Make late gc lower handle insertelement of alloca use. #58637
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vtjnash
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serenity4
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gbaraldi
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backport 1.11
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This was in DAECompiler.jl code found by @serenity4. He also mentioned that writing up how one might go and fix a bug like this so i'll give a quick writeup (this was a very simple bug so it might not be too interesting) The original crash which looked something like > %19 = alloca [10 x i64], align 8 %155 = insertelement <4 x ptr> poison, ptr %19, i32 0 Unexpected instruction > [898844] signal 6 (-6): Aborted in expression starting at /home/gbaraldi/DAECompiler.jl/test/reflection.jl:28 pthread_kill at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) gsignal at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) abort at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) RecursivelyVisit<llvm::IntrinsicInst, LateLowerGCFrame::PlaceRootsAndUpdateCalls(llvm::ArrayRef<int>, int, State&, std::map<llvm::Value*, std::pair<int, int> >)::<lambda(llvm::AllocaInst*&)>::<lambda(llvm::Use&)> > at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:803 operator() at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2560 [inlined] PlaceRootsAndUpdateCalls at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2576 runOnFunction at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2638 run at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2675 run at /home/gbaraldi/julia4/usr/include/llvm/IR/PassManagerInternal.h:91 which means it was crashing inside of late-gc-lowering, so the first thing I did was ran julia and the same test with LLVM_ASSERTIONS=1 and FORCE_ASSERTIONS=1 to see if LLVM complained about a malformed module, and both were fine. Next step was trying to get the failing code out for inspection. Easiest way is to do `export JULIA_LLVM_ARGS="--print-before=LateLowerGCFrame --print-module-scope"` and pipe the output to a file. The file is huge, but since it's a crash in LLVM we know that the last thing is what we want, and that gave me the IR I wanted. To verify that this is failing I did `make -C src install-analysis-deps` to install the LLVM machinery (opt...). That gets put in the `tools` directory of a julia build. Then I checked if this crashed outside of julia by doing `./opt -load-pass-plugin=../lib/libjulia-codegen.dylib --passes=LateLowerGCFrame -S test.ll -o tmp3.ll `. This is run from inside the tools dir so your paths might vary (the -S is so LLVM doesn't generate bitcode) and my code did crash, however it was over 500 lines of IR which makes it harder to debug and to write a test. Next step then is to minimize the crash by doing [`llvm-reduce`](https://llvm.org/docs/CommandGuide/llvm-reduce.html) over it (it's basically creduce but optimized for LLVM IR) which gave me a 2 line reproducer (in this case apparently just having the insertelement was enough for the pass to fail). One thing to be wary is that llvm-reduce will usually make very weird code, so it might be useful to modify the code slightly so it doesn't look odd (it will have unreachable basic-blocks and such). After the cleanup fixing the bug here wasn't interesting but this doesn't apply generally. And also always transform your reduced IR into a test to put in llvmpasses. (cherry picked from commit 906d348)
KristofferC
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Aug 19, 2025
This was in DAECompiler.jl code found by @serenity4. He also mentioned that writing up how one might go and fix a bug like this so i'll give a quick writeup (this was a very simple bug so it might not be too interesting) The original crash which looked something like > %19 = alloca [10 x i64], align 8 %155 = insertelement <4 x ptr> poison, ptr %19, i32 0 Unexpected instruction > [898844] signal 6 (-6): Aborted in expression starting at /home/gbaraldi/DAECompiler.jl/test/reflection.jl:28 pthread_kill at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) gsignal at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) abort at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) RecursivelyVisit<llvm::IntrinsicInst, LateLowerGCFrame::PlaceRootsAndUpdateCalls(llvm::ArrayRef<int>, int, State&, std::map<llvm::Value*, std::pair<int, int> >)::<lambda(llvm::AllocaInst*&)>::<lambda(llvm::Use&)> > at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:803 operator() at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2560 [inlined] PlaceRootsAndUpdateCalls at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2576 runOnFunction at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2638 run at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2675 run at /home/gbaraldi/julia4/usr/include/llvm/IR/PassManagerInternal.h:91 which means it was crashing inside of late-gc-lowering, so the first thing I did was ran julia and the same test with LLVM_ASSERTIONS=1 and FORCE_ASSERTIONS=1 to see if LLVM complained about a malformed module, and both were fine. Next step was trying to get