<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/71926>71926</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [X86][GISel] Assertion `isa<const TargetRegisterClass *>(VRegInfo[Reg.id()].first) != 0 && "Register class not set, wrong accessor"` failed
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:X86,
            llvm:globalisel,
            crash-on-valid
      </td>
    </tr>

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

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

<pre>
    Consider the following LLVM IR:
```llvm
define i8 @udiv(i2 %0) {
  %2 = sext i1 true to i8
  %3 = udiv i8 1, %2
  ret i8 %3
}
```
When lowered to x86 via GISel w/ no optimizations enabled through latest llc (`llc -march=x86 -O0 -global-isel in.ll`), the following assert is triggered:
```
llc: /root/llvm-project/llvm/include/llvm/CodeGen/MachineRegisterInfo.h:664: const llvm::TargetRegisterClass* llvm::MachineRegisterInfo::getRegClass(llvm::Register) const: Assertion `isa<const TargetRegisterClass *>(VRegInfo[Reg.id()].first) && "Register class not set, wrong accessor"' 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 -O0 -march=x86 -global-isel <source>
1.      Running pass 'Function Pass Manager' on module '<source>'.
2.      Running pass 'Fast Tile Register Preconfigure' on function '@udiv'
 #0 0x0000000003466158 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3466158)
 #1 0x00000000034638ac SignalHandler(int) Signals.cpp:0:0
 #2 0x00007f2c823e5420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #3 0x00007f2c81ea800b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #4 0x00007f2c81e87859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #5 0x00007f2c81e87729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #6 0x00007f2c81e98fd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #7 0x0000000001bb5bbe (anonymous namespace)::X86FastPreTileConfig::runOnMachineFunction(llvm::MachineFunction&) X86FastPreTileConfig.cpp:0:0
 #8 0x0000000002736b51 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0
 #9 0x0000000002cbfec9 llvm::FPPassManager::runOnFunction(llvm::Function&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x2cbfec9)
#10 0x0000000002cc0101 llvm::FPPassManager::runOnModule(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x2cc0101)
#11 0x0000000002cc0922 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x2cc0922)
#12 0x00000000006a28c3 main (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x6a28c3)
#13 0x00007f2c81e89083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#14 0x000000000075a01e _start (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x75a01e)
Program terminated with signal: SIGSEGV
Compiler returned: 139
```
Godbolt: https://llvm.godbolt.org/z/h3Kq1dz1z.

Haven't investigated it properly, though it seems like `VRegInfo` is empty by the time it is accessed with `VirtReg` being `0x80000000`.
https://github.com/llvm/llvm-project/blob/3af0ff99b1bf92dcac29bc1f9f896b5e41497dc0/llvm/lib/Target/X86/X86FastPreTileConfig.cpp#L668-L673

