[LLVMdev] undefs in phis

David Greene
Fri, 30 Jan 2009 01:29:53 -0000

On Thursday 29 January 2009 18:04, Eli Friedman wrote:
> On Thu, Jan 29, 2009 at 2:47 PM, David Greene <dag at cray.com>
wrote:
> > After phi elimination we have:
> >
> > bb134:
> >  %reg1645 = 1.0
> >
> > bb74:
> >  %reg1176 = MOVAPS %reg1645
> >  %reg1177 = MOVAPS %reg1646
> > [...]
> >
> > bb108:
> >  %reg1645 = <expr>
> >  %reg1646 = %reg1176
>
> I find it a little strange that the IMPLICIT_DEF disappears.  Besides
> that, it looks okay up to here.

I just verified that it does disappear.

> > Should llvm be able to handle situations like
> > this or is the result undefined?
>
> LLVM should be able to handle the IL in question, I think.  Using
> undef in the way the given IL is using it is looks legitimate.

Ok, that's good to know.  I'll continue tracking this one down.

                                       -Dave