weird loop formation

Ben Cheng bccheng at
Tue Jan 15 11:09:48 PST 2008

Thanks for the explanation Tom and Steve.

On Jan 14, 2008 2:48 PM, Tom Rodriguez <Thomas.Rodriguez at> wrote:

> Was your original loop representative of the problems you are seeing or
> was it just an oddity your noticed during analysis?
> tom
The original loop only has the extra-block problem. Method calls happen to
be completely inlined in the inner loop so there are no spills due to
registers being SOC in the normal runs. I stumbled onto the SOC/SOE issue
when I disabled inlining as it is easier to study the code with smaller code

At this moment I don't think either the extra block or the change in calling
convention can account for significant portion of the 25% performance loss,
as the extra jmp should be accurately predicted by the hardware and the
important calls are all inlined. I will try to use oprofile to get a global
view of both versions.

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