[RFC] tree-cfg.c: Check that a nonlocal label doesn't appear inthe middle of a basic block.

[Kazu Hirata <kazu at cs dot umass dot edu>]

Hi,

Attached is a patch to check that a nonlocal label doesn't appear in
the middle of a basic block.

Note that we don't consider a nonlocal label to be appearing in the
middle of a basic block if all the statements before the label are
also nonlocal labels.

This patch is based on the thread starting at

http://gcc.gnu.org/ml/gcc/2005-01/msg01036.html

Unfortunately, this patch introduces the following regressions (or
rather catches the following errors that went undetected previously).

+FAIL: gcc.c-torture/compile/20021108-1.c  -O0  (test for excess errors)
+FAIL: gcc.c-torture/compile/20021108-1.c  -O1  (test for excess errors)
+FAIL: gcc.c-torture/compile/20021108-1.c  -O2  (test for excess errors)
+FAIL: gcc.c-torture/compile/20021108-1.c  -O3 -fomit-frame-pointer  (test for excess errors)
+FAIL: gcc.c-torture/compile/20021108-1.c  -O3 -g  (test for excess errors)
+FAIL: gcc.c-torture/compile/20021108-1.c  -Os  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-1.c  -O0  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-1.c  -O1  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-1.c  -O2  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-1.c  -O3 -fomit-frame-pointer  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-1.c  -O3 -g  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-1.c  -Os  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-2.c  -O0  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-2.c  -O1  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-2.c  -O2  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-2.c  -O3 -fomit-frame-pointer  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-2.c  -O3 -g  (test for excess errors)
+FAIL: gcc.c-torture/compile/labels-2.c  -Os  (test for excess errors)
+FAIL: gcc.dg/pr16973.c (test for excess errors)

I have not analyzed what's causing these problems.

Kazu Hirata

2005-01-18  Kazu Hirata  <kazu@cs.umass.edu>

	* tree-cfg.c (tree_verify_flow_info): Check that a nonlocal
	label doesn't appear in the middle of a basic block.

Index: tree-cfg.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-cfg.c,v
retrieving revision 2.139
diff -c -d -p -r2.139 tree-cfg.c
*** tree-cfg.c	17 Jan 2005 18:44:18 -0000	2.139
--- tree-cfg.c	18 Jan 2005 16:19:56 -0000
*************** tree_verify_flow_info (void)
*** 3595,3619 ****
      {
        bool found_ctrl_stmt = false;
  
        /* Skip labels on the start of basic block.  */
        for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
  	{
! 	  if (TREE_CODE (bsi_stmt (bsi)) != LABEL_EXPR)
  	    break;
  
! 	  if (label_to_block (LABEL_EXPR_LABEL (bsi_stmt (bsi))) != bb)
  	    {
- 	      tree stmt = bsi_stmt (bsi);
  	      error ("Label %s to block does not match in bb %d\n",
  		     IDENTIFIER_POINTER (DECL_NAME (LABEL_EXPR_LABEL (stmt))),
  		     bb->index);
  	      err = 1;
  	    }
  
! 	  if (decl_function_context (LABEL_EXPR_LABEL (bsi_stmt (bsi)))
  	      != current_function_decl)
  	    {
- 	      tree stmt = bsi_stmt (bsi);
  	      error ("Label %s has incorrect context in bb %d\n",
  		     IDENTIFIER_POINTER (DECL_NAME (LABEL_EXPR_LABEL (stmt))),
  		     bb->index);
--- 3595,3630 ----
      {
        bool found_ctrl_stmt = false;
  
+       stmt = NULL_TREE;
+ 
        /* Skip labels on the start of basic block.  */
        for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
  	{
! 	  tree prev_stmt = stmt;
! 
! 	  stmt = bsi_stmt (bsi);
! 
! 	  if (TREE_CODE (stmt) != LABEL_EXPR)
  	    break;
  
! 	  if (prev_stmt && stmt_starts_bb_p (stmt, prev_stmt))
! 	    {
! 	      error ("Nonlocal and/or computed GOTO targets "
! 		     "in the middle of basic block bb %d", bb->index);
! 	      err = 1;
! 	    }
! 
! 	  if (label_to_block (LABEL_EXPR_LABEL (stmt)) != bb)
  	    {
  	      error ("Label %s to block does not match in bb %d\n",
  		     IDENTIFIER_POINTER (DECL_NAME (LABEL_EXPR_LABEL (stmt))),
  		     bb->index);
  	      err = 1;
  	    }
  
! 	  if (decl_function_context (LABEL_EXPR_LABEL (stmt))
  	      != current_function_decl)
  	    {
  	      error ("Label %s has incorrect context in bb %d\n",
  		     IDENTIFIER_POINTER (DECL_NAME (LABEL_EXPR_LABEL (stmt))),
  		     bb->index);