Rollup of 5 pull requests

compiler/rustc_abi/src/canon_abi.rs

@@ -28,6 +28,7 @@ pub enum CanonAbi {
     Rust,
     RustCold,
     RustPreserveNone,
+    RustTail,
 
     /// An ABI that rustc does not know how to call or define.
     Custom,
@@ -59,7 +60,10 @@ pub enum CanonAbi {
 impl CanonAbi {
     pub fn is_rustic_abi(self) -> bool {
         match self {
-            CanonAbi::Rust | CanonAbi::RustCold | CanonAbi::RustPreserveNone => true,
+            CanonAbi::Rust
+            | CanonAbi::RustCold
+            | CanonAbi::RustPreserveNone
+            | CanonAbi::RustTail => true,
             CanonAbi::C
             | CanonAbi::Custom
             | CanonAbi::Swift
@@ -81,6 +85,7 @@ impl fmt::Display for CanonAbi {
             CanonAbi::Rust => ExternAbi::Rust,
             CanonAbi::RustCold => ExternAbi::RustCold,
             CanonAbi::RustPreserveNone => ExternAbi::RustPreserveNone,
+            CanonAbi::RustTail => ExternAbi::RustTail,
             CanonAbi::Custom => ExternAbi::Custom,
             CanonAbi::Swift => ExternAbi::Swift,
             CanonAbi::Arm(arm_call) => match arm_call {

compiler/rustc_abi/src/extern_abi.rs

@@ -49,6 +49,11 @@ pub enum ExternAbi {
     /// forcing callers to save all registers.
     RustPreserveNone,
 
+    /// Ensures that calls in tail position can always be optimized into a jump.
+    ///
+    /// This ABI is not stable, and relies on LLVM implementation details.
+    RustTail,
+
     /// Unstable impl detail that directly uses Rust types to describe the ABI to LLVM.
     /// Even normally-compatible Rust types can become ABI-incompatible with this ABI!
     Unadjusted,
@@ -205,6 +210,7 @@ abi_impls! {
             System { unwind: true } =><= "system-unwind",
             SysV64 { unwind: false } =><= "sysv64",
             SysV64 { unwind: true } =><= "sysv64-unwind",
+            RustTail =><= "tail",
             Thiscall { unwind: false } =><= "thiscall",
             Thiscall { unwind: true } =><= "thiscall-unwind",
             Unadjusted =><= "unadjusted",
@@ -280,7 +286,7 @@ impl ExternAbi {
     /// - are subject to change between compiler versions
     pub fn is_rustic_abi(self) -> bool {
         use ExternAbi::*;
-        matches!(self, Rust | RustCall | RustCold | RustPreserveNone)
+        matches!(self, Rust | RustCall | RustCold | RustPreserveNone | RustTail)
     }
 
     /// Returns whether the ABI supports C variadics. This only controls whether we allow *imports*
@@ -354,6 +360,7 @@ impl ExternAbi {
             | Self::SysV64 { .. }
             | Self::Win64 { .. }
             | Self::RustPreserveNone
+            | Self::RustTail
             | Self::Swift => true,
         }
     }

compiler/rustc_ast_lowering/src/stability.rs

@@ -100,6 +100,9 @@ pub fn extern_abi_stability(abi: ExternAbi) -> Result<(), UnstableAbi> {
             feature: sym::rust_preserve_none_cc,
             explain: GateReason::Experimental,
         }),
+        ExternAbi::RustTail => {
+            Err(UnstableAbi { abi, feature: sym::rust_tail_cc, explain: GateReason::Experimental })
+        }
         ExternAbi::RustInvalid => {
             Err(UnstableAbi { abi, feature: sym::rustc_attrs, explain: GateReason::ImplDetail })
         }