the failing code out for inspection. Easiest way is to do `export JULIA_LLVM_ARGS="--print-before=LateLowerGCFrame --print-module-scope"` and pipe the output to a file. The file is huge, but since it's a crash in LLVM we know that the last thing is what we want, and that gave me the IR I wanted. To verify that this is failing I did `make -C src install-analysis-deps` to install the LLVM machinery (opt...). That gets put in the `tools` directory of a julia build. Then I checked if this crashed outside of julia by doing `./opt -load-pass-plugin=../lib/libjulia-codegen.dylib --passes=LateLowerGCFrame -S test.ll -o tmp3.ll `. This is run from inside the tools dir so your paths might vary (the -S is so LLVM doesn't generate bitcode) and my code did crash, however it was over 500 lines of IR which makes it harder to debug and to write a test. Next step then is to minimize the crash by doing [`llvm-reduce`](https://llvm.org/docs/CommandGuide/llvm-reduce.html) over it (it's basically creduce but optimized for LLVM IR) which gave me a 2 line reproducer (in this case apparently just having the insertelement was enough for the pass to fail). One thing to be wary is that llvm-reduce will usually make very weird code, so it might be useful to modify the code slightly so it doesn't look odd (it will have unreachable basic-blocks and such). After the cleanup fixing the bug here wasn't interesting but this doesn't apply generally. And also always transform your reduced IR into a test to put in llvmpasses. (cherry picked from commit 906d348)
KristofferC
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that referenced
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Aug 19, 2025
This was in DAECompiler.jl code found by @serenity4. He also mentioned that writing up how one might go and fix a bug like this so i'll give a quick writeup (this was a very simple bug so it might not be too interesting) The original crash which looked something like > %19 = alloca [10 x i64], align 8 %155 = insertelement <4 x ptr> poison, ptr %19, i32 0 Unexpected instruction > [898844] signal 6 (-6): Aborted in expression starting at /home/gbaraldi/DAECompiler.jl/test/reflection.jl:28 pthread_kill at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) gsignal at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) abort at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) RecursivelyVisit<llvm::IntrinsicInst, LateLowerGCFrame::PlaceRootsAndUpdateCalls(llvm::ArrayRef<int>, int, State&, std::map<llvm::Value*, std::pair<int, int> >)::<lambda(llvm::AllocaInst*&)>::<lambda(llvm::Use&)> > at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:803 operator() at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2560 [inlined] PlaceRootsAndUpdateCalls at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2576 runOnFunction at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2638 run at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2675 run at /home/gbaraldi/julia4/usr/include/llvm/IR/PassManagerInternal.h:91 which means it was crashing inside of late-gc-lowering, so the first thing I did was ran julia and the same test with LLVM_ASSERTIONS=1 and FORCE_ASSERTIONS=1 to see if LLVM complained about a malformed module, and both were fine. Next step was trying to get the failing code out for inspection. Easiest way is to do `export JULIA_LLVM_ARGS="--print-before=LateLowerGCFrame --print-module-scope"` and pipe the output to a file. The file is huge, but since it's a crash in LLVM we know that the last thing is what we want, and that gave me the IR I wanted. To verify that this is failing I did `make -C src install-analysis-deps` to install the LLVM machinery (opt...). That gets put in the `tools` directory of a julia build. Then I checked if this crashed outside of julia by doing `./opt -load-pass-plugin=../lib/libjulia-codegen.dylib --passes=LateLowerGCFrame -S test.ll -o tmp3.ll `. This is run from inside the tools dir so your paths might vary (the -S is so LLVM doesn't generate bitcode) and my code did crash, however it was over 500 lines of IR which makes it harder to debug and to write a test. Next step then is to minimize the crash by doing [`llvm-reduce`](https://llvm.org/docs/CommandGuide/llvm-reduce.html) over it (it's basically creduce but optimized for LLVM IR) which gave me a 2 line reproducer (in this case apparently just having the insertelement was enough for the pass to fail). One thing to be wary is that llvm-reduce will usually make very weird code, so it might be useful to modify the code slightly so it doesn't look odd (it will have unreachable basic-blocks and such). After the cleanup fixing the bug here wasn't interesting but this doesn't apply generally. And also always transform your reduced IR into a test to put in llvmpasses. (cherry picked from commit 906d348)
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DilumAluthge
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Aug 31, 2025
This reverts commit 47d905d.
DilumAluthge
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This reverts commit 47d905d.
DilumAluthge
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This reverts commit 47d905d.
