[LLVMdev] Contribute a new precise pointer analysis to LLVM

[Hal Finkel]

----- Original Message -----
> Hi Evan,
> 
> We did an experiment using the LLVM test suite: we compare the
> overhead of using our analysis to the LLVM default, both with -O2
> option.

It might also be interesting to try with -O3; I don't know if we have any significant vectorizable loops in the test suite with a large number of arrays, but if we do, this kind of analysis should help.

> 
> The overall overhead of compiling the whole test suite using our
> analysis is 36.5%.

Maybe a good candidate for -fexpensive-optimizations? (or -O4?)

> The biggest overhead is  observed in
> "SingleSource/Benchmarks/Misc/flops-5", where we are 5 times slower:
> 0.07s (with our analysis) compared to 0.0133s(default).
> This may not be accurate as the compilation time in both cases are
> quite small.

In my experience, compile-time measurements from a normal test-suite configuration less than 0.1s are too noisy to use.

> 
> Remind that the compilation time is reported by running our analysis
> over individual files, the compilation time overhead will be larger
> if
> we link all individual compilation units together and run the
> analysis over the whole application.

Yes, LTO tests would be interesting too.

Thanks again,
Hal

> 
> Regards,
> Lian
> 
> On Sat, Oct 19, 2013 at 7:56 AM, Evan Cheng <evan.cheng at apple.com>
> wrote:
> >
> > On Oct 17, 2013, at 10:51 PM, lian li <lianli at gmail.com> wrote:
> >
> >> Thanks, Chris.
> >>
> >> We are interested in contributing it to LLVM itself. Our manager
> >> agrees to commit resources for maintenance needs if it is accepted
> >> by
> >> the community.
> >
> > This is great. Please make sure Oracle legal sign off on explicitly
> > granting LLVM the use of the patents associated with the work.
> >
> > On the compile time front, can you do a comparison with the LLVM
> > default and your new AA? You can just build the LLVM test suite.
> >
> > Thanks,
> >
> > Evan
> >
> >>
> >> Regards,
> >> Lian
> >>
> >> On Fri, Oct 18, 2013 at 3:43 PM, Chris Lattner
> >> <clattner at apple.com> wrote:
> >>>
> >>> On Oct 17, 2013, at 5:20 PM, lian li <lianli at gmail.com> wrote:
> >>>
> >>> Hi All,
> >>>
> >>> This is Lian Li  from Oracle Labs in Brisbane Australia.
> >>>
> >>> We have developed a precise and highly efficient pointer analysis
> >>> framework on top of LLVM,  The approach is flow, context, and
> >>> field
> >>> sensitive, details are described in the two papers below:
> >>>
> >>> "Boosting the performance of flow-sensitive points-to analysis
> >>> using
> >>> value flow" (in ESEC-FSE 2011), and
> >>> "Precise and scalable context-sensitive pointer analysis via
> >>> value
> >>> flow graph" (in ISMM 2013).
> >>>
> >>> The analysis was initially developed for the purpose of bug
> >>> checking,
> >>> and is now extended to support compiler optimizations. We have
> >>> tested
> >>> it with existing compiler optimizations in LLVM, and have seen
> >>> promising results.
> >>>
> >>> We are now considering to make this analysis available to the
> >>> LLVM
> >>> community, and contribute resources for future maintenance needs,
> >>> provided that there is enough interest. We think that a new
> >>> precise
> >>> pointer analysis in LLVM can enable more new optimization and
> >>> analysis
> >>> techniques to be developed in LLVM.
> >>>
> >>> Any people interested in seeing a new precise pointer analysis in
> >>> LLVM?
> >>>
> >>>
> >>> This sounds very interesting.  Even if it isn't fast enough to be
> >>> used with
> >>> (for example) clang -O2 or -O3, having such a precise analysis
> >>> would be a
> >>> great baseline for doing other alias analysis work.
> >>>
> >>> Are you interested in contributing this to LLVM itself, or just
> >>> asking if
> >>> people would be interested to see the code in some other form?
> >>>
> >>> -Chris
> >>
> >>
> >>
> >> --
> >> // Copyright @ 2011 Authorized by ** LIAN LI **
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
> 
> 
> 
> --
> // Copyright @ 2011 Authorized by ** LIAN LI **
> _______________________________________________
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> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory