Implement some agent expressions for Ada

Ada historically has not implemented agent expressions, and some Ada
constructs probably cannot reasonably be converted to agent
expressions.  However, a subset of simple operations can be, and this
patch represents a first step in that direction.

On one internal AdaCore test case, this improves the performance of a
conditional breakpoint from 5 minutes to 5 seconds.

The main tricky part in this patch is ensuring the converted
expressions detect the cases that will not work.  This is done by
examining the code in the corresponding evaluation methods.

gdb/ada-exp.h

@@ -130,6 +130,14 @@ public:
 
   enum exp_opcode opcode () const override
   { return std::get<0> (m_storage)->opcode (); }
+
+protected:
+
+  void do_generate_ax (struct expression *exp,
+		       struct agent_expr *ax,
+		       struct axs_value *value,
+		       struct type *cast_type)
+    override;
 };
 
 /* An Ada string constant.  */
@@ -255,6 +263,18 @@ public:
 			    arg1, arg2);
   }
 
+  void do_generate_ax (struct expression *exp,
+		       struct agent_expr *ax,
+		       struct axs_value *value,
+		       struct type *cast_type)
+    override
+  {
+    gen_expr_binop (exp, opcode (),
+		    std::get<1> (this->m_storage).get (),
+		    std::get<2> (this->m_storage).get (),
+		    ax, value);
+  }
+
   enum exp_opcode opcode () const override
   { return std::get<0> (m_storage); }
 };
@@ -380,7 +400,11 @@ public:
 
 protected:
 
-  using operation::do_generate_ax;
+  void do_generate_ax (struct expression *exp,
+		       struct agent_expr *ax,
+		       struct axs_value *value,
+		       struct type *cast_type)
+    override;
 };
 
 /* Variant of var_msym_value_operation for Ada.  */

gdb/ada-lang.c

@@ -60,6 +60,7 @@
 #include <algorithm>
 #include "ada-exp.h"
 #include "charset.h"
+#include "ax-gdb.h"
 
 /* Define whether or not the C operator '/' truncates towards zero for
    differently signed operands (truncation direction is undefined in C).
@@ -9189,6 +9190,23 @@ ada_enum_name (const char *name)
     }
 }
 
+/* If TYPE is a dynamic type, return the base type.  Otherwise, if
+   there is no parallel type, return nullptr.  */
+
+static struct type *
+find_base_type (struct type *type)
+{
+  struct type *raw_real_type
+    = ada_check_typedef (ada_get_base_type (type));
+
+  /* No parallel XVS or XVE type.  */
+  if (type == raw_real_type
+      && ada_find_parallel_type (type, "___XVE") == nullptr)
+    return nullptr;
+
+  return raw_real_type;
+}
+
 /* If VAL is wrapped in an aligner or subtype wrapper, return the
    value it wraps.  */
 
@@ -9209,13 +9227,8 @@ unwrap_value (struct value *val)
     }
   else
     {
-      struct type *raw_real_type =
-	ada_check_typedef (ada_get_base_type (type));
-
-      /* If there is no parallel XVS or XVE type, then the value is
-	 already unwrapped.  Return it without further modification.  */
-      if ((type == raw_real_type)
-	  && ada_find_parallel_type (type, "___XVE") == NULL)
+      struct type *raw_real_type = find_base_type (type);
+      if (raw_real_type == nullptr)
 	return val;
 
       return
@@ -10641,6 +10654,21 @@ ada_wrapped_operation::evaluate (struct type *expect_type,
   return result;
 }
 
+void
+ada_wrapped_operation::do_generate_ax (struct expression *exp,
+				       struct agent_expr *ax,
+				       struct axs_value *value,
+				       struct type *cast_type)
+{
+  std::get<0> (m_storage)->generate_ax (exp, ax, value, cast_type);
+
+  struct type *type = value->type;
+  if (ada_is_aligner_type (type))
+    error (_("Aligner types cannot be handled in agent expressions"));
+  else if (find_base_type (type) != nullptr)
+    error (_("Dynamic types cannot be handled in agent expressions"));
+}
+
 value *
 ada_string_operation::evaluate (struct type *expect_type,
 				struct expression *exp,
@@ -10991,6 +11019,33 @@ ada_var_value_operation::resolve (struct expression *exp,
   return false;
 }
 
+void
+ada_var_value_operation::do_generate_ax (struct expression *exp,
+					 struct agent_expr *ax,
+					 struct axs_value *value,
+					 struct type *cast_type)
+{
+  symbol *sym = std::get<0> (m_storage).symbol;
+
+  if (sym->domain () == UNDEF_DOMAIN)
+    error (_("Unexpected unresolved symbol, %s, during evaluation"),
+	   sym->print_name ());
+
+  struct type *type = static_unwrap_type (sym->type ());
+  if (ada_is_tagged_type (type, 0)
+      || (type->code () == TYPE_CODE_REF
+	  && ada_is_tagged_type (type->target_type (), 0)))
+    error (_("Tagged types cannot be handled in agent expressions"));
+
+  if ((type->code () == TYPE_CODE_STRUCT
+       && dynamic_template_type (type) != NULL)
+      || (type->code () == TYPE_CODE_UNION
+	  && ada_find_parallel_type (type, "___XVU") != NULL))
+    error (_("Dynamic types cannot be handled in agent expressions"));
+
+  var_value_operation::do_generate_ax (exp, ax, value, cast_type);
+}
+
 value *
 ada_atr_val_operation::evaluate (struct type *expect_type,
 				 struct expression *exp,

gdb/testsuite/gdb.ada/ax-ada.exp

@@ -0,0 +1,31 @@
+# Copyright 2023 Free Software Foundation, Inc.
+
+# 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/>.
+
+load_lib "ada.exp"
+
+require allow_ada_tests
+
+standard_ada_testfile prog
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable {debug}] != ""} {
+    return -1
+}
+
+clean_restart ${testfile}
+
+set bp_location [gdb_get_line_number "START" ${testdir}/prog.adb]
+runto "prog.adb:$bp_location"
+
+gdb_test "maint agent-eval variable = 23" ".*end"

gdb/testsuite/gdb.ada/ax-ada/prog.adb

@@ -0,0 +1,20 @@
+--  Copyright 2023 Free Software Foundation, Inc.
+--
+--  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/>.
+
+procedure Prog is
+   Variable : Integer := 23;
+begin
+   null; -- START
+end Prog;