Re: #2 [Was: Re: Function attributes for make-docfile]

[Paul Eggert <eggert@cs.ucla.edu>]

[-- Attachment #1: Type: text/plain, Size: 1217 bytes --]

Dmitry Antipov wrote:
 > Why not use #pragma in the way similar to bytecode.c?

I'd rather not head down that direction, as it is ugly in a different way: seven 
lines' worth of preprocessor directives to silence one bogus diagnostic?!

 > '--enable-gcc-warnings --with-x-toolkit=no' build should have the
 > Fnext_read_file_uses_dialog_p-like issue with Fx_uses_old_gtk_dialog.
 > But I don't see it, and don't understand why

I don't know why either.  Apparently GCC does not do a perfect job of suggesting 
the attribute.

Stefan Monnier wrote:

> Easy, then: either you live with this warning, or you don't
> enable -Wsuggest-attribute=const.

Let's do the latter.  A couple of things.  First, I checked, and the attribute 
doesn't significantly help Emacs's performance, so it appears to be more trouble 
than it's worth for us.  Second, I audited the code and found five instances 
where we blindly followed GCC's advice and added ATTRIBUTE_CONST even though 
this was incorrect on some platforms; these mistakes suggest that we need to be 
more skeptical of GCC's diagnostics in this area on the rare occasions when we 
do use -Wsuggest-attribute=const.

I installed the attached patch to try to fix all this.

[-- Attachment #2: 0001-Give-up-on-Wsuggest-attribute-const.patch --]
[-- Type: text/x-patch, Size: 6761 bytes --]

From 64cdb38ed4483c089fff6f3ef6f1ad01f0a2a8d1 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 15 Jan 2015 20:37:05 -0800
Subject: [PATCH] Give up on -Wsuggest-attribute=const

The attribute doesn't help performance significantly, and the
warning seems to be more trouble than it's worth.  See the thread at:
http://lists.gnu.org/archive/html/emacs-devel/2015-01/msg00361.html
* configure.ac (WERROR_CFLAGS): Don't use -Wsuggest-attribute=const.
* lib-src/make-docfile.c (write_globals):
Remove special hack for Fnext_read_file_uses_dialog_p.
* src/decompress.c (Fzlib_available_p):
* src/gnutls.c (Fgnutls_available_p):
* src/gtkutil.h (xg_uses_old_file_dialog):
* src/xdisp.c (Ftool_bar_height):
* src/xmenu.c (popup_activated):
No longer const, since it's not const on at lest some
configurations, and we shouldn't lie to the compiler.
---
 ChangeLog              |  8 ++++++++
 configure.ac           |  5 ++++-
 lib-src/ChangeLog      |  6 ++++++
 lib-src/make-docfile.c | 12 ------------
 src/ChangeLog          | 11 +++++++++++
 src/decompress.c       |  3 +--
 src/gnutls.c           |  3 +--
 src/gtkutil.h          |  2 +-
 src/xdisp.c            |  3 +--
 src/xmenu.c            |  2 +-
 10 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index cca9100..309b04f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2015-01-16  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Give up on -Wsuggest-attribute=const
+	The attribute doesn't help performance significantly, and the
+	warning seems to be more trouble than it's worth.  See the thread at:
+	http://lists.gnu.org/archive/html/emacs-devel/2015-01/msg00361.html
+	* configure.ac (WERROR_CFLAGS): Don't use -Wsuggest-attribute=const.
+
 2015-01-11  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Default to 'configure --enable-silent-rules'
diff --git a/configure.ac b/configure.ac
index 4cad214..9db4bde 100644
--- a/configure.ac
+++ b/configure.ac
@@ -892,6 +892,10 @@ else
   # Emacs's use of alloca inhibits protecting the stack.
   nw="$nw -Wstack-protector"
 
+  # Emacs's use of partly-const functions such as Fgnutls_available_p
+  # make this option problematic.
+  nw="$nw -Wsuggest-attribute=const"
+
   # Emacs's use of partly-pure functions such as CHECK_TYPE make this
   # option problematic.
   nw="$nw -Wsuggest-attribute=pure"
@@ -1974,7 +1978,6 @@ fi
 if test "$window_system" = none && test "$gl_gcc_warnings" = yes; then
    # Too many warnings for now.
    nw=
-   nw="$nw -Wsuggest-attribute=const"
    nw="$nw -Wsuggest-attribute=noreturn"
    gl_MANYWARN_COMPLEMENT([WARN_CFLAGS], [$WARN_CFLAGS], [$nw])
 
