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Re: [RFC] Remove -freorder-blocks-and-partition


On Mon, Jul 25, 2011 at 6:30 PM, Joern Rennecke <amylaar@spamcop.net> wrote:
> Quoting Xinliang David Li <davidxl@google.com>:
>
>> In xalancbmk, with the partition option, most of object files have
>> nonzero size cold sections generated. The text size of the binary is
>> increased to 3572728 bytes from 3466790 bytes. ?Profiling the program
>> using the training input shows the following differences. With
>> partitioning, number of executed branch instructions slightly
>> increases, but itlb misses and icache load misses are significantly
>> lower compared with the binary without partitioning.
>
> It is nice to have confirmation that for this benchmark, the optimization
> causes a speedup because it works as intended, however...
>
>>>> dealII and bzip2 degrades about 1.4%.
>
> ... I think the question was more directed at what causes the
> performance degradation for these two benchmarks.
>
> If we could retain most of the speedups when the optimization works well
> but avoid most of the slowdown in the benchmarks that are currently hurt,
> we could improve the overall SPEC06 score. ?And hopefully, this would
> also be beneficial to other code.

Agree.  There are certainly problems in the partition pass, as for
bzip2 the icache misses actually go up with partition, which is not
expected. It needs further analysis.

David

>


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