WebAssembly backend assertion failure with unreachable

[majaha]

This code:

target triple = "wasm32-unknown-unknown"

declare void @llvm.trap() cold noreturn nounwind
declare i32 @return_i32()
declare void @take_i32(i32)

define void @assert_fail() {
  %a = call i32 @return_i32()
  call void @llvm.trap()
  call void @take_i32(i32 %a)
  ret void
}

causes an assertion failure:

llc: /root/llvm-project/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp:168: void query(const llvm::MachineInstr&, bool&, bool&, bool&, bool&): Assertion `!MI.isTerminator()' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/llc -o /app/output.s -x86-asm-syntax=intel <source>
1.	Running pass 'Function Pass Manager' on module '<source>'.
2.	Running pass 'WebAssembly Register Stackify' on function '@assert_fail'
 #0 0x00000000034145c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x34145c8)
 #1 0x0000000003411cfc SignalHandler(int) Signals.cpp:0:0
 #2 0x00007f9f6cda2420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #3 0x00007f9f6c86500b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #4 0x00007f9f6c844859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #5 0x00007f9f6c844729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #6 0x00007f9f6c855fd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #7 0x0000000001ac853e query(llvm::MachineInstr const&, bool&, bool&, bool&, bool&) WebAssemblyRegStackify.cpp:0:0
 #8 0x0000000001ac924f isSafeToMove(llvm::MachineOperand const*, llvm::MachineOperand const*, llvm::MachineInstr const*, llvm::WebAssemblyFunctionInfo const&, llvm::MachineRegisterInfo const&) (.isra.0) WebAssemblyRegStackify.cpp:0:0
 #9 0x0000000001acc728 (anonymous namespace)::WebAssemblyRegStackify::runOnMachineFunction(llvm::MachineFunction&) WebAssemblyRegStackify.cpp:0:0
#10 0x00000000026f1e21 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0
#11 0x0000000002c70009 llvm::FPPassManager::runOnFunction(llvm::Function&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x2c70009)
#12 0x0000000002c70241 llvm::FPPassManager::runOnModule(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x2c70241)
#13 0x0000000002c70a62 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x2c70a62)
#14 0x0000000000760e52 compileModule(char**, llvm::LLVMContext&) llc.cpp:0:0
#15 0x000000000069ec46 main (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x69ec46)
#16 0x00007f9f6c846083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#17 0x00000000007577ee _start (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x7577ee)
Program terminated with signal: SIGSEGV
Compiler returned: 139

Godbolt link

It seems like this line in WebAssemblyRegStackify::runOnMachineFunction calls isSafeToMove()
which calls query() in two places
which has the line assert(!MI.isTerminator());
which trips over the fact that unreachable (what @llvm.trap() is compiled to) is defined as a terminator

[llvmbot]

@llvm/issue-subscribers-backend-webassembly

Author: Matt Harding (majaha)

This code: ```llvm target triple = "wasm32-unknown-unknown"

declare void @llvm.trap() cold noreturn nounwind
declare i32 @return_i32()
declare void @take_i32(i32)

define void @assert_fail() {
%a = call i32 @return_i32()
call void @llvm.trap()
call void @take_i32(i32 %a)
ret void
}

causes an assertion failure:

llc: /root/llvm-project/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp:168: void query(const llvm::MachineInstr&, bool&, bool&, bool&, bool&): Assertion `!MI.isTerminator()' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0. Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/llc -o /app/output.s -x86-asm-syntax=intel <source>

