[llvm-dev] Uncovering non-determinism in LLVM - The Next Steps

Daniel Berlin via llvm-dev llvm-dev at lists.llvm.org
Sun Jul 9 10:26:33 PDT 2017

On Sun, Jul 9, 2017 at 9:19 AM, Jack Howarth via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>        FYI, I just successfully performed a 3-stage bootstrap with
> stage2/stage3 object file comparison on x86_64-apple-darwin16 for
> llvm/clang/clang-tools-extra/compiler-rt/libcxx/openmp/polly using our
> custom fink packaging scripts with the
> -DLLVM_REVERSE_ITERATION:BOOL=ON cmake option. There were no
> stage2/stage3 object file comparison failures or test suite
> regressions.
>        I do have one question though. Is there any particular reason
> not to leave this option on for deployed release builds of the
> compiler?

Because it wouldn't accomplish anything.
The goal is to have a different iteration order than the default.
If you make this the default, that doesn't help, because now the default is

> Other than possibly running into some extreme corner case of
> non-deterministism that the stage2/stage3 comparisons and test suites
> miss, is there any performance issues introduced in compile time by
> leaving  -DLLVM_REVERSE_ITERATION:BOOL=ON defaulted on?

Thanks in
> advance for any clarifications.
>             Jack
> ps Is it still the case that none of the llvm.org build bots are doing
> a full 3-stage bootstrap with stage2/stage3 file comparison (ala FSF
> gcc)?

Errr, last i looked, a ton were doing so?
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