[LLVMdev] project idea: llvm superoptimizer

Chris Lattner clattner at apple.com
Wed Dec 16 01:03:46 PST 2009

thanks, I added this to http://www.llvm.org/OpenProjects.html


On Dec 13, 2009, at 4:25 PM, John Regehr wrote:

> Here's an idea for a research project that I thought I'd put out there 
> since probably nobody in my group will have time to follow up on it.
> It would be interesting to take ideas from this superoptimizer for x86:
>   http://theory.stanford.edu/~aiken/publications/papers/asplos06.pdf
>   http://theory.stanford.edu/~sbansal/superoptimizer.html
> and adapt them to run on LLVM code.
> It would seem that operating on LLVM code would save a lot of time 
> because its semantics are much simpler than x86.  The cost of operating 
> on LLVM is that target-specific tricks would be missed.
> The outcome would be a new LLVM pass that subsumes at least the 
> instruction combiner, and probably a few other passes as well.  Benefits 
> would include not missing cases missed by the current combiner and also 
> more easily adapting to changes in the LLVM IR.
> All previous superoptimizers have worked on linear sequences of code. 
> It would seem much better to operate on small subgraphs of the program 
> dependency graph.  I haven't worked out the details...
> John Regehr
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