Re: [PATCH] Add if-chain to switch conversion pass.

["Martin Liška" <mliska@suse.cz>]

On 10/7/20 10:00 AM, Richard Biener wrote:
> As said I'd have a BB-local pass over BBs recording the index variable
> and the range covered by the BBs gcond, plus recording how many excess
> stmts there are for eventual code motion.
> 
> Only after that BB-local pass start to group BBs in a walk from dominated to
> dominating BBs looking for common indexes and building a case vector.
> 
> The main thing is to avoid repeatedly analyzing BBs conditions (so the first
> pass could be also a on-demand precompute thing) and making the
> case vector build optimal.

I have a patch that does that using the infrastructure from tree-ssa-reassoc.
Now I would like to implement the code hoisting. Am I right that we want
something like:

if (index == C0)
   goto BB_0;
else
{
   BB1_to_hoist_stmts;
   if (index == C1)
     goto BB_1;
   else
   {
     BB2_to_hoist_stmts;
     if (index == C2)
       goto BB_2;
     else
       goto default_BB;
   }
}

be converted into:

switch(index)
{
    case C0:
      goto BB_0;
    case C1:
      BB1_to_hoist_stmts;
      goto BB_1;
    case C2:
      BB1_to_hoist_stmts;
      BB2_to_hoist_stmts;
      goto BB_2;
    else:
      BB1_to_hoist_stmts;
      BB2_to_hoist_stmts;
      goto default_BB;
}

?

Thanks,
Martin