Why is LoopVectorization deprecated?

ChrisRackauckas · July 25, 2024, 8:45pm

github.com/JuliaSIMD/LoopVectorization.jl

LoopVectorization.jl causing segfaults on 1.11

opened 01:59PM - 10 Jan 24 UTC

closed 11:38AM - 07 May 24 UTC

LoopVectorization.jl's generated IR seems to cause segfaults on 1.11, as observe…d on PkgEval with at least 6 packages (MCPhylo,jl, LocalPoly.jl, VectorizedReduction.jl, NaNStatistics.jl, TimeSeriesClassification.jl, PlmDCA.jl). See this report for details: https://s3.amazonaws.com/julialang-reports/nanosoldier/pkgeval/by_hash/2cbecf4_vs_18b4f3f/report.html @chriselrod I'm opening a new issue because https://github.com/JuliaSIMD/LoopVectorization.jl/issues/518 was closed, and to list all issues in case somebody wants to tackle this. --- Some of the errors that I've encountered: An LLVM assertion, as seen with MCPhylo.jl (requires assertions build of Julia): ``` julia: /workspace/srcdir/llvm-project/llvm/lib/IR/Instructions.cpp:2561: void llvm::InsertValueInst::init(llvm::Value*, llvm::Value*, llvm::ArrayRef<unsigned int>, const llvm::Twine&): Assertion `ExtractValueInst::getIndexedType(Agg->getType(), Idxs) == Val->getType() && "Inserted value must match indexed type!"' failed. [177] signal 6 (-6): Aborted in expression starting at /home/pkgeval/.julia/packages/MCPhylo/KWPlY/test/distributions/phylodist.jl:1 gsignal at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) abort at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) unknown function (ip: 0x7fbeac0f040e) __assert_fail at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) _ZN4llvm15InsertValueInst4initEPNS_5ValueES2_NS_8ArrayRefIjEERKNS_5TwineE at /opt/julia/bin/../lib/julia/libLLVM-15jl.so (unknown line) InsertValueInst at /source/usr/include/llvm/IR/Instructions.h:2640 [inlined] Create at /source/usr/include/llvm/IR/Instructions.h:2565 [inlined] CreateInsertValue at /source/usr/include/llvm/IR/IRBuilder.h:2343 emit_new_struct at /source/src/cgutils.cpp:3870 emit_new_struct at /source/src/julia.h:1704 emit_expr at /source/src/codegen.cpp:5945 emit_ssaval_assign at /source/src/codegen.cpp:5367 emit_stmtpos at /source/src/codegen.cpp:5642 [inlined] emit_function at /source/src/codegen.cpp:8810 jl_emit_code at /source/src/codegen.cpp:9144 jl_emit_codeinst at /source/src/codegen.cpp:9227 _jl_compile_codeinst at /source/src/jitlayers.cpp:220 jl_generate_fptr_impl at /source/src/jitlayers.cpp:525 jl_compile_method_internal at /source/src/gf.c:2509 [inlined] jl_compile_method_internal at /source/src/gf.c:2397 _jl_invoke at /source/src/gf.c:2912 [inlined] ijl_apply_generic at /source/src/gf.c:3097 logpdf at /home/pkgeval/.julia/packages/MCPhylo/KWPlY/src/distributions/Phylodist.jl:118 ``` A segfault during `vload`, as seen with NaNStatistics.jl and PlmDCA.jl: ``` [60] signal 11 (2): Segmentation fault in expression starting at /home/pkgeval/.julia/packages/NaNStatistics/oBRaH/test/testArrayStats.jl:80 macro expansion at /home/pkgeval/.julia/packages/VectorizationBase/0dXyA/src/llvm_intrin/memory_addr.jl:987 [inlined] __vload at /home/pkgeval/.julia/packages/VectorizationBase/0dXyA/src/llvm_intrin/memory_addr.jl:987 [inlined] _vload at /home/pkgeval/.julia/packages/VectorizationBase/0dXyA/src/strided_pointers/stridedpointers.jl:95 [inlined] macro expansion at /home/pkgeval/.julia/packages/VectorizationBase/0dXyA/src/vecunroll/memory.jl:60 [inlined] _vload_unroll at /home/pkgeval/.julia/packages/VectorizationBase/0dXyA/src/vecunroll/memory.jl:535 [inlined] _vload at /home/pkgeval/.julia/packages/VectorizationBase/0dXyA/src/vecunroll/memory.jl:771 [inlined] macro expansion at /home/pkgeval/.julia/packages/LoopVectorization/7iB2K/src/reconstruct_loopset.jl:1107 [inlined] _turbo_! at /home/pkgeval/.julia/packages/LoopVectorization/7iB2K/src/reconstruct_loopset.jl:1107 [inlined] _nanmean at /home/pkgeval/.julia/packages/NaNStatistics/oBRaH/src/ArrayStats/ArrayStats.jl:344 __nanmean at /home/pkgeval/.julia/packages/NaNStatistics/oBRaH/src/ArrayStats/ArrayStats.jl:308 [inlined] #nanmean#5 at /home/pkgeval/.julia/packages/NaNStatistics/oBRaH/src/ArrayStats/ArrayStats.jl:307 [inlined] nanmean at /home/pkgeval/.julia/packages/NaNStatistics/oBRaH/src/ArrayStats/ArrayStats.jl:307 ``` A segfault during `vadd_fast` as seen with VectorizedReductions.jl: ``` [12] signal 11 (2): Segmentation fault in expression starting at /home/pkgeval/.julia/packages/VectorizedReduction/bsnWJ/test/reduce.jl:4 macro expansion at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/llvm_intrin/binary_ops.jl:31 [inlined] vadd_fast at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/llvm_intrin/binary_ops.jl:31 [inlined] fmap at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/vecunroll/fmap.jl:11 [inlined] fmap at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/vecunroll/fmap.jl:11 [inlined] fmap at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/vecunroll/fmap.jl:11 [inlined] fmap at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/vecunroll/fmap.jl:11 [inlined] fmap at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/vecunroll/fmap.jl:11 [inlined] fmap at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/vecunroll/fmap.jl:11 [inlined] fmap at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/vecunroll/fmap.jl:11 [inlined] vadd_fast at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/vecunroll/fmap.jl:111 [inlined] add_fast at /home/pkgeval/.julia/packages/VectorizationBase/xE5Tx/src/base_defs.jl:91 [inlined] macro expansion at /home/pkgeval/.julia/packages/LoopVectorization/7iB2K/src/reconstruct_loopset.jl:1107 [inlined] _turbo_! at /home/pkgeval/.julia/packages/LoopVectorization/7iB2K/src/reconstruct_loopset.jl:1107 [inlined] macro expansion at /home/pkgeval/.julia/packages/VectorizedReduction/bsnWJ/src/vmapreduce.jl:236 [inlined] vvmapreduce at /home/pkgeval/.julia/packages/VectorizedReduction/bsnWJ/src/vmapreduce.jl:231 vvreduce at /home/pkgeval/.julia/packages/VectorizedReduction/bsnWJ/src/vmapreduce.jl:147 ``` The source of bad IR hasn't been fully determined yet, but it seems to be the `Expr(:new)` that's generated to pass structs by value instead of by reference: https://github.com/JuliaLang/julia/issues/52702#issuecomment-1874492883. --- Deprecating LoopVectorization.jl isn't possible, because: - some packages, e.g. RecursiveFactorizations.jl, inspect LoopVectorization.jl internals: https://github.com/JuliaSIMD/LoopVectorization.jl/issues/520 - the transformation of `@turbo` changes semantics, https://github.com/JuliaSIMD/LoopVectorization.jl/pull/523#issuecomment-1884883071 So the only solution forwards seems fixing LoopVectorization.jl. I've taken a first attempt at it in https://github.com/JuliaSIMD/LoopVectorization.jl/pull/523, but just removing the `Expr(:new)` optimization isn't sufficient, and there's other issues (see above).

check_empty=true/false didn’t change between early Julia versions and 1.10.
We could make check_empty=true the default.

Closing this because tests pass on 1.11, while check_empty=false should’ve also caused segfaults in older Julia versions. Test cleanup · JuliaSIMD/LoopVectorization.jl@eeaa0b2 · GitHub

But if anyone wants to contribute towards v1.12, the SciML Small Grants outlines that project and we’d be happy to up the ante. Maintenance never ends, so it’ll need v1.13 updates too!