rtsan pass triggers assertion failure

[luca3s]

running opt with rtsan pass enabled crashes on:

declare void @my_very_own_hash() sanitize_realtime

Found while trying to debug rust-lang/rust#149250.
If the function doesn't have the sanitize_realtime attribute or the rtsan pass isn't enabled it doesn't crash.

Backtrace:

Assertion failed: (!NodePtr->isKnownSentinel()), function operator*, file ilist_iterator.h, line 168.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: ../rust/build/host/llvm/bin/opt --passes=rtsan test2-ir.ll -S
1.	Running pass "rtsan" on module "test2-ir.ll"
 #0 0x00000001049ec104 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/Users/_/rust/build/aarch64-apple-darwin/llvm/bin/opt+0x102894104)
 #1 0x00000001049e9e90 llvm::sys::RunSignalHandlers() (/Users/_/rust/build/aarch64-apple-darwin/llvm/bin/opt+0x102891e90)
 #2 0x00000001049ecbfc SignalHandler(int, __siginfo*, void*) (/Users/_/rust/build/aarch64-apple-darwin/llvm/bin/opt+0x102894bfc)
 #3 0x000000019c4416a4 (/usr/lib/system/libsystem_platform.dylib+0x1804ad6a4)
 #4 0x000000019c407848 (/usr/lib/system/libsystem_pthread.dylib+0x180473848)
 #5 0x000000019c3109e4 (/usr/lib/system/libsystem_c.dylib+0x18037c9e4)
 #6 0x000000019c30fc18 (/usr/lib/system/libsystem_c.dylib+0x18037bc18)
 #7 0x00000001056185a0 (anonymous namespace)::AArch64InstructionSelector::setupMF(llvm::MachineFunction&, llvm::GISelValueTracking*, llvm::CodeGenCoverage*, llvm::ProfileSummaryInfo*, llvm::BlockFrequencyInfo*) (.cold.8) (/Users/rust/build/aarch64-apple-darwin/llvm/bin/opt+0x1034c05a0)
 #8 0x0000000104624614 llvm::RealtimeSanitizerPass::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/Users/rust/build/aarch64-apple-darwin/llvm/bin/opt+0x1024cc614)
 #9 0x0000000104184f04 llvm::PassManager<llvm::Module, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/Users/rust/build/aarch64-apple-darwin/llvm/bin/opt+0x10202cf04)
#10 0x0000000104e2420c llvm::runPassPipeline(llvm::StringRef, llvm::Module&, llvm::TargetMachine*, llvm::TargetLibraryInfoImpl*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::StringRef, llvm::ArrayRef<llvm::PassPlugin>, llvm::ArrayRef<std::__1::function<void (llvm::PassBuilder&)>>, llvm::opt_tool::OutputKind, llvm::opt_tool::VerifierKind, bool, bool, bool, bool, bool, bool, bool) (/Users//rust/build/aarch64-apple-darwin/llvm/bin/opt+0x102ccc20c)
#11 0x0000000104e2bd88 optMain (/Users/rust/build/aarch64-apple-darwin/llvm/bin/opt+0x102cd3d88)
#12 0x000000019c066b98
zsh: abort      ../rust/build/host/llvm/bin/opt --passes=rtsan test2-ir.ll -S

[davidtrevelyan]

Update: @luca3s and I are investigating if this is an issue stemming from the sanitize_realtime attribute appearing on IR function declarations, which is a combination RTSan hasn't handled before. We'll report back when we know more.

[davidtrevelyan]

Update: it does indeed appear to be that the issue is with sanitize_realtime appearing on a declared function. RTSan hasn't needed to do this before, because we don't add the attribute to IR declarations in Clang. However, my opinion is that it would be helpful for RTSan to ignore it for downstream project stability. @cjappl if you have a moment, let's discuss this to confirm the approach.

[davidtrevelyan]

Update: I've drafted a PR for a fix here: #169577

@luca3s would you mind testing this with your use case and letting me know how you get on?