decl.c (attr_seen): New static variable.

2017-08-10  Fritz Reese <Reese-Fritz@zai.com>

    gcc/fortran/ChangeLog:

	* decl.c (attr_seen): New static variable.
	* decl.c (variable_decl): Match %FILL in STRUCTURE body.
	* gfortran.texi: Update documentation.

    gcc/testsuite/ChangeLog:

    gfortran.dg/
	* dec_structure_18.f90, dec_structure_19.f90, dec_structure_20.f90,
	dec_structure_21.f90: New.

From-SVN: r251023

3 files changed, 74 insertions, 2 deletions

diff --git a/gcc/fortran/ChangeLog b/gcc/fortran/ChangeLog
index 09138ab4..45b16d4 100644
--- a/gcc/fortran/ChangeLog
+++ b/gcc/fortran/ChangeLog
@@ -1,3 +1,9 @@
+2017-08-10  Fritz Reese <Reese-Fritz@zai.com>
+
+	* decl.c (attr_seen): New static variable.
+	* decl.c (variable_decl): Match %FILL in STRUCTURE body.
+	* gfortran.texi: Update documentation.
+
 2017-08-08  Martin Liska  <mliska@suse.cz>
 
 	* trans-types.c: Include header files.
diff --git a/gcc/fortran/decl.c b/gcc/fortran/decl.c
index 54ee5d3..b919f43 100644
--- a/gcc/fortran/decl.c
+++ b/gcc/fortran/decl.c
@@ -54,6 +54,7 @@ static gfc_typespec current_ts;
 static symbol_attribute current_attr;
 static gfc_array_spec *current_as;
 static int colon_seen;
+static int attr_seen;
 
 /* The current binding label (if any).  */
 static const char* curr_binding_label;
@@ -2140,6 +2141,7 @@ static match
 variable_decl (int elem)
 {
   char name[GFC_MAX_SYMBOL_LEN + 1];
+  static unsigned int fill_id = 0;
   gfc_expr *initializer, *char_len;
   gfc_array_spec *as;
   gfc_array_spec *cp_as; /* Extra copy for Cray Pointees.  */
@@ -2157,9 +2159,47 @@ variable_decl (int elem)
   /* When we get here, we've just matched a list of attributes and
      maybe a type and a double colon.  The next thing we expect to see
      is the name of the symbol.  */
-  m = gfc_match_name (name);
+
+  /* If we are parsing a structure with legacy support, we allow the symbol
+     name to be '%FILL' which gives it an anonymous (inaccessible) name.  */
+  m = MATCH_NO;
+  gfc_gobble_whitespace ();
+  if (gfc_peek_ascii_char () == '%')
+    {
+      gfc_next_ascii_char ();
+      m = gfc_match ("fill");
+    }
+
   if (m != MATCH_YES)
-    goto cleanup;
+    {
+      m = gfc_match_name (name);
+      if (m != MATCH_YES)
+	goto cleanup;
+    }
+
+  else
+    {
+      m = MATCH_ERROR;
+      if (gfc_current_state () != COMP_STRUCTURE)
+	{
+	  if (flag_dec_structure)
+	    gfc_error ("%qs not allowed outside STRUCTURE at %C", "%FILL");
+	  else
+	    gfc_error ("%qs at %C is a DEC extension, enable with "
+		       "%<-fdec-structure%>", "%FILL");
+	  goto cleanup;
+	}
+
+      if (attr_seen)
+	{
+	  gfc_error ("%qs entity cannot have attributes at %C", "%FILL");
+	  goto cleanup;
+	}
+
+      /* %FILL components are given invalid fortran names.  */
+      snprintf (name, GFC_MAX_SYMBOL_LEN + 1, "%%FILL%u", fill_id++);
+      m = MATCH_YES;
+    }
 
   var_locus = gfc_current_locus;
 
@@ -2260,6 +2300,14 @@ variable_decl (int elem)
 	}
     }
 
+  /* %FILL components may not have initializers.  */
+  if (strncmp (name, "%FILL", 5) == 0 && gfc_match_eos () != MATCH_YES)
+    {
+      gfc_error ("%qs entity cannot have an initializer at %C", "%FILL");
+      m = MATCH_ERROR;
+      goto cleanup;
+    }
+
   /*  If this symbol has already shown up in a Cray Pointer declaration,
       and this is not a component declaration,
       then we want to set the type & bail out.  */
@@ -3860,6 +3908,7 @@ match_attr_spec (void)
 
   current_as = NULL;
   colon_seen = 0;
+  attr_seen = 0;
 
   /* See if we get all of the keywords up to the final double colon.  */
   for (d = GFC_DECL_BEGIN; d != GFC_DECL_END; d++)
@@ -4228,6 +4277,8 @@ match_attr_spec (void)
     {
       if (seen[d] == 0)
 	continue;
+      else
+        attr_seen = 1;
 
       if ((d == DECL_STATIC || d == DECL_AUTOMATIC)
 	  && !flag_dec_static)
@@ -4436,6 +4487,7 @@ cleanup:
   gfc_current_locus = start;
   gfc_free_array_spec (current_as);
   current_as = NULL;
+  attr_seen = 0;
   return m;
 }
 
diff --git a/gcc/fortran/gfortran.texi b/gcc/fortran/gfortran.texi
index 85afdda..145ec7f 100644
--- a/gcc/fortran/gfortran.texi
+++ b/gcc/fortran/gfortran.texi
@@ -2220,6 +2220,20 @@ rules and exceptions:
 @item Structures act like derived types with the @code{SEQUENCE} attribute.
 Otherwise they may contain no specifiers.
 
+@item Structures may contain a special field with the name @code{%FILL}.
+This will create an anonymous component which cannot be accessed but occupies
+space just as if a component of the same type was declared in its place, useful
+for alignment purposes.  As an example, the following structure will consist
+of at least sixteen bytes:
+
+@smallexample
+structure /padded/
+  character(4) start
+  character(8) %FILL
+  character(4) end
+end structure
+@end smallexample
+
 @item Structures may share names with other symbols. For example, the following
 is invalid for derived types, but valid for structures: