Consolidate ad-hoc MIR lints into real pass-manager-based MIR lints

compiler/rustc_mir_transform/src/check_call_recursion.rs

@@ -0,0 +1,266 @@
+use std::ops::ControlFlow;
+
+use rustc_data_structures::graph::iterate::{
+    NodeStatus, TriColorDepthFirstSearch, TriColorVisitor,
+};
+use rustc_hir::def::DefKind;
+use rustc_middle::mir::{self, BasicBlock, BasicBlocks, Body, Terminator, TerminatorKind};
+use rustc_middle::ty::{self, GenericArg, GenericArgs, Instance, Ty, TyCtxt};
+use rustc_session::lint::builtin::UNCONDITIONAL_RECURSION;
+use rustc_span::Span;
+
+use crate::errors::UnconditionalRecursion;
+use crate::pass_manager::MirLint;
+
+pub(super) struct CheckCallRecursion;
+
+impl<'tcx> MirLint<'tcx> for CheckCallRecursion {
+    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
+        let def_id = body.source.def_id().expect_local();
+
+        if let DefKind::Fn | DefKind::AssocFn = tcx.def_kind(def_id) {
+            // If this is trait/impl method, extract the trait's args.
+            let trait_args = match tcx.trait_of_item(def_id.to_def_id()) {
+                Some(trait_def_id) => {
+                    let trait_args_count = tcx.generics_of(trait_def_id).count();
+                    &GenericArgs::identity_for_item(tcx, def_id)[..trait_args_count]
+                }
+                _ => &[],
+            };
+
+            check_recursion(tcx, body, CallRecursion { trait_args })
+        }
+    }
+}
+
+/// Requires drop elaboration to have been performed.
+pub(super) struct CheckDropRecursion;
+
+impl<'tcx> MirLint<'tcx> for CheckDropRecursion {
+    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
+        let def_id = body.source.def_id().expect_local();
+
+        // First check if `body` is an `fn drop()` of `Drop`
+        if let DefKind::AssocFn = tcx.def_kind(def_id)
+        && let Some(trait_ref) =
+            tcx.impl_of_method(def_id.to_def_id()).and_then(|def_id| tcx.impl_trait_ref(def_id))
+        && let Some(drop_trait) = tcx.lang_items().drop_trait()
+        && drop_trait == trait_ref.instantiate_identity().def_id
+        // avoid erroneous `Drop` impls from causing ICEs below
+        && let sig = tcx.fn_sig(def_id).instantiate_identity()
+        && sig.inputs().skip_binder().len() == 1
+        {
+            // It was. Now figure out for what type `Drop` is implemented and then
+            // check for recursion.
+            if let ty::Ref(_, dropped_ty, _) =
+                tcx.liberate_late_bound_regions(def_id.to_def_id(), sig.input(0)).kind()
+            {
+                check_recursion(tcx, body, RecursiveDrop { drop_for: *dropped_ty });
+            }
+        }
+    }
+}
+
+fn check_recursion<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body: &Body<'tcx>,
+    classifier: impl TerminatorClassifier<'tcx>,
+) {
+    let def_id = body.source.def_id().expect_local();
+
+    if let DefKind::Fn | DefKind::AssocFn = tcx.def_kind(def_id) {
+        let mut vis = Search { tcx, body, classifier, reachable_recursive_calls: vec![] };
+        if let Some(NonRecursive) =
+            TriColorDepthFirstSearch::new(&body.basic_blocks).run_from_start(&mut vis)
+        {
+            return;
+        }
+        if vis.reachable_recursive_calls.is_empty() {
+            return;
+        }
+
+        vis.reachable_recursive_calls.sort();
+
+        let sp = tcx.def_span(def_id);
+        let hir_id = tcx.local_def_id_to_hir_id(def_id);
+        tcx.emit_node_span_lint(UNCONDITIONAL_RECURSION, hir_id, sp, UnconditionalRecursion {
+            span: sp,
+            call_sites: vis.reachable_recursive_calls,
+        });
+    }
+}
+
+trait TerminatorClassifier<'tcx> {
+    fn is_recursive_terminator(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        body: &Body<'tcx>,
+        terminator: &Terminator<'tcx>,
+    ) -> bool;
+}
+
+struct NonRecursive;
+
+struct Search<'mir, 'tcx, C: TerminatorClassifier<'tcx>> {
+    tcx: TyCtxt<'tcx>,
+    body: &'mir Body<'tcx>,
+    classifier: C,
+
+    reachable_recursive_calls: Vec<Span>,
+}
+
+struct CallRecursion<'tcx> {
+    trait_args: &'tcx [GenericArg<'tcx>],
+}
+
+struct RecursiveDrop<'tcx> {
+    /// The type that `Drop` is implemented for.
+    drop_for: Ty<'tcx>,
+}
+
+impl<'tcx> TerminatorClassifier<'tcx> for CallRecursion<'tcx> {
+    /// Returns `true` if `func` refers to the function we are searching in.
+    fn is_recursive_terminator(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        body: &Body<'tcx>,
+        terminator: &Terminator<'tcx>,
+    ) -> bool {
+        let TerminatorKind::Call { func, args, .. } = &terminator.kind else {
+            return false;
+        };
+
+        // Resolving function type to a specific instance that is being called is expensive. To
+        // avoid the cost we check the number of arguments first, which is sufficient to reject
+        // most of calls as non-recursive.
+        if args.len() != body.arg_count {
+            return false;
+        }
+        let caller = body.source.def_id();
+        let typing_env = body.typing_env(tcx);
+
