Provide warning for missing jobserver.

	PR driver/94330
	* lto-wrapper.c (run_gcc): When using -flto=jobserver,
	report warning when the jobserver is not detected.

1 files changed, 25 insertions, 14 deletions

diff --git a/gcc/lto-wrapper.c b/gcc/lto-wrapper.c
index 46a88b233f6..19d0c224dad 100644
--- a/gcc/lto-wrapper.c
+++ b/gcc/lto-wrapper.c
@@ -1236,28 +1236,33 @@ init_num_threads (void)
 
 /* FIXME: once using -std=c++11, we can use std::thread::hardware_concurrency.  */
 
-/* Return true when a jobserver is running and can accept a job.  */
+/* Test and return reason why a jobserver cannot be detected.  */
 
-static bool
+static const char *
 jobserver_active_p (void)
 {
+  #define JS_PREFIX "jobserver is not available: "
+  #define JS_NEEDLE "--jobserver-auth="
+
   const char *makeflags = getenv ("MAKEFLAGS");
   if (makeflags == NULL)
-    return false;
+    return JS_PREFIX "%<MAKEFLAGS%> environment variable is unset";
 
-  const char *needle = "--jobserver-auth=";
-  const char *n = strstr (makeflags, needle);
+  const char *n = strstr (makeflags, JS_NEEDLE);
   if (n == NULL)
-    return false;
+    return JS_PREFIX "%<" JS_NEEDLE "%> is not present in %<MAKEFLAGS%>";
 
   int rfd = -1;
   int wfd = -1;
 
-  return (sscanf (n + strlen (needle), "%d,%d", &rfd, &wfd) == 2
-	  && rfd > 0
-	  && wfd > 0
-	  && is_valid_fd (rfd)
-	  && is_valid_fd (wfd));
+  if (sscanf (n + strlen (JS_NEEDLE), "%d,%d", &rfd, &wfd) == 2
+      && rfd > 0
+      && wfd > 0
+      && is_valid_fd (rfd)
+      && is_valid_fd (wfd))
+    return NULL;
+  else
+    return JS_PREFIX "cannot access %<" JS_NEEDLE "%> file descriptors";
 }
 
 /* Execute gcc. ARGC is the number of arguments. ARGV contains the arguments. */
@@ -1473,10 +1478,16 @@ run_gcc (unsigned argc, char *argv[])
       auto_parallel = 0;
       parallel = 0;
     }
-  else if (!jobserver && jobserver_active_p ())
+  else
     {
-      parallel = 1;
-      jobserver = 1;
+      const char *jobserver_error = jobserver_active_p ();
+      if (jobserver && jobserver_error != NULL)
+	warning (0, jobserver_error);
+      else if (!jobserver && jobserver_error == NULL)
+	{
+	  parallel = 1;
+	  jobserver = 1;
+	}
     }
 
   if (linker_output)