A latent bug - use of BRANCH_EDGE on trees.

[Kazu Hirata]

Hi Zdenek,

I think I found a latent bug.

loopify in cfgloopmanip.c is called from tree_ssa_loop_version and
unswitch_loop.  Of those, tree_ssa_loop_version obviously deals with
trees in SSA form.

Now, the problem is that loopify uses BRANCH_EDGE.  While we are in
trees, EDGE_FALLTHRU does not make sense for basic blocks ending with
COND_EXPR.  Here is the definition of BRANCH_EDGE.

#define BRANCH_EDGE(bb)			(EDGE_SUCC ((bb), 0)->flags & EDGE_FALLTHRU \
					 ? EDGE_SUCC ((bb), 1) : EDGE_SUCC ((bb), 0))

Any ideas?

I found this latent bug while trying to use VEC_safe_push instead of
VEC_safe_insert to insert an edge to an edge vector.  Here is a
testcase.

void bar (void);

void
foo (int x)
{
  goto L1;

 L0:
  bar ();

 L1:
  if (x == 0) goto L0; else goto L2;

 L2:
  if (x == 1) goto L0; else goto L3;

 L3:
  return;
}

I attach my VEC_safe_push patch for completeness.

If this is indeed a latent bug, we should probably use something like

  gcc_assert (ir_type () == 1);

in FALLTHRU_EDGE and BRANCH_EDGE to ensure that we don't use them in
trees.

Kazu Hirata

2004-10-24  Kazu Hirata  <kazu@cs.umass.edu>

	* cfg.c (unchecked_make_edge, redirect_edge_succ,
	redirect_edge_pred): Use VEC_safe_push instead of
	VEC_safe_insert.
	* cfgrtl.c (force_nonfallthru_and_redirect): Likewise.

Index: cfg.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cfg.c,v
retrieving revision 1.71
diff -u -p -r1.71 cfg.c
--- cfg.c	22 Oct 2004 22:55:47 -0000	1.71
+++ cfg.c	24 Oct 2004 00:27:29 -0000
@@ -270,8 +270,8 @@ unchecked_make_edge (basic_block src, ba
   e = ggc_alloc_cleared (sizeof (*e));
   n_edges++;
 
-  VEC_safe_insert (edge, src->succs, 0, e);
-  VEC_safe_insert (edge, dst->preds, 0, e);
+  VEC_safe_push (edge, src->succs, e);
+  VEC_safe_push (edge, dst->preds, e);
 
   e->src = src;
   e->dest = dst;
@@ -418,7 +418,7 @@ redirect_edge_succ (edge e, basic_block 
   gcc_assert (found);
 
   /* Reconnect the edge to the new successor block.  */
-  VEC_safe_insert (edge, new_succ->preds, 0, e);
+  VEC_safe_push (edge, new_succ->preds, e);
   e->dest = new_succ;
 }
 
@@ -476,7 +476,7 @@ redirect_edge_pred (edge e, basic_block 
   gcc_assert (found);
 
   /* Reconnect the edge to the new predecessor block.  */
-  VEC_safe_insert (edge, new_pred->succs, 0, e);
+  VEC_safe_push (edge, new_pred->succs, e);
   e->src = new_pred;
 }
 
Index: cfgrtl.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cfgrtl.c,v
retrieving revision 1.140
diff -u -p -r1.140 cfgrtl.c
--- cfgrtl.c	22 Oct 2004 22:55:47 -0000	1.140
+++ cfgrtl.c	24 Oct 2004 00:27:29 -0000
@@ -1069,7 +1069,7 @@ force_nonfallthru_and_redirect (edge e, 
 	  
 	  gcc_assert (found);
 	  
-	  VEC_safe_insert (edge, bb->succs, 0, e);
+	  VEC_safe_push (edge, bb->succs, e);
 	  make_single_succ_edge (ENTRY_BLOCK_PTR, bb, EDGE_FALLTHRU);
 	}
     }