Rollup merge of #119885 - DianQK:revert-pr-113923, r=petrochenkov

Revert #113923

Per [#t-compiler/meetings > [weekly] 2024-01-11](https://rust-lang.zulipchat.com/#narrow/stream/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202024-01-11) discussion, revert #113923. Also revert associated #118568.

The PR #113923 causes the regression issue #118609. We need more time to find a proper solution.

Discussions start at [412365838](https://rust-lang.zulipchat.com/#narrow/stream/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202024-01-11/near/412365838) and continue to [412369643](https://rust-lang.zulipchat.com/#narrow/stream/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202024-01-11/near/412369643).

Fixes #118609.

r? compiler

compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -60,7 +60,7 @@ fn prepare_lto(
     };
 
     let symbol_filter = &|&(ref name, info): &(String, SymbolExportInfo)| {
-        if info.level.is_below_threshold(export_threshold) || info.used || info.used_compiler {
+        if info.level.is_below_threshold(export_threshold) || info.used {
             Some(CString::new(name.as_str()).unwrap())
         } else {
             None

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -569,6 +569,7 @@ pub(crate) unsafe fn llvm_optimize(
         unroll_loops,
         config.vectorize_slp,
         config.vectorize_loop,
+        config.no_builtins,
         config.emit_lifetime_markers,
         sanitizer_options.as_ref(),
         pgo_gen_path.as_ref().map_or(std::ptr::null(), |s| s.as_ptr()),
@@ -677,14 +678,15 @@ pub(crate) unsafe fn codegen(
         unsafe fn with_codegen<'ll, F, R>(
             tm: &'ll llvm::TargetMachine,
             llmod: &'ll llvm::Module,
+            no_builtins: bool,
             f: F,
         ) -> R
         where
             F: FnOnce(&'ll mut PassManager<'ll>) -> R,
         {
             let cpm = llvm::LLVMCreatePassManager();
             llvm::LLVMAddAnalysisPasses(tm, cpm);
-            llvm::LLVMRustAddLibraryInfo(cpm, llmod);
+            llvm::LLVMRustAddLibraryInfo(cpm, llmod, no_builtins);
             f(cpm)
         }
 
@@ -785,7 +787,7 @@ pub(crate) unsafe fn codegen(
             } else {
                 llmod
             };
-            with_codegen(tm, llmod, |cpm| {
+            with_codegen(tm, llmod, config.no_builtins, |cpm| {
                 write_output_file(
                     dcx,
                     tm,
@@ -820,7 +822,7 @@ pub(crate) unsafe fn codegen(
                     (_, SplitDwarfKind::Split) => Some(dwo_out.as_path()),
                 };
 
-                with_codegen(tm, llmod, |cpm| {
+                with_codegen(tm, llmod, config.no_builtins, |cpm| {
                     write_output_file(
                         dcx,
                         tm,

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2173,8 +2173,13 @@ extern "C" {
         ArgsCstrBuff: *const c_char,
         ArgsCstrBuffLen: usize,
     ) -> *mut TargetMachine;
+
     pub fn LLVMRustDisposeTargetMachine(T: *mut TargetMachine);
-    pub fn LLVMRustAddLibraryInfo<'a>(PM: &PassManager<'a>, M: &'a Module);
+    pub fn LLVMRustAddLibraryInfo<'a>(
+        PM: &PassManager<'a>,
+        M: &'a Module,
+        DisableSimplifyLibCalls: bool,
+    );
     pub fn LLVMRustWriteOutputFile<'a>(
         T: &'a TargetMachine,
         PM: &PassManager<'a>,
@@ -2196,6 +2201,7 @@ extern "C" {
         UnrollLoops: bool,
         SLPVectorize: bool,
         LoopVectorize: bool,
+        DisableSimplifyLibCalls: bool,
         EmitLifetimeMarkers: bool,
         SanitizerOptions: Option<&SanitizerOptions>,
         PGOGenPath: *const c_char,

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -270,14 +270,8 @@ pub fn each_linked_rlib(
 
     for &cnum in crates {
         match fmts.get(cnum.as_usize() - 1) {
-            Some(&Linkage::NotLinked | &Linkage::Dynamic) => continue,
-            Some(&Linkage::IncludedFromDylib) => {
-                // We always link crate `compiler_builtins` statically. When enabling LTO, we include it as well.
-                if info.compiler_builtins != Some(cnum) {
-                    continue;
-                }
-            }
-            Some(&Linkage::Static) => {}
+            Some(&Linkage::NotLinked | &Linkage::Dynamic | &Linkage::IncludedFromDylib) => continue,
+            Some(_) => {}
             None => return Err(errors::LinkRlibError::MissingFormat),
         }
         let crate_name = info.crate_name[&cnum];
@@ -526,7 +520,8 @@ fn link_staticlib<'a>(
         &codegen_results.crate_info,
         Some(CrateType::Staticlib),
         &mut |cnum, path| {
-            let lto = are_upstream_rust_objects_already_included(sess);
+            let lto = are_upstream_rust_objects_already_included(sess)
+                && !ignored_for_lto(sess, &codegen_results.crate_info, cnum);
 
             let native_libs = codegen_results.crate_info.native_libraries[&cnum].iter();
             let relevant = native_libs.clone().filter(|lib| relevant_lib(sess, lib));
@@ -1277,6 +1272,24 @@ fn link_sanitizer_runtime(
     }
 }
 
+/// Returns a boolean indicating whether the specified crate should be ignored
+/// during LTO.
+///
+/// Crates ignored during LTO are not lumped together in the "massive object
+/// file" that we create and are linked in their normal rlib states. See
+/// comments below for what crates do not participate in LTO.
+///
+/// It's unusual for a crate to not participate in LTO. Typically only
+/// compiler-specific and unstable crates have a reason to not participate in
+/// LTO.
+pub fn ignored_for_lto(sess: &Session, info: &CrateInfo, cnum: CrateNum) -> bool {
+    // If our target enables builtin function lowering in LLVM then the
+    // crates providing these functions don't participate in LTO (e.g.
+    // no_builtins or compiler builtins crates).
+    !sess.target.no_builtins
+        && (info.compiler_builtins == Some(cnum) || info.is_no_builtins.contains(&cnum))
+}
+
 /// This functions tries to determine the appropriate linker (and corresponding LinkerFlavor) to use
 pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
     fn infer_from(
@@ -2742,6 +2755,10 @@ fn rehome_sysroot_lib_dir<'a>(sess: &'a Session, lib_dir: &Path) -> PathBuf {
 // symbols). We must continue to include the rest of the rlib, however, as
 // it may contain static native libraries which must be linked in.
 //
+// (*) Crates marked with `#![no_builtins]` don't participate in LTO and
+// their bytecode wasn't included. The object files in those libraries must
+// still be passed to the linker.
+//
 // Note, however, that if we're not doing LTO we can just pass the rlib
 // blindly to the linker (fast) because it's fine if it's not actually
 // included as we're at the end of the dependency chain.
@@ -2767,7 +2784,9 @@ fn add_static_crate<'a>(
         cmd.link_rlib(&rlib_path);
     };
 
-    if !are_upstream_rust_objects_already_included(sess) {
+    if !are_upstream_rust_objects_already_included(sess)
+        || ignored_for_lto(sess, &codegen_results.crate_info, cnum)
+    {
         link_upstream(cratepath);
         return;
     }
@@ -2781,6 +2800,8 @@ fn add_static_crate<'a>(
         let canonical_name = name.replace('-', "_");
         let upstream_rust_objects_already_included =
             are_upstream_rust_objects_already_included(sess);
+        let is_builtins =
+            sess.target.no_builtins || !codegen_results.crate_info.is_no_builtins.contains(&cnum);
 
         let mut archive = archive_builder_builder.new_archive_builder(sess);
         if let Err(error) = archive.add_archive(
@@ -2797,8 +2818,9 @@ fn add_static_crate<'a>(
 
                 // If we're performing LTO and this is a rust-generated object
                 // file, then we don't need the object file as it's part of the
-                // LTO module.
-                if upstream_rust_objects_already_included && is_rust_object {
+                // LTO module. Note that `#![no_builtins]` is excluded from LTO,
+                // though, so we let that object file slide.
+                if upstream_rust_objects_already_included && is_rust_object && is_builtins {
                     return true;
                 }
 

