Julia 1.10/1.11: Emission of JIT-constants broken during precompilation

[vchuravy]

@wsmoses is encountering embedded null pointers in IR emitted during precompilation.

The root cause for this is that we have a control flag .imaging that controls if we are emitting IR for JIT (with embedded pointers) or IR for caching with relocation.

https://github.com/JuliaLang/julia/blob/21eadc5e3129a557df1eb385113132a97996af5e/src/aotcompile.cpp#L342

That flag is either set as an argument by us (which we never turned on #125 #348) or calculated based on the startup flags of Julia

https://github.com/JuliaLang/julia/blob/21eadc5e3129a557df1eb385113132a97996af5e/src/jitlayers.h#L77-L78

This didn't show up before since outside precompilation imaging_default() returns false.

Likely the best way would be to follow the pattern we have for 1.13 and above

GPUCompiler.jl/src/jlgen.jl

Lines 770 to 786 in e2d8505

	# Since Julia 1.13, the caller is responsible for initializing global variables that
	# point to global values or bindings with their address in memory.
	num_gvars = Ref{Csize_t}(0)
	@ccall jl_get_llvm_gvs(native_code::Ptr{Cvoid}, num_gvars::Ptr{Csize_t},
	C_NULL::Ptr{Cvoid})::Nothing
	gvs = Vector{Ptr{LLVM.API.LLVMOpaqueValue}}(undef, num_gvars[])
	@ccall jl_get_llvm_gvs(native_code::Ptr{Cvoid}, num_gvars::Ptr{Csize_t},
	gvs::Ptr{LLVM.API.LLVMOpaqueValue})::Nothing
	inits = Vector{Ptr{Cvoid}}(undef, num_gvars[])
	@ccall jl_get_llvm_gv_inits(native_code::Ptr{Cvoid}, num_gvars::Ptr{Csize_t},
	inits::Ptr{Cvoid})::Nothing
	for (gv_ref, init) in zip(gvs, inits)
	gv = GlobalVariable(gv_ref)
	val = const_inttoptr(ConstantInt(Int64(init)), LLVM.PointerType())
	initializer!(gv, val)
	end

which makes the handling of global values consistent

#752 is an attempt to do that by looking at the table of global values, but we lack the infrastructure to access all the information needed.

[wsmoses]

also 1.12 as well [only 1.13 is fine, right?]