PR fortran/91413 Generate warning when making array static

When moving a local variable from the stack to static storage, the
procedure is no longer safe to be called recursively or concurrently
from multiple threads.  Thus generate a warning when this is done.
Also double the default limit for switching from stack to static.

Regtested on x86_64-pc-linux-gnu.

gcc/fortran/ChangeLog:

2019-08-11  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/91413
	* invoke.texi (-fmax-stack-var-size): Document increased default.
	* options.c (gfc_post_options): Increase default stack var size to
	65536 bytes.
	* trans-decl.c (gfc_finish_var_decl): Generate warning when local
	array moved to static storage.

From-SVN: r274264

gcc/fortran/ChangeLog

+2019-08-11  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	PR fortran/91413
+	* invoke.texi (-fmax-stack-var-size): Document increased default.
+	* options.c (gfc_post_options): Increase default stack var size to
+	65536 bytes.
+	* trans-decl.c (gfc_finish_var_decl): Generate warning when local
+	array moved to static storage.
+
 2019-08-10  Steven G. Kargl  <kargl@gcc.gnu.org>
 
 	* decl.c (match_old_style_init): Use a clearer error message.

gcc/fortran/invoke.texi

@@ -1720,7 +1720,7 @@ This option currently only affects local arrays declared with constant
 bounds, and may not apply to all character variables.
 Future versions of GNU Fortran may improve this behavior.
 
-The default value for @var{n} is 32768.
+The default value for @var{n} is 65536.
 
 @item -fstack-arrays
 @opindex @code{fstack-arrays}

gcc/fortran/options.c

@@ -437,7 +437,7 @@ gfc_post_options (const char **pfilename)
 
   /* Set default.  */
   if (flag_max_stack_var_size == -2)
-    flag_max_stack_var_size = 32768;
+    flag_max_stack_var_size = 65536;
 
   /* Implement -fno-automatic as -fmax-stack-var-size=0.  */
   if (!flag_automatic)

gcc/fortran/trans-decl.c

@@ -753,6 +753,16 @@ gfc_finish_var_decl (tree decl, gfc_symbol * sym)
 	  || sym->attr.allocatable)
       && !DECL_ARTIFICIAL (decl))
     {
+      gfc_warning (OPT_Wsurprising,
+		   "Array %qs at %L is larger than limit set by"
+		   " %<-fmax-stack-var-size=%>, moved from stack to static"
+		   " storage. This makes the procedure unsafe when called"
+		   " recursively, or concurrently from multiple threads."
+		   " Consider using %<-frecursive%>, or increase the"
+		   " %<-fmax-stack-var-size=%> limit, or change the code to"
+		   " use an ALLOCATABLE array.",
+		   sym->name, &sym->declared_at);
+
       TREE_STATIC (decl) = 1;
 
       /* Because the size of this variable isn't known until now, we may have