diff --git a/lib-src/ChangeLog b/lib-src/ChangeLog
index e9205fd..7cbf327 100644
--- a/lib-src/ChangeLog
+++ b/lib-src/ChangeLog
@@ -1,3 +1,9 @@
+2015-01-16  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Give up on -Wsuggest-attribute=const
+	* make-docfile.c (write_globals):
+	Remove special hack for Fnext_read_file_uses_dialog_p
+
 2015-01-13  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Don't say Fnext_read_file_uses_dialog_p is const
diff --git a/lib-src/make-docfile.c b/lib-src/make-docfile.c
index 741fa4b..79d421a 100644
--- a/lib-src/make-docfile.c
+++ b/lib-src/make-docfile.c
@@ -729,18 +729,6 @@ write_globals (void)
 
 	  if (globals[i].flags & DEFUN_const)
 	    fputs (" ATTRIBUTE_CONST", stdout);
-	  else if (strcmp (globals[i].name, "Fnext_read_file_uses_dialog_p")
-		   == 0)
-	    {
-	      /* It would be nice to have a cleaner way to deal with this
-		 special hack.  */
-	      fputs (("\n"
-		      "#if ! (defined USE_GTK || defined USE_MOTIF \\\n"
-		      "       || defined HAVE_NS || defined HAVE_NTGUI)\n"
-		      "\tATTRIBUTE_CONST\n"
-		      "#endif\n"),
-		     stdout);
-	    }
 
 	  puts (";");
 	}
diff --git a/src/ChangeLog b/src/ChangeLog
index 40d8b26..ae634f3 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,14 @@
+2015-01-16  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Give up on -Wsuggest-attribute=const
+	* decompress.c (Fzlib_available_p):
+	* gnutls.c (Fgnutls_available_p):
+	* gtkutil.h (xg_uses_old_file_dialog):
+	* xdisp.c (Ftool_bar_height):
+	* xmenu.c (popup_activated):
+	No longer const, since it's not const on at lest some
+	configurations, and we shouldn't lie to the compiler.
+
 2015-01-15  Eli Zaretskii  <eliz@gnu.org>
 
 	* fileio.c: Include binary-io.h.
diff --git a/src/decompress.c b/src/decompress.c
index b78dace..b14f0a2 100644
--- a/src/decompress.c
+++ b/src/decompress.c
@@ -88,8 +88,7 @@ unwind_decompress (void *ddata)
 }
 
 DEFUN ("zlib-available-p", Fzlib_available_p, Szlib_available_p, 0, 0, 0,
-       doc: /* Return t if zlib decompression is available in this instance of Emacs.  */
-       attributes: const)
+       doc: /* Return t if zlib decompression is available in this instance of Emacs.  */)
      (void)
 {
 #ifdef WINDOWSNT
diff --git a/src/gnutls.c b/src/gnutls.c
index 909542f..35f0eb4 100644
--- a/src/gnutls.c
+++ b/src/gnutls.c
@@ -1619,8 +1619,7 @@ This function may also return `gnutls-e-again', or
 #endif	/* HAVE_GNUTLS */
 
 DEFUN ("gnutls-available-p", Fgnutls_available_p, Sgnutls_available_p, 0, 0, 0,
-       doc: /* Return t if GnuTLS is available in this instance of Emacs.  */
-       attributes: const)
+       doc: /* Return t if GnuTLS is available in this instance of Emacs.  */)
      (void)
 {
 #ifdef HAVE_GNUTLS
diff --git a/src/gtkutil.h b/src/gtkutil.h
index 7d712c9..0ac49ca 100644
--- a/src/gtkutil.h
+++ b/src/gtkutil.h
@@ -78,7 +78,7 @@ typedef struct xg_menu_item_cb_data_
 
 } xg_menu_item_cb_data;
 
-extern bool xg_uses_old_file_dialog (void) ATTRIBUTE_CONST;
+extern bool xg_uses_old_file_dialog (void);
 
 extern char *xg_get_file_name (struct frame *f,
                                char *prompt,
diff --git a/src/xdisp.c b/src/xdisp.c
index 041a022..f006f8e 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -12276,8 +12276,7 @@ DEFUN ("tool-bar-height", Ftool_bar_height, Stool_bar_height,
        0, 2, 0,
        doc: /* Return the number of lines occupied by the tool bar of FRAME.
 If FRAME is nil or omitted, use the selected frame.  Optional argument
-PIXELWISE non-nil means return the height of the tool bar in pixels.  */
-       attributes: const)
+PIXELWISE non-nil means return the height of the tool bar in pixels.  */)
   (Lisp_Object frame, Lisp_Object pixelwise)
 {
   int height = 0;
diff --git a/src/xmenu.c b/src/xmenu.c
index 9063a8a..fdf1f6f 100644
--- a/src/xmenu.c
+++ b/src/xmenu.c
@@ -2288,7 +2288,7 @@ x_menu_show (struct frame *f, int x, int y, int menuflags,
 /* Detect if a dialog or menu has been posted.  MSDOS has its own
    implementation on msdos.c.  */
 
-int ATTRIBUTE_CONST
+int
 popup_activated (void)
 {
   return popup_activated_flag;
-- 
2.1.0