[LLVMdev] missed optimizations

[Chris Lattner]

On Mar 6, 2009, at 8:40 PM, John Regehr wrote:

> It turns out to be pretty easy to use our random program generator to
> search for missed optimizations by generating highly restricted  
> programs
> that are equivalent to "return 0" or similar, and then checking that
> LLVM properly evaporates the code.
>
> The result will be a lot of bug reports like this:
>
>   http://llvm.org/bugs/show_bug.cgi?id=3740
>
> Daniel says this is a boring phase ordering problem but there are also
> more interesting cases.
>
> Do people care?  Should we submit a string of these sorts of reports?

Hi John,

My take is "probably not".  If there are two or three instruction  
identities that we are missing, then I'd be interested in adding  
those, but completely random complex missed optimizations are less  
interesting to me.

There is an unbounded number of things the optimizer could potentially  
handle, but we only have a bounded amount of engineering effort.  I'd  
rather drive forward based on actual needs of code observed in the wild.

Just MHO,

-Chris