Auto merge of #83682 - bjorn3:mmap_wrapper, r=cjgillot

Add an Mmap wrapper to rustc_data_structures

This wrapper implements StableAddress and falls back to directly reading the file on wasm32.

Taken from #83640, which I will close due to the perf regression.

2 files changed, 3 insertions, 17 deletions

diff --git a/compiler/rustc_metadata/Cargo.toml b/compiler/rustc_metadata/Cargo.toml
index 48effed9274..29fa0b70069 100644
--- a/compiler/rustc_metadata/Cargo.toml
+++ b/compiler/rustc_metadata/Cargo.toml
@@ -11,7 +11,6 @@ doctest = false
 libc = "0.2"
 snap = "1"
 tracing = "0.1"
-memmap2 = "0.2.1"
 smallvec = { version = "1.6.1", features = ["union", "may_dangle"] }
 rustc_middle = { path = "../rustc_middle" }
 rustc_attr = { path = "../rustc_attr" }
diff --git a/compiler/rustc_metadata/src/locator.rs b/compiler/rustc_metadata/src/locator.rs
index 39a39917f57..7f6311861c1 100644
--- a/compiler/rustc_metadata/src/locator.rs
+++ b/compiler/rustc_metadata/src/locator.rs
@@ -216,6 +216,7 @@ use crate::creader::Library;
 use crate::rmeta::{rustc_version, MetadataBlob, METADATA_HEADER};
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::owning_ref::OwningRef;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::MetadataRef;
@@ -232,7 +233,6 @@ use rustc_target::spec::{Target, TargetTriple};
 
 use snap::read::FrameDecoder;
 use std::io::{Read, Result as IoResult, Write};
-use std::ops::Deref;
 use std::path::{Path, PathBuf};
 use std::{cmp, fmt, fs};
 use tracing::{debug, info, warn};
@@ -727,19 +727,6 @@ impl<'a> CrateLocator<'a> {
     }
 }
 
-/// A trivial wrapper for `Mmap` that implements `StableDeref`.
-struct StableDerefMmap(memmap2::Mmap);
-
-impl Deref for StableDerefMmap {
-    type Target = [u8];
-
-    fn deref(&self) -> &[u8] {
-        self.0.deref()
-    }
-}
-
-unsafe impl stable_deref_trait::StableDeref for StableDerefMmap {}
-
 fn get_metadata_section(
     target: &Target,
     flavor: CrateFlavor,
@@ -779,11 +766,11 @@ fn get_metadata_section(
             // mmap the file, because only a small fraction of it is read.
             let file = std::fs::File::open(filename)
                 .map_err(|_| format!("failed to open rmeta metadata: '{}'", filename.display()))?;
-            let mmap = unsafe { memmap2::Mmap::map(&file) };
+            let mmap = unsafe { Mmap::map(file) };
             let mmap = mmap
                 .map_err(|_| format!("failed to mmap rmeta metadata: '{}'", filename.display()))?;
 
-            rustc_erase_owner!(OwningRef::new(StableDerefMmap(mmap)).map_owner_box())
+            rustc_erase_owner!(OwningRef::new(mmap).map_owner_box())
         }
     };
     let blob = MetadataBlob::new(raw_bytes);