<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/63182>63182</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Wasm EH cannot handle unwind backedges
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:WebAssembly
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          aheejin
      </td>
    </tr>
</table>

<pre>
    test.ll:
```ll
target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
target triple = "wasm32-unknown-emscripten"

declare i32 @__gxx_wasm_personality_v0(...)

declare void @foo()

define void @test() personality ptr @__gxx_wasm_personality_v0 {
bb0:
  invoke void @foo()
          to label %bb1 unwind label %bb2

bb1: ; preds = %bb4, %bb0
 unreachable

bb2:                                              ; preds = %bb4, %bb0
  %catchswitch = catchswitch within none [label %bb3] unwind to caller

bb3:                                              ; preds = %bb2
  %catchpad = catchpad within %catchswitch [ptr null]
  catchret from %catchpad to label %bb4

bb4: ; preds = %bb3
  invoke void @foo()
          to label %bb1 unwind label %bb2
}
```

```console
llc -mattr=+exception-handling -wasm-enable-eh -exception-model=wasm -verify-machineinstrs test.ll

llc: /usr/local/google/home/aheejin/llvm-git/llvm/include/llvm/ADT/SmallVector.h:312: llvm::SmallVectorTemplateCommon::reference llvm::SmallVectorTemplateCommon<const llvm::MachineBasicBlock *>::back() [T = const llvm::MachineBasicBlock *]: Assertion `!empty()' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: /usr/local/google/home/aheejin/llvm-git/install.release/bin/llc -mattr=+exception-handling -wasm-enable-eh -exception-model=wasm -verify-machineinstrs t.ll
1.      Running pass 'Function Pass Manager' on module 't.ll'.
2.      Running pass 'WebAssembly CFG Stackify' on function '@test'
 #0 0x00007f669b1e29b3 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/usr/local/google/home/aheejin/llvm-git/install.release/bin/../lib/libLLVMSupport.so.17git+0x1e29b3)
 #1 0x00007f669b1e06ae llvm::sys::RunSignalHandlers() (/usr/local/google/home/aheejin/llvm-git/install.release/bin/../lib/libLLVMSupport.so.17git+0x1e06ae)
 #2 0x00007f669b1e2d4a SignalHandler(int) Signals.cpp:0:0
 #3 0x00007f669ae5af90 (/lib/x86_64-linux-gnu/libc.so.6+0x3bf90)
 #4 0x00007f669aea9ccc __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #5 0x00007f669ae5aef2 raise ./signal/../sysdeps/posix/raise.c:27:6
 #6 0x00007f669ae45472 abort ./stdlib/abort.c:81:7
 #7 0x00007f669ae45395 _nl_load_domain ./intl/loadmsgcat.c:1177:9
 #8 0x00007f669ae53df2 (/lib/x86_64-linux-gnu/libc.so.6+0x34df2)
 #9 0x00007f669e36b882 (anonymous namespace)::WebAssemblyCFGStackify::placeMarkers(llvm::MachineFunction&) WebAssemblyCFGStackify.cpp:0:0
#10 0x00007f669e3636c2 (anonymous namespace)::WebAssemblyCFGStackify::runOnMachineFunction(llvm::MachineFunction&) WebAssemblyCFGStackify.cpp:0:0
#11 0x00007f669d1af92d llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/usr/local/google/home/aheejin/llvm-git/install.release/bin/../lib/libLLVMCodeGen.so.17git+0x5af92d)
#12 0x00007f669b8448ab llvm::FPPassManager::runOnFunction(llvm::Function&) (/usr/local/google/home/aheejin/llvm-git/install.release/bin/../lib/libLLVMCore.so.17git+0x4448ab)
