Rollup merge of rust-lang#142923 - folkertdev:min-function-alignment-no-attributes, r=workingjubilee

fix `-Zmin-function-alignment` on functions without attributes

tracking issue: rust-lang#82232
related: rust-lang#142854

The minimum function alignment was skipped on functions without attributes (because the logic was in a loop that only runs if there is at least one attribute). The underlying reason we didn't catch this before is that in our testing we generally apply `#[no_mangle]` to functions that are tested. I've added a test now that deliberately has no attributes.

r? `@workingjubilee`

Author: workingjubilee

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -146,12 +146,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
             }
         }
 
-        // Apply the minimum function alignment here, so that individual backends don't have to.
-        codegen_fn_attrs.alignment = Ord::max(
-            codegen_fn_attrs.alignment,
-            tcx.sess.opts.unstable_opts.min_function_alignment,
-        );
-
         let Some(Ident { name, .. }) = attr.ident() else {
             continue;
         };
@@ -454,6 +448,10 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
 
     mixed_export_name_no_mangle_lint_state.lint_if_mixed(tcx);
 
+    // Apply the minimum function alignment here, so that individual backends don't have to.
+    codegen_fn_attrs.alignment =
+        Ord::max(codegen_fn_attrs.alignment, tcx.sess.opts.unstable_opts.min_function_alignment);
+
     let inline_span;
     (codegen_fn_attrs.inline, inline_span) = if let Some((inline_attr, span)) =
         find_attr!(attrs, AttributeKind::Inline(i, span) => (*i, *span))

tests/codegen/min-function-alignment.rs

@@ -1,17 +1,19 @@
 //@ revisions: align16 align1024
-//@ compile-flags: -C no-prepopulate-passes -Z mir-opt-level=0
+//@ 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
 
 #![crate_type = "lib"]
 #![feature(fn_align)]
 
-// functions without explicit alignment use the global minimum
+// Functions without explicit alignment use the global minimum.
 //
-// CHECK-LABEL: @no_explicit_align
+// NOTE: this function deliberately has zero (0) attributes! That is to make sure that
+// `-Zmin-function-alignment` is applied regardless of whether attributes are used.
+//
+// CHECK-LABEL: no_explicit_align
 // align16: align 16
 // align1024: align 1024
-#[no_mangle]
 pub fn no_explicit_align() {}
 
 // CHECK-LABEL: @lower_align