[llvm-dev] -O1 with clang and gcc

[M. Chaturvedi via llvm-dev]

Thanks for the quick reply.

`-O0` is too slow with Valgrind and `-O2` is not recommended.  We use `-O1`
in Valgrind runs.

> Use of -O2 and above is not recommended as Memcheck occasionally reports
uninitialised-value errors which don't really exist.
http://valgrind.org/docs/manual/quick-start.html



On Thu, May 31, 2018 at 5:34 PM, Michael Kruse <llvmdev at meinersbur.de>
wrote:

> What are you trying to achieve? If faster runs is the goal, why not
> compile with -O2?
>
> Michael
>
>
> 2018-05-31 16:27 GMT-05:00 M. Chaturvedi via llvm-dev <
> llvm-dev at lists.llvm.org>:
> > Hi,
> >
> > The binary gotten via clang's `-O1` runs much slower (3x) than that
> gotten
> > via GCC's `-O1`.
> >
> > Reproducible with:
> >
> > https://github.com/m-chaturvedi/test_valgrind_slowdown
> >
> > We are seeing this difference between gcc and clang at other places as
> well.
> >
> > The `-O0` and `-O2` times are comparable, however.   Are there some
> compile
> > time flags one could add to make the `-O1` times comparable?
> >
> > Apologies if this has been discussed somewhere already.
> >
> > Thank you,
> > Mmanu
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
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