[LLVMdev] Dependence Analysis [was: Flow-Sensitive AA]

Daniel Berlin dberlin at dberlin.org
Fri Aug 22 20:43:43 PDT 2008

On Fri, Aug 22, 2008 at 11:18 PM, John Regehr <regehr at cs.utah.edu> wrote:
>> before and it hurts about 3-5 without high level loop
>> opts/vectorization on.  With them on, they do roughly nothing in the
>> presence of -fwrapv because you can't determine bounds of any non
>> trivial loop.
> Very interesting, thanks!  Before hearing this I'd have said that
> Java-style overflow is the right language design, but if this makes loop
> optimizations impossible that is not so good.
Java JIT's work very hard to work around the fact that the language
backs them into a corner.
FWIW, You can replace i+=2 with i++ or i-- in my example and still not
be able to determine the loop bounds :(

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