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[google gcc-4_8] alternate hirate for builtin_expert


Hi,

Current default probably 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.


                              -Rong

Attachment: p2_patch.txt
Description: Text document


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