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -54,8 +54,8 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
     // export level, however, as they're just implementation details.
     // Down below we'll hardwire all of the symbols to the `Rust` export
     // level instead.
-    let is_compiler_builtins = tcx.is_compiler_builtins(LOCAL_CRATE);
-    let special_runtime_crate = tcx.is_panic_runtime(LOCAL_CRATE) || is_compiler_builtins;
+    let special_runtime_crate =
+        tcx.is_panic_runtime(LOCAL_CRATE) || tcx.is_compiler_builtins(LOCAL_CRATE);
 
     let mut reachable_non_generics: DefIdMap<_> = tcx
         .reachable_set(())
@@ -105,21 +105,16 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
             }
         })
         .map(|def_id| {
-            let codegen_attrs = tcx.codegen_fn_attrs(def_id.to_def_id());
             // We won't link right if this symbol is stripped during LTO.
             let name = tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())).name;
-            // We have to preserve the symbols of the built-in functions during LTO.
-            let is_builtin_fn = is_compiler_builtins
-                && symbol_export_level(tcx, def_id.to_def_id())
-                    .is_below_threshold(SymbolExportLevel::C)
-                && codegen_attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE);
             let used = name == "rust_eh_personality";
 
             let export_level = if special_runtime_crate {
                 SymbolExportLevel::Rust
             } else {
                 symbol_export_level(tcx, def_id.to_def_id())
             };
+            let codegen_attrs = tcx.codegen_fn_attrs(def_id.to_def_id());
             debug!(
                 "EXPORTED SYMBOL (local): {} ({:?})",
                 tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())),
@@ -139,7 +134,6 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
                 used: codegen_attrs.flags.contains(CodegenFnAttrFlags::USED)
                     || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
                     || used,
-                used_compiler: is_builtin_fn,
             };
             (def_id.to_def_id(), info)
         })
@@ -152,7 +146,6 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
                 level: SymbolExportLevel::C,
                 kind: SymbolExportKind::Data,
                 used: false,
-                used_compiler: false,
             },
         );
     }
@@ -201,7 +194,6 @@ fn exported_symbols_provider_local(
                         level: info.level,
                         kind: SymbolExportKind::Text,
                         used: info.used,
-                        used_compiler: false,
                     },
                 )
             })
@@ -218,7 +210,6 @@ fn exported_symbols_provider_local(
                 level: SymbolExportLevel::C,
                 kind: SymbolExportKind::Text,
                 used: false,
-                used_compiler: false,
             },
         ));
     }
@@ -238,7 +229,6 @@ fn exported_symbols_provider_local(
                     level: SymbolExportLevel::Rust,
                     kind: SymbolExportKind::Text,
                     used: false,
-                    used_compiler: false,
                 },
             ));
         }
@@ -251,7 +241,6 @@ fn exported_symbols_provider_local(
                 level: SymbolExportLevel::Rust,
                 kind: SymbolExportKind::Data,
                 used: false,
-                used_compiler: false,
             },
         ))
     }
@@ -271,7 +260,6 @@ fn exported_symbols_provider_local(
                     level: SymbolExportLevel::C,
                     kind: SymbolExportKind::Data,
                     used: false,
-                    used_compiler: false,
                 },
             )
         }));
@@ -297,7 +285,6 @@ fn exported_symbols_provider_local(
                     level: SymbolExportLevel::C,
                     kind: SymbolExportKind::Data,
                     used: false,
-                    used_compiler: false,
                 },
             )
         }));
@@ -315,7 +302,6 @@ fn exported_symbols_provider_local(
                 level: SymbolExportLevel::C,
                 kind: SymbolExportKind::Data,
                 used: true,
-                used_compiler: false,
             },
         ));
     }
@@ -356,7 +342,6 @@ fn exported_symbols_provider_local(
                                 level: SymbolExportLevel::Rust,
                                 kind: SymbolExportKind::Text,
                                 used: false,
-                                used_compiler: false,
                             },
                         ));
                     }
@@ -373,7 +358,6 @@ fn exported_symbols_provider_local(
                             level: SymbolExportLevel::Rust,
                             kind: SymbolExportKind::Text,
                             used: false,
-                            used_compiler: false,
                         },
                     ));
                 }