1. Running pass 'Function Pass Manager' on module '<source>'.
2. Running pass 'WebAssembly Register Stackify' on function '@assert_fail'
   #0 0x00000000034145c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x34145c8)
   #1 0x0000000003411cfc SignalHandler(int) Signals.cpp:0:0
   #2 0x00007f9f6cda2420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
   #3 0x00007f9f6c86500b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
   #4 0x00007f9f6c844859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
   #5 0x00007f9f6c844729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
   #6 0x00007f9f6c855fd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
   #7 0x0000000001ac853e query(llvm::MachineInstr const&, bool&, bool&, bool&, bool&) WebAssemblyRegStackify.cpp:0:0
   #8 0x0000000001ac924f isSafeToMove(llvm::MachineOperand const*, llvm::MachineOperand const*, llvm::MachineInstr const*, llvm::WebAssemblyFunctionInfo const&, llvm::MachineRegisterInfo const&) (.isra.0) WebAssemblyRegStackify.cpp:0:0
   #9 0x0000000001acc728 (anonymous namespace)::WebAssemblyRegStackify::runOnMachineFunction(llvm::MachineFunction&) WebAssemblyRegStackify.cpp:0:0
   #10 0x00000000026f1e21 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0
   #11 0x0000000002c70009 llvm::FPPassManager::runOnFunction(llvm::Function&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x2c70009)
   #12 0x0000000002c70241 llvm::FPPassManager::runOnModule(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x2c70241)
   #13 0x0000000002c70a62 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x2c70a62)
   #14 0x0000000000760e52 compileModule(char**, llvm::LLVMContext&) llc.cpp:0:0
   #15 0x000000000069ec46 main (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x69ec46)
   #16 0x00007f9f6c846083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
   #17 0x00000000007577ee _start (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x7577ee)
   Program terminated with signal: SIGSEGV
   Compiler returned: 139

[Godbolt link](https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:llvm,selection:(endColumn:25,endLineNumber:7,positionColumn:25,positionLineNumber:7,selectionStartColumn:25,selectionStartLineNumber:7,startColumn:25,startLineNumber:7),source:'target+triple+%3D+%22wasm32-unknown-unknown%22%0A%0Adeclare+void+@<!-- -->llvm.trap()+cold+noreturn+nounwind%0Adeclare+i32+@<!-- -->return_i32()%0Adeclare+void+@<!-- -->take_i32(i32)%0A%0Adefine+void+@<!-- -->assert_fail()+%7B%0A++%25a+%3D+call+i32+@<!-- -->return_i32()%0A++call+void+@<!-- -->llvm.trap()%0A++call+void+@<!-- -->take_i32(i32+%25a)%0A++ret+void%0A%7D'),l:'5',n:'0',o:'LLVM+IR+source+%231',t:'0')),k:28.102455380752453,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:compiler,i:(compiler:llc-assertions-trunk,deviceViewOpen:'1',filters:(b:'0',binary:'1',binaryObject:'1',commentOnly:'0',debugCalls:'1',demangle:'0',directives:'0',execute:'1',intel:'0',libraryCode:'0',trim:'1'),flagsViewOpen:'1',fontScale:14,fontUsePx:'0',j:2,lang:llvm,libs:!(),options:'___+',overrides:!(),paneName:'+llc+wasm',selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:'5',n:'0',o:'+llc+wasm',t:'0')),k:24.857851593775443,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:output,i:(compilerName:'llc+(assertions+trunk)',editorid:1,fontScale:14,fontUsePx:'0',j:2,wrap:'1'),l:'5',n:'0',o:'Output+of+llc+(assertions+trunk)+(Compiler+%232)',t:'0')),k:47.03969302547212,l:'4',n:'0',o:'',s:0,t:'0')),l:'2',n:'0',o:'',t:'0')),version:4)

It seems like [this line in WebAssemblyRegStackify::runOnMachineFunction calls isSafeToMove()](https://github.com/llvm/llvm-project/blob/bccf2c8468e2f364f8c364d613ffb78d61b67ceb/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp#L878C44-L878C44)
which [calls query() in two places](https://github.com/llvm/llvm-project/blob/bccf2c8468e2f364f8c364d613ffb78d61b67ceb/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp#L399C3-L399C8)
which has the line [`assert(!MI.isTerminator());`](https://github.com/llvm/llvm-project/blob/bccf2c8468e2f364f8c364d613ffb78d61b67ceb/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp#L168C25-L168C25)
which trips over the fact that unreachable (what `@<!-- -->llvm.trap()` is compiled to) [is defined as a terminator](https://github.com/llvm/llvm-project/blob/bccf2c8468e2f364f8c364d613ffb78d61b67ceb/llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td#L109C9-L109C9)
</details>

[majaha]

Possibly the solution is to have two kinds of UNREACHABLE instruction, one which is a terminator for llvm's unreachable, and one which isn't for @llvm.trap().