#13 0x00007f669b84cb81 llvm::FPPassManager::runOnModule(llvm::Module&) (/usr/local/google/home/aheejin/llvm-git/install.release/bin/../lib/libLLVMCore.so.17git+0x44cb81)
#14 0x00007f669b845365 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/usr/local/google/home/aheejin/llvm-git/install.release/bin/../lib/libLLVMCore.so.17git+0x445365)
#15 0x00005589ee6ef3f6 compileModule(char**, llvm::LLVMContext&) llc.cpp:0:0
#16 0x00005589ee6ed01d main (/usr/local/google/home/aheejin/llvm-git/install.release/bin/llc+0x1201d)
#17 0x00007f669ae4618a __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#18 0x00007f669ae46245 call_init ./csu/../csu/libc-start.c:128:20
#19 0x00007f669ae46245 __libc_start_main ./csu/../csu/libc-start.c:368:5
#20 0x00005589ee6e99c1 _start (/usr/local/google/home/aheejin/llvm-git/install.release/bin/llc+0xe9c1)
Aborted
```

It looks the backedge formed by the unwind edge from `bb4` to `bb2` is causing the problem.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzMWEuP27YW_jWcDSFDIvVceGGP47RAght0gnZpUNSRzQ5FCiSVGf_7C1LyQx7nIulN2g48skUdfjzfeZJi1oq9AliibI2yzQMb3EGbJTsA_CnUQ62b49KBdQspEV2heIPiFcrj8SPlOOCY2YPDDXNMsqMeHEZ0gxEhEHWIriDqEV1REi6RyFNEV3kaqTCSp9FTQkpEyAzLGdFLOOG8MNtREg3qWekXFUFnuRG9A3WeNl4b4JIZwIISjNJ4t9u_vu785F0PxmrFpHDH3ZcYkXKxWCBS3Zv8RYvGz261Rl6xG6FWqIuMN80ohK9WwL0z_3N9jIr1iFfX8dmuGAv1RT9_VQN8_nMaS1aDxIhkdZ3gQb0I1VyPzcxS1wmiK4zoGvcGGjuZNavrFJHH8Vc8rTEoA4wfWC1hDuGdhb_r75vW83ecOX6wL8LxQxC9vn8R7iAUVloBRtn6iiJF2ebE3GnMmZRg5jrTH6EzudW0Z81FTX8z6XjLJFv7OFCDlCjbnECChAGHW6O7GeTcqemcSfoVB9KfFzrF5ibdp1uSoGwtOrYHT4uUB-d664OYbBHZ7oU7DPWC6w6RrZRfTl9Rb_SfwB0iW2YtOIvItixIXlUFItuEEpLRtIko5WmUxi2Las5ZlFW8ZoQUaQz0JhPPanGtrD5Fq5QcRx1zziC6QWQNrxx6J7SKDkw1Uqg9jnxCRqB8iEdwwNFFptMNSEQ3XgJHX8CI9hh1jB-EAqGsMxafiuGVJlLy4B2yHazxdDVn0ptC670ERLYH3fmvqaieDLIX7mIiobgcGrgMrDafEdk-dUzK34E7bRYHXz-TkIZBhq4QXV0JfIaul8zBo-46rcbHBlowoDh825RHb0t3Jftx5L5mVvC11PwZI7JC9N34tGb8eap-KFt_HpPimxCyjaexshaMNzz2niQJdL07TmFLCtwyIaFZjEb-9OHd6ukdtkPdCYcZroc9NtBr43xIf3cMCmsH8DGImWrwZH3sDoC5YfaAPTVnGIdp-SfH-DNuhq4_l-t4MWbUJ6P3hnWYmf3QgXL2rweDjzEm5cKABGa9WD2J_OyoPod0MrH6bVDK4_bMWoxIsR0UD6765Ac-MsX2YLyXtMKdbgbfrEkRcEgxGY18BesPqL3ru1oe8eP2PQ7GFe1xgmtPSyFSnHtsMRUyRGiM49c4juOizfOqToBUNb2KOHu0449PRigXsD97TyJSXoQMe9lp6wywDpHcdyWhXAhkH34_0nd-n7GVoh6vHz78_vFp6H3cLqxeJEWYvI5fRxqXgo0ITW54xjmDezx_G9ST2Csmf_HBAMaecvIfo-I1nVEhty5rUoZnSiNSTh4Yh-2C9z7X4vB_BqLXQAwy1lbxRHRU7LXMd3kaSaGG12ivhvEB9xrmQTtat1U8Uy6dY7KKc453u94dDLBm9yyk3Imul-Czm4XI9IZQvfMWvRZb-EaQ-l5d5Bf87FZnaAk2TFgIODbwPZnXHm0Dva9MvbbiFZFtkAzIpPAb5gtwPgdOs7QgmNW-JgYo14w2CUMBofQbwatUKm4RaJXhnZI7qVmza3THxEhWqEDWD3d2z9kIlySFV-nKluUNV9q05Dv9kzYtmfmnusYEmtdlGTCZ0urY6cFixTqwfcjxasyJqxLzuH1_LjDhWS8Zh4_MPI-p8qZXnUpdKAwVvg_1Njx9xsY3qtKc_1-qmkH9R71R64eqPKsyTcLaijRv-_dpAV_9r1S7q9ONMn9DGXrUDbwHNS9DWaBy2TUSmszLUJmmJauvuG4_eXqn3vYvZGlgTjENDGYU6Q1FXpfJN1D8GFr4PLSmoX-Sntd-Ri-9oZfRPLuiJ2HP-JQ7V0R_7Xp5JvuvI-k5zEieGkaWlRVADi1tc8x11wsJZ0fxAzN-K-0_j1cmGFdRDl7dREtKfj_185t1mjhpcCj5P9wS_owU9gYkTuY5eduC8qRkeLfzTWFnHTNu50_2u3Mn4nZ42yunXnxvUjg3Fb4n08ui5e2iJM3CG4SdUMLdrjP-9OBRAB97Hyl9S74yZ3UPdMbkHom74DT34NkZm8Q3rqoqnuAR9ec5Cyp-yb6V30RAc_-dQLj-6rDU-tmGY5Q_QEGzB9xq00GD62MYnl43jE_CG5A8rusU5bE_xoUb4m-ExZwN1p8a_LTe6FpCt3holrSpaMUeYJnkZZ5USVomD4dlE9M0b0raJowXBUnysiJ10WYMKlqQIn8QSxITGudxGftGkCzqJk5bltAs5W0RpwylMXRMyIU30EKb_UM4Iy5zmpTkIbwfseEtKSGBm2rmvRsRgrLNg1kGA9fD3qI0lsI6e0F0wklY_uHPYe9-wZwppR0OR7izZU52sw-Dkcu_fq4Nav83AAD__7rxlr8">