[llvm-dev] Memory utilization problems in profile reader

Diego Novillo via llvm-dev llvm-dev at lists.llvm.org
Fri Dec 11 07:53:28 PST 2015

On Fri, Dec 11, 2015 at 9:58 AM, Diego Novillo <dnovillo at google.com> wrote:

> So, I traced it down to the DenseMaps in class FunctionSamples.  I've
> replaced them with two std::vector, and the read operation causes the
> compiler to grow from 70Mb to 280Mb.  With the DenseMaps, reading the
> profile causes the compiler to grow from 70Mb to 3Gb.
> Somehow the DenseMaps are causing a 10x growth factor.  Those keys are
> probably an issue.  Or perhaps we just need a different representation for
> sample records and call sites.

Yes. In going through DenseMap's implementation I see that large values for
keys will cause a lot of growth.  And the documentation confirms it
(someday I'll learn to read documentation first).
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