Port --enable-gcc-warnings to GCC 6.2.1

Backport from master.
* src/conf_post.h (GNUC_PREREQ): New macro.
* src/keyboard.c: Use it to work around GCC bug 54561.
* src/process.c (would_block): New function.
(server_accept_connection, wait_reading_process_output, send_process):
Use it.

3 files changed, 33 insertions, 25 deletions

diff --git a/src/conf_post.h b/src/conf_post.h
index 209f60792cf..f83965bf8b1 100644
--- a/src/conf_post.h
+++ b/src/conf_post.h
@@ -34,6 +34,17 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <stdbool.h>
 
+/* GNUC_PREREQ (V, W, X) is true if this is GNU C version V.W.X or later.
+   It can be used in a preprocessor expression.  */
+#ifndef __GNUC_MINOR__
+# define GNUC_PREREQ(v, w, x) false
+#elif ! defined __GNUC_PATCHLEVEL__
+# define GNUC_PREREQ(v, w, x) ((v) < __GNUC__ + ((w) <= __GNUC_MINOR__))
+#else
+# define GNUC_PREREQ(v, w, x) \
+    ((v) < __GNUC__ + ((w) <= __GNUC_MINOR__ + ((x) <= __GNUC_PATCHLEVEL__)))
+#endif
+
 /* The type of bool bitfields.  Needed to compile Objective-C with
    standard GCC.  It was also needed to port to pre-C99 compilers,
    although we don't care about that any more.  */
diff --git a/src/keyboard.c b/src/keyboard.c
index 918424630f3..f24d86e8833 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -70,6 +70,11 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include TERM_HEADER
 #endif /* HAVE_WINDOW_SYSTEM */
 
+/* Work around GCC bug 54561.  */
+#if GNUC_PREREQ (4, 3, 0)
+# pragma GCC diagnostic ignored "-Wclobbered"
+#endif
+
 /* Variables for blockinput.h:  */
 
 /* Positive if interrupt input is blocked right now.  */
diff --git a/src/process.c b/src/process.c
index 7ab92b0102c..e6ea2fbe8f7 100644
--- a/src/process.c
+++ b/src/process.c
@@ -151,6 +151,18 @@ bool inhibit_sentinels;
 # define SOCK_CLOEXEC 0
 #endif
 
+/* True if ERRNUM represents an error where the system call would
+   block if a blocking variant were used.  */
+static bool
+would_block (int errnum)
+{
+#ifdef EWOULDBLOCK
+  if (EWOULDBLOCK != EAGAIN && errnum == EWOULDBLOCK)
+    return true;
+#endif
+  return errnum == EAGAIN;
+}
+
 #ifndef HAVE_ACCEPT4
 
 /* Emulate GNU/Linux accept4 and socket well enough for this module.  */
@@ -4262,15 +4274,7 @@ server_accept_connection (Lisp_Object server, int channel)
   if (s < 0)
     {
       int code = errno;
-
-      if (code == EAGAIN)
-        return;
-#ifdef EWOULDBLOCK
-      if (code == EWOULDBLOCK)
-        return;
-#endif
-
-      if (!NILP (ps->log))
+      if (!would_block (code) && !NILP (ps->log))
         call3 (ps->log, server, Qnil,
                concat3 (build_string ("accept failed with code"),
                         Fnumber_to_string (make_number (code)),
@@ -4687,12 +4691,8 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
                   int nread = read_process_output (proc, wait_proc->infd);
                   if (nread < 0)
                     {
-                    if (errno == EIO || errno == EAGAIN)
-                      break;
-#ifdef EWOULDBLOCK
-                    if (errno == EWOULDBLOCK)
-                      break;
-#endif
+                      if (errno == EIO || would_block (errno))
+                        break;
                     }
                   else
                     {
@@ -5073,11 +5073,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
                   if (do_display)
                     redisplay_preserve_echo_area (12);
                 }
-#ifdef EWOULDBLOCK
-              else if (nread == -1 && errno == EWOULDBLOCK)
-                ;
-#endif
-              else if (nread == -1 && errno == EAGAIN)
+              else if (nread == -1 && would_block (errno))
                 ;
 #ifdef WINDOWSNT
               /* FIXME: Is this special case still needed?  */
@@ -5801,11 +5797,7 @@ send_process (Lisp_Object proc, const char *buf, ptrdiff_t len,
 
           if (rv < 0)
             {
-              if (errno == EAGAIN
-#ifdef EWOULDBLOCK
-                  || errno == EWOULDBLOCK
-#endif
-                  )
+              if (would_block (errno))
                 /* Buffer is full.  Wait, accepting input;
                    that may allow the program
                    to finish doing output and read more.  */