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

[antoniofrighetto]

Consider the following LLVM IR:

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.

llvm-project/llvm/lib/Target/X86/X86FastPreTileConfig.cpp

Lines 668 to 673 in 3af0ff9

	for (unsigned I = 0, E = NumVirtRegs; I != E; ++I) {
	Register VirtReg = Register::index2VirtReg(I);
	if (MRI->getRegClass(VirtReg)->getID() == X86::TILERegClassID) {
	HasVirtTileReg = true;
	break;
	}

cc/ @RKSimon

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Antonio Frighetto (antoniofrighetto)

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.

llvm-project/llvm/lib/Target/X86/X86FastPreTileConfig.cpp

Lines 668 to 673 in 3af0ff9

	for (unsigned I = 0, E = NumVirtRegs; I != E; ++I) {
	Register VirtReg = Register::index2VirtReg(I);
	if (MRI->getRegClass(VirtReg)->getID() == X86::TILERegClassID) {
	HasVirtTileReg = true;
	break;
	}

cc/ @RKSimon

[phoebewang]

@e-kud has a patch #70754 to solve it.