Rollup merge of #110145 - WaffleLapkin:share_slice_of_bytes, r=Nilstrieb

Share slice of bytes

r? `@Nilstrieb`
cc `@noamtashma`

10 files changed, 64 insertions, 37 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/metadata.rs b/compiler/rustc_codegen_ssa/src/back/metadata.rs
index 8968133bac5..8bf84772f08 100644
--- a/compiler/rustc_codegen_ssa/src/back/metadata.rs
+++ b/compiler/rustc_codegen_ssa/src/back/metadata.rs
@@ -14,8 +14,7 @@ use snap::write::FrameEncoder;
 
 use object::elf::NT_GNU_PROPERTY_TYPE_0;
 use rustc_data_structures::memmap::Mmap;
-use rustc_data_structures::owned_slice::try_slice_owned;
-use rustc_data_structures::sync::MetadataRef;
+use rustc_data_structures::owned_slice::{try_slice_owned, OwnedSlice};
 use rustc_metadata::fs::METADATA_FILENAME;
 use rustc_metadata::EncodedMetadata;
 use rustc_session::cstore::MetadataLoader;
@@ -39,7 +38,7 @@ pub struct DefaultMetadataLoader;
 fn load_metadata_with(
     path: &Path,
     f: impl for<'a> FnOnce(&'a [u8]) -> Result<&'a [u8], String>,
-) -> Result<MetadataRef, String> {
+) -> Result<OwnedSlice, String> {
     let file =
         File::open(path).map_err(|e| format!("failed to open file '{}': {}", path.display(), e))?;
 
@@ -49,7 +48,7 @@ fn load_metadata_with(
 }
 
 impl MetadataLoader for DefaultMetadataLoader {
-    fn get_rlib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> {
+    fn get_rlib_metadata(&self, _target: &Target, path: &Path) -> Result<OwnedSlice, String> {
         load_metadata_with(path, |data| {
             let archive = object::read::archive::ArchiveFile::parse(&*data)
                 .map_err(|e| format!("failed to parse rlib '{}': {}", path.display(), e))?;
@@ -69,7 +68,7 @@ impl MetadataLoader for DefaultMetadataLoader {
         })
     }
 
-    fn get_dylib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> {
+    fn get_dylib_metadata(&self, _target: &Target, path: &Path) -> Result<OwnedSlice, String> {
         load_metadata_with(path, |data| search_for_section(path, data, ".rustc"))
     }
 }
diff --git a/compiler/rustc_codegen_ssa/src/traits/backend.rs b/compiler/rustc_codegen_ssa/src/traits/backend.rs
index 5c88368bc87..d83bfc74082 100644
--- a/compiler/rustc_codegen_ssa/src/traits/backend.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/backend.rs
@@ -1,3 +1,5 @@
+use std::any::Any;
+
 use super::write::WriteBackendMethods;
 use super::CodegenObject;
 use crate::back::write::TargetMachineFactoryFn;
@@ -5,6 +7,7 @@ use crate::{CodegenResults, ModuleCodegen};
 
 use rustc_ast::expand::allocator::AllocatorKind;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::sync::{DynSend, DynSync};
 use rustc_errors::ErrorGuaranteed;
 use rustc_metadata::EncodedMetadata;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
@@ -20,11 +23,6 @@ use rustc_span::symbol::Symbol;
 use rustc_target::abi::call::FnAbi;
 use rustc_target::spec::Target;
 
-pub use rustc_data_structures::sync::MetadataRef;
-
-use rustc_data_structures::sync::{DynSend, DynSync};
-use std::any::Any;
-
 pub trait BackendTypes {
     type Value: CodegenObject;
     type Function: CodegenObject;
diff --git a/compiler/rustc_data_structures/src/owned_slice.rs b/compiler/rustc_data_structures/src/owned_slice.rs
index 311a42aa42a..cbb3047d884 100644
--- a/compiler/rustc_data_structures/src/owned_slice.rs
+++ b/compiler/rustc_data_structures/src/owned_slice.rs
@@ -1,5 +1,6 @@
 use std::{borrow::Borrow, ops::Deref};
 
+use crate::sync::Lrc;
 // Use our fake Send/Sync traits when on not parallel compiler,
 // so that `OwnedSlice` only implements/requires Send/Sync
 // for parallel compiler builds.
@@ -7,7 +8,7 @@ use crate::sync::{Send, Sync};
 
