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[AArch64] -fp-armv8 crash using select with half #129394
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[-]Crash related to `half` with `aarch64-unknown-none` and `-fp-armv8`[/-][+][AArch64] `-fp-armv8` crash using `select` with `half` (regression)[/+]on Mar 1, 2025 - added 2 commits that reference this issue
on Mar 1, 2025 - changed the title
[-][AArch64] `-fp-armv8` crash using `select` with `half` (regression)[/-][+][AArch64] `-fp-armv8` crash using `select` with `half`[/+]on Mar 1, 2025 - added 2 commits that reference this issue
on Mar 1, 2025 @llvm/issue-subscribers-backend-aarch64
Author: Trevor Gross (tgross35)
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With LLVM20, the following hits an unreachable:target triple = "aarch64-unknown-linux-gnu" define half @<!-- -->problem(i16 %x, i1 %sel) #<!-- -->1 { %x1 = select i1 %sel, half 0xH0000, half 0xH0001 ret half %x1 } attributes #<!-- -->1 = { "target-features" = "-fp-armv8" }
Don't know how to custom expand this UNREACHABLE executed at /root/llvm-project/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp:27434! 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 <source> 1. Running pass 'Function Pass Manager' on module '<source>'. 2. Running pass 'AArch64 Instruction Selection' on function '@<!-- -->problem' #<!-- -->0 0x0000000003dea3d8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3dea3d8) #<!-- -->1 0x0000000003de7d94 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0 #<!-- -->2 0x00007f2088c42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520) #<!-- -->3 0x00007f2088c969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc) #<!-- -->4 0x00007f2088c42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476) #<!-- -->5 0x00007f2088c287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3) #<!-- -->6 0x0000000003d3d47a (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3d3d47a) #<!-- -->7 0x0000000000d18395 llvm::AArch64TargetLowering::ReplaceNodeResults(llvm::SDNode*, llvm::SmallVectorImpl<llvm::SDValue>&, llvm::SelectionDAG&) const (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0xd18395) #<!-- -->8 0x0000000003c2ed76 llvm::DAGTypeLegalizer::CustomLowerNode(llvm::SDNode*, llvm::EVT, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3c2ed76) #<!-- -->9 0x0000000003cac753 llvm::DAGTypeLegalizer::SoftPromoteHalfResult(llvm::SDNode*, unsigned int) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3cac753) #<!-- -->10 0x0000000003c2f44b llvm::DAGTypeLegalizer::run() (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3c2f44b) #<!-- -->11 0x0000000003c30699 llvm::SelectionDAG::LegalizeTypes() (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3c30699) #<!-- -->12 0x0000000003b9873b llvm::SelectionDAGISel::CodeGenAndEmitDAG() (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3b9873b) #<!-- -->13 0x0000000003b9c3b5 llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3b9c3b5) #<!-- -->14 0x0000000003b9d655 llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3b9d655) #<!-- -->15 0x0000000003b8dacf llvm::SelectionDAGISelLegacy::runOnMachineFunction(llvm::MachineFunction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3b8dacf) #<!-- -->16 0x0000000002d6e5da llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0 #<!-- -->17 0x00000000033866ef llvm::FPPassManager::runOnFunction(llvm::Function&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x33866ef) #<!-- -->18 0x0000000003386aa1 llvm::FPPassManager::runOnModule(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3386aa1) #<!-- -->19 0x0000000003387341 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x3387341) #<!-- -->20 0x00000000008968d3 compileModule(char**, llvm::LLVMContext&) llc.cpp:0:0 #<!-- -->21 0x0000000000784dee main (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x784dee) #<!-- -->22 0x00007f2088c29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90) #<!-- -->23 0x00007f2088c29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40) #<!-- -->24 0x000000000088d0b5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/llc+0x88d0b5) Program terminated with signal: SIGSEGV Compiler returned: 139This worked correctly in LLVM19
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With LLVM20, the following hits an unreachable:
This worked correctly in LLVM19
https://llvm.godbolt.org/z/Ge8ozGxYG