+        let func_ty = func.ty(body, tcx);
+        if let ty::FnDef(callee, args) = *func_ty.kind() {
+            let Ok(normalized_args) = tcx.try_normalize_erasing_regions(typing_env, args) else {
+                return false;
+            };
+            let (callee, call_args) = if let Ok(Some(instance)) =
+                Instance::try_resolve(tcx, typing_env, callee, normalized_args)
+            {
+                (instance.def_id(), instance.args)
+            } else {
+                (callee, normalized_args)
+            };
+
+            // FIXME(#57965): Make this work across function boundaries
+
+            // If this is a trait fn, the args on the trait have to match, or we might be
+            // calling into an entirely different method (for example, a call from the default
+            // method in the trait to `<A as Trait<B>>::method`, where `A` and/or `B` are
+            // specific types).
+            return callee == caller && &call_args[..self.trait_args.len()] == self.trait_args;
+        }
+
+        false
+    }
+}
+
+impl<'tcx> TerminatorClassifier<'tcx> for RecursiveDrop<'tcx> {
+    fn is_recursive_terminator(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        body: &Body<'tcx>,
+        terminator: &Terminator<'tcx>,
+    ) -> bool {
+        let TerminatorKind::Drop { place, .. } = &terminator.kind else { return false };
+
+        let dropped_ty = place.ty(body, tcx).ty;
+        dropped_ty == self.drop_for
+    }
+}
+
+impl<'mir, 'tcx, C: TerminatorClassifier<'tcx>> TriColorVisitor<BasicBlocks<'tcx>>
+    for Search<'mir, 'tcx, C>
+{
+    type BreakVal = NonRecursive;
+
+    fn node_examined(
+        &mut self,
+        bb: BasicBlock,
+        prior_status: Option<NodeStatus>,
+    ) -> ControlFlow<Self::BreakVal> {
+        // Back-edge in the CFG (loop).
+        if let Some(NodeStatus::Visited) = prior_status {
+            return ControlFlow::Break(NonRecursive);
+        }
+
+        match self.body[bb].terminator().kind {
+            // These terminators return control flow to the caller.
+            TerminatorKind::UnwindTerminate(_)
+            | TerminatorKind::CoroutineDrop
+            | TerminatorKind::UnwindResume
+            | TerminatorKind::Return
+            | TerminatorKind::Unreachable
+            | TerminatorKind::Yield { .. } => ControlFlow::Break(NonRecursive),
+
+            // A InlineAsm without targets (diverging and contains no labels)
+            // is treated as non-recursing.
+            TerminatorKind::InlineAsm { ref targets, .. } => {
+                if !targets.is_empty() {
+                    ControlFlow::Continue(())
+                } else {
+                    ControlFlow::Break(NonRecursive)
+                }
+            }
+
+            // These do not.
+            TerminatorKind::Assert { .. }
+            | TerminatorKind::Call { .. }
+            | TerminatorKind::Drop { .. }
+            | TerminatorKind::FalseEdge { .. }
+            | TerminatorKind::FalseUnwind { .. }
+            | TerminatorKind::Goto { .. }
+            | TerminatorKind::SwitchInt { .. } => ControlFlow::Continue(()),
+
+            // Note that tail call terminator technically returns to the caller,
+            // but for purposes of this lint it makes sense to count it as possibly recursive,
+            // since it's still a call.
+            //
+            // If this'll be repurposed for something else, this might need to be changed.
+            TerminatorKind::TailCall { .. } => ControlFlow::Continue(()),
+        }
+    }
+
+    fn node_settled(&mut self, bb: BasicBlock) -> ControlFlow<Self::BreakVal> {
+        // When we examine a node for the last time, remember it if it is a recursive call.
+        let terminator = self.body[bb].terminator();
+
+        // FIXME(explicit_tail_calls): highlight tail calls as "recursive call site"
+        //
+        // We don't want to lint functions that recurse only through tail calls
+        // (such as `fn g() { become () }`), so just adding `| TailCall { ... }`
+        // here won't work.
+        //
+        // But at the same time we would like to highlight both calls in a function like
+        // `fn f() { if false { become f() } else { f() } }`, so we need to figure something out.
+        if self.classifier.is_recursive_terminator(self.tcx, self.body, terminator) {
+            self.reachable_recursive_calls.push(terminator.source_info.span);
+        }
+
+        ControlFlow::Continue(())
+    }
+
+    fn ignore_edge(&mut self, bb: BasicBlock, target: BasicBlock) -> bool {
+        let terminator = self.body[bb].terminator();
+        let ignore_unwind = terminator.unwind() == Some(&mir::UnwindAction::Cleanup(target))
+            && terminator.successors().count() > 1;
+        if ignore_unwind || self.classifier.is_recursive_terminator(self.tcx, self.body, terminator)
+        {
+            return true;
+        }
+        match &terminator.kind {
+            TerminatorKind::FalseEdge { imaginary_target, .. } => imaginary_target == &target,
+            _ => false,
+        }
+    }
+}

