llvm dev - May 2020 - Sanitizers + New Pass Manager

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.

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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+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?
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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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?
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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