KristofferC
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This was in DAECompiler.jl code found by @serenity4. He also mentioned that writing up how one might go and fix a bug like this so i'll give a quick writeup (this was a very simple bug so it might not be too interesting) The original crash which looked something like > %19 = alloca [10 x i64], align 8 %155 = insertelement <4 x ptr> poison, ptr %19, i32 0 Unexpected instruction > [898844] signal 6 (-6): Aborted in expression starting at /home/gbaraldi/DAECompiler.jl/test/reflection.jl:28 pthread_kill at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) gsignal at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) abort at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) RecursivelyVisit<llvm::IntrinsicInst, LateLowerGCFrame::PlaceRootsAndUpdateCalls(llvm::ArrayRef<int>, int, State&, std::map<llvm::Value*, std::pair<int, int> >)::<lambda(llvm::AllocaInst*&)>::<lambda(llvm::Use&)> > at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:803 operator() at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2560 [inlined] PlaceRootsAndUpdateCalls at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2576 runOnFunction at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2638 run at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2675 run at /home/gbaraldi/julia4/usr/include/llvm/IR/PassManagerInternal.h:91 which means it was crashing inside of late-gc-lowering, so the first thing I did was ran julia and the same test with LLVM_ASSERTIONS=1 and FORCE_ASSERTIONS=1 to see if LLVM complained about a malformed module, and both were fine. Next step was trying to get the failing code out for inspection. Easiest way is to do `export JULIA_LLVM_ARGS="--print-before=LateLowerGCFrame --print-module-scope"` and pipe the output to a file. The file is huge, but since it's a crash in LLVM we know that the last thing is what we want, and that gave me the IR I wanted. To verify that this is failing I did `make -C src install-analysis-deps` to install the LLVM machinery (opt...). That gets put in the `tools` directory of a julia build. Then I checked if this crashed outside of julia by doing `./opt -load-pass-plugin=../lib/libjulia-codegen.dylib --passes=LateLowerGCFrame -S test.ll -o tmp3.ll `. This is run from inside the tools dir so your paths might vary (the -S is so LLVM doesn't generate bitcode) and my code did crash, however it was over 500 lines of IR which makes it harder to debug and to write a test. Next step then is to minimize the crash by doing [`llvm-reduce`](https://llvm.org/docs/CommandGuide/llvm-reduce.html) over it (it's basically creduce but optimized for LLVM IR) which gave me a 2 line reproducer (in this case apparently just having the insertelement was enough for the pass to fail). One thing to be wary is that llvm-reduce will usually make very weird code, so it might be useful to modify the code slightly so it doesn't look odd (it will have unreachable basic-blocks and such). After the cleanup fixing the bug here wasn't interesting but this doesn't apply generally. And also always transform your reduced IR into a test to put in llvmpasses. (cherry picked from commit 906d348)
DilumAluthge
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Sep 5, 2025
Backported PRs: - [x] #54840 <!-- Add boundscheck in speccache_eq to avoid OOB access due to data race --> - [x] #42080 <!-- recommend explicit `using Foo: Foo, ...` in package code (was: "using considered harmful") --> - [x] #58127 <!-- [DOC] Update installation docs: /downloads/ => /install/ --> - [x] #58202 <!-- [release-1.11] malloc: use jl_get_current_task to fix null check --> - [x] #58584 <!-- Make `Ptr` values static-show w/ type-information --> - [x] #58637 <!-- Make late gc lower handle insertelement of alloca use. --> - [x] #58837 <!-- fix null comparisons for non-standard address spaces --> - [x] #57826 <!-- Add a `similar` method for `Type{<:CodeUnits}` --> - [x] #58293 <!-- fix trailing indices stackoverflow in reinterpreted array --> - [x] #58887 <!-- Pkg: Allow configuring can_fancyprint(io::IO) using IOContext --> - [x] #58937 <!-- Fix nthreadpools size in JLOptions --> - [x] #58978 <!-- Fix precompilepkgs warn loaded setting --> - [x] #58998 <!-- Bugfix: Use Base.aligned_sizeof instead of sizeof in Mmap.mmap --> - [x] #59120 <!-- Fix memory order typo in "src/julia_atomics.h" --> - [x] #59170 <!-- Clarify and enhance confusing precompile test --> Need manual backport: - [ ] #56329 <!-- loading: clean up more concurrency issues --> - [ ] #56956 <!-- Add "mea culpa" to foreign module assignment error. --> - [ ] #57035 <!-- linux: workaround to avoid deadlock inside dl_iterate_phdr in glibc --> - [ ] #57089 <!-- Block thread from receiving profile signal with stackwalk lock --> - [ ] #57249 <!