 /// An owned slice.
 ///
-/// This is similar to `Box<[u8]>` but allows slicing and using anything as the
+/// This is similar to `Lrc<[u8]>` but allows slicing and using anything as the
 /// backing buffer.
 ///
 /// See [`slice_owned`] for `OwnedSlice` construction and examples.
@@ -16,6 +17,7 @@ use crate::sync::{Send, Sync};
 ///
 /// This is essentially a replacement for `owning_ref` which is a lot simpler
 /// and even sound! 🌸
+#[derive(Clone)]
 pub struct OwnedSlice {
     /// This is conceptually a `&'self.owner [u8]`.
     bytes: *const [u8],
@@ -31,7 +33,7 @@ pub struct OwnedSlice {
     //       \/
     //      ⊂(´･◡･⊂ )∘˚˳° (I am the phantom remnant of #97770)
     #[expect(dead_code)]
-    owner: Box<dyn Send + Sync>,
+    owner: Lrc<dyn Send + Sync>,
 }
 
 /// Makes an [`OwnedSlice`] out of an `owner` and a `slicer` function.
@@ -72,10 +74,10 @@ where
     O: Send + Sync + 'static,
     F: FnOnce(&O) -> Result<&[u8], E>,
 {
-    // We box the owner of the bytes, so it doesn't move.
+    // We wrap the owner of the bytes in, so it doesn't move.
     //
     // Since the owner does not move and we don't access it in any way
-    // before drop, there is nothing that can invalidate the bytes pointer.
+    // before dropping, there is nothing that can invalidate the bytes pointer.
     //
     // Thus, "extending" the lifetime of the reference returned from `F` is fine.
     // We pretend that we pass it a reference that lives as long as the returned slice.
@@ -83,12 +85,39 @@ where
     // N.B. the HRTB on the `slicer` is important — without it the caller could provide
     // a short lived slice, unrelated to the owner.
 
-    let owner = Box::new(owner);
+    let owner = Lrc::new(owner);
     let bytes = slicer(&*owner)?;
 
     Ok(OwnedSlice { bytes, owner })
 }
 
+impl OwnedSlice {
+    /// Slice this slice by `slicer`.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use rustc_data_structures::owned_slice::{OwnedSlice, slice_owned};
+    /// let vec = vec![1, 2, 3, 4];
+    ///
+    /// // Identical to slicing via `&v[1..3]` but produces an owned slice
+    /// let slice: OwnedSlice = slice_owned(vec, |v| &v[..]);
+    /// assert_eq!(&*slice, [1, 2, 3, 4]);
+    ///
+    /// let slice = slice.slice(|slice| &slice[1..][..2]);
+    /// assert_eq!(&*slice, [2, 3]);
+    /// ```
+    ///
+    pub fn slice(self, slicer: impl FnOnce(&[u8]) -> &[u8]) -> OwnedSlice {
+        // This is basically identical to `try_slice_owned`,
+        // `slicer` can only return slices of its argument or some static data,
+        // both of which are valid while `owner` is alive.
+
+        let bytes = slicer(&self);
+        OwnedSlice { bytes, ..self }
+    }
+}
+
 impl Deref for OwnedSlice {
     type Target = [u8];
 
@@ -108,11 +137,11 @@ impl Borrow<[u8]> for OwnedSlice {
     }
 }
 
-// Safety: `OwnedSlice` is conceptually `(&'self.1 [u8], Box<dyn Send + Sync>)`, which is `Send`
+// Safety: `OwnedSlice` is conceptually `(&'self.1 [u8], Arc<dyn Send + Sync>)`, which is `Send`
 #[cfg(parallel_compiler)]
 unsafe impl Send for OwnedSlice {}
 
-// Safety: `OwnedSlice` is conceptually `(&'self.1 [u8], Box<dyn Send + Sync>)`, which is `Sync`
+// Safety: `OwnedSlice` is conceptually `(&'self.1 [u8], Arc<dyn Send + Sync>)`, which is `Sync`
 #[cfg(parallel_compiler)]
 unsafe impl Sync for OwnedSlice {}
 
diff --git a/compiler/rustc_data_structures/src/owned_slice/tests.rs b/compiler/rustc_data_structures/src/owned_slice/tests.rs
index e151b8c2de0..1eb5378cd1a 100644
--- a/compiler/rustc_data_structures/src/owned_slice/tests.rs
+++ b/compiler/rustc_data_structures/src/owned_slice/tests.rs
@@ -26,7 +26,7 @@ fn static_storage() {
 }
 
