Fix common-related error recovery ICE.

Fix an inconsistent state, between the in_common attribute
and the common_block pointer.

 - adding a symbol to a common block list in gfc_match_common is delayed
   after the call to gfc_add_in_common.
 - gfc_restore_latest_undo_checkpoint is changed to check the common_block
   pointer directly instead of the in_common attribute.
 - gfc_restore_old_symbol is changed to also restore
   the common-related pointers.  This is done using a new function created
   to factor the related memory management.
 - In gfc_restore_last_undo_checkpoint, when a symbol has been removed
   from the common block linked list, its common_next pointer is cleared.

	PR fortran/67758
gcc/fortran/
	* gfortran.h (gfc_symbol): Expand comment.
	* match.c (gfc_match_common): Delay adding the symbol to
	the common_block after the gfc_add_in_common call.
	* symbol.c (gfc_free_symbol): Move common block memory handling...
	(gfc_set_symbol_common_block): ... here as a new function.
	(restore_old_symbol): Restore common block fields.
	(gfc_restore_last_undo_checkpoint):
	Check the common_block pointer instead of the in_common attribute.
	When a symbol has been removed from the common block linked list,
	clear its common_next pointer.
gcc/testsuite/
	* gfortran.dg/common_25.f90: New file.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@228947 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 6 insertions, 2 deletions

diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index 9c0084be77c..b2894cc22c4 100644
--- a/gcc/fortran/gfortran.h
+++ b/gcc/fortran/gfortran.h
@@ -1411,8 +1411,12 @@ typedef struct gfc_symbol
 
   struct gfc_symbol *common_next;	/* Links for COMMON syms */
 
-  /* This is in fact a gfc_common_head but it is only used for pointer
-     comparisons to check if symbols are in the same common block.  */
+  /* This is only used for pointer comparisons to check if symbols
+     are in the same common block.
+     In opposition to common_block, the common_head pointer takes into account
+     equivalences: if A is in a common block C and A and B are in equivalence,
+     then both A and B have common_head pointing to C, while A's common_block
+     points to C and B's is NULL.  */
   struct gfc_common_head* common_head;
 
   /* Make sure setup code for dummy arguments is generated in the correct