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Re: Question re: SSA Aggressive Dead Code Elimination
- To: <law at redhat dot com>
- Subject: Re: Question re: SSA Aggressive Dead Code Elimination
- From: Daniel Berlin <dan at www dot cgsoftware dot com>
- Date: Wed, 27 Jun 2001 13:28:16 -0400 (EDT)
- cc: Michael Matz <matzmich at cs dot tu-berlin dot de>, <gcc at gcc dot gnu dot org>
On Wed, 27 Jun 2001 law@redhat.com wrote:
> In message <Pine.GSO.4.33.0106271629330.1705-100000@platon>you write:
> > Hi,
> >
> > On Wed, 27 Jun 2001, Daniel Berlin wrote:
> >
> > > The initial removing of the edge isn't strictly wrong, as long as you
> > > update the phi nodes accordingly.
> >
> > Well, suppose, you initially had this code:
> > a=b+c;
> > if (a>d) { b=b+c; }
> > return b;
> >
> > which is the back-translated RTL. If you in this situation remove any
> > edge resulting from the compare, there is no way, that you still have the
> > same semantic as the above code. That is why the removing of the edge
> > really was wrong from the beginning.
> Thanks. Maybe I should have posted some sample C code to make it clearer
> from the beginning. Clearly Dan has mis-understood the issue at hand.
Yes, I have.
Sorry for wasting your time.
Reading RTL still screws me up at times.
>
> jeff
>