[llvm-dev] Where to find the list of passes run by clang/opt with -O3

[Nitish Srivastava via llvm-dev]

Hi Martin,

Thanks for the help. -mllvm -disable-lsr worked for me.

Thanks a lot!

Best Regards,
Nitish



‌

On Tue, Sep 5, 2017 at 4:24 PM, Martin J. O'Riordan <MartinO at theheart.ie>
wrote:

> I had asked a similar question earlier this year regarding which passes
> are involved at a particular optimisation level (lists.llvm.org/pipermail/
> llvm-dev/2017-June/114543.html), and the most helpful suggestion I
> received was to invoke the compiler with the following options:
>
>   -O3 -mllvm -debug-pass=Structure
>
> So I ran the compiler with each of '-O0' .. '-O3' to get the answer I was
> looking for.
>
> I don't know how to generally disable a particular pass from the command
> line with LLVM v4.0, but the pass you want to disable identifies itself as:
>
>   Loop Strength Reduction
>
> and can be disabled with the option (see 'lib/CodeGen/TargetPassConfig.
> cpp'):
>
>   -mllvm -disable-lsr
>
> I haven't yet started working with LLVM v5.0 and the new pass manager
> though so this may already be an obsolete suggestion.
>
> All the best,
>
>     MartinO
>
> -----Original Message-----
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of
> Davide Italiano via llvm-dev
> Sent: 05 September 2017 20:54
> To: Nitish Srivastava <nks45 at cornell.edu>
> Cc: llvm-dev <llvm-dev at lists.llvm.org>
> Subject: Re: [llvm-dev] Where to find the list of passes run by clang/opt
> with -O3
>
> On Tue, Sep 5, 2017 at 12:51 PM, Davide Italiano <davide at freebsd.org>
> wrote:
> >
> >
> >
> > On Tue, Sep 5, 2017 at 8:16 AM, Nitish Srivastava via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >>
> >> Hi,
> >>
> >>   I am trying to locate the passes run by clang/opt when it is passed
> the option -O3. Can someone point me where to look at? Eventually, I want
> to turn off just the LoopStrengthReduction pass in the -O3 set of default
> passes.
> >>
>
> Also, the easiest hack to turn off LSR is that of probably just commenting
> out the line that adds the pass in PassManagerBuilder.cpp.
> If you use `opt` + the new pass manager there's a flag for testing to
> specify a custom pipeline, but that will be more work.
>
>
> --
> Davide
>
> "There are no solved problems; there are only problems that are more or
> less solved" -- Henri Poincare ______________________________
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