[llvm-dev] Question about Safecode optimizations

John Criswell via llvm-dev llvm-dev at lists.llvm.org
Mon Jun 20 08:36:44 PDT 2016

Dear Rigel,

The current version of SAFECode for LLVM 3.2 does not currently use all 
the fancy optimizations developed in previous research (namely, 
Dhurjati's et. al.'s type-safe load/store check elimination 
optimization).  As a result, it is essentially Jones/Kelley.  The source 
code for the optimizations are still there; they simply aren't enabled.

The reason for this is that we opted to make SAFECode a robust debugging 
tool first and then make its optimizations and soundness features robust 
later.  However, I graduated before we could make that code robust.

If you want a production quality tool, I recommend Address Sanitizer.  
If you want to use SAFECode and get the best speed out of it, be sure to 
use at least -O2 optimization or higher; using the SAFECode libLTO 
plugin may also help (though it may also hurt performance by making more 
checks complete).

As an FYI, we have a Google Summer of Code student working on Baggy 
Bounds with Accurate Checking (an extension of Baggy Bounds Checking 
that can do accurate bounds checking by storing extra meta-data within 
the padding area).  When sufficiently robust, this should speed up 
SAFECode significantly.  The goal is to get infrastructure up and 
running which we will be using within my research group; I hope that it 
will also be useful to others.

On a final note, while good run-time check techniques like Address 
Sanitizer and Baggy Bounds improve performance considerably, my hunch is 
that we won't get *really* good performance without aggressive 
inter-procedural compiler optimization.


John Criswell

On 6/20/16 1:51 AM, Rigel Gjomemo via llvm-dev wrote:
> Hello,
> I have been using Safecode to add bounds checks to some programs and 
> am getting very high running times for those programs. In average, the 
> slowdown is up by a factor of 30, sometimes even 90. Is there a way to 
> improve on this?
> I have followed the instructions about installing and using the Link 
> Time Optimizer on this page: 
> http://safecode.cs.illinois.edu/docs/Install.html
> Still, the runtime of the compiled files is about the same.
> Are there any additional instructions that I am missing? Any other 
> options that may be needed?
> Thank you
> Rigel
> _______________________________________________
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John Criswell
Assistant Professor
Department of Computer Science, University of Rochester

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