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[x86]: Cannot select: constant:i128<0> for llvm.maximum.f128 #139381
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@llvm/issue-subscribers-backend-x86
Author: None (Urgau)
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I'm seeing an error when trying to use llvm.minimum.f128 and llvm.maximum.f128 on x86.; Function Attrs: mustprogress nofree nosync nounwind nonlazybind readnone uwtable willreturn define fp128 @<!-- -->call_maximum_fp128_x86(fp128 %x, fp128 %y) unnamed_addr #<!-- -->0 { start: %0 = tail call fp128 @<!-- -->llvm.maximum.f128(fp128 %x, fp128 %y) #<!-- -->2 ret fp128 %0 } ; Function Attrs: mustprogress nofree nosync nounwind readnone speculatable willreturn declare fp128 @<!-- -->llvm.maximum.f128(fp128, fp128)
LLVM ERROR: Cannot select: 0x3ade0080: i8 = setcc 0x3addc768, Constant:i128<0>, seteq:ch 0x3addc768: i128 = bitcast 0x3addbe08 0x3addbe08: f128,ch = CopyFromReg 0x3ad783c0, Register:f128 %1 0x3addbd90: f128 = Register %1 0x3addfdb0: i128 = Constant<0> In function: call_maximum_fp128_x86 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 <source> 1. Running pass 'Function Pass Manager' on module '<source>'. 2. Running pass 'X86 DAG->DAG Instruction Selection' on function '@<!-- -->call_maximum_fp128_x86' #<!-- -->0 0x0000000003b49548 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-trunk/bin/llc+0x3b49548) #<!-- -->1 0x0000000003b47104 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0 #<!-- -->2 0x00007e645a842520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520) #<!-- -->3 0x00007e645a8969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc) #<!-- -->4 0x00007e645a842476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476) #<!-- -->5 0x00007e645a8287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3) #<!-- -->6 0x0000000000784592 llvm::UniqueStringSaver::save(llvm::Twine const&) (.cold) StringSaver.cpp:0:0 #<!-- -->7 0x00000000038f0888 llvm::SelectionDAGISel::CannotYetSelect(llvm::SDNode*) (/opt/compiler-explorer/clang-trunk/bin/llc+0x38f0888) #<!-- -->8 0x00000000038f6bf9 llvm::SelectionDAGISel::SelectCodeCommon(llvm::SDNode*, unsigned char const*, unsigned int) (/opt/compiler-explorer/clang-trunk/bin/llc+0x38f6bf9) #<!-- -->9 0x0000000001f70c6a (anonymous namespace)::X86DAGToDAGISel::Select(llvm::SDNode*) X86ISelDAGToDAG.cpp:0:0 #<!-- -->10 0x00000000038edd74 llvm::SelectionDAGISel::DoInstructionSelection() (/opt/compiler-explorer/clang-trunk/bin/llc+0x38edd74) #<!-- -->11 0x00000000038fc882 llvm::SelectionDAGISel::CodeGenAndEmitDAG() (/opt/compiler-explorer/clang-trunk/bin/llc+0x38fc882) #<!-- -->12 0x00000000038ff1fa llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x38ff1fa) #<!-- -->13 0x00000000039010d6 llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x39010d6) #<!-- -->14 0x00000000038ed8f1 llvm::SelectionDAGISelLegacy::runOnMachineFunction(llvm::MachineFunction&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x38ed8f1) #<!-- -->15 0x0000000002bb4a78 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) MachineFunctionPass.cpp:0:0 #<!-- -->16 0x0000000003135322 llvm::FPPassManager::runOnFunction(llvm::Function&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x3135322) #<!-- -->17 0x00000000031355b1 llvm::FPPassManager::runOnModule(llvm::Module&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x31355b1) #<!-- -->18 0x0000000003136f19 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/opt/compiler-explorer/clang-trunk/bin/llc+0x3136f19) #<!-- -->19 0x00000000008bec3f compileModule(char**, llvm::LLVMContext&) llc.cpp:0:0 #<!-- -->20 0x000000000079977e main (/opt/compiler-explorer/clang-trunk/bin/llc+0x79977e) #<!-- -->21 0x00007e645a829d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90) #<!-- -->22 0x00007e645a829e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40) #<!-- -->23 0x00000000008b6705 _start (/opt/compiler-explorer/clang-trunk/bin/llc+0x8b6705) Program terminated with signal: SIGSEGV Compiler returned: 139The problem is that the expansion for llvm.maximum uses is_fpclass, which in turn expands to an illegal i128 type.
And the reason this doesn't happen with direct uses of llvm.is.fpclass is this most wonderful hack:
llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
Lines 7036 to 7044 in 7fb2590
So the IS_FPCLASS usage in
is over-kill, as that code really only needs to distinguish the sign bit.llvm-project/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
Lines 8617 to 8622 in b4bc8c6
Doing that is still tricky though, because we can't use a plain bitcast, we have to cast through stack temporary. It looks like legalization has a helper for this use case here:
Of course, the code this will generate is very bad.
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I'm seeing an error when trying to use llvm.minimum.f128 and llvm.maximum.f128 on x86.
https://godbolt.org/z/z3arKMfjo