re PR fortran/37486 (alignment of data in COMMON blocks)

2008-09-22  Janus Weil  <janus@gcc.gnu.org>

	PR fortran/37486
	* gfortran.h (gfc_option_t): New members flag_align_commons and
	warn_align_commons. 
	* lang.opt: New options falign-commons and Walign-commons.
	* invoke.texi: Documentation for new options.
	* options.c (gfc_init_options): Initialize new options.
	(gfc_handle_options): Handle new options.
	* trans-common.c (translate_common): Implement new options.
	(gfc_trans_common): Set correct locus.


2008-09-22  Janus Weil  <janus@gcc.gnu.org>

	PR fortran/37486
	* gfortran.dg/common_align_1.f90: New.
	* gfortran.dg/warn_align_commons.f90: New.

From-SVN: r140546

6 files changed, 82 insertions, 17 deletions

diff --git a/gcc/fortran/ChangeLog b/gcc/fortran/ChangeLog
index e362413..7744ba4 100644
--- a/gcc/fortran/ChangeLog
+++ b/gcc/fortran/ChangeLog
@@ -1,3 +1,15 @@
+2008-09-22  Janus Weil  <janus@gcc.gnu.org>
+
+	PR fortran/37486
+	* gfortran.h (gfc_option_t): New members flag_align_commons and
+	warn_align_commons. 
+	* lang.opt: New options falign-commons and Walign-commons.
+	* invoke.texi: Documentation for new options.
+	* options.c (gfc_init_options): Initialize new options.
+	(gfc_handle_options): Handle new options.
+	* trans-common.c (translate_common): Implement new options.
+	(gfc_trans_common): Set correct locus.
+
 2008-09-21  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/37583
diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index 444027b..fa3f865 100644
--- a/gcc/fortran/gfortran.h
+++ b/gcc/fortran/gfortran.h
@@ -1969,6 +1969,7 @@ typedef struct
   int warn_intrinsics_std;
   int warn_character_truncation;
   int warn_array_temp;
+  int warn_align_commons;
   int max_errors;
 
   int flag_all_intrinsics;
@@ -2006,6 +2007,7 @@ typedef struct
   int flag_init_logical;
   int flag_init_character;
   char flag_init_character_value;
+  int flag_align_commons;
 
   int fpe;
 
diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index b854ce4..2f6f4b0 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -138,7 +138,8 @@ and warnings}.
 -fsyntax-only  -pedantic  -pedantic-errors @gol
 -Wall  -Waliasing  -Wampersand  -Warray-bounds -Wcharacter-truncation @gol
 -Wconversion -Wimplicit-interface  -Wline-truncation  -Wintrinsics-std @gol
--Wsurprising -Wno-tabs  -Wunderflow -Wunused-parameter -Wintrinsics-shadow}
+-Wsurprising -Wno-tabs  -Wunderflow -Wunused-parameter -Wintrinsics-shadow @gol
+-Wno-align-commons}
 
 @item Debugging Options
 @xref{Debugging Options,,Options for debugging your program or GNU Fortran}.
@@ -167,7 +168,7 @@ and warnings}.
 -fpack-derived  -frepack-arrays  -fshort-enums  -fexternal-blas @gol
 -fblas-matmul-limit=@var{n} -frecursive -finit-local-zero @gol
 -finit-integer=@var{n} -finit-real=@var{<zero|inf|-inf|nan>} @gol
--finit-logical=@var{<true|false>} -finit-character=@var{n}}
+-finit-logical=@var{<true|false>} -finit-character=@var{n} -fno-align-commons}
 @end table
 
 @menu
@@ -800,6 +801,14 @@ about unused dummy arguments, but about unused @code{PARAMETER} values.
 @option{-Wunused-parameter} is not included in @option{-Wall} but is
 implied by @option{-Wall -Wextra}.
 
+@item -Walign-commons
+@opindex @code{Walign-commons}
+@cindex warnings, alignment of COMMON blocks
+@cindex alignment of COMMON blocks
+By default, @command{gfortran} warns about any occasion of variables being
+padded for proper alignment inside a COMMON block. This warning can be turned
+off via @option{-Wno-align-commons}. See also @option{-falign-commons}.
+
 @item -Werror
 @opindex @code{Werror}
 @cindex warnings, to errors
@@ -1275,6 +1284,18 @@ future releases).
 
 Note that the @option{-finit-real=nan} option initializes @code{REAL}
 and @code{COMPLEX} variables with a quiet NaN.
+
+@item -falign-commons
+@opindex @code{falign-commons}
+@cindex alignment of COMMON blocks
+By default, @command{gfortran} enforces proper alignment of all variables in a
+COMMON block by padding them as needed. On certain platforms this is mandatory,
+on others it increases performance. If a COMMON block is not declared with
+consistent data types everywhere, this padding can cause trouble, and
+@option{-fno-align-commons } can be used to disable automatic alignment. The
+same form of this option should be used for all files that share a COMMON block.
+To avoid potential alignment issues in COMMON blocks, it is recommended to order
+objects from largests to smallest.
 @end table
 
 @xref{Code Gen Options,,Options for Code Generation Conventions,
diff --git a/gcc/fortran/lang.opt b/gcc/fortran/lang.opt
index 9321195..49055f3 100644
--- a/gcc/fortran/lang.opt
+++ b/gcc/fortran/lang.opt
@@ -72,6 +72,10 @@ Waliasing
 Fortran Warning
 Warn about possible aliasing of dummy arguments
 
