Don't compress dylib metadata

Dylib metadata compression increases code complexity and will become less
important once -Zsplit-metadata is introduced

Author: bjorn3

Cargo.lock

@@ -3595,7 +3595,6 @@ dependencies = [
  "rustc_symbol_mangling",
  "rustc_target",
  "smallvec",
- "snap",
  "tempfile",
  "thorin-dwp",
  "tracing",
@@ -3967,7 +3966,6 @@ dependencies = [
  "rustc_span",
  "rustc_target",
  "smallvec",
- "snap",
  "tracing",
 ]
 
@@ -4795,12 +4793,6 @@ version = "1.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1ecab6c735a6bb4139c0caafd0cc3635748bbb3acf4550e8138122099251f309"
 
-[[package]]
-name = "snap"
-version = "1.0.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "da73c8f77aebc0e40c300b93f0a5f1bece7a248a36eee287d4e095f35c7b7d6e"
-
 [[package]]
 name = "socket2"
 version = "0.4.1"

compiler/rustc_codegen_ssa/Cargo.toml

@@ -16,7 +16,6 @@ jobserver = "0.1.22"
 tempfile = "3.2"
 thorin-dwp = "0.2"
 pathdiff = "0.2.0"
-snap = "1"
 smallvec = { version = "1.6.1", features = ["union", "may_dangle"] }
 regex = "1.4"
 

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -1,7 +1,6 @@
 //! Reading of the rustc metadata for rlibs and dylibs
 
 use std::fs::File;
-use std::io::Write;
 use std::path::Path;
 
 use object::write::{self, StandardSegment, Symbol, SymbolSection};
@@ -10,8 +9,6 @@ use object::{
     SectionFlags, SectionKind, SymbolFlags, SymbolKind, SymbolScope,
 };
 
-use snap::write::FrameEncoder;
-
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::owning_ref::OwningRef;
 use rustc_data_structures::rustc_erase_owner;
@@ -260,12 +257,10 @@ pub fn create_compressed_metadata_file(
     metadata: &EncodedMetadata,
     symbol_name: &str,
 ) -> Vec<u8> {
-    let mut compressed = rustc_metadata::METADATA_HEADER.to_vec();
-    FrameEncoder::new(&mut compressed).write_all(metadata.raw_data()).unwrap();
     let mut file = if let Some(file) = create_object_file(sess) {
         file
     } else {
-        return compressed.to_vec();
+        return metadata.raw_data().to_vec();
     };
     let section = file.add_section(
         file.segment_name(StandardSegment::Data).to_vec(),
@@ -279,14 +274,14 @@ pub fn create_compressed_metadata_file(
         }
         _ => {}
     };
-    let offset = file.append_section_data(section, &compressed, 1);
+    let offset = file.append_section_data(section, metadata.raw_data(), 1);
 
     // For MachO and probably PE this is necessary to prevent the linker from throwing away the
     // .rustc section. For ELF this isn't necessary, but it also doesn't harm.
     file.add_symbol(Symbol {
         name: symbol_name.as_bytes().to_vec(),
         value: offset,
-        size: compressed.len() as u64,
+        size: metadata.raw_data().len() as u64,
         kind: SymbolKind::Data,
         scope: SymbolScope::Dynamic,
         weak: false,

compiler/rustc_metadata/Cargo.toml

@@ -9,7 +9,6 @@ doctest = false
 [dependencies]
 libloading = "0.7.1"
 odht = { version = "0.3.1", features = ["nightly"] }
-snap = "1"
 tracing = "0.1"
 smallvec = { version = "1.6.1", features = ["union", "may_dangle"] }
 rustc_middle = { path = "../rustc_middle" }

compiler/rustc_metadata/src/locator.rs

@@ -213,7 +213,7 @@
 //! metadata::locator or metadata::creader for all the juicy details!
 
 use crate::creader::Library;
-use crate::rmeta::{rustc_version, MetadataBlob, METADATA_HEADER};
+use crate::rmeta::{rustc_version, MetadataBlob};
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::memmap::Mmap;
@@ -231,11 +231,10 @@ use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
 use rustc_target::spec::{Target, TargetTriple};
 
-use snap::read::FrameDecoder;
 use std::fmt::Write as _;
-use std::io::{Read, Result as IoResult, Write};
+use std::io::{Result as IoResult, Write};
 use std::path::{Path, PathBuf};
-use std::{cmp, fmt, fs};
+use std::{fmt, fs};
 use tracing::{debug, info};
 
 #[derive(Clone)]
@@ -757,34 +756,7 @@ fn get_metadata_section<'p>(
             loader.get_rlib_metadata(target, filename).map_err(MetadataError::LoadFailure)?
         }
         CrateFlavor::Dylib => {
-            let buf =
-                loader.get_dylib_metadata(target, filename).map_err(MetadataError::LoadFailure)?;
-            // The header is uncompressed
-            let header_len = METADATA_HEADER.len();
-            debug!("checking {} bytes of metadata-version stamp", header_len);
-            let header = &buf[..cmp::min(header_len, buf.len())];
-            if header != METADATA_HEADER {
-                return Err(MetadataError::LoadFailure(format!(
-                    "invalid metadata version found: {}",
-                    filename.display()
-                )));
-            }
-
-            // Header is okay -> inflate the actual metadata
-            let compressed_bytes = &buf[header_len..];
-            debug!("inflating {} bytes of compressed metadata", compressed_bytes.len());
-            // Assume the decompressed data will be at least the size of the compressed data, so we
-            // don't have to grow the buffer as much.
-            let mut inflated = Vec::with_capacity(compressed_bytes.len());
-            match FrameDecoder::new(compressed_bytes).read_to_end(&mut inflated) {
-                Ok(_) => rustc_erase_owner!(OwningRef::new(inflated).map_owner_box()),
-                Err(_) => {
-                    return Err(MetadataError::LoadFailure(format!(
-                        "failed to decompress metadata: {}",
-                        filename.display()
-                    )));
-                }
-            }
+            loader.get_dylib_metadata(target, filename).map_err(MetadataError::LoadFailure)?
         }
         CrateFlavor::Rmeta => {
             // mmap the file, because only a small fraction of it is read.