[LLVMdev] Loss of precision with very large branch weights

[Diego Novillo]

On Fri, Apr 24, 2015 at 3:28 PM, Xinliang David Li <davidxl at google.com>
wrote:

> yes -- for count representation, 64 bit is needed. The branch weight
> here is different and does not needs to be 64bit to represent branch
> probability precisely.
>

Actually, the branch weights are really counts. They get converted to
frequencies.  For frequencies, we don't really need 64bits, as they're just
comparative values that can be squished into 32bits.  It's the branch
weights being 32 bit quantities that are throwing off the calculations.


Diego.
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