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -424,6 +424,7 @@ impl<'a> AstValidator<'a> {
                     | CanonAbi::Rust
                     | CanonAbi::RustCold
                     | CanonAbi::RustPreserveNone
+                    | CanonAbi::RustTail
                     | CanonAbi::Swift
                     | CanonAbi::Arm(_)
                     | CanonAbi::X86(_) => { /* nothing to check */ }

compiler/rustc_borrowck/src/type_check/constraint_conversion.rs

@@ -1,7 +1,7 @@
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::LocalDefId;
 use rustc_infer::infer::SubregionOrigin;
-use rustc_infer::infer::canonical::QueryRegionConstraints;
+use rustc_infer::infer::canonical::{QueryRegionConstraint, QueryRegionConstraints};
 use rustc_infer::infer::outlives::env::RegionBoundPairs;
 use rustc_infer::infer::outlives::obligations::{TypeOutlives, TypeOutlivesDelegate};
 use rustc_infer::infer::region_constraints::{GenericKind, VerifyBound};
@@ -74,9 +74,9 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         let assumptions =
             elaborate::elaborate_outlives_assumptions(self.infcx.tcx, assumptions.iter().copied());
 
-        for &(constraint, constraint_category, _) in constraints {
+        for &QueryRegionConstraint { constraint, category, .. } in constraints {
             constraint.iter_outlives().for_each(|predicate| {
-                self.convert(predicate, constraint_category, &assumptions);
+                self.convert(predicate, category, &assumptions);
             });
         }
     }
@@ -296,7 +296,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
                 // FIXME(higher_ranked_auto): What should we do with the assumptions here?
                 if let Some(QueryRegionConstraints { constraints, assumptions: _ }) = constraints {
                     next_outlives_predicates.extend(constraints.iter().flat_map(
-                        |(constraint, category, _)| {
+                        |QueryRegionConstraint { constraint, category, .. }| {
                             constraint.iter_outlives().map(|outlives| (outlives, *category))
                         },
                     ));

compiler/rustc_codegen_cranelift/src/abi/mod.rs

@@ -55,8 +55,9 @@ pub(crate) fn conv_to_call_conv(
     match c {
         CanonAbi::Rust | CanonAbi::RustCold | CanonAbi::C => default_call_conv,
 
-        // Cranelift doesn't currently have anything for this.
-        CanonAbi::RustPreserveNone => default_call_conv,
+        CanonAbi::RustPreserveNone | CanonAbi::RustTail => {
+            sess.dcx().fatal(format!("call conv {c:?} is LLVM-specific"))
+        }
 
         // Functions with this calling convention can only be called from assembly, but it is
         // possible to declare an `extern "custom"` block, so the backend still needs a calling
@@ -71,7 +72,7 @@ pub(crate) fn conv_to_call_conv(
         },
 
         CanonAbi::Interrupt(_) | CanonAbi::Arm(_) | CanonAbi::Swift => {
-            sess.dcx().fatal("call conv {c:?} is not yet implemented")
+            sess.dcx().fatal(format!("call conv {c:?} is not yet implemented"))
         }
         CanonAbi::GpuKernel => {
             unreachable!("tried to use {c:?} call conv which only exists on an unsupported target")

compiler/rustc_codegen_gcc/src/abi.rs

@@ -10,7 +10,7 @@ use rustc_middle::bug;
 use rustc_middle::ty::Ty;
 use rustc_middle::ty::layout::LayoutOf;
 #[cfg(feature = "master")]
-use rustc_session::config;
+use rustc_session::{Session, config};
 use rustc_target::callconv::{ArgAttributes, CastTarget, FnAbi, PassMode};
 #[cfg(feature = "master")]
 use rustc_target::spec::Arch;
@@ -230,32 +230,43 @@ impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
 
     #[cfg(feature = "master")]
     fn gcc_cconv(&self, cx: &CodegenCx<'gcc, 'tcx>) -> Option<FnAttribute<'gcc>> {
-        conv_to_fn_attribute(self.conv, &cx.tcx.sess.target.arch)
+        conv_to_fn_attribute(cx.sess(), self.conv)
     }
 }
 
