Rollup merge of #143206 - Jules-Bertholet:align-attr-fixes, r=workingjubilee

Align attr fixes

- Remove references to the superseded `repr(align)` syntax
- Allow the attribute on fn items in `extern` blocks
- Test attribute in combination with `async fn` and `dyn`

r? workingjubilee

Tracking issue: #82232
`@rustbot` label A-attributes F-fn_align T-compiler

Author: jhpratt

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -4,7 +4,7 @@ use rustc_abi::{Align, ExternAbi};
 use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, DiffActivity, DiffMode};
 use rustc_ast::{LitKind, MetaItem, MetaItemInner, attr};
 use rustc_attr_data_structures::{
-    AttributeKind, InlineAttr, InstructionSetAttr, OptimizeAttr, ReprAttr, UsedBy, find_attr,
+    AttributeKind, InlineAttr, InstructionSetAttr, OptimizeAttr, UsedBy, find_attr,
 };
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
@@ -109,14 +109,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
 
         if let hir::Attribute::Parsed(p) = attr {
             match p {
-                AttributeKind::Repr { reprs, first_span: _ } => {
-                    codegen_fn_attrs.alignment = reprs
-                        .iter()
-                        .filter_map(
-                            |(r, _)| if let ReprAttr::ReprAlign(x) = r { Some(*x) } else { None },
-                        )
-                        .max();
-                }
                 AttributeKind::Cold(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD,
                 AttributeKind::ExportName { name, .. } => {
                     codegen_fn_attrs.export_name = Some(*name);

compiler/rustc_passes/messages.ftl

@@ -13,6 +13,10 @@ passes_abi_ne =
 passes_abi_of =
     fn_abi_of({$fn_name}) = {$fn_abi}
 
+passes_align_attr_application =
+    `#[align(...)]` should be applied to a function item
+    .label = not a function item
+
 passes_align_should_be_repr_align =
     `#[align(...)]` is not supported on {$item} items
     .suggestion = use `#[repr(align(...))]` instead

compiler/rustc_passes/src/check_attr.rs

@@ -1915,7 +1915,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     /// Checks if the `#[align]` attributes on `item` are valid.
     fn check_align(&self, span: Span, target: Target, align: Align, repr_span: Span) {
         match target {
-            Target::Fn | Target::Method(_) => {}
+            Target::Fn | Target::Method(_) | Target::ForeignFn => {}
             Target::Struct | Target::Union | Target::Enum => {
                 self.dcx().emit_err(errors::AlignShouldBeReprAlign {
                     span: repr_span,
@@ -1924,10 +1924,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 });
             }
             _ => {
-                self.dcx().emit_err(errors::AttrApplication::StructEnumUnion {
-                    hint_span: repr_span,
-                    span,
-                });
+                self.dcx().emit_err(errors::AlignAttrApplication { hint_span: repr_span, span });
             }
         }
 

compiler/rustc_passes/src/errors.rs

@@ -1838,3 +1838,12 @@ pub(crate) struct AlignShouldBeReprAlign {
     pub item: &'static str,
     pub align_bytes: u64,
 }
+
+#[derive(Diagnostic)]
+#[diag(passes_align_attr_application)]
+pub(crate) struct AlignAttrApplication {
+    #[primary_span]
+    pub hint_span: Span,
+    #[label]
+    pub span: Span,
+}

tests/assembly/naked-functions/wasm32.rs

@@ -27,18 +27,16 @@ extern "C" fn nop() {
     naked_asm!("nop")
 }
 
-// CHECK: .section  .text.weak_aligned_nop,"",@
-// CHECK: .weak weak_aligned_nop
+// CHECK: .section  .text.weak_nop,"",@
+// CHECK: .weak weak_nop
 // CHECK-LABEL: nop:
-// CHECK: .functype weak_aligned_nop () -> ()
+// CHECK: .functype weak_nop () -> ()
 // CHECK-NOT: .size
 // CHECK: end_function
 #[no_mangle]
 #[unsafe(naked)]
 #[linkage = "weak"]
-// wasm functions cannot be aligned, so this has no effect
-#[align(32)]
-extern "C" fn weak_aligned_nop() {
+extern "C" fn weak_nop() {
     naked_asm!("nop")
 }
 

tests/codegen/align-fn.rs

@@ -1,4 +1,6 @@
 //@ compile-flags: -C no-prepopulate-passes -Z mir-opt-level=0 -Clink-dead-code
+//@ edition: 2024
+//@ ignore-wasm32 aligning functions is not currently supported on wasm (#143368)
 
 #![crate_type = "lib"]
 #![feature(fn_align)]
@@ -116,3 +118,24 @@ pub fn align_specified_twice_2() {}
 #[align(32)]
 #[align(256)]
 pub fn align_specified_twice_3() {}
+
+const _: () = {
+    // CHECK-LABEL: align_unmangled
+    // CHECK-SAME: align 256
+    #[unsafe(no_mangle)]
+    #[align(32)]
+    #[align(256)]
+    extern "C" fn align_unmangled() {}
+};
+
+unsafe extern "C" {
+    #[align(256)]
+    fn align_unmangled();
+}
+
+// FIXME also check `gen` et al
+// CHECK-LABEL: async_align
+// CHECK-SAME: align 64
+#[unsafe(no_mangle)]
+#[align(64)]
+pub async fn async_align() {}

tests/codegen/min-function-alignment.rs

@@ -2,6 +2,7 @@
 //@ compile-flags: -C no-prepopulate-passes -Z mir-opt-level=0 -Clink-dead-code
 //@ [align16] compile-flags: -Zmin-function-alignment=16
 //@ [align1024] compile-flags: -Zmin-function-alignment=1024
+//@ ignore-wasm32 aligning functions is not currently supported on wasm (#143368)
 
 #![crate_type = "lib"]
 #![feature(fn_align)]

tests/codegen/naked-fn/aligned.rs

@@ -1,6 +1,7 @@
 //@ compile-flags: -C no-prepopulate-passes -Copt-level=0
 //@ needs-asm-support
 //@ ignore-arm no "ret" mnemonic
+//@ ignore-wasm32 aligning functions is not currently supported on wasm (#143368)
 
 #![crate_type = "lib"]
 #![feature(fn_align)]

tests/codegen/naked-fn/min-function-alignment.rs

@@ -1,6 +1,7 @@
 //@ compile-flags: -C no-prepopulate-passes -Copt-level=0 -Zmin-function-alignment=16
 //@ needs-asm-support
 //@ ignore-arm no "ret" mnemonic
+//@ ignore-wasm32 aligning functions is not currently supported on wasm (#143368)
 
 #![feature(fn_align)]
 #![crate_type = "lib"]

tests/ui/attributes/fn-align-dyn.rs

@@ -0,0 +1,16 @@
+//@ run-pass
+//@ ignore-wasm32 aligning functions is not currently supported on wasm (#143368)
+#![feature(fn_align)]
+
+trait Test {
+    #[align(4096)]
+    fn foo(&self);
+
+    #[align(4096)]
+    fn foo1(&self);
+}
+
+fn main() {
+    assert_eq!((<dyn Test>::foo as fn(_) as usize & !1) % 4096, 0);
+    assert_eq!((<dyn Test>::foo1 as fn(_) as usize & !1) % 4096, 0);
+}