From 0eeb14eaba04025aa8a4612e1935f04f2ca3fb6b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Steinbrink?= Date: Thu, 12 May 2016 17:54:05 +0200 Subject: [PATCH] Improve derived implementations for enums with lots of fieldless variants A number of trait methods like PartialEq::eq or Hash::hash don't actually need a distinct arm for each variant, because the code within the arm only depends on the number and types of the fields in the variants. We can easily exploit this fact to create less and better code for enums with multiple variants that have no fields at all, the extreme case being C-like enums. For nickel.rs and its by now infamous 800 variant enum, this reduces optimized compile times by 25% and non-optimized compile times by 40%. Also peak memory usage is down by almost 40% (310MB down to 190MB). To be fair, most other crates don't benefit nearly as much, because they don't have as huge enums. The crates in the Rust distribution that I measured saw basically no change in compile times (I only tried optimized builds) and only 1-2% reduction in peak memory usage. --- src/libsyntax_ext/deriving/clone.rs | 4 +++ src/libsyntax_ext/deriving/cmp/eq.rs | 1 + src/libsyntax_ext/deriving/cmp/ord.rs | 1 + src/libsyntax_ext/deriving/cmp/partial_eq.rs | 1 + src/libsyntax_ext/deriving/cmp/partial_ord.rs | 2 ++ src/libsyntax_ext/deriving/debug.rs | 1 + src/libsyntax_ext/deriving/decodable.rs | 1 + src/libsyntax_ext/deriving/default.rs | 1 + src/libsyntax_ext/deriving/encodable.rs | 1 + src/libsyntax_ext/deriving/generic/mod.rs | 35 +++++++++++++++---- src/libsyntax_ext/deriving/hash.rs | 1 + .../auxiliary/custom_derive_plugin.rs | 1 + .../auxiliary/custom_derive_plugin_attr.rs | 1 + 13 files changed, 44 insertions(+), 7 deletions(-) diff --git a/src/libsyntax_ext/deriving/clone.rs b/src/libsyntax_ext/deriving/clone.rs index 2c21fd2cd5ed2..30fe0f2db8a1c 100644 --- a/src/libsyntax_ext/deriving/clone.rs +++ b/src/libsyntax_ext/deriving/clone.rs @@ -39,6 +39,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt, // Clone + Copy, and then there'd be no Clone impl at all if the user fills in something // that is Clone but not Copy. and until specialization we can't write both impls. let bounds; + let unify_fieldless_variants; let substructure; match *item { Annotatable::Item(ref annitem) => { @@ -49,6 +50,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt, && attr::contains_name(&annitem.attrs, "derive_Copy") => { bounds = vec![Literal(path_std!(cx, core::marker::Copy))]; + unify_fieldless_variants = true; substructure = combine_substructure(Box::new(|c, s, sub| { cs_clone("Clone", c, s, sub, Mode::Shallow) })); @@ -56,6 +58,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt, _ => { bounds = vec![]; + unify_fieldless_variants = false; substructure = combine_substructure(Box::new(|c, s, sub| { cs_clone("Clone", c, s, sub, Mode::Deep) })); @@ -84,6 +87,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt, ret_ty: Self_, attributes: attrs, is_unsafe: false, + unify_fieldless_variants: unify_fieldless_variants, combine_substructure: substructure, } ), diff --git a/src/libsyntax_ext/deriving/cmp/eq.rs b/src/libsyntax_ext/deriving/cmp/eq.rs index 1b855c56a48bf..8bd12c393370d 100644 --- a/src/libsyntax_ext/deriving/cmp/eq.rs +++ b/src/libsyntax_ext/deriving/cmp/eq.rs @@ -62,6 +62,7 @@ pub fn expand_deriving_eq(cx: &mut ExtCtxt, ret_ty: nil_ty(), attributes: attrs, is_unsafe: false, + unify_fieldless_variants: true, combine_substructure: combine_substructure(Box::new(|a, b, c| { cs_total_eq_assert(a, b, c) })) diff --git a/src/libsyntax_ext/deriving/cmp/ord.rs b/src/libsyntax_ext/deriving/cmp/ord.rs index 74706c470872a..6133adb8fc5d1 100644 --- a/src/libsyntax_ext/deriving/cmp/ord.rs +++ b/src/libsyntax_ext/deriving/cmp/ord.rs @@ -42,6 +42,7 @@ pub fn expand_deriving_ord(cx: &mut ExtCtxt, ret_ty: Literal(path_std!