compiler/rustc_monomorphize/src/mono_checks/abi_check.rs

//! This module ensures that if a function's ABI requires a particular target feature,
//! that target feature is enabled both on the callee and all callers.
use rustc_abi::{BackendRepr, CanonAbi, RegKind, X86Call};
use rustc_hir::{CRATE_HIR_ID, HirId};
use rustc_middle::mir::{self, Location, traversal};
use rustc_middle::ty::{self, Instance, InstanceKind, Ty, TyCtxt};
use rustc_span::def_id::DefId;
use rustc_span::{DUMMY_SP, Span, Symbol, sym};
use rustc_target::callconv::{FnAbi, PassMode};

use crate::errors;

/// Are vector registers used?
enum UsesVectorRegisters {
    /// e.g. `neon`
    FixedVector,
    /// e.g. `sve`
    ScalableVector,
    No,
}

/// Determines whether the combination of `mode` and `repr` will use fixed vector registers,
/// scalable vector registers or no vector registers.
fn passes_vectors_by_value(mode: &PassMode, repr: &BackendRepr) -> UsesVectorRegisters {
    match mode {
        PassMode::Ignore | PassMode::Indirect { .. } => UsesVectorRegisters::No,
        PassMode::Cast { pad_i32: _, cast }
            if cast.prefix.iter().any(|r| r.is_some_and(|x| x.kind == RegKind::Vector))
                || cast.rest.unit.kind == RegKind::Vector =>
        {
            UsesVectorRegisters::FixedVector
        }
        PassMode::Direct(..) | PassMode::Pair(..)
            if matches!(repr, BackendRepr::SimdVector { .. }) =>
        {
            UsesVectorRegisters::FixedVector
        }
        PassMode::Direct(..) | PassMode::Pair(..)
            if matches!(repr, BackendRepr::ScalableVector { .. }) =>
        {
            UsesVectorRegisters::ScalableVector
        }
        _ => UsesVectorRegisters::No,
    }
}

/// Checks whether a certain function ABI is compatible with the target features currently enabled
/// for a certain function.
/// `is_call` indicates whether this is a call-site check or a definition-site check;
/// this is only relevant for the wording in the emitted error.
fn do_check_simd_vector_abi<'tcx>(
    tcx: TyCtxt<'tcx>,
    abi: &FnAbi<'tcx, Ty<'tcx>>,
    def_id: DefId,
    is_call: bool,
    loc: impl Fn() -> (Span, HirId),
) {
    let codegen_attrs = tcx.codegen_fn_attrs(def_id);
    let have_feature = |feat: Symbol| {
        let target_feats = tcx.sess.unstable_target_features.contains(&feat);
        let fn_feats = codegen_attrs.target_features.iter().any(|x| x.name == feat);
        target_feats || fn_feats
    };
    for arg_abi in abi.args.iter().chain(std::iter::once(&abi.ret)) {
        let size = arg_abi.layout.size;
        match passes_vectors_by_value(&arg_abi.mode, &arg_abi.layout.backend_repr) {
            UsesVectorRegisters::FixedVector => {
                let feature_def = tcx.sess.target.features_for_correct_fixed_length_vector_abi();
                // Find the first feature that provides at least this vector size.
                let feature = match feature_def.iter().find(|(bits, _)| size.bits() <= *bits) {
                    Some((_, feature)) => feature,
                    None => {
                        let (span, _hir_id) = loc();
                        tcx.dcx().emit_err(errors::AbiErrorUnsupportedVectorType {
                            span,
                            ty: arg_abi.layout.ty,
                            is_call,
                        });
                        continue;
                    }
                };
                if !feature.is_empty() && !have_feature(Symbol::intern(feature)) {
                    let (span, _hir_id) = loc();
                    tcx.dcx().emit_err(errors::AbiErrorDisabledVectorType {
                        span,
                        required_feature: feature,
                        ty: arg_abi.layout.ty,
                        is_call,
                        is_scalable: false,
                    });
                }
            }
            UsesVectorRegisters::ScalableVector => {
                let Some(required_feature) =
                    tcx.sess.target.features_for_correct_scalable_vector_abi()
                else {
                    continue;
                };
                if !required_feature.is_empty() && !have_feature(Symbol::intern(required_feature)) {
                    let (span, _) = loc();
                    tcx.dcx().emit_err(errors::AbiErrorDisabledVectorType {
                        span,
                        required_feature,
                        ty: arg_abi.layout.ty,
                        is_call,
                        is_scalable: true,
                    });
                }
            }
            UsesVectorRegisters::No => {
                continue;
            }
        }
    }
    // The `vectorcall` ABI is special in that it requires SSE2 no matter which types are being passed.
    if abi.conv == CanonAbi::X86(X86Call::Vectorcall) && !have_feature(sym::sse2) {
        let (span, _hir_id) = loc();
        tcx.dcx().emit_err(errors::AbiRequiredTargetFeature {
            span,
            required_feature: "sse2",
            abi: "vectorcall",
            is_call,
        });
    }
}

