Re: [tree-ssa]: PRE updates and note on bug

[Andrew MacLeod <amacleod at redhat dot com>]

On Tue, 2003-07-22 at 12:57, Daniel Berlin wrote:
> > I thought we resolved this last week? You had a patch for
> > remove_stmt()...
> >
> > Or did it not fix your problem?
> 
> If you apply the following patch, you can see where we still have
> problems (this includes when a cond_expr is the end of the bb, and we
> remove it, when we remove empty statements and the previous statement is
> an empty statement, etc).
> 
> We probably should use this patch (without the #if 0'd code, of course, i
> was just trying to start attacking the various cases) once all the cases
> are handled, or to force ourselves to fix the bugs.

but....  are you sure you are looking at the right thing?

Im not convinced that it isn't something else.. like a bug in the
reverse iterators or a missing bb_for_stmt...

out_of_ssa doesnt use the reverse iterators, but it does use the
FOR_EACH_STMT_IN_REVERSE macro because its processes things backwards,
and its not having any problems. If things were screwed up by DCE,
something would get the wrong live range, or get missed, and I would
expect something to break later on.

If the end of block pointer is actually set wrong, the forward iterators
would be missing stmts or something I would think.

If a stmt has been inserted into a block and bb_for_stmt wasn't set
properly, it would  cause a lot of these problems too. For instance:
is 33 the right number of stmts in the block? If a stmt has been added
(say the 34th of 35), and its block number wasn't set, the forward
iterators would quit at number 33. The reverse iterator would start with
#35, step back one, find a stmt without the correct block and quit.
Giving you 1...

Note that the end block pointer doesn't have to be a non-null stmt, it
can point to anything it wants. It doesnt have to be a BSI valid stmt.
Neither does the head pointer. All that matters is that bb_for_stmt is
set right on them all.  My guess is since you are only encountering this
in PRE that somewhere you've messed up the BB value.

try walking the trees from bb->head_tree_p to bb->end_tree_p and check
bb_for_stmt on each element.

Andrew