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profile thoughts and feedback


Here are some collected notes based on two disjoint conversations about
the recently contributed profile mode, one with Paolo and one with
Silvius Rus.

1. Docs
  - need news item for http://gcc.gnu.org/news.html
  - need 4.5 release note changes item for
    http://gcc.gnu.org/gcc-4.5/changes.html
  - public link for CGO paper requested
    Perflint: A Context Sensitive Performance Advisor for C++ Programs
    http://www.computer.org/portal/web/csdl/doi/10.1109/CGO.2009.36
    explore hosting this as part of
    http://research.google.com/pubs/papers.html

2. Diagnostics
  - under development are the following
    vector_to_deque
    list_to_forward_list
    list_to_set
    iterator*
  - interest in these
    string: c++2003 vs. c++200x
    string vs. vector
    __gnu_cxx::__versa_string policies, 
    __rc_string_base vs. __sso_string_base in various sizes (which?)

3. More accurate cost models
  - trunk has constant defaults
  - exploring a host-specific, generated cost model. Approach being
    considered is to generate some emperical cost model by
    synthetic runs measured on the host machine.

  - outstanding questions
    a. interface to performance counters uncertain
        PAPI http://icl.cs.utk.edu/papi/
        SystemTap http://sourceware.org/systemtap/

    b. where to put the generation tools? This something kind of like
    abi_check, in that it is a built executable that is then used as
    part of testing/analysis. Something like scripts for .py files, but
    for binaries? Host external to libstdc++?

    c. how much of this is defaulted constants, how much algorithmic,
    how much measured and stored in a persistent format? How is this
    situation similar to FDO?

4. Branch development
  - branch will continue to merge in all new changes
  - checkpoint at the end of november to see where branch stands WRT
    cost model development

-benjamin


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