+Walign-commons
+Fortran Warning
+Warn about alignment of COMMON blocks
+
 Wampersand
 Fortran Warning
 Warn about missing ampersand in continued character constants
@@ -132,6 +136,10 @@ d
 Fortran Joined
 -d[DIMNU]	Dump details about macro names and definitions during preprocessing
 
+falign-commons
+Fortran
+Enable alignment of COMMON blocks
+
 fall-intrinsics
 Fortran RejectNegative
 All intrinsics procedures are available regardless of selected standard
diff --git a/gcc/fortran/options.c b/gcc/fortran/options.c
index 4ecb8f9..52174b3 100644
--- a/gcc/fortran/options.c
+++ b/gcc/fortran/options.c
@@ -78,6 +78,7 @@ gfc_init_options (unsigned int argc, const char **argv)
   gfc_option.warn_underflow = 1;
   gfc_option.warn_intrinsic_shadow = 0;
   gfc_option.warn_intrinsics_std = 0;
+  gfc_option.warn_align_commons = 1;
   gfc_option.max_errors = 25;
 
   gfc_option.flag_all_intrinsics = 0;
@@ -117,6 +118,7 @@ gfc_init_options (unsigned int argc, const char **argv)
   gfc_option.flag_init_logical = GFC_INIT_LOGICAL_OFF;
   gfc_option.flag_init_character = GFC_INIT_CHARACTER_OFF;
   gfc_option.flag_init_character_value = (char)0;
+  gfc_option.flag_align_commons = 1;
   
   gfc_option.fpe = 0;
 
@@ -517,6 +519,10 @@ gfc_handle_option (size_t scode, const char *arg, int value)
       gfc_option.warn_intrinsic_shadow = value;
       break;
 
+    case OPT_Walign_commons:
+      gfc_option.warn_align_commons = value;
+      break;
+
     case OPT_fall_intrinsics:
       gfc_option.flag_all_intrinsics = 1;
       break;
@@ -825,6 +831,10 @@ gfc_handle_option (size_t scode, const char *arg, int value)
     case OPT_frecursive:
       gfc_option.flag_recursive = 1;
       break;
+
+    case OPT_falign_commons:
+      gfc_option.flag_align_commons = value;
+      break;
     }
 
   return result;
diff --git a/gcc/fortran/trans-common.c b/gcc/fortran/trans-common.c
index 9e55792..92edd20 100644
--- a/gcc/fortran/trans-common.c
+++ b/gcc/fortran/trans-common.c
@@ -1059,7 +1059,9 @@ translate_common (gfc_common_head *common, gfc_symbol *var_list)
   bool saw_equiv;
 
   common_segment = NULL;
+  offset = 0;
   current_offset = 0;
+  align = 1;
   max_align = 1;
   saw_equiv = false;
 
@@ -1100,16 +1102,27 @@ translate_common (gfc_common_head *common, gfc_symbol *var_list)
 		       "extension to COMMON '%s' at %L", sym->name,
 		       common->name, &common->where);
 
-	  offset = align_segment (&align);
+	  if (gfc_option.flag_align_commons)
+	    offset = align_segment (&align);
 
 	  if (offset & (max_align - 1))
 	    {
 	      /* The required offset conflicts with previous alignment
 		 requirements.  Insert padding immediately before this
 		 segment.  */
-	      gfc_warning ("Padding of %d bytes required before '%s' in "
-			   "COMMON '%s' at %L", (int)offset, s->sym->name,
-			   common->name, &common->where);
+	      if (gfc_option.warn_align_commons)
+		{
+		  if (strcmp (common->name, BLANK_COMMON_NAME))
+		    gfc_warning ("Padding of %d bytes required before '%s' in "
+				 "COMMON '%s' at %L; reorder elements or use "
+				 "-fno-align-commons", (int)offset,
+				 s->sym->name, common->name, &common->where);
+		  else
+		    gfc_warning ("Padding of %d bytes required before '%s' in "
+				 "COMMON at %L; reorder elements or use "
+				 "-fno-align-commons", (int)offset,
+				 s->sym->name, &common->where);
+		}
 	    }
 	  else
 	    {
@@ -1138,10 +1151,16 @@ translate_common (gfc_common_head *common, gfc_symbol *var_list)
       return;
     }
 
-  if (common_segment->offset != 0)
+  if (common_segment->offset != 0 && gfc_option.warn_align_commons)
     {
-      gfc_warning ("COMMON '%s' at %L requires %d bytes of padding at start",
-		   common->name, &common->where, (int)common_segment->offset);
+      if (strcmp (common->name, BLANK_COMMON_NAME))
+	gfc_warning ("COMMON '%s' at %L requires %d bytes of padding at start; "
+		     "reorder elements or use -fno-align-commons",
+		     common->name, &common->where, (int)common_segment->offset);
+      else
+	gfc_warning ("COMMON at %L requires %d bytes of padding at start; "
+		     "reorder elements or use -fno-align-commons",
+		     &common->where, (int)common_segment->offset);
     }
 
   create_common (common, common_segment, saw_equiv);
@@ -1225,14 +1244,7 @@ gfc_trans_common (gfc_namespace *ns)
   if (ns->blank_common.head != NULL)
     {
       c = gfc_get_common_head ();
-
-      /* We've lost the real location, so use the location of the
-	 enclosing procedure.  */
-      if (ns->proc_name != NULL)
-	c->where = ns->proc_name->declared_at;
-      else
-	c->where = ns->blank_common.head->common_head->where;
-
+      c->where = ns->blank_common.head->common_head->where;
       strcpy (c->name, BLANK_COMMON_NAME);
       translate_common (c, ns->blank_common.head);
     }