Attacking quadratic behaviors associated with SWITCH_EXPR

[Kazu Hirata]

Hi Daniel,

> > Yes.  I am thinking about starting with SWITCH_EXPR.  After that's
> > complete, we can probably remove GOTO_EXPR from COND_EXPR during the
> > lifetime of CFG.
> 
> If this means i can simply redirect edges instead of frobbing around with 
> labels, edges, and little bits of fairy dust, go for it.

Yes, that's what I meant.

> Let me give you an eaxmple of real code today, and if you could, can you 
> tell me what will still be required?
> 
>   then_label = build1 (GOTO_EXPR, void_type_node, tree_block_label 
> (latchbb));
>    else_label = build1 (GOTO_EXPR, void_type_node, tree_block_label 
> (olddest));
>    cond_stmt = build (COND_EXPR, void_type_node,
>                       build (NE_EXPR, boolean_type_node,
>                              integer_one_node,
>                              integer_zero_node),
>                       then_label, else_label);
>    bsi = bsi_start (bodybb);
>    bsi_insert_after (&bsi, cond_stmt, BSI_NEW_STMT);
>    make_edge (bodybb, olddest, EDGE_FALSE_VALUE);
>    make_edge (bodybb, latchbb, EDGE_TRUE_VALUE);
> 
> 
> I'm guessing all i'll need is something like
>    thenedge = make_edge (bodybb, latchbb, EDGE_TRUE_VALUE)
>    elseedge = make_edge (bodybb, olddest, EDGE_FALSE_VALUE)
>    cond_stmt = build (COND_EXPR, void_type_node,
>                       build (NE_EXPR, boolean_type_node,
>                              integer_one_node,
>                              integer_zero_node),
>                       thenedge, elseedge);
>    bsi = bsi_start (bodybb);
>    bsi_insert_after (&bsi, cond_stmt, BSI_NEW_STMT);
> 
> Is that about right?

I wasn't thinking of increasing the number of arguments to build()
because make_edge installs an edge to corresponding edge vectors.  So,
in your example, you would write something like

  thenedge = make_edge (bodybb, latchbb, EDGE_TRUE_VALUE)
  elseedge = make_edge (bodybb, olddest, EDGE_FALSE_VALUE)
  cond_stmt = build (COND_EXPR, void_type_node,
                     build (NE_EXPR, boolean_type_node,
                            integer_one_node,
                            integer_zero_node),
                     NULL_TREE, NULL_TREE);          <- Notice this line!
  bsi = bsi_start (bodybb);
  bsi_insert_after (&bsi, cond_stmt, BSI_NEW_STMT);

Kazu Hirata