gdb: make frame_info_ptr auto-reinflatable

This is the second step of making frame_info_ptr automatic, reinflate on
demand whenever trying to obtain the wrapper frame_info pointer, either
through the get method or operator->.  Make the reinflate method
private, it is used as a convenience method in those two.

Add an "is_null" method, because it is often needed to know whether the
frame_info_ptr wraps an frame_info or is empty.

Make m_ptr mutable, so that it's possible to reinflate const
frame_info_ptr objects.  Whether m_ptr is nullptr or not does not change
the logical state of the object, because we re-create it on demand.  I
believe this is the right use case for mutable.

Change-Id: Icb0552d0035e227f81eb3c121d8a9bb2f9d25794
Reviewed-By: Bruno Larsen <blarsen@redhat.com>

gdb/frame.c

@@ -3224,8 +3224,8 @@ frame_info_ptr::frame_info_ptr (struct frame_info *ptr)
 
 /* See frame-info-ptr.h.  */
 
-void
+frame_info *
-frame_info_ptr::reinflate ()
+frame_info_ptr::reinflate () const
 {
   /* Ensure we have a valid frame level (sentinel frame or above).  */
   gdb_assert (m_cached_level >= -1);
@@ -3233,7 +3233,7 @@ frame_info_ptr::reinflate ()
   if (m_ptr != nullptr)
     {
       /* The frame_info wasn't invalidated, no need to reinflate.  */
-      return;
+      return m_ptr;
     }
 
   if (m_cached_id.user_created_p)
@@ -3255,6 +3255,7 @@ frame_info_ptr::reinflate ()
     }
 
   gdb_assert (m_ptr != nullptr);
+  return m_ptr;
 }
 
 void _initialize_frame ();

gdb/frame.h

@@ -275,29 +275,38 @@ public:
   }
 
   frame_info *operator-> () const
-  {
+  { return this->reinflate (); }
-    return m_ptr;
-  }
 
   /* Fetch the underlying pointer.  Note that new code should
      generally not use this -- avoid it if at all possible.  */
   frame_info *get () const
   {
-    return m_ptr;
+    if (this->is_null ())
+      return nullptr;
+
+    return this->reinflate ();
   }
 
+  /* Return true if this object is empty (does not wrap a frame_info
+     object).  */
+
+  bool is_null () const
+  {
+    return m_cached_level == this->invalid_level;
+  };
+
   /* This exists for compatibility with pre-existing code that checked
      a "frame_info *" using "!".  */
   bool operator! () const
   {
-    return m_ptr == nullptr;
+    return this->is_null ();
   }
 
   /* This exists for compatibility with pre-existing code that checked
      a "frame_info *" like "if (ptr)".  */
   explicit operator bool () const
   {
-    return m_ptr != nullptr;
+    return !this->is_null ();
   }
 
   /* Invalidate this pointer.  */
@@ -306,17 +315,18 @@ public:
     m_ptr = nullptr;
   }
 
-  /* Use the cached frame_id to reinflate the pointer.  */
-  void reinflate ();
-
 private:
   /* We sometimes need to construct frame_info_ptr objects around the
      sentinel_frame, which has level -1.  Therefore, make the invalid frame
      level value -2.  */
   static constexpr int invalid_level = -2;
 
+  /* Use the cached frame level and id to reinflate the pointer, and return
+     it.  */
+  frame_info *reinflate () const;
+
   /* The underlying pointer.  */
-  frame_info *m_ptr = nullptr;
+  mutable frame_info *m_ptr = nullptr;
 
   /* The frame_id of the underlying pointer.
 
