bjoernager/rust
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Use object crate for .rustc metadata generation

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We already use the object crate for generating uncompressed .rmeta
metadata object files. This switches the generation of compressed
.rustc object files to use the object crate as well. These have
slightly different requirements in that .rmeta should be completely
excluded from any final compilation artifacts, while .rustc should
be part of shared objects, but not loaded into memory.

The primary motivation for this change is #90326: In LLVM 14, the
current way of setting section flags (and in particular, preventing
the setting of SHF_ALLOC) will no longer work. There are other ways
we could work around this, but switching to the object crate seems
like the most elegant, as we already use it for .rmeta, and as it
makes this independent of the codegen backend. In particular, we
don't need separate handling in codegen_llvm and codegen_gcc.
codegen_cranelift should be able to reuse the implementation as
well, though I have omitted that here, as it is not based on
codegen_ssa.

This change mostly extracts the existing code for .rmeta handling
to allow using it for .rustc as well, and adjust the codegen
infrastructure to handle the metadata object file separately: We
no longer create a backend-specific module for it, and directly
produce the compiled module instead.

This does not fix #90326 by itself yet, as .llvmbc will need to be
handled separately.
This commit is contained in:
Nikita Popov 2021-12-02 12:24:25 +01:00
parent d9baa36190
commit 9488cacc52
12 changed files with 246 additions and 288 deletions
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66
compiler/rustc_codegen_ssa/src/base.rs
View file

@ -1,3 +1,4 @@
use crate::back::metadata::create_compressed_metadata_file;
use crate::back::write::{
compute_per_cgu_lto_type, start_async_codegen, submit_codegened_module_to_llvm,
submit_post_lto_module_to_llvm, submit_pre_lto_module_to_llvm, ComputedLtoType, OngoingCodegen,
@ -8,7 +9,7 @@ use crate::mir;
use crate::mir::operand::OperandValue;
use crate::mir::place::PlaceRef;
use crate::traits::*;
use crate::{CachedModuleCodegen, CrateInfo, MemFlags, ModuleCodegen, ModuleKind};
use crate::{CachedModuleCodegen, CompiledModule, CrateInfo, MemFlags, ModuleCodegen, ModuleKind};
use rustc_attr as attr;
use rustc_data_structures::fx::FxHashMap;
@ -20,13 +21,14 @@ use rustc_hir::lang_items::LangItem;
use rustc_index::vec::Idx;
use rustc_metadata::EncodedMetadata;
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
use rustc_middle::middle::exported_symbols;
use rustc_middle::middle::lang_items;
use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder, MonoItem};
use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
use rustc_session::cgu_reuse_tracker::CguReuse;
use rustc_session::config::{self, EntryFnType};
use rustc_session::config::{self, EntryFnType, OutputType};
use rustc_session::Session;
use rustc_span::symbol::sym;
use rustc_target::abi::{Align, VariantIdx};
@ -491,7 +493,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
) -> OngoingCodegen<B> {
// Skip crate items and just output metadata in -Z no-codegen mode.
if tcx.sess.opts.debugging_opts.no_codegen || !tcx.sess.opts.output_types.should_codegen() {
let ongoing_codegen = start_async_codegen(backend, tcx, target_cpu, metadata, 1);
let ongoing_codegen = start_async_codegen(backend, tcx, target_cpu, metadata, None, 1);
ongoing_codegen.codegen_finished(tcx);
@ -517,8 +519,41 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
}
}
let ongoing_codegen =
start_async_codegen(backend.clone(), tcx, target_cpu, metadata, codegen_units.len());
let metadata_module = if need_metadata_module {
// Emit compressed metadata object.
let metadata_cgu_name =
cgu_name_builder.build_cgu_name(LOCAL_CRATE, &["crate"], Some("metadata")).to_string();
tcx.sess.time("write_compressed_metadata", || {
let file_name =
tcx.output_filenames(()).temp_path(OutputType::Metadata, Some(&metadata_cgu_name));
let data = create_compressed_metadata_file(
tcx.sess,
&metadata,
&exported_symbols::metadata_symbol_name(tcx),
);
if let Err(err) = std::fs::write(&file_name, data) {
tcx.sess.fatal(&format!("error writing metadata object file: {}", err));
}
Some(CompiledModule {
name: metadata_cgu_name,
kind: ModuleKind::Metadata,
object: Some(file_name),
dwarf_object: None,
bytecode: None,
})
})
} else {
None
};
let ongoing_codegen = start_async_codegen(
backend.clone(),
tcx,
target_cpu,
metadata,
metadata_module,
codegen_units.len(),
);
let ongoing_codegen = AbortCodegenOnDrop::<B>(Some(ongoing_codegen));
// Codegen an allocator shim, if necessary.
@ -558,27 +593,6 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
ongoing_codegen.submit_pre_codegened_module_to_llvm(tcx, allocator_module);
}
if need_metadata_module {
// Codegen the encoded metadata.
let metadata_cgu_name =
cgu_name_builder.build_cgu_name(LOCAL_CRATE, &["crate"], Some("metadata")).to_string();
let mut metadata_llvm_module = backend.new_metadata(tcx, &metadata_cgu_name);
tcx.sess.time("write_compressed_metadata", || {
backend.write_compressed_metadata(
tcx,
&ongoing_codegen.metadata,
&mut metadata_llvm_module,
);
});
let metadata_module = ModuleCodegen {
name: metadata_cgu_name,
module_llvm: metadata_llvm_module,
kind: ModuleKind::Metadata,
};
ongoing_codegen.submit_pre_codegened_module_to_llvm(tcx, metadata_module);
}
// For better throughput during parallel processing by LLVM, we used to sort
// CGUs largest to smallest. This would lead to better thread utilization
// by, for example, preventing a large CGU from being processed last and