[llvm-dev] Metadata and compile time performance

Philip Reames via llvm-dev llvm-dev at lists.llvm.org
Mon Feb 22 09:40:50 PST 2016

On 02/19/2016 04:47 AM, Norilo Vesa-Petri via llvm-dev wrote:
> Dear LLVMers,
> I’m investigating the response time of my JIT, and according to 
> profiling, optimization takes 85% of the compile time, while the rest 
> is being split evenly between the front-end and machine code 
> generation. Much of the optimizer time is spent in various alias 
> analysis passes.
Could you share more detailed profiling information?  It's possible 
you're tripping across a compile time bug or that seeing what sections 
are hot would given insights into how to tweak your code to avoid the 
> I’m happy with the generated code quality and wouldn’t like to lower 
> the optimization level (O2).
> Would generating alias metadata from the front-end help and speed up 
> optimization?
> If so, what kind of AA would have the best return on investment in 
> terms of compile time? TBAA is not applicable to my language, but I 
> could provide C99 restrict and related semantics fairly easily.
In general, if you can give "easier" answers, that's always a good 
thing.  If you're using LLVM for inlining, you may find that "noalias" 
attributes are quite useful for controlling compile time (i.e. enable 
optimizations of callee before inlining).  Without knowing more about 
your source language and where you're currently spending time, I can't 
really help more than that.
> Thanks!!
> Vesa Norilo
> Lecturer
> Centre for Music and Technology
> University of Arts Helsinki
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