  return true;
+}
+
+static inline bool
+check_constant (const struct block *block)
+{
+  return true;
+}
+
+static inline bool
+check_constant (const std::string &str)
+{
+  return true;
+}
+
+static inline bool
+check_constant (struct objfile *objfile)
+{
+  return true;
+}
+
+static inline bool
+check_constant (ULONGEST cst)
+{
+  return true;
+}
+
+static inline bool
+check_constant (struct symbol *sym)
+{
+  enum address_class sc = SYMBOL_CLASS (sym);
+  return (sc == LOC_BLOCK
+	  || sc == LOC_CONST
+	  || sc == LOC_CONST_BYTES
+	  || sc == LOC_LABEL);
+}
+
+template<typename T>
+static inline bool
+check_constant (const std::vector<T> &collection)
+{
+  for (const auto &item : collection)
+    if (!check_constant (item))
+      return false;
+  return true;
+}
+
+template<typename S, typename T>
+static inline bool
+check_constant (const std::pair<S, T> &item)
+{
+  return check_constant (item.first) && check_constant (item.second);
+}
+
+/* Base class for concrete operations.  This class supplies an
+   implementation of 'constant_p' that works by checking the
+   operands.  */
+template<typename... Arg>
+class maybe_constant_operation
+  : public tuple_holding_operation<Arg...>
+{
+public:
+
+  using tuple_holding_operation<Arg...>::tuple_holding_operation;
+
+  bool constant_p () const override
+  {
+    return do_check_constant<0, Arg...> (this->m_storage);
+  }
+
+private:
+
+  template<int I, typename... T>
+  typename std::enable_if<I == sizeof... (T), bool>::type
+  do_check_constant (const std::tuple<T...> &value) const
+  {
+    return true;
+  }
+
+  template<int I, typename... T>
+  typename std::enable_if<I < sizeof... (T), bool>::type
+  do_check_constant (const std::tuple<T...> &value) const
+  {
+    if (!check_constant (std::get<I> (value)))
+      return false;
+    return do_check_constant<I + 1, T...> (value);
+  }
+};
+
+} /* namespace expr */
+
+#endif /* EXPOP_H */