bjoernager/rust
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Auto merge of #118568 - DianQK:no-builtins-symbols, r=pnkfelix

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Avoid adding builtin functions to `symbols.o`

We found performance regressions in #113923. The problem seems to be that `--gc-sections` does not remove these symbols. I tested that lld removes these symbols, but ld and gold do not.

I found that `used` adds symbols to `symbols.o` at 3e202ead60/compiler/rustc_codegen_ssa/src/back/linker.rs (L1786-L1791).
The PR removes builtin functions.

Note that under LTO, ld still preserves these symbols. (lld will still remove them.)

The first commit also fixes #118559. But I think the second commit also makes sense.
This commit is contained in:
bors 2023-12-07 20:31:55 +00:00
commit 503e129328
6 changed files with 30 additions and 4 deletions
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18
compiler/rustc_codegen_ssa/src/back/symbol_export.rs
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@ -105,20 +105,21 @@ 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);
let used = is_builtin_fn || name == "rust_eh_personality";
.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())),
@ -138,6 +139,7 @@ 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)
})
@ -150,6 +152,7 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
level: SymbolExportLevel::C,
kind: SymbolExportKind::Data,
used: false,
used_compiler: false,
},
);
}
@ -198,6 +201,7 @@ fn exported_symbols_provider_local(
level: info.level,
kind: SymbolExportKind::Text,
used: info.used,
used_compiler: false,
},
)
})
@ -214,6 +218,7 @@ fn exported_symbols_provider_local(
level: SymbolExportLevel::C,
kind: SymbolExportKind::Text,
used: false,
used_compiler: false,
},
));
}
@ -233,6 +238,7 @@ fn exported_symbols_provider_local(
level: SymbolExportLevel::Rust,
kind: SymbolExportKind::Text,
used: false,
used_compiler: false,
},
));
}
@ -245,6 +251,7 @@ fn exported_symbols_provider_local(
level: SymbolExportLevel::Rust,
kind: SymbolExportKind::Data,
used: false,
used_compiler: false,
},
))
}
@ -264,6 +271,7 @@ fn exported_symbols_provider_local(
level: SymbolExportLevel::C,
kind: SymbolExportKind::Data,
used: false,
used_compiler: false,
},
)
}));
@ -289,6 +297,7 @@ fn exported_symbols_provider_local(
level: SymbolExportLevel::C,
kind: SymbolExportKind::Data,
used: false,
used_compiler: false,
},
)
}));
@ -306,6 +315,7 @@ fn exported_symbols_provider_local(
level: SymbolExportLevel::C,
kind: SymbolExportKind::Data,
used: true,
used_compiler: false,
},
));
}
@ -346,6 +356,7 @@ fn exported_symbols_provider_local(
level: SymbolExportLevel::Rust,
kind: SymbolExportKind::Text,
used: false,
used_compiler: false,
},
));
}
@ -362,6 +373,7 @@ fn exported_symbols_provider_local(
level: SymbolExportLevel::Rust,
kind: SymbolExportKind::Text,
used: false,
used_compiler: false,
},
));
}