[llvm-dev] llvm pass is very slow

[John Criswell via llvm-dev]

On 7/14/18 9:21 PM, Muhui Jiang via llvm-dev wrote:
> Hi
>
> I write a LLVM function pass. The pass will loop the basicblock in the 
> function, check the instruction's type with dyn_cast<switchinst>, 
> print the instruction and the basicblock's successors. I think it is 
> not very complex.
>
> My bitcode file is about 30M. My CPU is i7-7700(3.6GHz). It has been 
> running for 60 hours but it is still running. I am not sure whether 
> this is a normal behavior. If so, any options or suggestions to help 
> me speed up the analysis. Many Thanks

The first thing you should check is whether you've written the loop 
properly.  It's possible that you've somehow written an infinite loop.  
If your pass is adding instructions, be careful that you're not 
invalidating the iterator that you're using to loop over the 
instructions.  That might cause a non-obvious error.

The second thing to consider is to use the InstVisitor class instead of 
writing a loop.  Look at InstVisitor.h in the LLVM source code; it has 
comments that show you how to use it.  In a nutshell, your FunctionPass 
will be a subclass of InstVisitor.  You then implement the 
visitSwitchInst() method and call visit() on the function in 
runOnFunction, and you're done.

http://llvm.org/doxygen/classllvm_1_1InstVisitor.html

Regards,

John Criswell

>
> Regards
> Muhui
>
>
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-- 
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
http://www.cs.rochester.edu/u/criswell

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