Another problem with "Recommit r265547, and r265610,r265639,r265657"

[Mikael Holmén via llvm-commits]

Hi Wei,

On 04/29/2016 11:26 PM, Wei Mi wrote:
[...]
>> I'm a little concerned about the "0 at x 1 at x" things in %vreg29's range which
>> I've no idea if they do any harm and if or how they should be removed.
>
> I think they are fine. @x means the VNI is unused. Look at function
> LiveRange::markValNoForDeletion. It is a lazy way to delete VNIs from
> valnos.

Ok, good!

> The analysis is reasonable and I cannot come up a solution better than
> yours :-). Although ideally we can have a solution in the end which
> don't penalize normal cases.

Ok!

So, this fix in RegisterCoalescer solves the last problem I ran into.

But the previous problem where we had an instruction with a tied 
operand... How do we solve that?

We've done

@@ -257,0 +258,7 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr 
*MI, ToShrinkSet &ToShrink) {
+  // To avoid situations where Def is tied and the same Def/Use 
registers gets
+  //  new reg ids and we end up with a use of an undefined register 
(bug #10189)
+  if (MI->isRegTiedToUseOperand(0)) {
+    DEBUG(dbgs() << "Can't delete, def is tied to operand: " << Idx << 
'\t' << *MI);
+    return;
+  }
+

early in LiveRangeEdit::eliminateDeadDef but I'm not sure if you had a 
better fix for it?

>
> Thanks,
> Wei.
>