[PATCH] Inliner Enhancement

[Jiangning Liu]

Hi David,

Regarding your patch, I think the simple loop heuristic may be a reasonable
> incremental improvement, but you really need to wait for Chandler's pass
> manager change instead of doing all the ordering tricks.
>

Loop analysis is critical for my patch and it is expensive. The ordering
tricks (3.b) is only for compile-time reduction. As I mentioned in replying
Yin's comments, (3.b) itself can actually reduce compile-time a lot (~5% or
more for llvm bootstrap) without changing performance generally. If I don't
add (3.b), we would see ~10% compile-time regression. I don't think it is
acceptable. So now the only difference is how we update loop info. i.e. use
my current naive solution, or use new pass manager to help it?

So do you know when Chandler's pass manager change can be ready for
inlining use? Why we can't just use this native method first, and I can add
//FIXME to highlight it, and then when Chandler's great new pass manager is
ready for inlining use, we just switch to it? Eventually we would be able
to see big compile-time reduction.


> On the other hand, I don't see the 'same callee' heuristics is generally
> valid.  How much size contribution does it have? Is it just skewed by one
> benchmark?
>

OK. I agree with this. I can get it removed, and actually the code size
impact for SPEC overall is about ~2% for this rule. I just personally think
it's unreasonable to inline a callee being called a lot of times naively.
Actually this is just real case for one of SPEC2000 benchmarks, but
generally I think it is meaningful. For abnormal request like building
Android for one of the huge functions, if you want inline everything, then
that's fine, we can just using command line option to enable it. But
generally for common programming, I still think it's wired to inline this
case.

Thanks,
-Jiangning
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