[cfe-dev] [OT?] real-world interest of the polly optimiser

[Krzysztof Parzyszek via cfe-dev]

On 5/22/2017 9:17 AM, C Bergström via cfe-dev wrote:
> You statement just came across as something like either llvm's loop 
> optimizer sucks so bad that polly is required

In applications like linear algebra a lot of performance comes from 
optimizing loop nests for cache locality. Doing things like loop 
interchange, loop nest distribution, unroll and jam, etc. helps a lot 
with it, and to the best of my knowledge LLVM does none of that. There 
is some basic support for loop fusion and distribution, but I don't 
think it works on the nest level. Given how important that is in 
high-performance computing, the 20x difference sounds believable.

I don't know what the general plan is: if there is any interest in loop 
nest optimizations in the LLVM itself, or whether this task is delegated 
to Polly to handle at some point. In any case, without those 
optimizations there is only so much that can be done.

-Krzysztof

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