Adds `#[rustc_force_inline]` which is similar to always inlining but
reports an error if the inlining was not possible, and which always
attempts to inline annotated items, regardless of optimisation levels.
It can only be applied to free functions to guarantee that the MIR
inliner will be able to resolve calls.
See llvm/llvm-project#121851
For LLVM 20+, this function (`renameModuleForThinLTO`) has no return
value. For prior versions of LLVM, this never failed, but had a
signature which allowed an error value people were handling.
Add a notion of "some ABIs require certain target features"
I think I finally found the right shape for the data and checks that I recently added in https://github.com/rust-lang/rust/pull/133099, https://github.com/rust-lang/rust/pull/133417, https://github.com/rust-lang/rust/pull/134337: we have a notion of "this ABI requires the following list of target features, and it is incompatible with the following list of target features". Both `-Ctarget-feature` and `#[target_feature]` are updated to ensure we follow the rules of the ABI. This removes all the "toggleability" stuff introduced before, though we do keep the notion of a fully "forbidden" target feature -- this is needed to deal with target features that are actual ABI switches, and hence are needed to even compute the list of required target features.
We always explicitly (un)set all required and in-conflict features, just to avoid potential trouble caused by the default features of whatever the base CPU is. We do this *before* applying `-Ctarget-feature` to maintain backward compatibility; this poses a slight risk of missing some implicit feature dependencies in LLVM but has the advantage of not breaking users that deliberately toggle ABI-relevant target features. They get a warning but the feature does get toggled the way they requested.
For now, our logic supports x86, ARM, and RISC-V (just like the previous logic did). Unsurprisingly, RISC-V is the nicest. ;)
As a side-effect this also (unstably) allows *enabling* `x87` when that is harmless. I used the opportunity to mark SSE2 as required on x86-64, to better match the actual logic in LLVM and because all x86-64 chips do have SSE2. This infrastructure also prepares us for requiring SSE on x86-32 when we want to use that for our ABI (and for float semantics sanity), see https://github.com/rust-lang/rust/issues/133611, but no such change is happening in this PR.
r? `@workingjubilee`
Variants::Single: do not use invalid VariantIdx for uninhabited enums
~~Stacked on top of https://github.com/rust-lang/rust/pull/133681, only the last commit is new.~~
Currently, `Variants::Single` for an empty enum contains a `VariantIdx` of 0; looking that up in the enum variant list will ICE. That's quite confusing. So let's fix that by adding a new `Variants::Empty` case for types that have 0 variants.
try-job: i686-msvc
forbid toggling x87 and fpregs on hard-float targets
Part of https://github.com/rust-lang/rust/issues/116344, follow-up to https://github.com/rust-lang/rust/pull/129884:
The `x87` target feature on x86 and the `fpregs` target feature on ARM must not be disabled on a hardfloat target, as that would change the float ABI. However, *enabling* `fpregs` on ARM is [explicitly requested](https://github.com/rust-lang/rust/issues/130988) as it seems to be useful. Therefore, we need to refine the distinction of "forbidden" target features and "allowed" target features: all (un)stable target features can determine on a per-target basis whether they should be allowed to be toggled or not. `fpregs` then checks whether the current target has the `soft-float` feature, and if yes, `fpregs` is permitted -- otherwise, it is not. (Same for `x87` on x86).
Also fixes https://github.com/rust-lang/rust/issues/132351. Since `fpregs` and `x87` can be enabled on some builds and disabled on others, it would make sense that one can query it via `cfg`. Therefore, I made them behave in `cfg` like any other unstable target feature.
The first commit prepares the infrastructure, but does not change behavior. The second commit then wires up `fpregs` and `x87` with that new infrastructure.
r? `@workingjubilee`
codegen `#[naked]` functions using global asm
tracking issue: https://github.com/rust-lang/rust/issues/90957Fixes#124375
This implements the approach suggested in the tracking issue: use the existing global assembly infrastructure to emit the body of `#[naked]` functions. The main advantage is that we now have full control over what gets generated, and are no longer dependent on LLVM not sneakily messing with our output (inlining, adding extra instructions, etc).
I discussed this approach with `@Amanieu` and while I think the general direction is correct, there is probably a bunch of stuff that needs to change or move around here. I'll leave some inline comments on things that I'm not sure about.
Combined with https://github.com/rust-lang/rust/pull/127853, if both accepted, I think that resolves all steps from the tracking issue.
r? `@Amanieu`
