Right. But we've also observed non-determinism / undefined behavior in Clang 10:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=246630#c26

==120363== Conditional jump or move depends on uninitialised value(s)
==120363== at 0x1634474: llvm::ConstantExpr::getGetElementPtr(llvm::Type*, llvm::Constant*, llvm::ArrayRef<llvm::Value*>, bool, llvm::Optional<unsigned int>, llvm::Type*) (Constants.cpp:2191)
==120363== by 0x112D6D9: getGetElementPtr (Constants.h:1163)
==120363== by 0x112D6D9: (anonymous namespace)::SymbolicallyEvaluateGEP(llvm::GEPOperator const*, llvm::ArrayRef<llvm::Constant*>, llvm::DataLayout const&, llvm::TargetLibraryInfo const*) (ConstantFolding.cpp:1005)
==120363== by 0x112DF70: (anonymous namespace)::ConstantFoldInstOperandsImpl(llvm::Value const*, unsigned int, llvm::ArrayRef<llvm::Constant*>, llvm::DataLayout const&, llvm::TargetLibraryInfo const*) (ConstantFolding.cpp:1039)
==120363== by 0x112C165: (anonymous namespace)::ConstantFoldConstantImpl(llvm::Constant const*, llvm::DataLayout const&, llvm::TargetLibraryInfo const*, llvm::SmallDenseMap<llvm::Constant*, llvm::Constant*, 4u, llvm::DenseMapInfo<llvm::Constant*>, llvm::detail::DenseMapPair<llvm::Constant*, llvm::Constant*> >&) [clone .part.0] (ConstantFolding.cpp:1114)
==120363== by 0x112C5CF: llvm::ConstantFoldConstant(llvm::Constant const*, llvm::DataLayout const&, llvm::TargetLibraryInfo const*) (ConstantFolding.cpp:1194)
==120363== by 0x188F410: prepareICWorklistFromFunction (InstructionCombining.cpp:3584)
==120363== by 0x188F410: combineInstructionsOverFunction(llvm::Function&, llvm::InstCombineWorklist&, llvm::AAResults*, llvm::AssumptionCache&, llvm::TargetLibraryInfo&, llvm::DominatorTree&, llvm::OptimizationRemarkEmitter&, llvm::BlockFrequencyInfo*, llvm::ProfileSummaryInfo*, unsigned int, llvm::LoopInfo*) (InstructionCombining.cpp:3703)
==120363== by 0x189205F: runOnFunction (InstructionCombining.cpp:3789)
==120363== by 0x189205F: llvm::InstructionCombiningPass::runOnFunction(llvm::Function&) (InstructionCombining.cpp:3768)
==120363== by 0x16F4352: llvm::FPPassManager::runOnFunction(llvm::Function&) (LegacyPassManager.cpp:1482)
==120363== by 0x16F4DE8: llvm::FPPassManager::runOnModule(llvm::Module&) (LegacyPassManager.cpp:1518)
==120363== by 0x16F51A2: runOnModule (LegacyPassManager.cpp:1583)
==120363== by 0x16F51A2: llvm::legacy::PassManagerImpl::run(llvm::Module&) (LegacyPassManager.cpp:1695)
==120363== by 0x1FF4CFE: EmitAssembly (BackendUtil.cpp:954)
==120363== by 0x1FF4CFE: clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::DataLayout const&, llvm::Module*, clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream> >) (BackendUtil.cpp:1677)
==120363== by 0x2C471A8: clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (CodeGenAction.cpp:335)
==120363== Uninitialised value was created by a stack allocation
==120363== at 0x112C653: (anonymous namespace)::SymbolicallyEvaluateGEP(llvm::GEPOperator const*, llvm::ArrayRef<llvm::Constant*>, llvm::DataLayout const&, llvm::TargetLibraryInfo const*) (ConstantFolding.c