llvm dev - Nov 2019 - Output step count for constant expression

I have a function which exceeds default constexpr step limit of clang. I 
would like to optimize that function, but it is very hard to see whether 
or not the changes I've made do in fact reduce number of steps per 
evaluation. I have not found how to see that number for a specific 
expression, and wanted to see if it is possible to add that feature. It 
could be a diagnostic, or just a file output.

I've looked a little at ExprConstant.cpp in AST, but there is a lot 
going on in that file. I've found StepsLeft variable, which tracks how 
many steps has been executed already, but I'm struggling to understand 
where constexpr execution begins and ends, and how to output the 
necessary message. I have literally several hours of experience with the 
code base and cannot wrap my head around it.

If someone could help out with adding that diagnostic, or provide other 
ways to get number of execution steps, that would be great.

Regards,
Nikita Alekseev

You might want to also ask on cfe-dev at lists.llvm.org as it sounds related
to Clang.


On Sat, Nov 23, 2019 at 4:36 AM Nikita via llvm-dev <llvm-dev at
lists.llvm.org>
wrote:
> I have a function which exceeds default constexpr step limit of clang. I
> would like to optimize that function, but it is very hard to see whether
> or not the changes I've made do in fact reduce number of steps per
> evaluation. I have not found how to see that number for a specific
> expression, and wanted to see if it is possible to add that feature. It
> could be a diagnostic, or just a file output.
>
> I've looked a little at ExprConstant.cpp in AST, but there is a lot
> going on in that file. I've found StepsLeft variable, which tracks how
> many steps has been executed already, but I'm struggling to understand
> where constexpr execution begins and ends, and how to output the
> necessary message. I have literally several hours of experience with the
> code base and cannot wrap my head around it.
>
> If someone could help out with adding that diagnostic, or provide other
> ways to get number of execution steps, that would be great.
>
> Regards,
> Nikita Alekseev
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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