Merge from rustc

Author: oli-obk

Cargo.lock

@@ -65,6 +65,12 @@ dependencies = [
  "rand_xorshift",
 ]
 
+[[package]]
+name = "allocator-api2"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c4f263788a35611fba42eb41ff811c5d0360c58b97402570312a350736e2542e"
+
 [[package]]
 name = "ammonia"
 version = "3.2.0"
@@ -1522,6 +1528,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "33ff8ae62cd3a9102e5637afc8452c55acf3844001bd5374e0b0bd7b6616c038"
 dependencies = [
  "ahash 0.8.2",
+]
+
+[[package]]
+name = "hashbrown"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2c6201b9ff9fd90a5a3bac2e56a830d0caa509576f0e503818ee82c181b3437a"
+dependencies = [
+ "allocator-api2",
  "compiler_builtins",
  "rustc-std-workspace-alloc",
  "rustc-std-workspace-core",
@@ -4633,7 +4648,7 @@ dependencies = [
  "core",
  "dlmalloc",
  "fortanix-sgx-abi",
- "hashbrown 0.13.1",
+ "hashbrown 0.14.0",
  "hermit-abi 0.3.0",
  "libc",
  "miniz_oxide",

compiler/rustc_abi/src/layout.rs

@@ -57,48 +57,54 @@ pub trait LayoutCalculator {
         // run and bias niches to the right and then check which one is closer to one of the struct's
         // edges.
         if let Some(layout) = &layout {
-            if let Some(niche) = layout.largest_niche {
-                let head_space = niche.offset.bytes();
-                let niche_length = niche.value.size(dl).bytes();
-                let tail_space = layout.size.bytes() - head_space - niche_length;
-
-                // This may end up doing redundant work if the niche is already in the last field
-                // (e.g. a trailing bool) and there is tail padding. But it's non-trivial to get
-                // the unpadded size so we try anyway.
-                if fields.len() > 1 && head_space != 0 && tail_space > 0 {
-                    let alt_layout = univariant(self, dl, fields, repr, kind, NicheBias::End)
-                        .expect("alt layout should always work");
-                    let niche = alt_layout
-                        .largest_niche
-                        .expect("alt layout should have a niche like the regular one");
-                    let alt_head_space = niche.offset.bytes();
-                    let alt_niche_len = niche.value.size(dl).bytes();
-                    let alt_tail_space = alt_layout.size.bytes() - alt_head_space - alt_niche_len;
-
-                    debug_assert_eq!(layout.size.bytes(), alt_layout.size.bytes());
-
-                    let prefer_alt_layout =
-                        alt_head_space > head_space && alt_head_space > tail_space;
-
-                    debug!(
-                        "sz: {}, default_niche_at: {}+{}, default_tail_space: {}, alt_niche_at/head_space: {}+{}, alt_tail: {}, num_fields: {}, better: {}\n\
-                        layout: {}\n\
-                        alt_layout: {}\n",
-                        layout.size.bytes(),
-                        head_space,
-                        niche_length,
-                        tail_space,
-                        alt_head_space,
-                        alt_niche_len,
-                        alt_tail_space,
-                        layout.fields.count(),
-                        prefer_alt_layout,
-                        format_field_niches(&layout, &fields, &dl),
-                        format_field_niches(&alt_layout, &fields, &dl),
-                    );
-
-                    if prefer_alt_layout {
-                        return Some(alt_layout);
+            // Don't try to calculate an end-biased layout for unsizable structs,
+            // otherwise we could end up with different layouts for
+            // Foo<Type> and Foo<dyn Trait> which would break unsizing
+            if !matches!(kind, StructKind::MaybeUnsized) {
+                if let Some(niche) = layout.largest_niche {
+                    let head_space = niche.offset.bytes();
+                    let niche_length = niche.value.size(dl).bytes();
+                    let tail_space = layout.size.bytes() - head_space - niche_length;
+
+                    // This may end up doing redundant work if the niche is already in the last field
+                    // (e.g. a trailing bool) and there is tail padding. But it's non-trivial to get
+                    // the unpadded size so we try anyway.
+                    if fields.len() > 1 && head_space != 0 && tail_space > 0 {
+                        let alt_layout = univariant(self, dl, fields, repr, kind, NicheBias::End)
+                            .expect("alt layout should always work");
+                        let niche = alt_layout
+                            .largest_niche
+                            .expect("alt layout should have a niche like the regular one");
+                        let alt_head_space = niche.offset.bytes();
+                        let alt_niche_len = niche.value.size(dl).bytes();
+                        let alt_tail_space =
+                            alt_layout.size.bytes() - alt_head_space - alt_niche_len;
+
+                        debug_assert_eq!(layout.size.bytes(), alt_layout.size.bytes());
+
+                        let prefer_alt_layout =
+                            alt_head_space > head_space && alt_head_space > tail_space;
+
+                        debug!(
+                            "sz: {}, default_niche_at: {}+{}, default_tail_space: {}, alt_niche_at/head_space: {}+{}, alt_tail: {}, num_fields: {}, better: {}\n\
+                            layout: {}\n\
+                            alt_layout: {}\n",
+                            layout.size.bytes(),
+                            head_space,
+                            niche_length,
+                            tail_space,
+                            alt_head_space,
+                            alt_niche_len,
+                            alt_tail_space,
+                            layout.fields.count(),
+                            prefer_alt_layout,
+                            format_field_niches(&layout, &fields, &dl),
+                            format_field_niches(&alt_layout, &fields, &dl),
+                        );
+
+                        if prefer_alt_layout {
+                            return Some(alt_layout);
+                        }
                     }
                 }
             }
@@ -828,6 +834,7 @@ fn univariant(
     if optimize && fields.len() > 1 {
         let end = if let StructKind::MaybeUnsized = kind { fields.len() - 1 } else { fields.len() };
         let optimizing = &mut inverse_memory_index.raw[..end];
+        let fields_excluding_tail = &fields.raw[..end];
 
