llvm dev - Jun 2017 - Definitive list of optimisations at each optimisation level

I am often asked what optimisations "our" compiler performs at each
level.
But "our" compiler is actually CLang/LLVM which we have retargeted to
our
proprietary target.

 

Most of the work we do is in maintaining our target specific backend.
Certainly there are optimisations that we do to take best advantage of our
instruction set during lowering and instruction selection, and we have also
added a couple of additional passes which manipulate the IR in advance of
lowering to better shape it for our target.

 

But in practice the vast majority of optimisations are contributed by the
continuously evolving and excellent LLVM target independent passes, and have
little or nothing to do with the work we do in our backend - though it is
obviously directed/tuned by the various target call-backs and the target
cost models.

 

Is there a "one stop shop" list of the optimisation passes that LLVM
performs, and identification of which are enabled by default for each of the
4 standard optimisation levels '-O0' thru '-O3'?

 

The reason that I ask, is that I really don't have an honest or informed
answer that I can provide to people when they ask, and I haven't found a
definitive statement of this in the LLVM documentation that I could refer
them to.

 

Thanks,

 

            MartinO

 

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Have u looked in the pass manager?

On Jun 24, 2017 10:10 AM, "Martin J. O'Riordan via llvm-dev" <
llvm-dev at lists.llvm.org> wrote:
> I am often asked what optimisations “our” compiler performs at each
> level.  But “our” compiler is actually CLang/LLVM which we have retargeted
> to our proprietary target.
>
>
>
> Most of the work we do is in maintaining our target specific backend.
> Certainly there are optimisations that we do to take best advantage of our
> instruction set during lowering and instruction selection, and we have also
> added a couple of additional passes which manipulate the IR in advance of
> lowering to better shape it for our target.
>
>
>
> But in practice the vast majority of optimisations are contributed by the
> continuously evolving and excellent LLVM target independent passes, and
> have little or nothing to do with the work we do in our backend - though it
> is obviously directed/tuned by the various target call-backs and the target
> cost models.
>
>
>
> Is there a “one stop shop” list of the optimisation passes that LLVM
> performs, and identification of which are enabled by default for each of
> the 4 standard optimisation levels ‘-O0’ thru ‘-O3’?
>
>
>
> The reason that I ask, is that I really don’t have an honest or informed
> answer that I can provide to people when they ask, and I haven’t found a
> definitive statement of this in the LLVM documentation that I could refer
> them to.
>
>
>
> Thanks,
>
>
>
>             MartinO
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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The most definitive list you can probably hope to get will be obtained by
passing -mllvm -debug-pass=Structure to a clang invocation.

-- Sean Silva

On Jun 24, 2017 7:10 AM, "Martin J. O'Riordan via llvm-dev" <
llvm-dev at lists.llvm.org> wrote:

I am often asked what optimisations “our” compiler performs at each level.
But “our” compiler is actually CLang/LLVM which we have retargeted to our
proprietary target.



Most of the work we do is in maintaining our target specific backend.
Certainly there are optimisations that we do to take best advantage of our
instruction set during lowering and instruction selection, and we have also
added a couple of additional passes which manipulate the IR in advance of
lowering to better shape it for our target.



But in practice the vast majority of optimisations are contributed by the
continuously evolving and excellent LLVM target independent passes, and
have little or nothing to do with the work we do in our backend - though it
is obviously directed/tuned by the various target call-backs and the target
cost models.



Is there a “one stop shop” list of the optimisation passes that LLVM
performs, and identification of which are enabled by default for each of
the 4 standard optimisation levels ‘-O0’ thru ‘-O3’?



The reason that I ask, is that I really don’t have an honest or informed
answer that I can provide to people when they ask, and I haven’t found a
definitive statement of this in the LLVM documentation that I could refer
them to.



Thanks,



            MartinO



_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Right but then you'll have to call each opt level. Have u looked in the
pass manager?

On Jun 24, 2017 3:52 PM, "Sean Silva via llvm-dev" <llvm-dev at
lists.llvm.org>
wrote:
> The most definitive list you can probably hope to get will be obtained by
> passing -mllvm -debug-pass=Structure to a clang invocation.
>
> -- Sean Silva
>
> On Jun 24, 2017 7:10 AM, "Martin J. O'Riordan via llvm-dev"
<
> llvm-dev at lists.llvm.org> wrote:
>
> I am often asked what optimisations “our” compiler performs at each
> level.  But “our” compiler is actually CLang/LLVM which we have retargeted
> to our proprietary target.
>
>
>
> Most of the work we do is in maintaining our target specific backend.
> Certainly there are optimisations that we do to take best advantage of our
> instruction set during lowering and instruction selection, and we have also
> added a couple of additional passes which manipulate the IR in advance of
> lowering to better shape it for our target.
>
>
>
> But in practice the vast majority of optimisations are contributed by the
> continuously evolving and excellent LLVM target independent passes, and
> have little or nothing to do with the work we do in our backend - though it
> is obviously directed/tuned by the various target call-backs and the target
> cost models.
>
>
>
> Is there a “one stop shop” list of the optimisation passes that LLVM
> performs, and identification of which are enabled by default for each of
> the 4 standard optimisation levels ‘-O0’ thru ‘-O3’?
>
>
>
> The reason that I ask, is that I really don’t have an honest or informed
> answer that I can provide to people when they ask, and I haven’t found a
> definitive statement of this in the LLVM documentation that I could refer
> them to.
>
>
>
> Thanks,
>
>
>
>             MartinO
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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