cc/ @RKSimon
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJy8V01v4zgS_TX0hbBBUdbXwQfHbmeCSWOCZNA7N4OiSjK3KVJLUonTv35BSnastA_p2ewEiRFL5KvHqqfSK2ataBTACiU3KNnOWO8O2qyYcloJXRvRHMA5PSt19braaGVFBQa7A-BaS6lfhGrw_f23r_juEcVrRLaIrFFKhl8pn9vhUgW1UIBFjtGS9JV4RjQXFCOaEEQLjLKbYR32lyhG8RZbODosIuxMD9hpLPKLJXFY4oE8ZoToJmw8rTDgQiyaxCOlbPuO2_D1XwdQWOoXMFD5IMc8xc-C4du7J5D4BdEdVhrrzolW_GBOaGUxKFZKv_xgdN8csGQOrMNScoxoHo7N8bxlhh9QvPWI8z8InjdSl0zOhQWJhVpI6UnQwlOfppNZC8ZhYbEzomk8tZ9TO3yVkqN4jRHdGa0dojuf8Xln9L-Bn74iuhOKy76CtwsbXcEtKER3Xxk_CAWP0AjrwNypWi8OKF6n6dIjc63C0Z5bTyFe_8lMA-60eiOZtYiuLxZcwRtuDNvGHfnbhtNKL4MQzYddhxQIrTBKibAMxZuByZX4GNE1ir8gmn97hCYETG4eoVmIypeDFijZLmphrAtKoymiKUaUnkAwDyhKO2zB-XK8GO3LwDlYqw2iFNEM10xIqBZD3h_uv6yfvmDbl61wmOGyb7CBThvnRXRwrrP-dHSH6K4R7tCXC67bt_y_K5OwtgfrxcZUhcdqBVVww-wBl4x_d4ZxGMM_Oca_46pvu7MwyAKR4sHoxrAWM9P0LShnR3Hozkfhuu2EBDOHYye18SnfcclUM2endNu5M736juiuFCrw5HiuPQTrOg_Uu653C4vnxzydM9vO7aty7IjirVAO5KD0ifQvZY_ijdW94eDrFWhHnvZjr5QXfjdUM9v1iofiP_gLX5lijSebYa1wq6tegl81AaPZmBp6FZB56QgJ-Fz0BwNcq1o0vYERuj6F9eCnLpWNLQXRmGByJKefeJmmUZJfKN--2uGfByOUCyX609dsonbDXvbaOgOsDUrcYKFGXeb_Y6EQvSHHkZZX_Zl39I53nDOOn0SjmPyNqUp6_HykMVy2C955aZHwdwaiI1BWU57TGJIlJXi_N2CdNrA3bjyFFCWiu2Oe7tPlXArVH-eN6ocbnTsYYNXC6gUJjKPlkpIJ3_gyTAQsJ6TEhgkLH8DnHjkNyMuYkHKCvJwi51meFJiV-kPML5ApzZNigpy8R87ONf0wZkanmOkUs8jrKv01zDiuq3SCmV1qISrLpCxDVpnS6rXVvcWKtWC7oNti0OxfeeofoAcD_hHahKdmVHOv_lBjxz89tBO5_3TPs8HXAK8rLr-kS7M4LZPo55fNCd63iwtiVxm9o4JovuiYcYtgQ67gXedVTHjxsgZeXPDaPfitp8b1y4w-oxGMpM7F932ATFlzEpHoA6y_hpY7ret46XMZB0ITxtF7xgWlF4wlNIy_jl33jftd28kz_3-Ed-E9wgVvesmbpIzmPMYtE-qzgg6Qk5jv2mZekDzG-73vCHvrmHH7CwIfbUpLkk-jLCcnyxJGIsAD_medbQA9Rz2ZGgemFYo5qPCLcAdsw6vKO5ynu9unL7ffhuWbMbCfAXqjgnfGUVxc9c-3uiq1DJZzatq8ZBbNcHehTYPo7geiu0P8-3-i6kf0Y3Qbw-dv7Nl76cxhoZ7BOtEElsLhzugOjHwdTH6YFoS3mdBaLMV38Pb27FpT4j0_tJ17xeVrsH9OtOB3CDva0dPh_T5hvBH220rwbgelhBzzsTIoJSPHX3ajpdReHDGrSV0XRRmVdUErzjgtSh7VRZ0XaZnAMloWWcXJBU4Q1WDREd39lafD5_VmT-P7NM3n92kWXyaTc--D0ZI8_v4kWq1m1SquirhgM1hFaVGkUZJE0eywyghPScbyOEkYFJwSntUZy3Mas5jVZT4TK0p8D4lIFNEkihasYlWaJgkpa1imtERLAi0TchGqrU0zC0Z8lUUFTWeSlSBtmIsp9Q4cVDW8DcNEsEGUjo1lsLje4Z7vBN8-12r-zKSfQ6ifrc0qZLrsG4uWRArr7FtoJ5wMU7gPkGxRchNmUJRs_6_TUOTnaPI3x6KUjGPRrDdy9ffHnpDw_wYAAP__LlUJ5Q">