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Bug in Libomptarget when state initialization comes from outside the translation unit #54208

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jhuber6 opened this issue Mar 4, 2022 · 7 comments
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Bug in Libomptarget when state initialization comes from outside the translation unit #54208

jhuber6 opened this issue Mar 4, 2022 · 7 comments
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jhuber6 commented Mar 4, 2022

Libomptarget uses some shared variables to track certain internal stated in the runtime. This causes problems when we have code that contains no OpenMP kernels. These variables are normally initialized upon kernel entry, but if there are no kernels we will see no initialization. Currently we load the runtime into each source file when not running in LTO mode, so these variables will be erroneously considered undefined or dead and removed, causing miscompiles.
@jhuber6 jhuber6 added the openmp label Mar 4, 2022
@jhuber6 jhuber6 added this to the LLVM 14.0.0 Release milestone Mar 4, 2022
@jhuber6 jhuber6 self-assigned this Mar 4, 2022
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llvmbot commented Mar 4, 2022

@llvm/issue-subscribers-openmp

@jhuber6 jhuber6 closed this as completed in e2dcc22 Mar 4, 2022
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jhuber6 commented Mar 4, 2022

/cherry-pick e2dcc22

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For backport.

@EugeneZelenko EugeneZelenko reopened this Mar 4, 2022
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llvmbot commented Mar 4, 2022

/branch llvmbot/llvm-project/issue54208

llvmbot pushed a commit to llvmbot/llvm-project that referenced this issue Mar 4, 2022
@jhuber6 @llvmbot
[Libomptarget] Work around bug in initialization of libomptarget
5dcf8b1 
Libomptarget uses some shared variables to track certain internal stated
in the runtime. This causes problems when we have code that contains no
OpenMP kernels. These variables are normally initialized upon kernel
entry, but if there are no kernels we will see no initialization.
Currently we load the runtime into each source file when not running in
LTO mode, so these variables will be erroneously considered undefined or
dead and removed, causing miscompiles. This patch temporarily works
around the most obvious case, but others still exhibit this problem. We
will need to fix this more soundly later.

Fixes llvm#54208.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D121007

(cherry picked from commit e2dcc22)
@llvmbot llvmbot mentioned this issue Mar 4, 2022
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llvmbot commented Mar 4, 2022

/pull-request llvmbot#119

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tstellar commented Mar 5, 2022

@jdoerfert What do you think about backporting this? e2dcc22

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I'm torn. I initially thought we should but I'm not so sure anymore. I fear the performance impact on a lot of codes is not worth it for the few this might help (to actually run). For the next version we'll have to have a proper solution. Let's keep 14 as is.

@tstellar tstellar closed this as completed Mar 7, 2022
@EugeneZelenko EugeneZelenko removed this from the LLVM 14.0.0 Release milestone Mar 7, 2022
@jhuber6 jhuber6 mentioned this issue Jul 5, 2022
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