Remove ffi_returns_twice feature

Author: clubby789

compiler/rustc_codegen_gcc/src/attributes.rs

@@ -62,9 +62,6 @@ pub fn from_fn_attrs<'gcc, 'tcx>(
         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
             func.add_attribute(FnAttribute::Cold);
         }
-        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_RETURNS_TWICE) {
-            func.add_attribute(FnAttribute::ReturnsTwice);
-        }
         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_PURE) {
             func.add_attribute(FnAttribute::Pure);
         }

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -356,9 +356,6 @@ pub fn from_fn_attrs<'ll, 'tcx>(
     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
         to_add.push(AttributeKind::Cold.create_attr(cx.llcx));
     }
-    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_RETURNS_TWICE) {
-        to_add.push(AttributeKind::ReturnsTwice.create_attr(cx.llcx));
-    }
     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_PURE) {
         to_add.push(MemoryEffects::ReadOnly.create_attr(cx.llcx));
     }

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -185,7 +185,6 @@ pub enum AttributeKind {
     SanitizeMemory = 22,
     NonLazyBind = 23,
     OptimizeNone = 24,
-    ReturnsTwice = 25,
     ReadNone = 26,
     SanitizeHWAddress = 28,
     WillReturn = 29,

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -103,9 +103,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         match name {
             sym::cold => codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD,
             sym::rustc_allocator => codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR,
-            sym::ffi_returns_twice => {
-                codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE
-            }
             sym::ffi_pure => codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE,
             sym::ffi_const => codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST,
             sym::rustc_nounwind => codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND,

compiler/rustc_error_codes/src/error_codes/E0724.md

@@ -463,7 +463,6 @@ E0718: 0718,
 E0719: 0719,
 E0720: 0720,
 E0722: 0722,
-E0724: 0724,
 E0725: 0725,
 E0726: 0726,
 E0727: 0727,
@@ -675,5 +674,6 @@ E0797: 0797,
 //  E0709, // multiple different lifetimes used in arguments of `async fn`
 //  E0721, // `await` keyword
 //  E0723, // unstable feature in `const` context
+//  E0723, // `ffi_returns_twice` on something other than foreign function
 //  E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
 //  E0744, // merged into E0728

compiler/rustc_error_codes/src/lib.rs

@@ -440,9 +440,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         experimental!(optimize),
     ),
 
-    gated!(
-        ffi_returns_twice, Normal, template!(Word), WarnFollowing, experimental!(ffi_returns_twice)
-    ),
     gated!(ffi_pure, Normal, template!(Word), WarnFollowing, experimental!(ffi_pure)),
     gated!(ffi_const, Normal, template!(Word), WarnFollowing, experimental!(ffi_const)),
     gated!(

compiler/rustc_feature/src/builtin_attrs.rs

@@ -95,6 +95,9 @@ declare_features! (
     /// Allows `#[doc(include = "some-file")]`.
     (removed, external_doc, "1.54.0", Some(44732),
      Some("use #[doc = include_str!(\"filename\")] instead, which handles macro invocations")),
+    /// Allows using `#[ffi_returns_twice]` on foreign functions.
+    (removed, ffi_returns_twice, "CURRENT_RUSTC_VERSION", Some(58314),
+     Some("being investigated by the ffi-unwind project group")),
     /// Allows generators to be cloned.
     (removed, generator_clone, "1.65.0", Some(95360), Some("renamed to `coroutine_clone`")),
     /// Allows defining generators.

compiler/rustc_feature/src/removed.rs

@@ -467,8 +467,6 @@ declare_features! (
     (unstable, ffi_const, "1.45.0", Some(58328)),
     /// Allows the use of `#[ffi_pure]` on foreign functions.
     (unstable, ffi_pure, "1.45.0", Some(58329)),
-    /// Allows using `#[ffi_returns_twice]` on foreign functions.
-    (unstable, ffi_returns_twice, "1.34.0", Some(58314)),
     /// Allows using `#[repr(align(...))]` on function items
     (unstable, fn_align, "1.53.0", Some(82232)),
     /// Support delegating implementation of functions to other already implemented functions.

compiler/rustc_feature/src/unstable.rs

@@ -76,7 +76,6 @@ enum LLVMRustAttribute {
   SanitizeMemory = 22,
   NonLazyBind = 23,
   OptimizeNone = 24,
-  ReturnsTwice = 25,
   ReadNone = 26,
   SanitizeHWAddress = 28,
   WillReturn = 29,

compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h

@@ -250,8 +250,6 @@ static Attribute::AttrKind fromRust(LLVMRustAttribute Kind) {
     return Attribute::NonLazyBind;
   case OptimizeNone:
     return Attribute::OptimizeNone;
-  case ReturnsTwice:
-    return Attribute::ReturnsTwice;
   case ReadNone:
     return Attribute::ReadNone;
   case SanitizeHWAddress:

