Re: [tree-ssa]: After edge insertion, two bb's share the same heda

[Andrew MacLeod <amacleod at redhat dot com>]

On Fri, 2003-07-25 at 16:06, Daniel Berlin wrote:
> After insertion into a switch statement, I end up with two bb's that 
> share the same head pointer
> 
> (gdb) p bb->index
> $7 = 345
> (gdb) p bb->head_tree_p
> $8 = (tree *) 0x42afe2dc
> (gdb) p basic_block_info.data.bb[444].head_tree_p
> $9 = (tree *) 0x42afe2dc
> 
> Is this allowed?

No. Big problems.

> It screws up normal insertion royally.
> 

Not suprised :-)

> Note that 345 was an empty block (but still had the same head_tree_p) 
> at the time 444 was created by bsi_insert_on_edge_immediate.
> 
> The edge we insert on is also from 54->346 (346 is the successor block 
> of 345), so it looks like collateral damage that we chose the same 
> head_tree_p as block 345.
> 
Soooo. What block is the switch stmt in? Whats block 345? I clearly need
more context :-)
 
> We end up with head_tree_p of block 345, and using it, after line 3820 
> of tree-cfg.c:
> 
> 3820      tsi = tsi_last (&BIND_EXPR_BODY (SWITCH_BODY (sw_stmt)));
> 
> IE after this line, tsi points to block 345's head_tree_p, and we build 
> a statement and append it into the new bb, and the new bb gets 345's 
> head_tree_p:
> 
> We then append this to the new bb here:
> 3827      append_stmt_to_bb (tsi_container (tsi), new_bb, sw_stmt);
> 
> 
> Andrew, the switch statement insertion is beyond my comprehension.  If 
> I send you the test case and instructions, can you look at this?
> 
Its the child no one wants to talk about :-)  Yep, I'll take a look. As
long as its simple enough of an example for me to understand :-) Even a
breakdown of whats in each block and what the relationship between the
edge you are inserting on and the pred/succs of the involved blocks is
probably enough for me to sort it out. It seems there is a switch
involved, what edge are you inserting on, and what are the pred/succs
which cause this to be a critical edge?

Andrew