 #[cfg(feature = "master")]
-pub fn conv_to_fn_attribute<'gcc>(conv: CanonAbi, arch: &Arch) -> Option<FnAttribute<'gcc>> {
+pub fn conv_to_fn_attribute<'gcc>(sess: &Session, conv: CanonAbi) -> Option<FnAttribute<'gcc>> {
     let attribute = match conv {
         CanonAbi::C | CanonAbi::Rust => return None,
-        // gcc/gccjit does not have anything for this.
-        CanonAbi::RustPreserveNone => return None,
+        CanonAbi::RustPreserveNone => {
+            // This calling convention is LLVM-specific and unspecified.
+            sess.dcx()
+                .fatal("gcc/gccjit backend does not support RustPreserveNone calling convention")
+        }
+        CanonAbi::RustTail => {
+            // This calling convention is LLVM-specific and unspecified.
+            sess.dcx().fatal("gcc/gccjit backend does not support RustTail calling convention")
+        }
         CanonAbi::RustCold => FnAttribute::Cold,
         // Functions with this calling convention can only be called from assembly, but it is
         // possible to declare an `extern "custom"` block, so the backend still needs a calling
         // convention for declaring foreign functions.
         CanonAbi::Custom => return None,
-        // gcc/gccjit does not have anything for Swift's calling convention.
-        CanonAbi::Swift => panic!("gcc/gccjit backend does not support Swift calling convention"),
+        CanonAbi::Swift => {
+            // gcc/gccjit does not have anything for Swift's calling convention.
+            sess.dcx().fatal("gcc/gccjit backend does not support Swift calling convention")
+        }
         CanonAbi::Arm(arm_call) => match arm_call {
             ArmCall::CCmseNonSecureCall => FnAttribute::ArmCmseNonsecureCall,
             ArmCall::CCmseNonSecureEntry => FnAttribute::ArmCmseNonsecureEntry,
             ArmCall::Aapcs => FnAttribute::ArmPcs("aapcs"),
         },
-        CanonAbi::GpuKernel => match arch {
+        CanonAbi::GpuKernel => match &sess.target.arch {
             &Arch::AmdGpu => FnAttribute::GcnAmdGpuHsaKernel,
             &Arch::Nvptx64 => FnAttribute::NvptxKernel,
-            arch => panic!("Arch {arch} does not support GpuKernel calling convention"),
+            arch => sess
+                .dcx()
+                .fatal(format!("Arch {arch} does not support GpuKernel calling convention")),
         },
         // FIXME(antoyo): check if those AVR attributes are mapped correctly.
         CanonAbi::Interrupt(interrupt_kind) => match interrupt_kind {

compiler/rustc_codegen_gcc/src/context.rs

@@ -486,10 +486,10 @@ impl<'gcc, 'tcx> MiscCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
     fn declare_c_main(&self, fn_type: Self::Type) -> Option<Self::Function> {
         let entry_name = self.sess().target.entry_name.as_ref();
         if !self.functions.borrow().contains_key(entry_name) {
-            #[cfg(feature = "master")]
-            let conv = conv_to_fn_attribute(self.sess().target.entry_abi, &self.sess().target.arch);
-            #[cfg(not(feature = "master"))]
-            let conv = None;
+            let conv = cfg_select! {
+                feature = "master" => conv_to_fn_attribute(self.sess(), self.sess().target.entry_abi),
+                _ => None,
+            };
             Some(self.declare_entry_fn(entry_name, fn_type, conv))
         } else {
             // If the symbol already exists, it is an error: for example, the user wrote

compiler/rustc_codegen_llvm/src/abi.rs

@@ -723,6 +723,10 @@ pub(crate) fn to_llvm_calling_convention(sess: &Session, abi: CanonAbi) -> llvm:
             Arch::X86_64 | Arch::AArch64 => llvm::PreserveNone,
             _ => llvm::CCallConv,
         },
+        CanonAbi::RustTail => match &sess.target.arch {
+            Arch::X86 | Arch::X86_64 | Arch::AArch64 => llvm::Tail,
+            _ => sess.dcx().fatal("extern \"tail\" is only supported on x86_64 and aarch64"),
+        },
         // Functions with this calling convention can only be called from assembly, but it is
         // possible to declare an `extern "custom"` block, so the backend still needs a calling
         // convention for declaring foreign functions.

