JuliaGPU / JuliaGPU/GPUCompiler.jl
`exp` on `SIMD.Vec` triggers LLVM error
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bug
ptx
- Dominant language
- Julia
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- Forks
- 69
- Avg merge
- 1d 12h
- Merged PRs (30d)
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Description
To reproduce
The Minimal Working Example (MWE) for this bug:
using CUDA
using Adapt
using SIMD
using KernelAbstractions
@inline function vload(::Type{SIMD.Vec{N, T}}, ptr::Core.LLVMPtr{T, AS}) where {N, T, AS}
alignment = sizeof(T) * N
vec_ptr = Base.bitcast(Core.LLVMPtr{SIMD.Vec{N, T}, AS}, ptr)
return unsafe_load(vec_ptr, 1, Val(alignment))
end
@inline function vstore!(ptr::Core.LLVMPtr{T, AS}, x::SIMD.Vec{N, T}) where {N, T, AS}
alignment = sizeof(T) * N
vec_ptr = Base.bitcast(Core.LLVMPtr{SIMD.Vec{N, T}, AS}, ptr)
unsafe_store!(vec_ptr, x, 1, Val(alignment))
return
end
@kernel function ker!(y, x)
i = @index(Global)
v = vload(SIMD.Vec{4, Float32}, pointer(x))
v = exp(v)
vstore!(pointer(y), v)
end
function tt(kab)
x = Adapt.adapt(kab, ones(Float32, 4))
y = Adapt.adapt(kab, ones(Float32, 4))
ker!(kab)(y, x; ndrange=1)
@show y
return
end
tt(CUDABackend())
Error:
ERROR: LLVM error: Undefined external symbol "expf"
Stacktrace:
[1] handle_error(reason::Cstring)
@ LLVM ~/.julia/packages/LLVM/b3kFs/src/core/context.jl:194
[2] LLVMTargetMachineEmitToMemoryBuffer(T::LLVM.TargetMachine, M::LLVM.Module, codegen::LLVM.API.LLVMCodeGenFileType, ErrorMessage::Base.RefValue{Cstring}, OutMemBuf::Base.RefValue{Ptr{…}})
@ LLVM.API ~/.julia/packages/LLVM/b3kFs/lib/16/libLLVM.jl:11138
[3] emit(tm::LLVM.TargetMachine, mod::LLVM.Module, filetype::LLVM.API.LLVMCodeGenFileType)
@ LLVM ~/.julia/packages/LLVM/b3kFs/src/targetmachine.jl:118
[4] mcgen(job::GPUCompiler.CompilerJob, mod::LLVM.Module, format::LLVM.API.LLVMCodeGenFileType)
@ GPUCompiler ~/.julia/packages/GPUCompiler/OGnEB/src/mcgen.jl:75
[5] mcgen(job::GPUCompiler.CompilerJob{GPUCompiler.PTXCompilerTarget, CUDA.CUDACompilerParams}, mod::LLVM.Module, format::LLVM.API.LLVMCodeGenFileType)
@ CUDA ~/.julia/packages/CUDA/1kIOw/src/compiler/compilation.jl:127
[6] macro expansion
@ ~/.julia/packages/GPUCompiler/OGnEB/src/driver.jl:400 [inlined]
[7] emit_asm(job::GPUCompiler.CompilerJob, ir::LLVM.Module; strip::Bool, validate::Bool, format::LLVM.API.LLVMCodeGenFileType)
@ GPUCompiler ~/.julia/packages/GPUCompiler/OGnEB/src/utils.jl:110
[8] emit_asm
@ ~/.julia/packages/GPUCompiler/OGnEB/src/utils.jl:108 [inlined]
[9] codegen(output::Symbol, job::GPUCompiler.CompilerJob; toplevel::Bool, libraries::Bool, optimize::Bool, cleanup::Bool, validate::Bool, strip::Bool, only_entry::Bool, parent_job::Nothing)
@ GPUCompiler ~/.julia/packages/GPUCompiler/OGnEB/src/driver.jl:120
...
Contributor guide
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the provided Julia MWE with CUDA, Adapt, SIMD, and KernelAbstractions to reproduce the LLVM error. Trace compilation of the exp(v) call through the GPUCompiler path and inspect why expf remains an undefined external symbol. Done means the kernel compiles and runs without this LLVM error.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- julia
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100