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -148,12 +148,23 @@ impl ModuleConfig {
 
         let emit_obj = if !should_emit_obj {
             EmitObj::None
-        } else if sess.target.obj_is_bitcode || sess.opts.cg.linker_plugin_lto.enabled() {
+        } else if sess.target.obj_is_bitcode
+            || (sess.opts.cg.linker_plugin_lto.enabled() && !no_builtins)
+        {
             // This case is selected if the target uses objects as bitcode, or
             // if linker plugin LTO is enabled. In the linker plugin LTO case
             // the assumption is that the final link-step will read the bitcode
             // and convert it to object code. This may be done by either the
             // native linker or rustc itself.
+            //
+            // Note, however, that the linker-plugin-lto requested here is
+            // explicitly ignored for `#![no_builtins]` crates. These crates are
+            // specifically ignored by rustc's LTO passes and wouldn't work if
+            // loaded into the linker. These crates define symbols that LLVM
+            // lowers intrinsics to, and these symbol dependencies aren't known
+            // until after codegen. As a result any crate marked
+            // `#![no_builtins]` is assumed to not participate in LTO and
+            // instead goes on to generate object code.
             EmitObj::Bitcode
         } else if need_bitcode_in_object(tcx) {
             EmitObj::ObjectCode(BitcodeSection::Full)
@@ -1023,6 +1034,9 @@ fn start_executing_work<B: ExtraBackendMethods>(
 
     let mut each_linked_rlib_for_lto = Vec::new();
     drop(link::each_linked_rlib(crate_info, None, &mut |cnum, path| {
+        if link::ignored_for_lto(sess, crate_info, cnum) {
+            return;
+        }
         each_linked_rlib_for_lto.push((cnum, path.to_path_buf()));
     }));
 

compiler/rustc_codegen_ssa/src/base.rs

@@ -859,6 +859,7 @@ impl CrateInfo {
             local_crate_name,
             compiler_builtins,
             profiler_runtime: None,
+            is_no_builtins: Default::default(),
             native_libraries: Default::default(),
             used_libraries: tcx.native_libraries(LOCAL_CRATE).iter().map(Into::into).collect(),
             crate_name: Default::default(),
@@ -885,14 +886,19 @@ impl CrateInfo {
             if tcx.is_profiler_runtime(cnum) {
                 info.profiler_runtime = Some(cnum);
             }
+            if tcx.is_no_builtins(cnum) {
+                info.is_no_builtins.insert(cnum);
+            }
         }
 
         // Handle circular dependencies in the standard library.
         // See comment before `add_linked_symbol_object` function for the details.
         // If global LTO is enabled then almost everything (*) is glued into a single object file,
         // so this logic is not necessary and can cause issues on some targets (due to weak lang
         // item symbols being "privatized" to that object file), so we disable it.
-        // (*) Native libs are not glued, and we assume that they cannot define weak lang items.
+        // (*) Native libs, and `#[compiler_builtins]` and `#[no_builtins]` crates are not glued,
+        // and we assume that they cannot define weak lang items. This is not currently enforced
+        // by the compiler, but that's ok because all this stuff is unstable anyway.
         let target = &tcx.sess.target;
         if !are_upstream_rust_objects_already_included(tcx.sess) {
             let missing_weak_lang_items: FxHashSet<Symbol> = info

compiler/rustc_codegen_ssa/src/lib.rs

@@ -25,7 +25,7 @@ extern crate tracing;
 extern crate rustc_middle;
 
 use rustc_ast as ast;
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::sync::Lrc;
 use rustc_hir::def_id::CrateNum;
 use rustc_middle::dep_graph::WorkProduct;
@@ -158,6 +158,7 @@ pub struct CrateInfo {
     pub local_crate_name: Symbol,
     pub compiler_builtins: Option<CrateNum>,
     pub profiler_runtime: Option<CrateNum>,
+    pub is_no_builtins: FxHashSet<CrateNum>,
     pub native_libraries: FxHashMap<CrateNum, Vec<NativeLib>>,
     pub crate_name: FxHashMap<CrateNum, Symbol>,
     pub used_libraries: Vec<NativeLib>,