[PATCH] D12066: Introduce the ScopExpander as a SCEVExpander replacement

[Tobias Grosser via llvm-commits]

grosser added a comment.

> > The SCEVExpander cannot deal with all SCEVs Polly allows in all kinds

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> >   of expressions. To this end we introduce a ScopExpander that handles

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> >   the additional expressions separatly and falls back to the

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> >   SCEVExpander for everything else.

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> Shouldn't you just enhance SCEVExpander?


Hi Hal,

thanks for jumping in. The point is that Polly starts to support thinks that go beyond what we
expression in SCEV generally. The current expressions we are facing, sDiv and sRem, could probably be added
to SCEV and consequently the SCEVExpander as well, but the next step will be piecewise expressions
such as a < b ? c : d. I am less convinced this really needs to be added to SCEV. Or at least,
I feel that we better keep this in Polly for a while, gain some experience, and move it if the
added value of this becomes really visible. In general I am trying to push as much of the stuff we
are doing directly into LLVM, but at the same time I feel we need to make sure we don't create too
much code that is only useful for Polly ATM.

I would be interested if you agree/disagree with this reasoning.

Best,
Tobias


http://reviews.llvm.org/D12066