opt -passes='loop-interchange' crashes with "bad subscript classification UNREACHABLE executed at ../lib/Analysis/DependenceAnalysis.cpp:3833!"

[mikaelholmen]

Bugzilla Link	52170
Version	trunk
OS	Linux
Attachments	bbi-61519.ll reproducer

Extended Description

llvm commit: 0fbd3aa

Reproduce with:
opt -passes='loop-interchange' -o /dev/null bbi-61519.ll

Result:
bad subscript classification
UNREACHABLE executed at ../lib/Analysis/DependenceAnalysis.cpp:3833!
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace.
Stack dump:
0. Program arguments: ../../master-github/llvm/build-all/bin/opt -passes=loop-interchange -o /dev/null bbi-61519.ll
#​0 0x0000000002b5b8c3 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (../../master-github/llvm/build-all/bin/opt+0x2b5b8c3)
#​1 0x0000000002b5953e llvm::sys::RunSignalHandlers() (../../master-github/llvm/build-all/bin/opt+0x2b5953e)
#​2 0x0000000002b5bc46 SignalHandler(int) Signals.cpp:0:0
#​3 0x00007efe70534630 __restore_rt sigaction.c:0:0
#​4 0x00007efe6dc67387 raise (/lib64/libc.so.6+0x36387)
#​5 0x00007efe6dc68a78 abort (/lib64/libc.so.6+0x37a78)
#​6 0x0000000002ad8d5f (../../master-github/llvm/build-all/bin/opt+0x2ad8d5f)
#​7 0x0000000001a4e606 llvm::DependenceInfo::depends(llvm::Instruction*, llvm::Instruction*, bool) (../../master-github/llvm/build-all/bin/opt+0x1a4e606)
#​8 0x00000000028ec1db (anonymous namespace)::LoopInterchange::processLoopList(llvm::ArrayRefllvm::Loop*) LoopInterchange.cpp:0:0
#​9 0x00000000028eb21a llvm::LoopInterchangePass::run(llvm::LoopNest&, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>&, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&) (../../master-github/llvm/build-all/bin/opt+0x28eb21a)
#​10 0x0000000002e606dd llvm::detail::PassModel<llvm::LoopNest, llvm::LoopInterchangePass, llvm::PreservedAnalyses, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&>::run(llvm::LoopNest&, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>&, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&) crtstuff.c:0:0
#​11 0x0000000003375b6c llvm::Optionalllvm::PreservedAnalyses llvm::PassManager<llvm::Loop, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&>::runSinglePass<llvm::LoopNest, std::unique_ptr<llvm::detail::PassConcept<llvm::LoopNest, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&>, std::default_delete<llvm::detail::PassConcept<llvm::LoopNest, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&> > > >(llvm::LoopNest&, std::unique_ptr<llvm::detail::PassConcept<llvm::LoopNest, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&>, std::default_delete<llvm::detail::PassConcept<llvm::LoopNest, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&> > >&, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>&, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&, llvm::PassInstrumentation&) (../../master-github/llvm/build-all/bin/opt+0x3375b6c)
#​12 0x0000000003374fb3 llvm::PassManager<llvm::Loop, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&>::runWithLoopNestPasses(llvm::Loop&, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>&, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&) (../../master-github/llvm/build-all/bin/opt+0x3374fb3)
#​13 0x0000000003374b91 llvm::PassManager<llvm::Loop, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&>::run(llvm::Loop&, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>&, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&) (../../master-github/llvm/build-all/bin/opt+0x3374b91)
#​14 0x0000000002e3256d llvm::detail::PassModel<llvm::Loop, llvm::PassManager<llvm::Loop, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&>, llvm::PreservedAnalyses, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&>::run(llvm::Loop&, llvm::AnalysisManager<llvm::Loop, llvm::LoopStandardAnalysisResults&>&, llvm::LoopStandardAnalysisResults&, llvm::LPMUpdater&) crtstuff.c:0:0
#​15 0x0000000003376a6b llvm::FunctionToLoopPassAdaptor::run(llvm::Function&, llvm::AnalysisManagerllvm::Function&) (../../master-github/llvm/build-all/bin/opt+0x3376a6b)
#​16 0x0000000002e4dc8d llvm::detail::PassModel<llvm::Function, llvm::FunctionToLoopPassAdaptor, llvm::PreservedAnalyses, llvm::AnalysisManagerllvm::Function >::run(llvm::Function&, llvm::AnalysisManagerllvm::Function&) crtstuff.c:0:0
#​17 0x0000000002308fd5 llvm::PassManager<llvm::Function, llvm::AnalysisManagerllvm::Function >::run(llvm::Function&, llvm::AnalysisManagerllvm::Function&) (../../master-github/llvm/build-all/bin/opt+0x2308fd5)
#​18 0x0000000000ad615d llvm::detail::PassModel<llvm::Function, llvm::PassManager<llvm::Function, llvm::AnalysisManagerllvm::Function >, llvm::PreservedAnalyses, llvm::AnalysisManagerllvm::Function >::run(llvm::Function&, llvm::AnalysisManagerllvm::Function&) crtstuff.c:0:0
#​19 0x000000000230d356 llvm::ModuleToFunctionPassAdaptor::run(llvm::Module&, llvm::AnalysisManagerllvm::Module&) (../../master-github/llvm/build-all/bin/opt+0x230d356)
#​20 0x000000000078f47d llvm::detail::PassModel<llvm::Module, llvm::ModuleToFunctionPassAdaptor, llvm::PreservedAnalyses, llvm::AnalysisManagerllvm::Module >::run(llvm::Module&, llvm::AnalysisManagerllvm::Module&) crtstuff.c:0:0
#​21 0x0000000002308118 llvm::PassManager<llvm::Module, llvm::AnalysisManagerllvm::Module >::run(llvm::Module&, llvm::AnalysisManagerllvm::Module&) (../../master-github/llvm/build-all/bin/opt+0x2308118)
#​22 0x00000000007872a2 llvm::runPassPipeline(llvm::StringRef, llvm::Module&, llvm::TargetMachine*, llvm::TargetLibraryInfoImpl*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::StringRef, llvm::ArrayRefllvm::StringRef, llvm::opt_tool::OutputKind, llvm::opt_tool::VerifierKind, bool, bool, bool, bool, bool) (../../master-github/llvm/build-all/bin/opt+0x7872a2)
#​23 0x0000000000799e86 main (../../master-github/llvm/build-all/bin/opt+0x799e86)
#​24 0x00007efe6dc53555 __libc_start_main (/lib64/libc.so.6+0x22555)
#​25 0x00000000007826fc _start (../../master-github/llvm/build-all/bin/opt+0x7826fc)
Abort

