[LLVMdev] fix for loop scale limiting in BFI

[Chandler Carruth]

On Fri, Mar 27, 2015 at 1:36 PM, Xinliang David Li <xinliangli at gmail.com>
wrote:

> To be on the safe side, my patch is mapping them down to a 32bit
>> space, but I am squishing them too much on  the lower end. So regions
>> of the CFG that before had distinct temperatures are now showing up
>> with frequency == 1.
>>
>> I need a better smoother for the mapping from the Scale64 floats down
>> to 64bit (or 32bit) integers.
>>
>
>
> This seems to show another weakness of the block frequency propagation --
>  it can not handle infinite loops.  We need to think about how to handle it
> ..
>

I think we should just have a synthetic "max" and not balloon the range due
to it. Then we can pin the max at some fixed multiple of the actual max
when scaling it down.
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