Automatic detect jobserver

This commit adds a way to automatic detect if a GNU Make jobserver is
up and running by checking if provided file descriptors are FIFOs.

gcc/ChangeLog
2020-07-29  Giuliano Belinassi  <giuliano.belinassi@usp.br>

	* cgraphunit.c (maybe_compile_in_parallel): Implement automatic
	jobserver detection flag.
	* jobserver.cc (jobserver_initialize): Check if Make fds are FIFOs.

3 files changed, 31 insertions, 26 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ed48394..79e5c1c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2020-07-29  Giuliano Belinassi  <giuliano.belinassi@usp.br>
+
+	* cgraphunit.c (maybe_compile_in_parallel): Implement automatic
+	jobserver detection flag.
+	* jobserver.cc (jobserver_initialize): Check if Make fds are FIFOs.
+	(jobserver_finalize): Set nonblock_mode back to false.
+
 2020-07-27  Giuliano Belinassi  <giuliano.belinassi@usp.br>
 
 	* Makefile.in: Mark jobserver.cc to be compiled.
diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
index a029455..c9f413c 100644
--- a/gcc/cgraphunit.c
+++ b/gcc/cgraphunit.c
@@ -2774,22 +2774,35 @@ static bool maybe_compile_in_parallel (void)
   bool promote_statics = param_promote_statics;
   bool balance = param_balance_partitions;
   bool jobserver = false;
+  bool job_auto = false;
   int num_jobs = -1;
 
   if (!flag_parallel_jobs || !split_outputs)
     return false;
 
-  if (!strcmp (flag_parallel_jobs, "jobserver"))
+  if (!strcmp (flag_parallel_jobs, "auto"))
+    {
+      jobserver = jobserver_initialize ();
+      job_auto = true;
+    }
+  else if (!strcmp (flag_parallel_jobs, "jobserver"))
     jobserver = jobserver_initialize ();
   else if (is_number (flag_parallel_jobs))
     num_jobs = atoi (flag_parallel_jobs);
   else
     gcc_unreachable ();
 
+  if (job_auto && !jobserver)
+    {
+      num_jobs = sysconf (_SC_NPROCESSORS_CONF);
+      if (num_jobs > 2)
+	num_jobs = 2;
+    }
+
   if (num_jobs < 0 && !jobserver)
     {
-      error (UNKNOWN_LOCATION,
-	      "'-fparallel-jobs=jobserver', but no GNU Jobserver found");
+      inform (UNKNOWN_LOCATION,
+	      "-fparallel-jobs=jobserver, but no GNU Jobserver found");
       return false;
     }
 
diff --git a/gcc/jobserver.cc b/gcc/jobserver.cc
index 4c879cc..9c6bcb6 100644
--- a/gcc/jobserver.cc
+++ b/gcc/jobserver.cc
@@ -72,6 +72,13 @@ bool jobserver_initialize ()
   if (!success)
     return false;
 
+  struct stat statbuf;
+  if (fstat (rfd, &statbuf) < 0
+      || (statbuf.st_mode & S_IFMT) != S_IFIFO
+      || fstat (wfd, &statbuf) < 0
+      || (statbuf.st_mode & S_IFMT) != S_IFIFO)
+    return false;
+
   int flags = fcntl (rfd, F_GETFL);
   if (flags < 0)
     return false;
@@ -81,29 +88,6 @@ bool jobserver_initialize ()
     nonblock_mode = true;
 
   return (jobserver_initialized = true);
-
-#if 0
-  /* Test if we can read from the rfd.  */
-  jobserver_token_t token;
-  ssize_t r = read (rfd, &token, sizeof (jobserver_token_t));
-
-  gcc_assert (r == sizeof (jobserver_token_t) || r == 0 || r == -1);
-
-  if (r < 0)
-    {
-      /* Check errno.  We may have no problem at all.  */
-      if (errno != EAGAIN)
-	return false;
-    }
-
-  /* Reading 0 bytes indicate that fd was closed by parent process.  */
-  if (r == 0)
-    return false;
-
-  /* Check if we got a important token that we have to return.  */
-  if (token != JOBSERVER_NULL_TOKEN)
-    jobserver_return_token (token);
-#endif
 }
 
 /* Finalize the jobserver, so this interface could be used again later.  */
@@ -116,6 +100,7 @@ bool jobserver_finalize ()
   close (wfd);
 
   rfd = wfd = -1;
+  nonblock_node = false;
 
   jobserver_initialized = false;
   return true;