compiler/rustc_mir_transform/src/check_inline.rs

@@ -0,0 +1,91 @@
+//! Check that a body annotated with `#[rustc_force_inline]` will not fail to inline based on its
+//! definition alone (irrespective of any specific caller).
+
+use rustc_attr_parsing::InlineAttr;
+use rustc_hir::def_id::DefId;
+use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
+use rustc_middle::mir::{Body, TerminatorKind};
+use rustc_middle::ty;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::sym;
+
+use crate::pass_manager::MirLint;
+
+pub(super) struct CheckForceInline;
+
+impl<'tcx> MirLint<'tcx> for CheckForceInline {
+    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
+        let def_id = body.source.def_id();
+        if !tcx.hir().body_owner_kind(def_id).is_fn_or_closure() || !def_id.is_local() {
+            return;
+        }
+        let InlineAttr::Force { attr_span, .. } = tcx.codegen_fn_attrs(def_id).inline else {
+            return;
+        };
+
+        if let Err(reason) =
+            is_inline_valid_on_fn(tcx, def_id).and_then(|_| is_inline_valid_on_body(tcx, body))
+        {
+            tcx.dcx().emit_err(crate::errors::InvalidForceInline {
+                attr_span,
+                callee_span: tcx.def_span(def_id),
+                callee: tcx.def_path_str(def_id),
+                reason,
+            });
+        }
+    }
+}
+
+pub(super) fn is_inline_valid_on_fn<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    def_id: DefId,
+) -> Result<(), &'static str> {
+    let codegen_attrs = tcx.codegen_fn_attrs(def_id);
+    if tcx.has_attr(def_id, sym::rustc_no_mir_inline) {
+        return Err("#[rustc_no_mir_inline]");
+    }
+
+    // FIXME(#127234): Coverage instrumentation currently doesn't handle inlined
+    // MIR correctly when Modified Condition/Decision Coverage is enabled.
+    if tcx.sess.instrument_coverage_mcdc() {
+        return Err("incompatible with MC/DC coverage");
+    }
+
+    let ty = tcx.type_of(def_id);
+    if match ty.instantiate_identity().kind() {
+        ty::FnDef(..) => tcx.fn_sig(def_id).instantiate_identity().c_variadic(),
+        ty::Closure(_, args) => args.as_closure().sig().c_variadic(),
+        _ => false,
+    } {
+        return Err("C variadic");
+    }
+
+    if codegen_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
+        return Err("cold");
+    }
+
+    // Intrinsic fallback bodies are automatically made cross-crate inlineable,
+    // but at this stage we don't know whether codegen knows the intrinsic,
+    // so just conservatively don't inline it. This also ensures that we do not
+    // accidentally inline the body of an intrinsic that *must* be overridden.
+    if tcx.has_attr(def_id, sym::rustc_intrinsic) {
+        return Err("callee is an intrinsic");
+    }
+
+    Ok(())
+}
+
+pub(super) fn is_inline_valid_on_body<'tcx>(
+    _: TyCtxt<'tcx>,
+    body: &Body<'tcx>,
+) -> Result<(), &'static str> {
+    if body
+        .basic_blocks
+        .iter()
+        .any(|bb| matches!(bb.terminator().kind, TerminatorKind::TailCall { .. }))
+    {
+        return Err("can't inline functions with tail calls");
+    }
+
+    Ok(())
+}

compiler/rustc_mir_transform/src/errors.rs

@@ -9,6 +9,28 @@ use rustc_span::{Span, Symbol};
 
 use crate::fluent_generated as fluent;
 
