Switch containing holes via table lookup

[Hans Wennborg]

+llvm-commits, trying to get the thread back on the list.

On Mon, Feb 24, 2014 at 10:28 AM, Hans Wennborg <hans at hanshq.net> wrote:
> On Sun, February 23, 2014 16:29, Jasper Neumann wrote:
>> Hello Hans!
>>
>>  > Hmm, I replied on the 18th: >
>> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140217/205303.html,
>>
>>  > with jn at sirrida.de in the To: field and the list as CC.
>>
>> I'm very sorry I missed this.
>> It might be that your email never reached me because I had problems with
>> receiving emails from the LLVM mailing lists; I got 5 emails containing
>> text like this:
>>
>> "Your membership in the mailing list llvm-commits has been disabled due
>> to excessive bounces The last bounce received from you was dated
>> 22-Feb-2014.  You will not get any more messages from this list until
>> you re-enable your membership.  You will receive 3 more reminders like
>> this before your membership in the list is deleted."
>>
>> It might help to read the forum posts online instead of only waiting for
>> emails...
>>
>>
>>  > Anyway, at the bottom of my reply I pointed out that I think our
>>  > problem is that your patch adds a new branch to the "default" BB.
>>  > If that BB had a phi node in it, it will now have a new incoming
>>  > edge without a value, and that would cause the assertion you're
>>  > hitting.
>>
>> This is about what I thought.
>> But what are the magic words I should cast to cure this?
>> It tried stuff like
>>    AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, LookupBB);
>> but until now had no success.
>
> If I put this:
>
>   AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, SI->getParent());
>
> right after your line that creates the conditional branch at the end of
> BranchBB, everything seems to work.
>
> I also made up a test case that's easier to work with. This seems to fail
> with the same assert you were seeing:
>
> int f(int x) {
>   int z;
>   int y;
>
>   if (x % 123 == 0)  {
>     y = 1;
>     goto label;
>   }
>   y = 2;
>
>   switch (x) {
>     case 0:
>       z = 1;
>       break;
>     case 1:
>       z = 2;
>       break;
>     case 2:
>       z = 3;
>       break;
>     case 7:
>       z = 4;
>       break;
>
>     default:
>     label:
>       z = y;
>   }
>
>   return z;
> }
>
> int h(int x) {
>   return f(x);
> }
>
> Thanks,
> Hans