Starts crashing with commit 7086025:
[Dependence Analysis] Enable delinearization of fixed sized arrays

Patch by Artem Radzikhovskyy!

Allow delinearization of fixed sized arrays if we can prove that the GEP indices do not overflow the array dimensions. The checks applied are similar to the ones that are used for delinearization of parametric size arrays. Make sure that the GEP indices are non-negative and that they are smaller than the range of that dimension.

Changes Summary:

- Updated the LIT tests with more exact values, as we are able to delinearize and apply more exact tests
- profitability.ll - now able to delinearize in all cases, no need to use -da-disable-delinearization-checks flag and run the test twice
- loop-interchange-optimization-remarks.ll - in one of the cases we are able to delinearize without using -da-disable-delinearization-checks
- SimpleSIVNoValidityCheckFixedSize.ll - removed unnecessary "-da-disable-delinearization-checks" flag. Now can get the exact answer without it.
- SimpleSIVNoValidityCheckFixedSize.ll and PreliminaryNoValidityCheckFixedSize.ll - made negative tests more explicit, in order to demonstrate the need for "-da-disable-delinearization-checks" flag

Differential Revision: https://reviews.llvm.org/D101486

[llvmbot]

@llvm/issue-subscribers-bug

[fhahn]

cc @andykaylor

[artemrad]

The following commit 7086025 enabled delinearization of fixed sized arrays. It is now possible to propagate SIV constraints to other coupled subscripts in more cases, resulting in more accurate dependence analysis. When a SIV constraint is propagated we re-classify the other non-SIV subscripts. It is possible that the re-classified subscript is now marked as non-linear, in cases where we cannot prove that the taken backedge of the loop may not overflow. In such cases DependenceAnalysis should conservatively report that a dependence may be present instead of crashing the compiler with llvm_unreachable.

Actively working on a fix.

[artemrad]

Posted a review https://reviews.llvm.org/D119261

[dfszabo]

Shouldn't this issue be closed already?

[bjope]

Afaict it still hits UNREACHABLE: https://godbolt.org/z/MY5seqoPc

[mikaelholmen]

Shouldn't this issue be closed already?

As @bjope said the reproducer in the description still hits the descibed UNREACHABLE.
The review https://reviews.llvm.org/D119261 never got accepted or submitted.