[llvm-dev] RFC: A change in InstCombine canonical form

[James Y Knight via llvm-dev]

On Tue, Mar 22, 2016 at 5:44 PM, Ehsan Amiri via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Thanks.
>
> *Phillip, *As Hal said I do not think (1) is a very large item. Please
> let me know if I am mistaken.
>
> *David *I think (1) is more inline with typeless pointer work than (2).
> Contributing to typeless pointer work will be great, but given its unknown
> time frame we cannot stop fixing existing problems. Of course, we should
> follow an approach consistent with the long-term solution.
>

It seems to me that the question to ask is what would be the best state of
the code, assuming that the typeless pointers work had already been done.
Is it the current canonical form? Or the newly proposed one?

I think it'd be the current one? If so, I'd suggest that proposal #2 is
more compatible with the typeless pointer work. That is because (if done
properly), code which knows how to look through pointer bitcast nodes is
something which will be much more easily deletable once pointer bitcast
nodes cease to exist, than to change the canonicalization of memcpy back
and remove any backend code which was added only to compensate for that
change.
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