[LLVMdev] AliasAnalysis as a Loadable Module, Possible 2.6->2.7 issue

[John Criswell]

Dear Will,

If you're seeing the wrong method executed, it's probably because you're 
using multiple inheritance in your analysis group (which is a very 
common thing to do).

LLVM 2.7 made a change which alleviated the need for RTTI or some other 
undesirable C++ feature.  However, it also broke multiple inheritance 
with analysis group passes.  To fix it, your analysis group needs to 
implement a getAdjustedAnalysisPointer() method.  The implementation 
should look something like this:

/// When chaining analyses, changing the pointer to the correct pass
virtual void *getAdjustedAnalysisPointer(const PassInfo *PI) {
    if (PI->isPassID(&ArrayBoundsCheckGroup::ID))
        return (ArrayBoundsCheckGroup*)this;
    return this;
}

Just replace "ArrayBoundsCheckGroup" with whatever the name of your 
analysis group is, and it should work.

-- John T.


Will Dietz wrote:
> Thanks for the response, Eli.
>
> The header suggestion could certainly cause this issue (I panicked for
> a second), but unfortunately as far as I can tell the headers are in
> fact from LLVM 2.7.
>
> The pass is built as a project configured by llvm, so hopefully that
> would make things right, but also:
> --include paths look legit (make VERBOSE=1, etc)
> --strace on the build process for the project confirms no headers
> outside the llvm 2.7 tree are read, and 'svn diff' confirms I haven't
> managed to botch those.
>
> The code is from the "release_27" branch, for what it's worth.
>
> I'm not at all convinced I haven't somehow broken my build
> environment, but it's not clear to me how.
>
> Thoughts on anything else I could look into?
>
> For what it's worth, attached is the project triggering the issue, if
> someone gets bored and either wants to try it or tell me what I'm
> doing wrong :).
>
> Thanks for your time,
>
> ~Will
>
> On Tue, May 25, 2010 at 10:13 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
>   
>> On Tue, May 25, 2010 at 5:53 PM, Will Dietz <willdtz at gmail.com> wrote:
>>     
>>> Hi all,
>>>
>>> First time posting to llvmdev, be gentle :).
>>>
>>> I'm working on an AliasAnalysis implementation and running into an
>>> issue on 2.7, that doesn't exist in 2.6 as far as I can tell.
>>>
>>> Short version: has anyone been able to load an AliasAnalysis module
>>> into 2.7's opt?
>>>
>>> Longer version:
>>>
>>> Even with a dummy pass implementation (just returns MayAlias for
>>> everything), I'm getting very strange behavior:
>>>
>>> All calls to FooAA::alias go to FooAA::print, resulting in
>>> understandably painful failure thereafter, generally a segfault.
>>>       
>> Are you sure you built your module against LLVM 2.7 headers?
>>
>> -Eli
>>     
> >