update to rustc 1.98

[Firestar99]

Requires #610

Warning

This is an in-the-middle nightly

Notable changes:

• This commit does a few cleanups, assuming ScalarPairs are passed by PassMode::ScalarPair exclusively. But rust-gpu readjusts the fn abi here to pass any non-slice ScalarPair as PassMode::Direct. Removing this ABI change breaks a bunch of code in all kinds of weird ways, primarily ByteAddressableBuffer intrinsics and panic!() format args decompiler complaining about function pointers and pointer casts. It's just that rust-gpu can't properly handle PassMode::ScalarPair in so many places... So we'll keep our abi adjustments and I just undo that upstream cleanup.

close #605

[Firestar99]

Going from working nightly-2026-06-12 (rust-lang/rust@b30f3df) to nighty-2026-06-13 (rust-lang/rust@6540795) causes our compiletests to break due to some upstream change I can't identify.

The only two PRs that change anything in rustc_codegen_ssa in that range are:

• Move create_scope_map to rustc_codegen_ssa. rust-lang/rust#157722 which only touches debug info (and requires us to remove some todo!s that now get called) it's this PR
• codegen_ssa: peel trans. wrappers on scalable vecs rust-lang/rust#157768 which should only affect scaleable vecs (aarch64 SIMD stuff) which we're not using

UPDATE: We can fix the compiletests by just removing this flag:

-        "-Cdebuginfo=2",

This flag is responsible for controlling debug symbol emission, 2 means all the debug symbols and it defaults to 0 (I think) meaning none.

How the hell does turning on debug symbol emission cause fundamental compilation errors?

• Move create_scope_map to rustc_codegen_ssa. rust-lang/rust#157722 moved debug symbol emission from cg_lllvm to cg_ssa so cg_gcc could take advantage of the shared code path. This included refactoring the cg_ssa API to account for the new emission format.
• They removed this function in particular:

    fn create_function_debug_context(
        &self,
        _instance: Instance<'tcx>,
        _fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
        _llfn: Self::Function,
        _mir: &mir::Body<'tcx>,
    ) -> Option<FunctionDebugContext<'tcx, Self::DIScope, Self::DILocation>> {
        // TODO: This is ignored. Do we want to implement this at some point?
        None
    }

• Notice how it returns an Option and we always return None? With the debug symbol refactor, codegen backends can't choose to just return None and disable debug info emission. Whether to emit or not is exclusively determined by the debuginfo flag. Which is why I had to remove a bunch of todo!()s in all our dbg fn impls.
• To correctly emit debug information, the new cg_ssa impl needs to monomorphise inlined functions, which causes them to be emitted to our codegen backend. Specifically, I see a lot of <usize>::unchecked_add calling <usize>::unchecked_add::precondition_check with a &str as an argument.
• That &str value is a [u8] constant, which are represented as a RuntimeArray in rust-gpu's codegen and not well supported. Eventually it hits this zombification, erroring with error: unsupported unsized [u8] constant.

I beliebe the fix I made here is only a temporary fix, I suspect any debug build of sufficient complexity will fail. Don't yet know what to do about that.