[llvm-dev] Sanitizers + New Pass Manager

[Alina Sbirlea via llvm-dev]

Is it the case that with the legacy PM there is no inlining at either -O2
or -O3 and with newPM there is? Or is there something else going on?

Sounds like this needs pinpointing where the behavior should be different
than what's currently happening.
Inlining in the NPM doesn't seem the issue, it's what it triggers
afterwards. Is it that the lifetime intrinsics shouldn't have been
stripped, or is it that ASan shouldn't rely on these to add instrumentation
because previous optimizations may have removed them (hence it should not
rely on what optimizations are done or not done; as you suggested, maybe
changing the pass pipeline to add ASan earlier may be needed?), or is it
something else?


Alina

On Wed, May 13, 2020 at 1:04 PM Arthur Eubanks <aeubanks at google.com> wrote:

> Just tested it out, that test does indeed fail under the old PM at -O3 and
> even at -O2.
>
> If the ASan pass runs after optimizations and is designed to detect
> undefined behavior at runtime, I don't see how it can be super reliable at
> higher optimization levels.
>
> On Wed, May 13, 2020 at 12:39 PM David Blaikie <dblaikie at gmail.com> wrote:
>
>> +some sanitizer/new pass manager folks
>>
>>
>>
>> On Wed, May 13, 2020 at 12:22 PM Arthur Eubanks via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hi,
>>>
>>> I've been trying to burn down the remaining sanitizer failures under the
>>> new pass manager. Right now I'm stuck on some ASan tests.
>>>
>>> Some ASan tests run under -O1. There are a couple differences between
>>> the old and new pass managers under -O1, e.g. the old PM doesn't inline
>>> whereas the new PM does. The differences seem to cause some lifetime
>>> intrinsics to get stripped out (e.g. via SROA, InstCombine). It might be
>>> due to ASan specifically testing undefined behavior, and different
>>> optimizations run means different behavior. For a specific example,
>>> use-after-scope-dtor-order.cpp runs under -O1 and fails under the new PM
>>> because SROA strips out the lifetime intrinsics and by the time the ASan
>>> pass runs it doesn't find the lifetime intrinsics to add its own
>>> instrumentation.
>>>
>>
>> That, to me, sounds like a real bug in the optimizations/asan
>> implementation if this choice fo optimizations makes the diagnosis go away.
>> (is ASan able to diagnose the problem at -O3 (where I guess SROA and other
>> things run) with the legacy pass manager?)
>>
>>
>>>
>>> What's the proper way to resolve this? Run the tests under -O0? Change
>>> the passes pipeline under the new PM when ASan (and maybe other sanitizers)
>>> is detected?
>>> _______________________________________________
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>>> llvm-dev at lists.llvm.org
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>>>
>>
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