[llvm-dev] Sanitizers + New Pass Manager

[David Blaikie via llvm-dev]

I believe it's meant to run after /some/ optimizations to make it a bit
more efficient, while not so optimized that it misses opportunities to
detect bugs - but I could be wrong there. I'll leave it up to other folks
to chime in.

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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>>>
>>
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