[llvm-dev] RFC: Killing undef and spreading poison

[Reid Kleckner via llvm-dev]

On Tue, Oct 25, 2016 at 10:44 AM, Daniel Berlin via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Easier is a relative term.
> I expect optimally choosing  which freezes to eliminate where, etc,
>  reduces to a covering problem variant (or just straight ILP) :)
>

I think it's fine for GVN to fold them all to the same thing. The only
difference between freeze(poison) and zero is that you can use a
pre-existing register like RBP or RSP that says constant across the
lifetime of the function so you don't need to materialize a zero if you
don't have one already.
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