 #[test]
-fn slice_the_slice() {
+fn slice_owned_the_slice() {
     let slice = slice_owned(vec![1, 2, 3, 4, 5, 6], Vec::as_slice);
     let slice = slice_owned(slice, |s| &s[1..][..4]);
     let slice = slice_owned(slice, |s| s);
@@ -36,6 +36,16 @@ fn slice_the_slice() {
 }
 
 #[test]
+fn slice_the_slice() {
+    let slice = slice_owned(vec![1, 2, 3, 4, 5, 6], Vec::as_slice)
+        .slice(|s| &s[1..][..4])
+        .slice(|s| s)
+        .slice(|s| &s[1..]);
+
+    assert_eq!(&*slice, &[1, 2, 3, 4, 5, 6][1..][..4][1..]);
+}
+
+#[test]
 fn try_and_fail() {
     let res = try_slice_owned(vec![0], |v| v.get(12..).ok_or(()));
 
diff --git a/compiler/rustc_data_structures/src/sync.rs b/compiler/rustc_data_structures/src/sync.rs
index 8a778866a77..6c3197d8ec2 100644
--- a/compiler/rustc_data_structures/src/sync.rs
+++ b/compiler/rustc_data_structures/src/sync.rs
@@ -40,7 +40,6 @@
 //! [^2] `MTLockRef` is a typedef.
 
 pub use crate::marker::*;
-use crate::owned_slice::OwnedSlice;
 use std::collections::HashMap;
 use std::hash::{BuildHasher, Hash};
 use std::ops::{Deref, DerefMut};
@@ -92,6 +91,7 @@ mod mode {
 }
 
 pub use mode::{is_dyn_thread_safe, set_dyn_thread_safe_mode};
+
 cfg_if! {
     if #[cfg(not(parallel_compiler))] {
         pub unsafe auto trait Send {}
@@ -244,8 +244,6 @@ cfg_if! {
             r
         }
 
-        pub type MetadataRef = OwnedSlice;
-
         pub use std::rc::Rc as Lrc;
         pub use std::rc::Weak as Weak;
         pub use std::cell::Ref as ReadGuard;
@@ -517,8 +515,6 @@ cfg_if! {
             }
         }
 
-        pub type MetadataRef = OwnedSlice;
-
         /// This makes locks panic if they are already held.
         /// It is only useful when you are running in a single thread
         const ERROR_CHECKING: bool = false;
diff --git a/compiler/rustc_metadata/src/locator.rs b/compiler/rustc_metadata/src/locator.rs
index c6af8d63289..6c4d121fd01 100644
--- a/compiler/rustc_metadata/src/locator.rs
+++ b/compiler/rustc_metadata/src/locator.rs
@@ -220,7 +220,6 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::owned_slice::slice_owned;
 use rustc_data_structures::svh::Svh;
-use rustc_data_structures::sync::MetadataRef;
 use rustc_errors::{DiagnosticArgValue, FatalError, IntoDiagnosticArg};
 use rustc_fs_util::try_canonicalize;
 use rustc_session::config::{self, CrateType};
@@ -782,7 +781,7 @@ fn get_metadata_section<'p>(
     if !filename.exists() {
         return Err(MetadataError::NotPresent(filename));
     }
-    let raw_bytes: MetadataRef = match flavor {
+    let raw_bytes = match flavor {
         CrateFlavor::Rlib => {
             loader.get_rlib_metadata(target, filename).map_err(MetadataError::LoadFailure)?
         }
@@ -843,7 +842,7 @@ fn get_metadata_section<'p>(
             slice_owned(mmap, Deref::deref)
         }
     };
-    let blob = MetadataBlob::new(raw_bytes);
+    let blob = MetadataBlob(raw_bytes);
     if blob.is_compatible() {
         Ok(blob)
     } else {
diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 1c36d5e82da..699e1f49ed6 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -7,6 +7,7 @@ use crate::rmeta::*;
 use rustc_ast as ast;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::owned_slice::OwnedSlice;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::{AppendOnlyVec, Lock, Lrc, OnceCell};
 use rustc_data_structures::unhash::UnhashMap;
@@ -50,7 +51,7 @@ mod cstore_impl;
 /// A `MetadataBlob` internally is just a reference counted pointer to
 /// the actual data, so cloning it is cheap.
 #[derive(Clone)]
-pub(crate) struct MetadataBlob(Lrc<MetadataRef>);
+pub(crate) struct MetadataBlob(pub(crate) OwnedSlice);
 
