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Avoid generating empty closures for fieldless enums

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For many enums, this avoids generating lots of tiny stubs that need to be
codegen'd and then inlined and removed by LLVM.
This commit is contained in:
Mark Rousskov 2021-10-12 10:43:39 -04:00
parent 65f3f8b220
commit 3228603cce
3 changed files with 46 additions and 7 deletions
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25
compiler/rustc_macros/src/serialize.rs
View File

@ -247,13 +247,24 @@ fn encodable_body(
})
.collect();
let result = quote! { ::rustc_serialize::Encoder::emit_enum_variant(
__encoder,
#variant_name,
#variant_idx,
#field_idx,
|__encoder| { ::std::result::Result::Ok({ #encode_fields }) }
) };
let result = if field_idx != 0 {
quote! {
::rustc_serialize::Encoder::emit_enum_variant(
__encoder,
#variant_name,
#variant_idx,
#field_idx,
|__encoder| { ::std::result::Result::Ok({ #encode_fields }) }
)
}
} else {
quote! {
::rustc_serialize::Encoder::emit_fieldless_enum_variant::<#variant_idx>(
__encoder,
#variant_name,
)
}
};
variant_idx += 1;
result
});

14
compiler/rustc_serialize/src/json.rs
View File

@ -589,6 +589,13 @@ impl<'a> crate::Encoder for Encoder<'a> {
}
}
fn emit_fieldless_enum_variant<const ID: usize>(
&mut self,
name: &str,
) -> Result<(), Self::Error> {
escape_str(self.writer, name)
}
fn emit_enum_variant_arg<F>(&mut self, first: bool, f: F) -> EncodeResult
where
F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
@ -885,6 +892,13 @@ impl<'a> crate::Encoder for PrettyEncoder<'a> {
}
}
fn emit_fieldless_enum_variant<const ID: usize>(
&mut self,
name: &str,
) -> Result<(), Self::Error> {
escape_str(self.writer, name)
}
fn emit_enum_variant_arg<F>(&mut self, first: bool, f: F) -> EncodeResult
where
F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,

14
compiler/rustc_serialize/src/serialize.rs
View File

@ -58,6 +58,20 @@ pub trait Encoder {
f(self)
}
// We put the field index in a const generic to allow the emit_usize to be
// compiled into a more efficient form. In practice, the variant index is
// known at compile-time, and that knowledge allows much more efficient
// codegen than we'd otherwise get. LLVM isn't always able to make the
// optimization that would otherwise be necessary here, likely due to the
// multiple levels of inlining and const-prop that are needed.
#[inline]
fn emit_fieldless_enum_variant<const ID: usize>(
&mut self,
_v_name: &str,
) -> Result<(), Self::Error> {
self.emit_usize(ID)
}
#[inline]
fn emit_enum_variant_arg<F>(&mut self, _first: bool, f: F) -> Result<(), Self::Error>
where