+#[derive(LintDiagnostic)]
+#[diag(mir_transform_unconditional_recursion)]
+#[help]
+pub(crate) struct UnconditionalRecursion {
+    #[label]
+    pub(crate) span: Span,
+    #[label(mir_transform_unconditional_recursion_call_site_label)]
+    pub(crate) call_sites: Vec<Span>,
+}
+
+#[derive(Diagnostic)]
+#[diag(mir_transform_force_inline_attr)]
+#[note]
+pub(crate) struct InvalidForceInline {
+    #[primary_span]
+    pub attr_span: Span,
+    #[label(mir_transform_callee)]
+    pub callee_span: Span,
+    pub callee: String,
+    pub reason: &'static str,
+}
+
 #[derive(LintDiagnostic)]
 pub(crate) enum ConstMutate {
     #[diag(mir_transform_const_modify)]

compiler/rustc_mir_transform/src/inline.rs

@@ -21,8 +21,8 @@ use tracing::{debug, instrument, trace, trace_span};
 use crate::cost_checker::CostChecker;
 use crate::deref_separator::deref_finder;
 use crate::simplify::simplify_cfg;
-use crate::util;
 use crate::validate::validate_types;
+use crate::{check_inline, util};
 
 pub(crate) mod cycle;
 
@@ -575,7 +575,7 @@ fn try_inlining<'tcx, I: Inliner<'tcx>>(
     check_mir_is_available(inliner, caller_body, callsite.callee)?;
 
     let callee_attrs = tcx.codegen_fn_attrs(callsite.callee.def_id());
-    rustc_mir_build::check_inline::is_inline_valid_on_fn(tcx, callsite.callee.def_id())?;
+    check_inline::is_inline_valid_on_fn(tcx, callsite.callee.def_id())?;
     check_codegen_attributes(inliner, callsite, callee_attrs)?;
 
     let terminator = caller_body[callsite.block].terminator.as_ref().unwrap();
@@ -590,7 +590,7 @@ fn try_inlining<'tcx, I: Inliner<'tcx>>(
     }
 
     let callee_body = try_instance_mir(tcx, callsite.callee.def)?;
-    rustc_mir_build::check_inline::is_inline_valid_on_body(tcx, callee_body)?;
+    check_inline::is_inline_valid_on_body(tcx, callee_body)?;
     inliner.check_callee_mir_body(callsite, callee_body, callee_attrs)?;
 
     let Ok(callee_body) = callsite.callee.try_instantiate_mir_and_normalize_erasing_regions(

compiler/rustc_mir_transform/src/lib.rs

@@ -114,6 +114,8 @@ declare_passes! {
     mod add_moves_for_packed_drops : AddMovesForPackedDrops;
     mod add_retag : AddRetag;
     mod add_subtyping_projections : Subtyper;
+    mod check_inline : CheckForceInline;
+    mod check_call_recursion : CheckCallRecursion, CheckDropRecursion;
     mod check_alignment : CheckAlignment;
     mod check_const_item_mutation : CheckConstItemMutation;
     mod check_packed_ref : CheckPackedRef;
@@ -375,6 +377,8 @@ fn mir_built(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
         &mut body,
         &[
             // MIR-level lints.
+            &Lint(check_inline::CheckForceInline),
+            &Lint(check_call_recursion::CheckCallRecursion),
             &Lint(check_packed_ref::CheckPackedRef),
             &Lint(check_const_item_mutation::CheckConstItemMutation),
             &Lint(function_item_references::FunctionItemReferences),
@@ -505,10 +509,6 @@ fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &
 
     run_analysis_to_runtime_passes(tcx, &mut body);
 
-    // Now that drop elaboration has been performed, we can check for
-    // unconditional drop recursion.
-    rustc_mir_build::lints::check_drop_recursion(tcx, &body);
-
     tcx.alloc_steal_mir(body)
 }
 
@@ -570,6 +570,8 @@ fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         // Calling this after `PostAnalysisNormalize` ensures that we don't deal with opaque types.
         &add_subtyping_projections::Subtyper,
         &elaborate_drops::ElaborateDrops,
+        // Needs to happen after drop elaboration.
+        &Lint(check_call_recursion::CheckDropRecursion),
         // This will remove extraneous landing pads which are no longer
         // necessary as well as forcing any call in a non-unwinding
         // function calling a possibly-unwinding function to abort the process.