llvm dev - Apr 2016 - soundness and precision of LazyValueInfo and ValueTracking

I've been testing LVI and getKnownBits() using this little custom pass:

   https://github.com/regehr/llvm-test-lvi

It rewrites the code to dynamically check that compile-time dataflow 
facts are sound. So far it hasn't turned up any errors, for example in 
SPEC CPU 2006.

On the other hand, its debugging output has found some pretty obvious 
room for improvement in the precision of LVI:

   https://llvm.org/bugs/show_bug.cgi?id=27433
   https://llvm.org/bugs/show_bug.cgi?id=27434

See also this earlier one:

   https://llvm.org/bugs/show_bug.cgi?id=27296

Would it make sense to make to add some code for printing the results of 
LVI and ValueTracking so that we can test for precision regressions?

John

----- Original Message -----
> From: "John Regehr via llvm-dev" <llvm-dev at
lists.llvm.org>
> To: llvm-dev at lists.llvm.org
> Sent: Wednesday, April 20, 2016 7:21:56 AM
> Subject: [llvm-dev] soundness and precision of LazyValueInfo and
ValueTracking
> 
> I've been testing LVI and getKnownBits() using this little custom
> pass:
> 
>    https://github.com/regehr/llvm-test-lvi
> 
> It rewrites the code to dynamically check that compile-time dataflow
> facts are sound. So far it hasn't turned up any errors, for example
> in
> SPEC CPU 2006.
> 
> On the other hand, its debugging output has found some pretty obvious
> room for improvement in the precision of LVI:
> 
>    https://llvm.org/bugs/show_bug.cgi?id=27433
>    https://llvm.org/bugs/show_bug.cgi?id=27434
> 
> See also this earlier one:
> 
>    https://llvm.org/bugs/show_bug.cgi?id=27296
> 
> Would it make sense to make to add some code for printing the results
> of
> LVI and ValueTracking so that we can test for precision regressions?
I think it makes sense for these to be independently testable.

 -Hal
 
> John
> 
> 
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> llvm-dev at lists.llvm.org
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> 
-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory