[llvm-commits] Improvements to PassManager

Tue Nov 27 06:17:32 PST 2012

On Mon, Nov 26, 2012 at 10:23 PM, Kostya Serebryany <kcc at google.com> wrote:

>
>
> On Mon, Nov 26, 2012 at 9:39 PM, Pedro Artigas <partigas at apple.com> wrote:
>
>>
>> Hello All,
>>
>>
>> To summarize the thread and make sure everybody is on the same page I
>> will repeat some information below.
>>
>> - doInitialization and doFinalization are expected to be called
>> before/after runOn???? for each pass on a given module, if more than one
>> module exist in the compilation it will be called multiple times. No other
>> assumption exists. (that is, for example, doFinalization may be called
>> before or after runOn??? of other, unrelated, passes)
>>
>> - ASAN violates this model and it is currently being fixed to split the
>> part that does transformations on the module in doFinalization into a
>> separate module pass (where the code to transform will be called in the run
>> function on the module and, therefore, has proper ordering with other
>> passes)
>>
>
> I've implemented part of the fix in asan, hope to finish it this week.
>

The rest of the fix is sent for review:
http://llvm-reviews.chandlerc.com/D137
http://llvm-reviews.chandlerc.com/D138

--kcc

>
> --kcc
>
>
>> - the short term plan is to workaround the limitation in ASAN by imposing
>> a more restrictive ordering in the doFinalization for function passes (must
>> be run after runOnFunction on each function) so that ASAN works for now,
>> but this limitation should be lifted in the future.
>>
>> If the above is the conclusion I am happy to implement item #3 and defer
>> the fixing of ASAN until time permits. It will unblock me.
>>
>> Thanks everyone,
>>
>> Pedro Artigas
>>
>>
>> On Nov 21, 2012, at 7:22 PM, Kostya Serebryany <kcc at google.com> wrote:
>>
>>
>>
>> On Tue, Nov 20, 2012 at 4:12 PM, 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?
>>>
>>>
>>>> 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?)
>>>
>>>
>>>>
>>>> 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.
>>>
>>
>>
>> Some progress: I've ripped of the creation of global redzones into a
>> separate class.
>> Now I'll need to actually create a separate ModulePass.
>>
>> --kcc
>>
>>
>>>
>>> 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).
>>>
>>> --kcc
>>>
>>
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>>
>>
>
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