Add -flto=auto option value.

2019-08-09  Martin Liska  <mliska@suse.cz>

	* doc/invoke.texi: Document the option value.
	* lto-wrapper.c (run_gcc): Set auto_parallel
	only with -flto=auto.
2019-08-09  Martin Liska  <mliska@suse.cz>

	* g++.dg/lto/devirt-19_0.C: Add -flto=auto.

From-SVN: r274232

gcc/ChangeLog

 2019-08-09  Martin Liska  <mliska@suse.cz>
 
+	* doc/invoke.texi: Document the option value.
+	* lto-wrapper.c (run_gcc): Set auto_parallel
+	only with -flto=auto.
+
+2019-08-09  Martin Liska  <mliska@suse.cz>
+
 	* opts.c (common_handle_option): Error for an invalid argument
 	to -flto=.
 

gcc/doc/invoke.texi

@@ -10415,8 +10415,7 @@ If you specify the optional @var{n}, the optimization and code
 generation done at link time is executed in parallel using @var{n}
 parallel jobs by utilizing an installed @command{make} program.  The
 environment variable @env{MAKE} may be used to override the program
-used.  The default value for @var{n} is automatically detected based
-on number of cores.
+used.
 
 You can also specify @option{-flto=jobserver} to use GNU make's
 job server mode to determine the number of parallel jobs. This
@@ -10425,6 +10424,10 @@ You must prepend a @samp{+} to the command recipe in the parent Makefile
 for this to work.  This option likely only works if @env{MAKE} is
 GNU make.
 
+Use @option{-flto=auto} to use GNU make's job server, if available,
+or otherwise fall back to autodetection of the number of CPU threads
+present in your system.
+
 @item -flto-partition=@var{alg}
 @opindex flto-partition
 Specify the partitioning algorithm used by the link-time optimizer.

gcc/lto-wrapper.c

@@ -1252,8 +1252,7 @@ run_gcc (unsigned argc, char *argv[])
   char *list_option_full = NULL;
   const char *linker_output = NULL;
   const char *collect_gcc, *collect_gcc_options;
-  /* Make linking parallel by default.  */
-  int parallel = 1;
+  int parallel = 0;
   int jobserver = 0;
   int auto_parallel = 0;
   bool no_partition = false;
@@ -1380,6 +1379,11 @@ run_gcc (unsigned argc, char *argv[])
 	case OPT_flto_:
 	  if (strcmp (option->arg, "jobserver") == 0)
 	    jobserver = 1;
+	  else if (strcmp (option->arg, "auto") == 0)
+	    {
+	      parallel = 1;
+	      auto_parallel = 1;
+	    }
 	  else
 	    {
 	      parallel = atoi (option->arg);
@@ -1423,14 +1427,8 @@ run_gcc (unsigned argc, char *argv[])
       auto_parallel = 0;
       parallel = 0;
     }
-  else if (!jobserver && parallel)
-    {
-      /* If there's no explicit usage of jobserver and
-	 parallel is enabled, then automatically detect
-	 jobserver or number of cores.  */
-      auto_parallel = 1;
-      jobserver = jobserver_active_p ();
-    }
+  else if (!jobserver && auto_parallel)
+    jobserver = jobserver_active_p ();
 
   if (linker_output)
     {

gcc/opts.c

@@ -2825,6 +2825,7 @@ common_handle_option (struct gcc_options *opts,
     case OPT_flto_:
       if (strcmp (arg, "none") != 0
 	  && strcmp (arg, "jobserver") != 0
+	  && strcmp (arg, "auto") != 0
 	  && atoi (arg) == 0)
 	error_at (loc,
 		  "unrecognized argument to %<-flto=%> option: %qs", arg);

gcc/testsuite/ChangeLog

 2019-08-09  Martin Liska  <mliska@suse.cz>
 
+	* g++.dg/lto/devirt-19_0.C: Add -flto=auto.
+
+2019-08-09  Martin Liska  <mliska@suse.cz>
+
 	* gcc.dg/spellcheck-options-21.c: New test.
 
 2019-08-09  Martin Liska  <mliska@suse.cz>

gcc/testsuite/g++.dg/lto/devirt-19_0.C

 /* { dg-lto-do link } */
 /* { dg-lto-options { "-O2 -fdump-ipa-cp -Wno-return-type -flto -r -nostdlib" } } */
-/* { dg-extra-ld-options "-flinker-output=nolto-rel" } */
+/* { dg-extra-ld-options "-flinker-output=nolto-rel -flto=auto" } */
 #include "../ipa/devirt-19.C"
 /* { dg-final { scan-wpa-ipa-dump-times "Discovered a virtual call to a known target" 1 "cp"  } } */