Bugzilla Link	42719
Resolution	FIXED
Resolved on	Aug 05, 2019 02:03
Version	trunk
OS	Linux
Blocks	#41819
CC	@gburgessiv,@zmodem,@hfinkel,@ormris,@pogo59,@smithp35

Extended Description

I recently noticed that the two unit tests in llvm/unittests/Analysis/BasicAliasAnalysisTest.cpp started failing in our internal linux build bot:

LLVM-Unit::BasicAATest.AliasInstWithFullObjectOfImpreciseSize
LLVM-Unit::BasicAATest.AliasInstWithObjectOfImpreciseSize

These tests have also been failing for a while it seems in two of the upstream build bots:

http://lab.llvm.org:8011/builders/clang-cmake-x86_64-avx2-linux/builds/10285
http://lab.llvm.org:8011/builders/clang-cmake-x86_64-sde-avx512-linux/builds/24658

For the upstream bot clang-cmake-x86_64-avx2-linux, it started failing in build #​10285 (testing r365700-r365711), but I don't think any of those changes actually caused the problem.

For the upstream bot clang-cmake-x86_64-sde-avx512-linux, the failure appears in the bot history as far back as it currently goes (currently the oldest build is the build of r366312).

Internally, our build bot started hitting the failure somewhere between r365857 and r365866. I highly doubt that any of these changes were actually the cause of the problem, as I was able to go back to when the test was added and reproduce the failure internally at that point. What is even odder is that sometimes the test would fail when run within the LIT test framework, but when run on its own, it would fail!

When the failing unit test is run in gdb, the error is a SIGSEGV due to an invalid address. The one time I was able to get a stack trace, here is what it looked like:

#​0 0x00005555555b16b6 in __gnu_cxx::__normal_iterator<std::unique_ptr<llvm::AAResults::Concept, std::default_deletellvm::AAResults::Concept >, std::vector<std::unique_ptr<llvm::AAResults::Concept, std::default_deletellvm::AAResults::Concept >, std::allocator<std::unique_ptr<llvm::AAResults::Concept, std::default_deletellvm::AAResults::Concept > > > >::__normal_iterator (this=0x7fffffffdb10, __i=)
at /usr/include/c++/8/bits/stl_iterator.h:784
#​1 0x00005555555b17de in std::vector<std::unique_ptr<llvm::AAResults::Concept, std::default_deletellvm::AAResults::Concept >, std::allocator<std::unique_ptr<llvm::AAResults::Concept, std::default_deletellvm::AAResults::Concept > >>::begin (this=0x1013) at /usr/include/c++/8/bits/stl_vector.h:699
#​2 0x00005555556c74cd in llvm::AAResults::alias (this=0x100b, LocA=..., LocB=...)
at /mnt/sources/git/merge/llvm/lib/Analysis/AliasAnalysis.cpp:104
#​3 0x00005555556f01ae in llvm::AAResultBasellvm::BasicAAResult::AAResultsProxy::alias (this=0x7fffffffdcb0,
LocA=..., LocB=...) at /mnt/sources/git/merge/llvm/include/llvm/Analysis/AliasAnalysis.h:896
#​4 0x00005555556ec2df in llvm::BasicAAResult::aliasCheck (this=0x55555666f918, V1=0x555556684ac0, V1Size=...,
V1AAInfo=..., V2=0x555556686488, V2Size=..., V2AAInfo=..., O1=0x555556684ac0, O2=0x555556686488)
at /mnt/sources/git/merge/llvm/lib/Analysis/BasicAliasAnalysis.cpp:1787
#​5 0x00005555556e89da in llvm::BasicAAResult::alias (this=0x55555666f918, LocA=..., LocB=...)
at /mnt/sources/git/merge/llvm/lib/Analysis/BasicAliasAnalysis.cpp:780
#​6 0x00005555555b804b in BasicAATest_AliasInstWithObjectOfImpreciseSize_Test::TestBody (this=0x55555666f260)
at /mnt/sources/git/merge/llvm/unittests/Analysis/BasicAliasAnalysisTest.cpp:93
#​7 0x0000555555e3a8e4 in testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void> (
object=0x55555666f260, method=&virtual testing::Test::TestBody(), location=0x555556319b3b "the test body")
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/src/gtest.cc:2402
#​8 0x0000555555e352c2 in testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void> (
object=0x55555666f260, method=&virtual testing::Test::TestBody(), location=0x555556319b3b "the test body")
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/src/gtest.cc:2455
#​9 0x0000555555e1d842 in testing::Test::Run (this=0x55555666f260)
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/src/gtest.cc:2474
#​10 0x0000555555e1e000 in testing::TestInfo::Run (this=0x555556657d70)
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/src/gtest.cc:2656
#​11 0x0000555555e1e5ea in testing::TestCase::Run (this=0x555556657f10)
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/src/gtest.cc:2774
#​12 0x0000555555e244f8 in testing::internal::UnitTestImpl::RunAllTests (this=0x555556657120)
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/src/gtest.cc:4649
#​13 0x0000555555e3ba52 in testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool> (object=0x555556657120,
method=(bool (testing::internal::UnitTestImpl::)(testing::internal::UnitTestImpl * const)) 0x555555e24226 testing::internal::UnitTestImpl::RunAllTests(),
location=0x55555631a378 "auxiliary test code (environments or event listeners)")
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/src/gtest.cc:2402
#​14 0x0000555555e35cc9 in testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool> (object=0x555556657120,
method=(bool (testing::internal::UnitTestImpl::*)(testing::internal::UnitTestImpl * const)) 0x555555e24226 testing::internal::UnitTestImpl::RunAllTests(),
location=0x55555631a378 "auxiliary test code (environments or event listeners)")
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/src/gtest.cc:2455
#​15 0x0000555555e23389 in testing::UnitTest::Run (this=0x555556644680 testing::UnitTest::GetInstance()::instance)
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/src/gtest.cc:4257
#​16 0x0000555555e16b1b in RUN_ALL_TESTS ()
at /mnt/sources/git/merge/llvm/utils/unittest/googletest/include/gtest/gtest.h:2233
#​17 0x0000555555e16a95 in main (argc=1, argv=0x7fffffffe378)
at /mnt/sources/git/merge/llvm/utils/unittest/UnitTestMain/TestMain.cpp:51

