[PATCH, Pointer Bounds Checker 14/x] Passes [15/n] Optimize redundant checks

[Jeff Law]

On 10/10/14 09:50, Ilya Enkovich wrote:
> Checks and and intersection removal code was added as a simple pass
> catching trivial cases.  I'm sure there are optimizations having
> common elements with what checker optimizer does.  But initially we
> didn't want to adopt existing optimizers because GIMPLE representation
> of instrumentation was not stable and also we still don't know what
> are important targets for optimizations.
Understood.

>
> The plan is to have stable version first.  After enabling we want to
> make performance analysis and determine which optimizations are most
> required (it may appear checks removal doesn't give any significant
> performance gain at all), determine which of current infrastructure
> may be re-used (if any) and implement proper checker optimization.
>
> Current optimizer is a simple code cleanup.  I do not think we should
> make any significant rework of it as a part of enabling.  If current
> approach seems to require significant changes to go to trunk then it
> should be probably delayed and go separately from instrumentation
> pass.
Well, I think it should be trivial to handle the redundant check 
elimination in DOM.

Most likely eliminate_redundant_computations needs some work to allow it 
to look inside those checks and get them recorded into its tables.  With 
that in place, DOM should optimize this stuff without further 
intervention.  It's probably less code than you've already written :-)

The swapping variant feels like it should be simple to implement with 
the existing dominator walkers.  But I haven't thought nearly as much 
about that one.

jeff