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -74,35 +74,32 @@ bitflags! {
         /// `#[used]`: indicates that LLVM can't eliminate this function (but the
         /// linker can!).
         const USED                      = 1 << 9;
-        /// `#[ffi_returns_twice]`, indicates that an extern function can return
-        /// multiple times
-        const FFI_RETURNS_TWICE         = 1 << 10;
         /// `#[track_caller]`: allow access to the caller location
-        const TRACK_CALLER              = 1 << 11;
+        const TRACK_CALLER              = 1 << 10;
         /// #[ffi_pure]: applies clang's `pure` attribute to a foreign function
         /// declaration.
-        const FFI_PURE                  = 1 << 12;
+        const FFI_PURE                  = 1 << 11;
         /// #[ffi_const]: applies clang's `const` attribute to a foreign function
         /// declaration.
-        const FFI_CONST                 = 1 << 13;
+        const FFI_CONST                 = 1 << 12;
         /// #[cmse_nonsecure_entry]: with a TrustZone-M extension, declare a
         /// function as an entry function from Non-Secure code.
-        const CMSE_NONSECURE_ENTRY      = 1 << 14;
+        const CMSE_NONSECURE_ENTRY      = 1 << 13;
         /// `#[coverage(off)]`: indicates that the function should be ignored by
         /// the MIR `InstrumentCoverage` pass and not added to the coverage map
         /// during codegen.
-        const NO_COVERAGE               = 1 << 15;
+        const NO_COVERAGE               = 1 << 14;
         /// `#[used(linker)]`:
         /// indicates that neither LLVM nor the linker will eliminate this function.
-        const USED_LINKER               = 1 << 16;
+        const USED_LINKER               = 1 << 15;
         /// `#[rustc_deallocator]`: a hint to LLVM that the function only deallocates memory.
-        const DEALLOCATOR               = 1 << 17;
+        const DEALLOCATOR               = 1 << 16;
         /// `#[rustc_reallocator]`: a hint to LLVM that the function only reallocates memory.
-        const REALLOCATOR               = 1 << 18;
+        const REALLOCATOR               = 1 << 17;
         /// `#[rustc_allocator_zeroed]`: a hint to LLVM that the function only allocates zeroed memory.
-        const ALLOCATOR_ZEROED          = 1 << 19;
+        const ALLOCATOR_ZEROED          = 1 << 18;
         /// `#[no_builtins]`: indicates that disable implicit builtin knowledge of functions for the function.
-        const NO_BUILTINS               = 1 << 20;
+        const NO_BUILTINS               = 1 << 19;
     }
 }
 rustc_data_structures::external_bitflags_debug! { CodegenFnAttrFlags }

compiler/rustc_middle/src/middle/codegen_fn_attrs.rs

@@ -323,9 +323,6 @@ passes_ffi_const_invalid_target =
 passes_ffi_pure_invalid_target =
     `#[ffi_pure]` may only be used on foreign functions
 
-passes_ffi_returns_twice_invalid_target =
-    `#[ffi_returns_twice]` may only be used on foreign functions
-
 passes_has_incoherent_inherent_impl =
     `rustc_has_incoherent_inherent_impls` attribute should be applied to types or traits.
     .label = only adts, extern types and traits are supported

compiler/rustc_passes/messages.ftl

@@ -190,7 +190,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 }
                 sym::ffi_pure => self.check_ffi_pure(attr.span, attrs, target),
                 sym::ffi_const => self.check_ffi_const(attr.span, target),
-                sym::ffi_returns_twice => self.check_ffi_returns_twice(attr.span, target),
                 sym::rustc_const_unstable
                 | sym::rustc_const_stable
                 | sym::unstable
@@ -1307,15 +1306,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_ffi_returns_twice(&self, attr_span: Span, target: Target) -> bool {
-        if target == Target::ForeignFn {
-            true
-        } else {
-            self.dcx().emit_err(errors::FfiReturnsTwiceInvalidTarget { attr_span });
-            false
-        }
-    }
-
     /// Warns against some misuses of `#[must_use]`
     fn check_must_use(&self, hir_id: HirId, attr: &Attribute, target: Target) -> bool {
         if !matches!(

compiler/rustc_passes/src/check_attr.rs

@@ -390,13 +390,6 @@ pub struct FfiConstInvalidTarget {
     pub attr_span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(passes_ffi_returns_twice_invalid_target, code = E0724)]
-pub struct FfiReturnsTwiceInvalidTarget {
-    #[primary_span]
-    pub attr_span: Span,
-}
-
 #[derive(LintDiagnostic)]
 #[diag(passes_must_use_async)]
 pub struct MustUseAsync {

compiler/rustc_passes/src/errors.rs

@@ -14,7 +14,7 @@ use std::path::{Path, PathBuf};
 // #73494.
 const ENTRY_LIMIT: usize = 900;
 const ISSUES_ENTRY_LIMIT: usize = 1807;
-const ROOT_ENTRY_LIMIT: usize = 870;
+const ROOT_ENTRY_LIMIT: usize = 868;
 
 const EXPECTED_TEST_FILE_EXTENSIONS: &[&str] = &[
     "rs",     // test source files