Rust bootstrap hangs forever while compiling stage1 librustc_mir with >1 CGU units

[petrochenkov]

Reproduces on x86_64-pc-windows-gnu with default config.toml, doesn't happen if codegen-units = 1 are added.

Building stage1 compiler artifacts (x86_64-pc-windows-gnu -> x86_64-pc-windows-gnu)
   ...
   Compiling rustc_mir v0.0.0 (file:///C:/msys64/home/we/rust/src/librustc_mir)

Stack trace:

Attaching to process 1780
[New Thread 1780.0x1b7c]
[New Thread 1780.0xb1c]
[New Thread 1780.0x1d60]
[New Thread 1780.0x19c4]
[New Thread 1780.0x444]
[New Thread 1780.0x1bd8]
Reading symbols from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc.exe...done.
0x00007ff8d2642281 in ntdll!DbgBreakPoint ()
   from C:\Windows\SYSTEM32\ntdll.dll
(gdb) info thread
  Id   Target Id         Frame
* 6    Thread 1780.0x1bd8 0x00007ff8d2642281 in ntdll!DbgBreakPoint ()
   from C:\Windows\SYSTEM32\ntdll.dll
  5    Thread 1780.0x444 0x00000000038933e9 in llvm::DominatorTree::dominates(llvm::Instruction const*, llvm::Instruction const*) const ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
  4    Thread 1780.0x19c4 0x00007ff8d264221a in ntdll!ZwWaitForAlertByThreadId
    () from C:\Windows\SYSTEM32\ntdll.dll
  3    Thread 1780.0x1d60 0x00007ff8d264221a in ntdll!ZwWaitForAlertByThreadId
    () from C:\Windows\SYSTEM32\ntdll.dll
  2    Thread 1780.0xb1c 0x00007ff8d264221a in ntdll!ZwWaitForAlertByThreadId
    () from C:\Windows\SYSTEM32\ntdll.dll
  1    Thread 1780.0x1b7c 0x00007ff8d264079a in ntdll!ZwWaitForSingleObject ()
   from C:\Windows\SYSTEM32\ntdll.dll
(gdb) thread 5
[Switching to thread 5 (Thread 1780.0x444)]
#0  0x00000000038933e9 in llvm::DominatorTree::dominates(llvm::Instruction const*, llvm::Instruction const*) const ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
(gdb) where
#0  0x00000000038933e9 in llvm::DominatorTree::dominates(llvm::Instruction const*, llvm::Instruction const*) const ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#1  0x000000000324db30 in llvm::ScalarEvolution::isLoopBackedgeGuardedByCond(llvm::Loop const*, llvm::CmpInst::Predicate, llvm::SCEV const*, llvm::SCEV const*) ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#2  0x000000000324160b in llvm::ScalarEvolution::getZeroExtendExpr(llvm::SCEV const*, llvm::Type*) ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#3  0x00000000033bd10f in llvm::simplifyUsersOfIV(llvm::PHINode*, llvm::ScalarEvolution*, llvm::DominatorTree*, llvm::LoopInfo*, llvm::SmallVectorImpl<llvm::WeakVH>&, llvm::IVVisitor*) ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#4  0x0000000002bf86ff in (anonymous namespace)::IndVarSimplify::simplifyAndExtend(llvm::Loop*, llvm::SCEVExpander&, llvm::LoopInfo*) [clone .constprop.438]
    ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#5  0x0000000002bfe3e9 in (anonymous namespace)::IndVarSimplify::run(llvm::Loop*) [clone .part.422] ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#6  0x0000000002e05c56 in (anonymous namespace)::IndVarSimplifyLegacyPass::runOnLoop(llvm::Loop*, llvm::LPPassManager&) [clone .part.423] ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#7  0x000000000310563f in llvm::LPPassManager::runOnFunction(llvm::Function&)
    ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#8  0x00000000030f830f in llvm::FPPassManager::runOnFunction(llvm::Function&)
    ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#9  0x0000000002bb74b2 in (anonymous namespace)::CGPassManager::runOnModule(llvm::Module&) ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#10 0x00000000036760a6 in llvm::legacy::PassManagerImpl::run(llvm::Module&) ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#11 0x00000000027d3239 in LLVMRunPassManager ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_llvm-893cdac51017c26f.dll
#12 0x000000006a2ff765 in rustc_trans::back::lto::run_pass_manager::ha9ac3996c7d0c27d ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_trans-9dbf48abd39e3863.dll
#13 0x000000006a2fc473 in rustc_trans::back::lto::LtoModuleTranslation::optimize::h719e586b1cc5ebba ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_trans-9dbf48abd39e3863.dll
#14 0x000000006a3e65a9 in rustc_trans::back::write::execute_work_item::h5b3d73b59b481809 ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_trans-9dbf48abd39e3863.dll
#15 0x000000006a3af743 in std::sys_common::backtrace::__rust_begin_short_backtrace::h612d8b59f6a133dd ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_trans-9dbf48abd39e3863.dll
#16 0x000000006a3cb509 in std::panicking::try::do_call::hc93086c132a5a3ea ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_trans-9dbf48abd39e3863.dll
#17 0x000000006ec4c4a9 in __rust_maybe_catch_panic ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\std-b1b09a5d7798628b.dll
#18 0x000000006a3d7fb9 in _$LT$F$u20$as$u20$alloc..boxed..FnBox$LT$A$GT$$GT$::call_box::h30ec2bcae50c9446 ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\rustc_trans-9dbf48abd39e3863.dll
#19 0x000000006ec140f0 in std::sys_common::thread::start_thread::h55c7159741396635 ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\std-b1b09a5d7798628b.dll
#20 0x000000006ec40769 in std::sys::windows::thread::Thread::new::thread_start::hecbc47bdd027efcc ()
   from C:\msys64\home\we\rust\build\x86_64-pc-windows-gnu\stage1\bin\std-b1b09a5d7798628b.dll
#21 0x00007ff8d1b413d2 in KERNEL32!BaseThreadInitThunk ()
   from C:\Windows\system32\kernel32.dll
#22 0x00007ff8d25c54f4 in ntdll!RtlUserThreadStart ()
   from C:\Windows\SYSTEM32\ntdll.dll
#23 0x0000000000000000 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

[petrochenkov]

cc @alexcrichton @michaelwoerister

[petrochenkov]

This is a regression from maybe couple of weeks or so.

[alexcrichton]

Is this perhaps related to #46449 where #47220 isn't included in beta yet?

[michaelwoerister]

Looks like it.

[michaelwoerister]

@nagisa, do you have time to do a backport of #47220?

[alexcrichton]

@petrochenkov is this still an issue?

[petrochenkov]

@alexcrichton
Yes, this is still an issue.

[petrochenkov]

This was fixed somehow.