[llvm-commits] [llvm] r70509 - in /llvm/trunk: include/llvm/Analysis/ScalarEvolution.h lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/2008-11-18-Stride1.ll test/Analysis/ScalarEvolution/max-trip-count.ll test/Analysis/ScalarEvolution/trip-count3.ll

[Dan Gohman]

On May 2, 2009, at 12:21 PM, Chris Lattner wrote:

>
> On Apr 30, 2009, at 1:47 PM, Dan Gohman wrote:
>
>> Author: djg
>> Date: Thu Apr 30 15:47:05 2009
>> New Revision: 70509
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=70509&view=rev
>> Log:
>> Extend ScalarEvolution's getBackedgeTakenCount to be able to
>> compute an upper-bound value for the trip count, in addition to
>> the actual trip count. Use this to allow getZeroExtendExpr and
>> getSignExtendExpr to fold casts in more cases.
>>
>> This may eventually morph into a more general value-range
>> analysis capability; there are certainly plenty of places where
>> more complete value-range information would allow more folding.
>
> Very cool.  Can this also be used to handle things like:
>
> int A[20000];
>
> ...
>   for (i = 0; i < N; ++i)
>      A[i];
> ...
>
> Knowing that A has a max value of 19999?

Yes, though the analysis for that will probably be
done in a separate pass.

Dan