/// Emit an error when a non-rustic ABI has unsized parameters.
/// Unsized types do not have a stable layout, so should not be used with stable ABIs.
/// `is_call` indicates whether this is a call-site check or a definition-site check;
/// this is only relevant for the wording in the emitted error.
fn do_check_unsized_params<'tcx>(
    tcx: TyCtxt<'tcx>,
    fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
    is_call: bool,
    loc: impl Fn() -> (Span, HirId),
) {
    // Unsized parameters are allowed with the (unstable) "Rust" (and similar) ABIs.
    if fn_abi.conv.is_rustic_abi() {
        return;
    }

    for arg_abi in fn_abi.args.iter() {
        if !arg_abi.layout.layout.is_sized() {
            let (span, _hir_id) = loc();
            tcx.dcx().emit_err(errors::AbiErrorUnsupportedUnsizedParameter {
                span,
                ty: arg_abi.layout.ty,
                is_call,
            });
        }
    }
}

/// Checks the ABI of an Instance, emitting an error when:
///
/// - a non-rustic ABI uses unsized parameters
/// - the signature requires target features that are not enabled
fn check_instance_abi<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
    let typing_env = ty::TypingEnv::fully_monomorphized();
    let Ok(abi) = tcx.fn_abi_of_instance(typing_env.as_query_input((instance, ty::List::empty())))
    else {
        // An error will be reported during codegen if we cannot determine the ABI of this
        // function.
        tcx.dcx().delayed_bug("ABI computation failure should lead to compilation failure");
        return;
    };
    // Unlike the call-site check, we do also check "Rust" ABI functions here.
    // This should never trigger, *except* if we start making use of vector registers
    // for the "Rust" ABI and the user disables those vector registers (which should trigger a
    // warning as that's clearly disabling a "required" target feature for this target).
    // Using such a function is where disabling the vector register actually can start leading
    // to soundness issues, so erroring here seems good.
    let loc = || {
        let def_id = instance.def_id();
        (
            tcx.def_span(def_id),
            def_id.as_local().map(|did| tcx.local_def_id_to_hir_id(did)).unwrap_or(CRATE_HIR_ID),
        )
    };
    do_check_unsized_params(tcx, abi, /*is_call*/ false, loc);
    do_check_simd_vector_abi(tcx, abi, instance.def_id(), /*is_call*/ false, loc);
}

/// Check the ABI at a call site, emitting an error when:
///
/// - a non-rustic ABI uses unsized parameters
/// - the signature requires target features that are not enabled
fn check_call_site_abi<'tcx>(
    tcx: TyCtxt<'tcx>,
    callee: Ty<'tcx>,
    caller: InstanceKind<'tcx>,
    loc: impl Fn() -> (Span, HirId) + Copy,
) {
    if callee.fn_sig(tcx).abi().is_rustic_abi() {
        // We directly handle the soundness of Rust ABIs -- so let's skip the majority of
        // call sites to avoid a perf regression.
        return;
    }
    let typing_env = ty::TypingEnv::fully_monomorphized();
    let callee_abi = match *callee.kind() {
        ty::FnPtr(..) => {
            tcx.fn_abi_of_fn_ptr(typing_env.as_query_input((callee.fn_sig(tcx), ty::List::empty())))
        }
        ty::FnDef(def_id, args) => {
            // Intrinsics are handled separately by the compiler.
            if tcx.intrinsic(def_id).is_some() {
                return;
            }
            let instance = ty::Instance::expect_resolve(tcx, typing_env, def_id, args, DUMMY_SP);
            tcx.fn_abi_of_instance(typing_env.as_query_input((instance, ty::List::empty())))
        }
        _ => {
            panic!("Invalid function call");
        }
    };

    let Ok(callee_abi) = callee_abi else {
        // ABI failed to compute; this will not get through codegen.
        return;
    };
    do_check_unsized_params(tcx, callee_abi, /*is_call*/ true, loc);
    do_check_simd_vector_abi(tcx, callee_abi, caller.def_id(), /*is_call*/ true, loc);
}

fn check_callees_abi<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>, body: &mir::Body<'tcx>) {
    // Check all function call terminators.
    for (bb, _data) in traversal::mono_reachable(body, tcx, instance) {
        let terminator = body.basic_blocks[bb].terminator();
        match terminator.kind {
            mir::TerminatorKind::Call { ref func, ref fn_span, .. }
            | mir::TerminatorKind::TailCall { ref func, ref fn_span, .. } => {
                let callee_ty = func.ty(body, tcx);
                let callee_ty = instance.instantiate_mir_and_normalize_erasing_regions(
                    tcx,
                    ty::TypingEnv::fully_monomorphized(),
                    ty::EarlyBinder::bind(callee_ty),
                );
                check_call_site_abi(tcx, callee_ty, body.source.instance, || {
                    let loc = Location {
                        block: bb,
                        statement_index: body.basic_blocks[bb].statements.len(),
                    };
                    (
                        *fn_span,
                        body.source_info(loc)
                            .scope
                            .lint_root(&body.source_scopes)
                            .unwrap_or(CRATE_HIR_ID),
                    )
                });
            }
            _ => {}
        }
    }
}

pub(crate) fn check_feature_dependent_abi<'tcx>(
    tcx: TyCtxt<'tcx>,
    instance: Instance<'tcx>,
    body: &'tcx mir::Body<'tcx>,
) {
    check_instance_abi(tcx, instance);
    check_callees_abi(tcx, instance, body);
}