-- restore non-freebsd-unix fix for profiling --> - [ ] #58011 <!-- Remove try-finally scope from `@time_imports` `@trace_compile` `@trace_dispatch` --> - [ ] #58062 <!-- remove unnecessary edge from `exp_impl` to `pow` --> - [ ] #58157 <!-- add showing a string to REPL precompile workload --> - [ ] #58209 <!-- Specialize `one` for the `SizedArray` test helper --> - [ ] #58108 <!-- Base.get_extension & Dates.format made public --> - [ ] #58356 <!-- codegen: remove readonly from abstract type calling convention --> - [ ] #58415 <!-- [REPL] more reliable extension loading --> - [ ] #58510 <!-- Don't filter `Core` methods from newly-inferred list --> - [ ] #58110 <!-- relax dispatch for the `IteratorSize` method for `Generator` --> - [ ] #58965 <!-- Fix `hygienic-scope`s in inner macro expansions --> - [ ] #58971 <!-- Fix alignment of failed precompile jobs on CI --> - [ ] #59066 <!-- build: Also pass -fno-strict-aliasing for C++ --> Contains multiple commits, manual intervention needed: - [ ] #55877 <!-- fix FileWatching designs and add workaround for a stat bug on Apple --> - [ ] #56755 <!-- docs: fix scope type of a `struct` to hard --> - [ ] #57809 <!-- Fix fptrunc Float64 -> Float16 rounding through Float32 --> - [ ] #57398 <!-- Make remaining float intrinsics require float arguments --> - [ ] #56351 <!-- Fix `--project=@script` when outside script directory --> - [ ] #57129 <!-- clarify that time_ns is monotonic --> - [ ] #58134 <!-- Note annotated string API is experimental in Julia 1.11 in HISTORY.md --> - [ ] #58401 <!-- check that hashing of types does not foreigncall (`jl_type_hash` is concrete evaluated) --> - [ ] #58435 <!-- Fix layout flags for types that have oddly sized primitive type fields --> - [ ] #58483 <!-- Fix tbaa usage when storing into heap allocated immutable structs --> - [ ] #58512 <!-- Make more types jl_static_show readably --> - [ ] #58012 <!-- Re-enable tab completion of kwargs for large method tables --> - [ ] #58683 <!-- Add 0 predecessor to entry basic block and handle it in inlining --> - [ ] #59112 <!-- Add builtin function name to add methods error --> Non-merged PRs with backport label: - [ ] #59329 <!-- aotcompile: destroy LLVM context after serializing combined module --> - [ ] #58848 <!-- Set array size only when safe to do so --> - [ ] #58535 <!-- gf.c: include const-return methods in `--trace-compile` --> - [ ] #58038 <!-- strings/cstring: `transcode`: prevent Windows sysimage invalidation --> - [ ] #57604 <!-- `@nospecialize` for `string_index_err` --> - [ ] #57366 <!-- Use ptrdiff_t sized offsets for gvars_offsets to allow large sysimages --> - [ ] #56890 <!-- Enable getting non-boxed LLVM type from Julia Type --> - [ ] #56823 <!-- Make version of opaque closure constructor in world --> - [ ] #55958 <!-- also redirect JL_STDERR etc. when redirecting to devnull --> - [ ] #55956 <!-- Make threadcall gc safe --> - [ ] #55534 <!-- Set stdlib sources as read-only during installation --> - [ ] #55499 <!-- propagate the terminal's `displaysize` to the `IOContext` used by the REPL --> - [ ] #55458 <!-- Allow for generically extracting unannotated string --> - [ ] #55457 <!-- Make AnnotateChar equality consider annotations --> - [ ] #55220 <!-- `isfile_casesensitive` fixes on Windows --> - [ ] #53957 <!-- tweak how filtering is done for what packages should be precompiled --> - [ ] #51479 <!-- prevent code loading from lookin in the versioned environment when building Julia --> - [ ] #50813 <!-- More doctests for Sockets and capitalization fix --> - [ ] #50157 <!-- improve docs for `@inbounds` and `Base.@propagate_inbounds` --> --------- Co-authored-by: Kiran Pamnany <[email protected]> Co-authored-by: adienes <[email protected]> Co-authored-by: Gabriel Baraldi <[email protected]> Co-authored-by: Keno Fischer <[email protected]> Co-authored-by: Simeon David Schaub <[email protected]> Co-authored-by: Jameson Nash <[email protected]> Co-authored-by: Alex Arslan <[email protected]> Co-authored-by: Fons van der Plas <[email protected]> Co-authored-by: Ian Butterworth <[email protected]> Co-authored-by: JonasIsensee <[email protected]> Co-authored-by: Curtis Vogt <[email protected]> Co-authored-by: Dilum Aluthge <[email protected]> Co-authored-by: DilumAluthgeBot <[email protected]> Co-authored-by: DilumAluthge <[email protected]>
