Re: broken JIT support on Fedora 40

> On Fri, Mar 15, 2024 at 01:54:38PM +1300, Thomas Munro wrote:
> For me it seems that the LLVMRunPasses() call, new in
>
> commit 76200e5ee469e4a9db5f9514b9d0c6a31b496bff
> Author: Thomas Munro <tmunro(at)postgresql(dot)org>
> Date: Wed Oct 18 22:15:54 2023 +1300
>
> jit: Changes for LLVM 17.
>
> is reaching code that segfaults inside libLLVM, specifically in
> llvm::InlineFunction(llvm::CallBase&, llvm::InlineFunctionInfo&, bool,
> llvm::AAResults*, bool, llvm::Function*). First obvious question
> would be: is that NULL argument still acceptable? Perhaps it wants
> our LLVMTargetMachineRef there:
>
> err = LLVMRunPasses(module, passes, NULL, options);
>
> But then when we see what is does with that argument, it arrives at a
> place that apparently accepts nullptr.
>
> https://github.com/llvm/llvm-project/blob/6b2bab2839c7a379556a10287034bd55906d7094/llvm/lib/Passes/PassBuilderBindings.cpp#L56
> https://github.com/llvm/llvm-project/blob/6b2bab2839c7a379556a10287034bd55906d7094/llvm/include/llvm/Passes/PassBuilder.h#L124
>
> Hrmph. Might need an assertion build to learn more. I'll try to look
> again next week or so.

Looks like I can reproduce this as well, libLLVM crashes when reaching
AddReturnAttributes inside InlineFunction, when trying to access
operands of the return instruction. I think, for whatever reason, the
latest LLVM doesn't like (i.e. do not expect this when performing
inlining pass) return instructions that do not have a return value, and
this is what happens in the outblock of deform function we generate
(slot_compile_deform).

For verification, I've modified the deform.outblock to call LLVMBuildRet
instead of LLVMBuildRetVoid and this seems to help -- inline and deform
stages are still performed as before, but nothing crashes. But of course
it doesn't sound right that inlining pass cannot process such code.
Unfortunately I don't see any obvious change in the recent LLVM history
that would justify this outcome, might be a genuine bug, will
investigate further.