[llvm-dev] Sanitizers + New Pass Manager

[Arthur Eubanks via llvm-dev]

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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