compiler/rustc_feature/src/unstable.rs

@@ -709,6 +709,8 @@ declare_features! (
     (unstable, rust_cold_cc, "1.63.0", Some(97544)),
     /// Allows `extern "rust-preserve-none"`.
     (unstable, rust_preserve_none_cc, "1.95.0", Some(151401)),
+    /// Allows `extern "tail"`.
+    (unstable, rust_tail_cc, "CURRENT_RUSTC_VERSION", Some(157427)),
     /// Target features on s390x.
     (unstable, s390x_target_feature, "1.82.0", Some(150259)),
     /// Allows the use of the `sanitize` attribute.

compiler/rustc_hir_typeck/src/callee.rs

@@ -205,6 +205,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             | CanonAbi::Rust
             | CanonAbi::RustCold
             | CanonAbi::RustPreserveNone
+            | CanonAbi::RustTail
             | CanonAbi::Swift
             | CanonAbi::Arm(_)
             | CanonAbi::X86(_) => {}

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -4796,7 +4796,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let hir::Node::Expr(rcvr) = self.tcx.hir_node(hir_id) else {
             return false;
         };
-        let trait_ref = ty::TraitRef::new(self.tcx, trait_def_id, rcvr_ty.into_iter());
+        // The trait may have generic parameters beyond `Self` (e.g. `Borrow<Borrowed>`), and
+        // `rcvr_ty` may even be unknown. We only ever know the receiver type (the `Self` arg),
+        // so fill `Self` from `rcvr_ty` when available and the remaining parameters with fresh
+        // inference variables; building a `TraitRef` with a partial arg list would otherwise trip
+        // `debug_assert_args_compatible` and ICE. See #157189.
+        let trait_ref = ty::TraitRef::new_from_args(
+            self.tcx,
+            trait_def_id,
+            ty::GenericArgs::for_item(self.tcx, trait_def_id, |param, _| {
+                if param.index == 0
+                    && let Some(rcvr_ty) = rcvr_ty
+                {
+                    rcvr_ty.into()
+                } else {
+                    self.var_for_def(rcvr.span, param)
+                }
+            }),
+        );
         let trait_pred = ty::Binder::dummy(ty::TraitPredicate {
             trait_ref,
             polarity: ty::PredicatePolarity::Positive,

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -13,7 +13,7 @@ use std::iter;
 use rustc_index::{Idx, IndexVec};
 use rustc_middle::arena::ArenaAllocatable;
 use rustc_middle::bug;
-use rustc_middle::infer::canonical::CanonicalVarKind;
+use rustc_middle::infer::canonical::{CanonicalVarKind, QueryRegionConstraint};
 use rustc_middle::ty::{self, BoundVar, GenericArg, GenericArgKind, Ty, TyCtxt, TypeFoldable};
 use tracing::{debug, instrument};
 
@@ -188,7 +188,9 @@ impl<'tcx> InferCtxt<'tcx> {
         let InferOk { value: result_args, obligations } =
             self.query_response_instantiation(cause, param_env, original_values, query_response)?;
 
-        for (constraint, _category, vis) in &query_response.value.region_constraints.constraints {
+        for QueryRegionConstraint { constraint, visible_for_leak_check: vis, .. } in
+            &query_response.value.region_constraints.constraints
+        {
             let constraint = instantiate_value(self.tcx, &result_args, *constraint);
             match constraint {
                 ty::RegionConstraint::Outlives(predicate) => {
@@ -285,11 +287,12 @@ impl<'tcx> InferCtxt<'tcx> {
 
                 (GenericArgKind::Lifetime(v_o), GenericArgKind::Lifetime(v_r)) => {
                     if v_o != v_r {
-                        output_query_region_constraints.constraints.push((
-                            ty::RegionEqPredicate(v_o, v_r).into(),
-                            constraint_category,
-                            ty::VisibleForLeakCheck::Yes,
-                        ));
+                        let constraint = QueryRegionConstraint {
+                            constraint: ty::RegionEqPredicate(v_o, v_r).into(),
+                            category: constraint_category,
+                            visible_for_leak_check: ty::VisibleForLeakCheck::Yes,
+                        };
+                        output_query_region_constraints.constraints.push(constraint);
                     }
                 }
 
@@ -321,7 +324,7 @@ impl<'tcx> InferCtxt<'tcx> {
                 let r_c = instantiate_value(self.tcx, &result_args, r_c);
 