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This was in DAECompiler.jl code found by @serenity4. He also mentioned that writing up how one might go and fix a bug like this so i'll give a quick writeup (this was a very simple bug so it might not be too interesting) The original crash which looked something like > %19 = alloca [10 x i64], align 8 %155 = insertelement <4 x ptr> poison, ptr %19, i32 0 Unexpected instruction > [898844] signal 6 (-6): Aborted in expression starting at /home/gbaraldi/DAECompiler.jl/test/reflection.jl:28 pthread_kill at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) gsignal at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) abort at /lib/x86_64-linux-gnu/libc.so.6 (unknown line) RecursivelyVisit<llvm::IntrinsicInst, LateLowerGCFrame::PlaceRootsAndUpdateCalls(llvm::ArrayRef<int>, int, State&, std::map<llvm::Value*, std::pair<int, int> >)::<lambda(llvm::AllocaInst*&)>::<lambda(llvm::Use&)> > at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:803 operator() at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2560 [inlined] PlaceRootsAndUpdateCalls at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2576 runOnFunction at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2638 run at /home/gbaraldi/julia4/src/llvm-late-gc-lowering.cpp:2675 run at /home/gbaraldi/julia4/usr/include/llvm/IR/PassManagerInternal.h:91 which means it was crashing inside of late-gc-lowering, so the first thing I did was ran julia and the same test with LLVM_ASSERTIONS=1 and FORCE_ASSERTIONS=1 to see if LLVM complained about a malformed module, and both were fine. Next step was trying to get the failing code out for inspection. Easiest way is to do `export JULIA_LLVM_ARGS="--print-before=LateLowerGCFrame --print-module-scope"` and pipe the output to a file. The file is huge, but since it's a crash in LLVM we know that the last thing is what we want, and that gave me the IR I wanted. To verify that this is failing I did `make -C src install-analysis-deps` to install the LLVM machinery (opt...). That gets put in the `tools` directory of a julia build. Then I checked if this crashed outside of julia by doing `./opt -load-pass-plugin=../lib/libjulia-codegen.dylib --passes=LateLowerGCFrame -S test.ll -o tmp3.ll `. This is run from inside the tools dir so your paths might vary (the -S is so LLVM doesn't generate bitcode) and my code did crash, however it was over 500 lines of IR which makes it harder to debug and to write a test. Next step then is to minimize the crash by doing [`llvm-reduce`](https://llvm.org/docs/CommandGuide/llvm-reduce.html) over it (it's basically creduce but optimized for LLVM IR) which gave me a 2 line reproducer (in this case apparently just having the insertelement was enough for the pass to fail). One thing to be wary is that llvm-reduce will usually make very weird code, so it might be useful to modify the code slightly so it doesn't look odd (it will have unreachable basic-blocks and such). After the cleanup fixing the bug here wasn't interesting but this doesn't apply generally. And also always transform your reduced IR into a test to put in llvmpasses. (cherry picked from commit 906d348)
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This was in DAECompiler.jl code found by @serenity4. He also mentioned that writing up how one might go and fix a bug like this so i'll give a quick writeup (this was a very simple bug so it might not be too interesting)
The original crash which looked something like
which means it was crashing inside of late-gc-lowering, so the first thing I did was ran julia and the same test with LLVM_ASSERTIONS=1 and FORCE_ASSERTIONS=1 to see if LLVM complained about a malformed module, and both were fine. Next step was trying to get the failing code out for inspection.
Easiest way is to do
export JULIA_LLVM_ARGS="--print-before=LateLowerGCFrame --print-module-scope"and pipe the output to a file.The file is huge, but since it's a crash in LLVM we know that the last thing is what we want, and that gave me the IR I wanted.
To verify that this is failing I did
make -C src install-analysis-depsto install the LLVM machinery (opt...). That gets put in thetoolsdirectory of a julia build. Then I checked if this crashed outside of julia by doing./opt -load-pass-plugin=../lib/libjulia-codegen.dylib --passes=LateLowerGCFrame -S test.ll -o tmp3.ll. This is run from inside the tools dir so your paths might vary (the -S is so LLVM doesn't generate bitcode) and my code did crash, however it was over 500 lines of IR which makes it harder to debug and to write a test.Next step then is to minimize the crash by doing
llvm-reduceover it (it's basically creduce but optimized for LLVM IR) which gave me a 2 line reproducer (in this case apparently just having the insertelement was enough for the pass to fail). One thing to be wary is that llvm-reduce will usually make very weird code, so it might be useful to modify the code slightly so it doesn't look odd (it will have unreachable basic-blocks and such).After the cleanup fixing the bug here wasn't interesting but this doesn't apply generally. And also always transform your reduced IR into a test to put in llvmpasses.