Re: Lower VLA representation to pointers

[Richard Henderson <rth at redhat dot com>]

On Wed, Aug 11, 2004 at 01:29:06PM -0700, Richard Henderson wrote:
> On Wed, Aug 11, 2004 at 07:25:13PM +0000, Joseph S. Myers wrote:
> > In standard terms there is no new block, neither after the label (which 
> > indeed could be in a nested block) nor before the VLA, and the scope is 
> > the same (same scope being defined as scope ending at same point) as that 
> > of other declarations in the block.
> 
> Huh.  Perhaps I was confusing with C++, or just confused.
> Anyway, testing a patch that adds an artifical BIND_EXPR,
> but not a lexical scope.

Like so.


r~



        * c-common.h (STATEMENT_LIST_HAS_LABEL): New.
        * c-semantics.c (add_stmt): Set it.
        * c-decl.c (finish_decl): Use it to create a new BIND_EXPR
        before instantiating a variable sized type.

Index: c-common.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-common.h,v
retrieving revision 1.255
diff -c -p -d -r1.255 c-common.h
*** c-common.h	6 Aug 2004 02:03:18 -0000	1.255
--- c-common.h	12 Aug 2004 04:06:53 -0000
*************** Software Foundation, 59 Temple Place - S
*** 35,41 ****
        STMT_IS_FULL_EXPR_P (in _STMT)
        STATEMENT_LIST_STMT_EXPR (in STATEMENT_LIST)
     2: unused
!    3: unused
     4: unused
  */
  
--- 35,41 ----
        STMT_IS_FULL_EXPR_P (in _STMT)
        STATEMENT_LIST_STMT_EXPR (in STATEMENT_LIST)
     2: unused
!    3: STATEMENT_LIST_HAS_LABEL (in STATEMENT_LIST)
     4: unused
  */
  
*************** extern void finish_file	(void);
*** 708,713 ****
--- 708,717 ----
  #define STATEMENT_LIST_STMT_EXPR(NODE) \
    TREE_LANG_FLAG_1 (STATEMENT_LIST_CHECK (NODE))
  
+ /* Nonzero if a label has been added to the statement list.  */
+ #define STATEMENT_LIST_HAS_LABEL(NODE) \
+   TREE_LANG_FLAG_3 (STATEMENT_LIST_CHECK (NODE))
+ 
  /* WHILE_STMT accessors. These give access to the condition of the
     while statement and the body of the while statement, respectively.  */
  #define WHILE_COND(NODE)        TREE_OPERAND (WHILE_STMT_CHECK (NODE), 0)
Index: c-decl.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-decl.c,v
retrieving revision 1.553
diff -c -p -d -r1.553 c-decl.c
*** c-decl.c	6 Aug 2004 02:03:18 -0000	1.553
--- c-decl.c	12 Aug 2004 04:06:54 -0000
*************** finish_decl (tree decl, tree init, tree 
*** 3061,3067 ****
  	    }
  
  	  if (TREE_CODE (decl) != FUNCTION_DECL)
! 	    add_stmt (build_stmt (DECL_EXPR, decl));
  	}
    
  
--- 3061,3084 ----
  	    }
  
  	  if (TREE_CODE (decl) != FUNCTION_DECL)
! 	    {
! 	      /* If we're building a variable sized type, and we might be
! 		 reachable other than via the top of the current binding
! 		 level, then create a new BIND_EXPR so that we deallocate
! 		 the object at the right time.  */
! 	      /* Note that DECL_SIZE can be null due to errors.  */
! 	      if (DECL_SIZE (decl)
! 		  && !TREE_CONSTANT (DECL_SIZE (decl))
! 		  && STATEMENT_LIST_HAS_LABEL (cur_stmt_list))
! 		{
! 		  tree bind;
! 		  bind = build (BIND_EXPR, void_type_node, NULL, NULL, NULL);
! 		  TREE_SIDE_EFFECTS (bind) = 1;
! 		  add_stmt (bind);
! 		  BIND_EXPR_BODY (bind) = push_stmt_list ();
! 		}
! 	      add_stmt (build_stmt (DECL_EXPR, decl));
! 	    }
  	}
    
  
Index: c-semantics.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-semantics.c,v
retrieving revision 1.91
diff -c -p -d -r1.91 c-semantics.c
*** c-semantics.c	5 Aug 2004 05:51:50 -0000	1.91
--- c-semantics.c	12 Aug 2004 04:06:54 -0000
*************** add_stmt (tree t)
*** 140,145 ****
--- 140,148 ----
        STMT_IS_FULL_EXPR_P (t) = stmts_are_full_exprs_p ();
      }
  
+   if (code == LABEL_EXPR || code == CASE_LABEL_EXPR)
+     STATEMENT_LIST_HAS_LABEL (cur_stmt_list) = 1;
+ 
    /* Add T to the statement-tree.  Non-side-effect statements need to be
       recorded during statement expressions.  */
    append_to_statement_list_force (t, &cur_stmt_list);
Index: testsuite/gcc.c-torture/execute/20040811-1.c
===================================================================
RCS file: testsuite/gcc.c-torture/execute/20040811-1.c
diff -N testsuite/gcc.c-torture/execute/20040811-1.c
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- testsuite/gcc.c-torture/execute/20040811-1.c	12 Aug 2004 04:08:18 -0000
***************
*** 0 ****
--- 1,19 ----
+ /* Ensure that we deallocate X when branching back before its
+    declaration.  */
+ 
+ void *volatile p;
+                                                                                 
+ int
+ main (void)
+ {
+   int n = 0;
+  lab:;
+   int x[n % 1000 + 1];
+   x[0] = 1;
+   x[n % 1000] = 2;
+   p = x;
+   n++;
+   if (n < 1000000)
+     goto lab;
+   return 0;
+ }