[llvm-dev] [RFC] Interprocedural MIR-level outlining pass

[Andrey Bokhanko via llvm-dev]

On Tue, Aug 30, 2016 at 7:28 PM, Daniel Berlin <dberlin at dberlin.org> wrote:

> I tend to agree with Hal -- value numbering computes equivalent *values*,
>>
> Sorry, but this is just flat out wrong
>
> "A Global Value Numbering(GVN) algorithm is considered to be complete (or
> precise), if it can detect all Herbrand equivalences among expressions in a
> program.
> Two expressions are said to be Herbrand equivalent (or transparent
> equivalent ), if they are computed by the same operator applied to
> equivalent operands "
>
> This is, AFAIK, precisely what you want.
>
>
I'm not entirely happy with this definition (IMHO, it's overly
restrictive), but this in irrelevant.

What relevant is what one considers to be "equivalent operands". Take my
example again -- for outlining (Jessica's name) / code folding (your name)
optimization reads of "a" and "b" globals are equivalent; for VN and its
users they are not.

Yours,
Andrey
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