Re: [patch] Avoid ssa update in cfg cleanup

[Diego Novillo <dnovillo at redhat dot com>]

Zdenek Dvorak wrote:

> 1) V_MAY_DEF may become V_MUST_DEF after copy propagation.  In this
>    case, we would lose the old ssa names in update_stmt, which would force
>    us to use update_ssa.  The tree-ssa-operands changes ensure that
>    V_MUST_DEF operands may inherit the ssa names of old V_MAY_DEF operands.
> 
Hmm, I'm a bit hesitant about this change.  I would like Andrew's
opinion first.  I understand why it's needed and I tend to agree,
however, we do lose the static checking provided by the separate types.
 Perhaps we will need to add a checking feature like we have on trees,
so that at least accessors like MUSTDEF_KILL can assert that they're
indeed operating on a V_MUST_DEF.  Andrew?

> --- 358,366 ----
>   
>     /* If the pass has caused the SSA form to be out-of-date, update it
>        now.  */
> !   if (update_flag)
> !     update_ssa (update_flag);
> !   gcc_assert (!need_ssa_update_p ());
>   
Need comment in function header specfiying that if UPDATE_FLAG is 0, we
won't call update_ssa.

The rest looks fine.