 impl std::ops::Deref for MetadataBlob {
     type Target = [u8];
@@ -660,10 +661,6 @@ impl<'a, 'tcx, I: Idx, T> Decodable<DecodeContext<'a, 'tcx>> for LazyTable<I, T>
 implement_ty_decoder!(DecodeContext<'a, 'tcx>);
 
 impl MetadataBlob {
-    pub(crate) fn new(metadata_ref: MetadataRef) -> MetadataBlob {
-        MetadataBlob(Lrc::new(metadata_ref))
-    }
-
     pub(crate) fn is_compatible(&self) -> bool {
         self.blob().starts_with(METADATA_HEADER)
     }
diff --git a/compiler/rustc_metadata/src/rmeta/def_path_hash_map.rs b/compiler/rustc_metadata/src/rmeta/def_path_hash_map.rs
index 05402a58701..4f280bb9d80 100644
--- a/compiler/rustc_metadata/src/rmeta/def_path_hash_map.rs
+++ b/compiler/rustc_metadata/src/rmeta/def_path_hash_map.rs
@@ -1,6 +1,5 @@
 use crate::rmeta::DecodeContext;
 use crate::rmeta::EncodeContext;
-use rustc_data_structures::owned_slice::slice_owned;
 use rustc_data_structures::owned_slice::OwnedSlice;
 use rustc_hir::def_path_hash_map::{Config as HashMapConfig, DefPathHashMap};
 use rustc_middle::parameterized_over_tcx;
@@ -47,7 +46,7 @@ impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for DefPathHashMapRef<'static>
     fn decode(d: &mut DecodeContext<'a, 'tcx>) -> DefPathHashMapRef<'static> {
         let len = d.read_usize();
         let pos = d.position();
-        let o = slice_owned(d.blob().clone(), |blob| &blob[pos..pos + len]);
+        let o = d.blob().clone().0.slice(|blob| &blob[pos..pos + len]);
 
         // Although we already have the data we need via the `OwnedSlice`, we still need
         // to advance the `DecodeContext`'s position so it's in a valid state after
diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index 9eaf330b536..987a484049f 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -7,7 +7,6 @@ use table::TableBuilder;
 use rustc_ast as ast;
 use rustc_attr as attr;
 use rustc_data_structures::svh::Svh;
-use rustc_data_structures::sync::MetadataRef;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind, DocLinkResMap};
 use rustc_hir::def_id::{CrateNum, DefId, DefIndex, DefPathHash, StableCrateId};
diff --git a/compiler/rustc_session/src/cstore.rs b/compiler/rustc_session/src/cstore.rs
index 8089d81cc22..dc475e8c6d5 100644
--- a/compiler/rustc_session/src/cstore.rs
+++ b/compiler/rustc_session/src/cstore.rs
@@ -6,7 +6,8 @@ use crate::search_paths::PathKind;
 use crate::utils::NativeLibKind;
 use crate::Session;
 use rustc_ast as ast;
-use rustc_data_structures::sync::{self, AppendOnlyIndexVec, MetadataRef, RwLock};
+use rustc_data_structures::owned_slice::OwnedSlice;
+use rustc_data_structures::sync::{self, AppendOnlyIndexVec, RwLock};
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, StableCrateId, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash, Definitions};
 use rustc_span::hygiene::{ExpnHash, ExpnId};
@@ -203,8 +204,8 @@ pub enum ExternCrateSource {
 /// metadata in library -- this trait just serves to decouple rustc_metadata from
 /// the archive reader, which depends on LLVM.
 pub trait MetadataLoader: std::fmt::Debug {
-    fn get_rlib_metadata(&self, target: &Target, filename: &Path) -> Result<MetadataRef, String>;
-    fn get_dylib_metadata(&self, target: &Target, filename: &Path) -> Result<MetadataRef, String>;
+    fn get_rlib_metadata(&self, target: &Target, filename: &Path) -> Result<OwnedSlice, String>;
+    fn get_dylib_metadata(&self, target: &Target, filename: &Path) -> Result<OwnedSlice, String>;
 }
 
 pub type MetadataLoaderDyn = dyn MetadataLoader + Send + Sync + sync::DynSend + sync::DynSync;