Unfortunately I do not know what revision I was building/testing with, but this should give some context hopefully.

I did run the failure once in LLDB, but it was also not able to find symbols and couldn't give much more information, but I am including it here in case it helps:

[----------] 2 tests from BasicAATest
[ RUN ] BasicAATest.AliasInstWithObjectOfImpreciseSize
Process 16335 stopped

• thread #​1: tid = 16335, 0x0000000000525199 AnalysisTestsllvm::AAResults::alias(llvm::MemoryLocation const&, llvm::MemoryLocation const&, llvm::AAQueryInfo&) + 41, name = 'AnalysisTests', stop reason = signal SIGSEGV: invalid address (fault address: 0xfffffffffffffffe) frame #​0: 0x0000000000525199 AnalysisTestsllvm::AAResults::alias(llvm::MemoryLocation const&, llvm::MemoryLocation const&, llvm::AAQueryInfo&) + 41
  AnalysisTests`llvm::AAResults::alias:
  -> 0x525199 <+41>: movq (%rbx), %rdi
  0x52519c <+44>: movq %r12, %rcx
  0x52519f <+47>: movq %r13, %rdx
  0x5251a2 <+50>: movq %r14, %rsi
  (lldb) bt
• thread #​1: tid = 16335, 0x0000000000525199 AnalysisTests`llvm::AAResults::alias(llvm::MemoryLocation const&, llvm::MemoryLocation const&, llvm::AAQueryInfo&) + 41, name = 'AnalysisTests', stop reason = signal SIGSEGV: invalid address
  (fault address: 0xfffffffffffffffe)
  • frame #​0: 0x0000000000525199 AnalysisTestsllvm::AAResults::alias(llvm::MemoryLocation const&, llvm::MemoryLocation const&, llvm::AAQueryInfo&) + 41 frame #​1: 0x000000000053de1c AnalysisTestsllvm::BasicAAResult::aliasCheck(llvm::Value const*, llvm::LocationSize, llvm::AAMDNodes, llvm::Value const*, llvm::LocationSize, llvm::AAMDNodes, llvm::AAQueryInfo&, llvm::Value const*, llvm::Value const*) + 2300
    frame #​2: 0x000000000053fcb8 AnalysisTestsllvm::BasicAAResult::alias(llvm::MemoryLocation const&, llvm::MemoryLocation const&, llvm::AAQueryInfo&) + 568 frame #​3: 0x0000000000435acb AnalysisTestsBasicAATest_AliasInstWithObjectOfImpreciseSize_Test::TestBody() + 1003
    frame #​4: 0x0000000000848b72 AnalysisTeststesting::Test::Run() + 162 frame #​5: 0x0000000000848cb0 AnalysisTeststesting::TestInfo::Run() + 272
    frame #​6: 0x0000000000848d75 AnalysisTeststesting::TestCase::Run() + 165 frame #​7: 0x000000000084c7a7 AnalysisTeststesting::internal::UnitTestImpl::RunAllTests() + 599
    frame #​8: 0x000000000084cac1 AnalysisTeststesting::UnitTest::Run() + 81 frame #​9: 0x0000000000427fc5 AnalysisTestsmain + 117
    frame #​10: 0x00007ffff6d3a830 libc.so.6__libc_start_main(main=(AnalysisTestsmain), argc=1, argv=0x00007fffffffe4e8, init=, fini=, rtld_fini=, stack_end=0x00007fffffffe4d8) + 240 at libc-start.c:291
    frame #​11: 0x00000000004285b9 AnalysisTests`_start + 41