[llvm-dev] Why is Partial Unrolling off by default?

[Friedman, Eli via llvm-dev]

On 7/30/2018 9:02 AM, Bhatu via llvm-dev wrote:
> Hi all,
>
> Why is partial unrolling off by default? Did enabling partial 
> unrolling result in any significant runtime or compile time 
> regressions in any benchmarks?

It's not off by default on all targets; it's controlled by the 
getUnrollingPreferences() target hook.  The exact threshold which makes 
sense tends to be target-specific (especially for CPUs which have 
special optimizations for small loops).

-Eli

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