@@ -341,37 +351,46 @@ private:
 static inline bool
 operator== (const frame_info *self, const frame_info_ptr &other)
 {
+  if (self == nullptr || other.is_null ())
+    return self == nullptr && other.is_null ();
+
   return self == other.get ();
 }
 
 static inline bool
 operator== (const frame_info_ptr &self, const frame_info_ptr &other)
 {
+  if (self.is_null () || other.is_null ())
+    return self.is_null () && other.is_null ();
+
   return self.get () == other.get ();
 }
 
 static inline bool
 operator== (const frame_info_ptr &self, const frame_info *other)
 {
+  if (self.is_null () || other == nullptr)
+    return self.is_null () && other == nullptr;
+
   return self.get () == other;
 }
 
 static inline bool
 operator!= (const frame_info *self, const frame_info_ptr &other)
 {
-  return self != other.get ();
+  return !(self == other);
 }
 
 static inline bool
 operator!= (const frame_info_ptr &self, const frame_info_ptr &other)
 {
-  return self.get () != other.get ();
+  return !(self == other);
 }
 
 static inline bool
 operator!= (const frame_info_ptr &self, const frame_info *other)
 {
-  return self.get () != other;
+  return !(self == other);
 }
 
 /* For every stopped thread, GDB tracks two frames: current and

gdb/infcall.c

@@ -857,8 +857,6 @@ call_function_by_hand_dummy (struct value *function,
 	     "target calling convention."),
 	   get_function_name (funaddr, name_buf, sizeof (name_buf)));
 
-  frame.reinflate ();
-
   if (values_type == NULL || values_type->is_stub ())
     values_type = default_return_type;
   if (values_type == NULL)

gdb/infcmd.c

@@ -1915,7 +1915,6 @@ finish_command (const char *arg, int from_tty)
 
       print_stack_frame (callee_frame, 1, LOCATION, 0);
     }
-  frame.reinflate ();
 
   if (execution_direction == EXEC_REVERSE)
     finish_backward (sm);

gdb/mi/mi-cmd-stack.c

@@ -180,7 +180,6 @@ mi_cmd_stack_list_frames (const char *command, char **argv, int argc)
 	     If args is 0, don't print the arguments.  */
 	  print_frame_info (user_frame_print_options,
 			    fi, 1, LOC_AND_ADDRESS, 0 /* args */, 0);
-	  fi.reinflate ();
 	}
     }
 }

gdb/stack.c

@@ -367,7 +367,6 @@ print_stack_frame (frame_info_ptr frame, int print_level,
       print_frame_info (user_frame_print_options,
 			frame, print_level, print_what, 1 /* print_args */,
 			set_current_sal);
-      frame.reinflate ();
       if (set_current_sal)
 	set_current_sal_from_frame (frame);
     }
@@ -903,7 +902,6 @@ print_frame_args (const frame_print_options &fp_opts,
 	    }
 
 	  first = 0;
-	  frame.reinflate ();
 	}
     }
 
@@ -1173,7 +1171,6 @@ print_frame_info (const frame_print_options &fp_opts,
 
 	  print_source_lines (sal.symtab, sal.line, sal.line + 1, 0);
 	}
-      frame.reinflate ();
 
       /* If disassemble-next-line is set to on and there is line debug
 	 messages, output assembly codes for next line.  */
@@ -1676,8 +1673,6 @@ info_frame_command_core (frame_info_ptr fi, bool selected_frame_p)
 
 	print_frame_args (user_frame_print_options,
 			  func, fi, numargs, gdb_stdout);
-	fi.reinflate ();
-
 	gdb_puts ("\n");
       }
   }
@@ -2077,7 +2072,6 @@ backtrace_command_1 (const frame_print_options &fp_opts,
 	    print_frame_local_vars (fi, false, NULL, NULL, 1, gdb_stdout);
 
 	  /* Save the last frame to check for error conditions.  */
-	  fi.reinflate ();
 	  trailing = fi;
 	}
 

gdb/unittests/frame_info_ptr-selftests.c

@@ -41,7 +41,6 @@ user_created_frame_callee (frame_info_ptr frame)
   validate_user_created_frame (get_frame_id (frame));
 
   reinit_frame_cache ();
-  frame.reinflate ();
 
   validate_user_created_frame (get_frame_id (frame));
 
@@ -61,7 +60,6 @@ test_user_created_frame ()
      validate that the reinflation in both the callee and caller restore the
      same frame_info object.  */
   frame_info_ptr callees_frame_info = user_created_frame_callee (frame);
-  frame.reinflate ();
 
   validate_user_created_frame (get_frame_id (frame));
   SELF_CHECK (frame.get () == callees_frame_info.get ());