         // If `-Z randomize-layout` was enabled for the type definition we can shuffle
         // the field ordering to try and catch some code making assumptions about layouts
@@ -844,8 +851,11 @@ fn univariant(
             }
             // Otherwise we just leave things alone and actually optimize the type's fields
         } else {
-            let max_field_align = fields.iter().map(|f| f.align().abi.bytes()).max().unwrap_or(1);
-            let largest_niche_size = fields
+            // To allow unsizing `&Foo<Type>` -> `&Foo<dyn Trait>`, the layout of the struct must
+            // not depend on the layout of the tail.
+            let max_field_align =
+                fields_excluding_tail.iter().map(|f| f.align().abi.bytes()).max().unwrap_or(1);
+            let largest_niche_size = fields_excluding_tail
                 .iter()
                 .filter_map(|f| f.largest_niche())
                 .map(|n| n.available(dl))

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -364,7 +364,12 @@ impl<'a> AstValidator<'a> {
         self.err_handler().emit_err(errors::BoundInContext { span, ctx });
     }
 
-    fn check_foreign_ty_genericless(&self, generics: &Generics, where_span: Span) {
+    fn check_foreign_ty_genericless(
+        &self,
+        generics: &Generics,
+        before_where_clause: &TyAliasWhereClause,
+        after_where_clause: &TyAliasWhereClause,
+    ) {
         let cannot_have = |span, descr, remove_descr| {
             self.err_handler().emit_err(errors::ExternTypesCannotHave {
                 span,
@@ -378,9 +383,14 @@ impl<'a> AstValidator<'a> {
             cannot_have(generics.span, "generic parameters", "generic parameters");
         }
 
-        if !generics.where_clause.predicates.is_empty() {
-            cannot_have(where_span, "`where` clauses", "`where` clause");
-        }
+        let check_where_clause = |where_clause: &TyAliasWhereClause| {
+            if let TyAliasWhereClause(true, where_clause_span) = where_clause {
+                cannot_have(*where_clause_span, "`where` clauses", "`where` clause");
+            }
+        };
+
+        check_where_clause(before_where_clause);
+        check_where_clause(after_where_clause);
     }
 
     fn check_foreign_kind_bodyless(&self, ident: Ident, kind: &str, body: Option<Span>) {
@@ -1039,7 +1049,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 self.check_defaultness(fi.span, *defaultness);
                 self.check_foreign_kind_bodyless(fi.ident, "type", ty.as_ref().map(|b| b.span));
                 self.check_type_no_bounds(bounds, "`extern` blocks");
-                self.check_foreign_ty_genericless(generics, where_clauses.0.1);
+                self.check_foreign_ty_genericless(generics, &where_clauses.0, &where_clauses.1);
                 self.check_foreign_item_ascii_only(fi.ident);
             }
             ForeignItemKind::Static(_, _, body) => {