                 // Screen out `'a: 'a` or `'a == 'a` cases.
-                if r_c.0.is_trivial() { None } else { Some(r_c) }
+                if r_c.constraint.is_trivial() { None } else { Some(r_c) }
             }),
         );
 
@@ -616,7 +619,7 @@ pub fn make_query_region_constraints<'tcx>(
 
     debug!(?constraints);
 
-    let constraints: Vec<_> = constraints
+    let constraints: Vec<QueryRegionConstraint<'tcx>> = constraints
         .iter()
         .map(|(c, origin)| match c.kind {
             ConstraintKind::VarSubVar
@@ -625,22 +628,30 @@ pub fn make_query_region_constraints<'tcx>(
             | ConstraintKind::RegSubReg => {
                 // Swap regions because we are going from sub (<=) to outlives (>=).
                 let constraint = ty::OutlivesPredicate(c.sup.into(), c.sub).into();
-                (constraint, origin.to_constraint_category(), c.visible_for_leak_check)
+                QueryRegionConstraint {
+                    constraint,
+                    category: origin.to_constraint_category(),
+                    visible_for_leak_check: c.visible_for_leak_check,
+                }
             }
 
             ConstraintKind::VarEqVar | ConstraintKind::VarEqReg | ConstraintKind::RegEqReg => {
                 let constraint = ty::RegionEqPredicate(c.sup, c.sub).into();
-                (constraint, origin.to_constraint_category(), c.visible_for_leak_check)
+                QueryRegionConstraint {
+                    constraint,
+                    category: origin.to_constraint_category(),
+                    visible_for_leak_check: c.visible_for_leak_check,
+                }
             }
         })
         .chain(outlives_obligations.into_iter().map(
             |TypeOutlivesConstraint { sub_region, sup_type, origin }| {
-                (
-                    ty::OutlivesPredicate(sup_type.into(), sub_region).into(),
-                    origin.to_constraint_category(),
+                QueryRegionConstraint {
+                    constraint: ty::OutlivesPredicate(sup_type.into(), sub_region).into(),
+                    category: origin.to_constraint_category(),
                     // We don't do leak checks for type outlives
-                    ty::VisibleForLeakCheck::Unreachable,
-                )
+                    visible_for_leak_check: ty::VisibleForLeakCheck::Unreachable,
+                }
             },
         ))
         .collect();

compiler/rustc_middle/src/infer/canonical.rs

@@ -135,9 +135,12 @@ impl<'tcx, R> QueryResponse<'tcx, R> {
     }
 }
 
-// FIXME: Convert this into a struct
-pub type QueryRegionConstraint<'tcx> =
-    (ty::RegionConstraint<'tcx>, ConstraintCategory<'tcx>, ty::VisibleForLeakCheck);
+#[derive(Debug, StableHash, Hash, Eq, PartialEq, TypeVisitable, Clone, TypeFoldable, Copy)]
+pub struct QueryRegionConstraint<'tcx> {
+    pub constraint: ty::RegionConstraint<'tcx>,
+    pub category: ConstraintCategory<'tcx>,
+    pub visible_for_leak_check: ty::VisibleForLeakCheck,
+}
 
 #[derive(Default)]
 pub struct CanonicalParamEnvCache<'tcx> {

compiler/rustc_middle/src/ty/layout.rs

@@ -1305,7 +1305,9 @@ pub fn fn_can_unwind(tcx: TyCtxt<'_>, fn_def_id: Option<DefId>, abi: ExternAbi)
         | RustInvalid
         | Swift
         | Unadjusted => false,
-        Rust | RustCall | RustCold | RustPreserveNone => tcx.sess.panic_strategy().unwinds(),
+        Rust | RustCall | RustCold | RustPreserveNone | RustTail => {
+            tcx.sess.panic_strategy().unwinds()
+        }
     }
 }
 

compiler/rustc_public/src/abi.rs

@@ -455,6 +455,7 @@ pub enum CallConvention {
     PreserveMost,
     PreserveAll,
     PreserveNone,
+    Tail,
 
     Custom,