[llvm-commits] Improvements to PassManager

[Chandler Carruth]

On Tue, Nov 20, 2012 at 4:12 AM, Kostya Serebryany <kcc at google.com> wrote:
>
>
> On Tue, Nov 20, 2012 at 3:05 PM, Chandler Carruth <chandlerc at google.com>
> wrote:
>>
>> On Mon, Nov 19, 2012 at 4:46 AM, Kostya Serebryany <kcc at google.com> wrote:
>> >
>> >
>> > On Mon, Nov 19, 2012 at 4:33 PM, Chandler Carruth <chandlerc at google.com>
>> > wrote:
>> >>
>> >> FYI, it shouldn't be moved back to a module pass. I'm just suggesting
>> >> the
>> >> logic in doFinalization should be lifted into a module pass.
>> >
>> > You mean split the AddressSanitizer class into two? This will cause some
>> > pain.
>> > There are things computed at doInitialization or at runOnFunction, and
>> > then
>> > used in doFinalization.
>> > E.g. DynamicallyInitializedGlobals will need to be computed twice.
>> > GlobalsCreatedByAsan will have to be replaced with some other way to
>> > mark
>> > globals created by asan (use metadata nodes? match name strings?)
>>
>> This is what I meant... I realize it's not trivial, but I think it's
>> the correct thing to do.
>>
>> Essentially, transforms on globals themselves should be done as a
>> module pass (much like globalopt is today a module pass), and
>> transforms on the functions as a function pass.The global transforms
>> are also much simpler / more constrained, and so it seems less likely
>> for them to benefit from being a function pass.
>
>
> Makes sense. (The downside, of course, is increased code complexity.
> Hopefully not too much).
>
>
>>
>>
>>
>> To address your specific points:
>>
>> DynamicallyInitializedGlobals appears to only be created inside the
>> finalization step, even though it is referenced from outside of it...
>> I've no idea how the outside references can work currently.
>
>
> hah! This is a performance bug in asan-initialization-order mode!
> (The global transform phase was done in doInitialization until recently).
> I'll fix this with a unit test this time ;)
>
>
>>
>> That said,
>> computing this twice (once in the initialization step of the function
>> pass, once in the module pass) doesn't seem terribly costly.
>
>
> Not too bad, indeed.
>
>>
>>
>> GlobalsCreatedByAsan should indeed be handled in some other way. I'm
>> hopeful that the new attribute system will be generalized to support
>> globals as well as functions, which would allow us to just not mark
>> the ASan globals as instrumented.
>
>
> But that won't happen for at lest a couple of months, right?

The attribute stuff is going in presently, but still may not want to wait.

>
>>
>> I'd also be fine using a particular
>> naming convention, there are already some naming convention stuff done
>> in ASan, so it wouldn't be too weird.
>
>
> I will probably have to use names for now (e.g. __asan_gen_1234?)

FWIW, this seems fine...

>
>>
>>
>> Are there any other bits that would be made particularly awkward by this
>> split?
>
>
> Nothing awkward, just quite a few duplicated lines.
>
>>
>>
>>
>> Is this something you folks have bandwidth for? I can look at it if not.
>
>
> Depends on what is the ETA. I'll do it, but don't promise to finish it
> immediately.
>
> This all is a bit sad.
> Mainly because the behavior of doInitialization is a) not what I expected it
> to be and b) not at all understood (by me).

One point -- doFinalization is the real problem here. I think ASan's
doInitialization is fine as-is.

So what would you want the behavior of doFinalization to be? That is,
what are you looking for in these routines? Just a way to share common
state between a FunctionPass and a ModulePass?