new layout

Co-authored-by: Dario Nieuwenhuis <dirbaio@dirbaio.net>

Author: dingxiangfei2009

compiler/rustc_abi/src/lib.rs

@@ -1508,8 +1508,10 @@ pub enum Variants<FieldIdx: Idx, VariantIdx: Idx> {
     /// a struct, and they all have space reserved for the tag.
     /// For enums, the tag is the sole field of the layout.
     Multiple {
+        /// Tag definition
         tag: Scalar,
         tag_encoding: TagEncoding<VariantIdx>,
+        /// Index of tag among fields
         tag_field: usize,
         variants: IndexVec<VariantIdx, LayoutData<FieldIdx, VariantIdx>>,
     },
@@ -1545,6 +1547,7 @@ pub enum TagEncoding<VariantIdx: Idx> {
 pub struct Niche {
     pub offset: Size,
     pub value: Primitive,
+    /// A range of valid values with both endpoints being inclusive
     pub valid_range: WrappingRange,
 }
 
@@ -1555,17 +1558,23 @@ impl Niche {
         if niche.available(cx) > 0 { Some(niche) } else { None }
     }
 
+    /// Compute how many values are outside the valid range, available for optimisation through niche filling
     pub fn available<C: HasDataLayout>(&self, cx: &C) -> u128 {
         let Self { value, valid_range: v, .. } = *self;
         let size = value.size(cx);
         assert!(size.bits() <= 128);
         let max_value = size.unsigned_int_max();
 
-        // Find out how many values are outside the valid range.
         let niche = v.end.wrapping_add(1)..v.start;
         niche.end.wrapping_sub(niche.start) & max_value
     }
 
+    /// Try to enlarge the valid value range to include another `count` values,
+    /// so that they can be used for niche-filling optimisation.
+    /// `None` signals impossibility of reservation.
+    /// Otherwise, `Some((start, scalar))` signifies that a reservation is possible,
+    /// the first value in the reservation is `start`, and the new scalar including
+    /// the reserved values is defined in `scalar`.
     pub fn reserve<C: HasDataLayout>(&self, cx: &C, count: u128) -> Option<(u128, Scalar)> {
         assert!(count > 0);
 

compiler/rustc_feature/src/unstable.rs

@@ -434,6 +434,8 @@ declare_features! (
     (unstable, const_try, "1.56.0", Some(74935)),
     /// Allows coroutines to be cloned.
     (unstable, coroutine_clone, "1.65.0", Some(95360)),
+    /// Allows aggressive merging coroutine saved slots
+    (unstable, coroutine_new_layout, "CURRENT_RUSTC_VERSION", Some(99999)),
     /// Allows defining coroutines.
     (unstable, coroutines, "1.21.0", Some(43122)),
     /// Allows function attribute `#[coverage(on/off)]`, to control coverage

compiler/rustc_span/src/symbol.rs

@@ -661,6 +661,7 @@ symbols! {
         core_panic_macro,
         coroutine,
         coroutine_clone,
+        coroutine_new_layout,
         coroutine_resume,
         coroutine_return,
         coroutine_state,

compiler/rustc_ty_utils/src/layout.rs

@@ -31,6 +31,7 @@ use crate::errors::{
     MultipleArrayFieldsSimdType, NonPrimitiveSimdType, OversizedSimdType, ZeroLengthSimdType,
 };
 
+mod coroutine;
 mod invariant;
 
 pub(crate) fn provide(providers: &mut Providers) {
@@ -393,7 +394,13 @@ fn layout_of_uncached<'tcx>(
             tcx.mk_layout(unit)
         }
 
-        ty::Coroutine(def_id, args) => coroutine_layout(cx, ty, def_id, args)?,
+        ty::Coroutine(def_id, args) => {
+            if tcx.features().coroutine_new_layout() {
+                coroutine::coroutine_layout(cx, ty, def_id, args)?
+            } else {
+                coroutine_layout(cx, ty, def_id, args)?
+            }
+        }
 
         ty::Closure(_, args) => {
             let tys = args.as_closure().upvar_tys();
@@ -1156,8 +1163,10 @@ fn variant_info_for_coroutine<'tcx>(
         .zip_eq(upvar_names)
         .enumerate()
         .map(|(field_idx, (_, name))| {
-            let field_layout = layout.field(cx, field_idx);
-            let offset = layout.fields.offset(field_idx);
+            // Upvars occupies the Unresumed variant at index zero
+            let variant_layout = layout.for_variant(cx, VariantIdx::ZERO);
+            let field_layout = variant_layout.field(cx, field_idx);
+            let offset = variant_layout.fields.offset(field_idx);
             upvars_size = upvars_size.max(offset + field_layout.size);
             FieldInfo {
                 kind: FieldKind::Upvar,
@@ -1177,12 +1186,11 @@ fn variant_info_for_coroutine<'tcx>(
             let variant_layout = layout.for_variant(cx, variant_idx);
             let mut variant_size = Size::ZERO;
             let fields = variant_def
-                .iter()
-                .enumerate()
+                .iter_enumerated()
                 .map(|(field_idx, local)| {
                     let field_name = coroutine.field_names[*local];
-                    let field_layout = variant_layout.field(cx, field_idx);
-                    let offset = variant_layout.fields.offset(field_idx);
+                    let field_layout = variant_layout.field(cx, field_idx.index());
+                    let offset = variant_layout.fields.offset(field_idx.index());
                     // The struct is as large as the last field's end
                     variant_size = variant_size.max(offset + field_layout.size);
                     FieldInfo {