llvm dev - Sep 2017 - [RFC] Polly Status and Integration

On 09/28, Alexandre Isoard wrote:
> Polly is oriented towards providing a full blown polyhedral compiler
> pipeline, this is great in the sense that it allows to do all the high
> level transformations we can dream of, but this is also difficult to
> compose with current LLVM passes, we lose debug information, and it is
> relatively hard to control what happen. As such, it might be fine in its
> own folder, I don't see much interest in "not compiling
Polly" except if to
> not have the isl library as a dependency.
> 
> Polyhedral Analysis is oriented towards providing new tools for any LLVM
> analysis or transformation passes. There is a wide range of applicability
> to this (it can at least be used almost everywhere ScalarEvolution can),
> and because it can represent set and relations (instead of only functions
> like SCEV) I suspect it can be used in an even wider range of applications
> and a lot of them are outside the polyhedral realm (aka. will hardly ever
> fit into Polly's pipeline).
Precisely! I think part of this email chain is conflating these two 
separate issues. As an example, for our LLVM-based DSL compiler we are 
directly using isl for various index set operations, without requiring 
Polly. So, future Polyhedral Analysis pass(es) can hopefully provide a 
native LLVM interface for such operations.