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[PATCH] alternative hirate for builtin_expert


Hi,



  Current default probability for builtin_expect is 0.9996.
This makes the freq of unlikely bb very low (4), which
suppresses the inlining of any calls within those bb.

We used FDO data to measure the branch probably for
the branch annotated with builtin_expert.
For google internal benchmarks, the weight average
(the profile count value as the weight) is 0.9081.

Linux kernel is another program that is heavily annotated
with builtin-expert. We measured its weight average as 0.8717,
using google search as the workload.

This patch sets the alternate hirate probability for builtin_expert
to 90%. With the alternate hirate, we measured performance
improvement for google benchmarks and Linux kernel.

An earlier discussion is
https://mail.google.com/mail/u/0/?pli=1#label/gcc-paches/1415c5910054630b

This new patch is for the trunk and addresses Honza's comments.

Honza: this new probability is off by default. When we backport to google
branch we will make it the default. Let me know if you want to do the same
here.

Thanks,

-Rong

Attachment: p2_patch
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