<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/73106>73106</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Need support for variadic functions on X86 GISel path
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

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

<pre>
    We are working towards enhancing support for GISel on X86 https://discourse.llvm.org/t/rfc-globalisel-support-for-x86/73424

One of the missing capabilities is variadic functions. X86 bails out of GISel when it sees a variadic function.

Consider C example : https://godbolt.org/z/nEMMEWoYn
and the corresponding llvm IR example: https://godbolt.org/z/PP8rvsfKf

(The flag -mllvm -global-isel-abort=1 seems to have been ignored by clang, so recreated the issue using IR)

Stack dump:

LLVM ERROR: unable to lower arguments: ptr (in function: get_sum)
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-trunk/bin/llc -o /app/output.s -x86-asm-syntax=intel -march=x86 -global-isel <source>
1.      Running pass 'Function Pass Manager' on module '<source>'.
2.      Running pass 'IRTranslator' on function '@get_sum'
 #0 0x0000000003150508 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-trunk/bin/llc+0x3150508)
 #1 0x000000000314de7c SignalHandler(int) Signals.cpp:0:0
 #2 0x00007f0d0f022420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #3 0x00007f0d0eae500b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #4 0x00007f0d0eac4859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #5 0x00000000006a3da6 llvm::RISCVISAInfo::updateImplication() (.cold) RISCVISAInfo.cpp:0:0
 #6 0x000000000353d132 (/opt/compiler-explorer/clang-trunk/bin/llc+0x353d132)
 #7 0x0000000003559ec7 llvm::IRTranslator::runOnMachineFunction(llvm::MachineFunction&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x3559ec7)
 #8 0x000000000254cf20 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0
 #9 0x0000000002a44df2 llvm::FPPassManager::runOnFunction(llvm::Function&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x2a44df2)
#10 0x0000000002a44f71 llvm::FPPassManager::runOnModule(llvm::Module&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x2a44f71)
#11 0x0000000002a46bf0 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x2a46bf0)
#12 0x000000000076c2d0 compileModule(char**, llvm::LLVMContext&) llc.cpp:0:0
#13 0x00000000006ae94a main (/opt/compiler-explorer/clang-trunk/bin/llc+0x6ae94a)
#14 0x00007f0d0eac6083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#15 0x00000000007642fe _start (/opt/compiler-explorer/clang-trunk/bin/llc+0x7642fe)
Program terminated with signal: SIGSEGV
Compiler returned: 139

Relevant source:

`bool X86CallLowering::lowerFormalArguments(...
...
  // TODO: handle variadic function
  if (F.isVarArg())
    return false;
`

</pre>
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