`@llvm.julia.gc_preserve_begin` does not dominate all uses

[udesou]

Issue found when running LinearAlgebra CI tests here: https://github.com/mmtk/mmtk-julia/actions/runs/17565220495/job/49890688363

Does not seem deterministic - re-running the tests may make them succeed.

[qinsoon]

I also observed this in the tests for another PR. It happened for non moving plans. We observed this with LinearAlgebra/matmul and addmul.

LinearAlgebra/matmul               (2) |        started at 2025-09-09T06:21:51.074
      From worker 3:	Instruction does not dominate all uses!
      From worker 3:	  %102 = call token (...) @llvm.julia.gc_preserve_begin(ptr addrspace(10) nonnull %99), !dbg !82
      From worker 3:	  call void @llvm.julia.gc_preserve_end(token %102), !dbg !82
      From worker 3:	Instruction does not dominate all uses!
      From worker 3:	  %102 = call token (...) @llvm.julia.gc_preserve_begin(ptr addrspace(10) nonnull %99), !dbg !82
      From worker 3:	  call void @llvm.julia.gc_preserve_end(token %102), !dbg !82
      From worker 3:	Instruction does not dominate all uses!
      From worker 3:	  %102 = call token (...) @llvm.julia.gc_preserve_begin(ptr addrspace(10) nonnull %99), !dbg !82
      From worker 3:	  call void @llvm.julia.gc_preserve_end(token %102), !dbg !82
      From worker 3:	Instruction does not dominate all uses!
      From worker 3:	  %102 = call token (...) @llvm.julia.gc_preserve_begin(ptr addrspace(10) nonnull %99), !dbg !82
      From worker 3:	  call void @llvm.julia.gc_preserve_end(token %102), !dbg !82
      From worker 3:	Instruction does not dominate all uses!
      From worker 3:	  %102 = call token (...) @llvm.julia.gc_preserve_begin(ptr addrspace(10) nonnull %99), !dbg !82
      From worker 3:	  call void @llvm.julia.gc_preserve_end(token %102), !dbg !82
      From worker 3:	Instruction does not dominate all uses!
      From worker 3:	  %102 = call token (...) @llvm.julia.gc_preserve_begin(ptr addrspace(10) nonnull %99), !dbg !82
      From worker 3:	  call void @llvm.julia.gc_preserve_end(token %102), !dbg !82
      From worker 3:	Instruction does not dominate all uses!
      From worker 3:	  %102 = call token (...) @llvm.julia.gc_preserve_begin(ptr addrspace(10) nonnull %99), !dbg !82
      From worker 3:	  call void @llvm.julia.gc_preserve_end(token %102), !dbg !82
      From worker 3:	Instruction does not dominate all uses!
      From worker 3:	  %102 = call token (...) @llvm.julia.gc_preserve_begin(ptr addrspace(10) nonnull %99), !dbg !82
      From worker 3:	  call void @llvm.julia.gc_preserve_end(token %102), !dbg !82
      From worker 3:	Instruction does not dominate all uses!
      From worker 3:	  %102 = call token (...) @llvm.julia.gc_preserve_begin(ptr addrspace(10) nonnull %99), !dbg !82
      From worker 3:	  call void @llvm.julia.gc_preserve_end(token %102), !dbg !82
...