(cx, core::cmp::Ordering)), attributes: attrs, is_unsafe: false, + unify_fieldless_variants: true, combine_substructure: combine_substructure(Box::new(|a, b, c| { cs_cmp(a, b, c) })), diff --git a/src/libsyntax_ext/deriving/cmp/partial_eq.rs b/src/libsyntax_ext/deriving/cmp/partial_eq.rs index 6406ee59a5eb5..e5890d7213bed 100644 --- a/src/libsyntax_ext/deriving/cmp/partial_eq.rs +++ b/src/libsyntax_ext/deriving/cmp/partial_eq.rs @@ -73,6 +73,7 @@ pub fn expand_deriving_partial_eq(cx: &mut ExtCtxt, ret_ty: Literal(path_local!(bool)), attributes: attrs, is_unsafe: false, + unify_fieldless_variants: true, combine_substructure: combine_substructure(Box::new(|a, b, c| { $f(a, b, c) })) diff --git a/src/libsyntax_ext/deriving/cmp/partial_ord.rs b/src/libsyntax_ext/deriving/cmp/partial_ord.rs index e49c77285ab02..cfc6dbe5cd030 100644 --- a/src/libsyntax_ext/deriving/cmp/partial_ord.rs +++ b/src/libsyntax_ext/deriving/cmp/partial_ord.rs @@ -38,6 +38,7 @@ pub fn expand_deriving_partial_ord(cx: &mut ExtCtxt, ret_ty: Literal(path_local!(bool)), attributes: attrs, is_unsafe: false, + unify_fieldless_variants: true, combine_substructure: combine_substructure(Box::new(|cx, span, substr| { cs_op($op, $equal, cx, span, substr) })) @@ -62,6 +63,7 @@ pub fn expand_deriving_partial_ord(cx: &mut ExtCtxt, ret_ty: ret_ty, attributes: attrs, is_unsafe: false, + unify_fieldless_variants: true, combine_substructure: combine_substructure(Box::new(|cx, span, substr| { cs_partial_cmp(cx, span, substr) })) diff --git a/src/libsyntax_ext/deriving/debug.rs b/src/libsyntax_ext/deriving/debug.rs index 323c6c388fb64..d86eae820a884 100644 --- a/src/libsyntax_ext/deriving/debug.rs +++ b/src/libsyntax_ext/deriving/debug.rs @@ -45,6 +45,7 @@ pub fn expand_deriving_debug(cx: &mut ExtCtxt, ret_ty: Literal(path_std!(cx, core::fmt::Result)), attributes: Vec::new(), is_unsafe: false, + unify_fieldless_variants: false, combine_substructure: combine_substructure(Box::new(|a, b, c| { show_substructure(a, b, c) })) diff --git a/src/libsyntax_ext/deriving/decodable.rs b/src/libsyntax_ext/deriving/decodable.rs index 9387cf05ac7d1..04888d046ad2d 100644 --- a/src/libsyntax_ext/deriving/decodable.rs +++ b/src/libsyntax_ext/deriving/decodable.rs @@ -85,6 +85,7 @@ fn expand_deriving_decodable_imp(cx: &mut ExtCtxt, )), attributes: Vec::new(), is_unsafe: false, + unify_fieldless_variants: false, combine_substructure: combine_substructure(Box::new(|a, b, c| { decodable_substructure(a, b, c, krate) })), diff --git a/src/libsyntax_ext/deriving/default.rs b/src/libsyntax_ext/deriving/default.rs index bee63a98c252f..a6a4830fab7f8 100644 --- a/src/libsyntax_ext/deriving/default.rs +++ b/src/libsyntax_ext/deriving/default.rs @@ -42,6 +42,7 @@ pub fn expand_deriving_default(cx: &mut ExtCtxt, ret_ty: Self_, attributes: attrs, is_unsafe: false, + unify_fieldless_variants: false, combine_substructure: combine_substructure(Box::new(|a, b, c| { default_substructure(a, b, c) })) diff --git a/src/libsyntax_ext/deriving/encodable.rs b/src/libsyntax_ext/deriving/encodable.rs index 5b47d8da8b642..66672305829b9 100644 --- a/src/libsyntax_ext/deriving/encodable.rs +++ b/src/libsyntax_ext/deriving/encodable.rs @@ -161,6 +161,7 @@ fn expand_deriving_encodable_imp(cx: &mut ExtCtxt, )), attributes: Vec::new(), is_unsafe: false, + unify_fieldless_variants: false, combine_substructure: combine_substructure(Box::new(|a, b, c| { encodable_substructure(a, b, c, krate) })), diff --git a/src/libsyntax_ext/deriving/generic/mod.rs b/src/libsyntax_ext/deriving/generic/mod.rs index 1d5fc13c72008..45029c8eb943b 100644 --- a/src/libsyntax_ext/deriving/generic/mod.rs +++ b/src/libsyntax_ext/deriving/generic/mod.rs @@ -257,6 +257,9 @@ pub struct MethodDef<'a> { // Is it an `unsafe fn`? pub is_unsafe: bool, + /// Can we combine fieldless variants for enums into a single match arm? + pub unify_fieldless_variants: bool, + pub combine_substructure: RefCell>, } @@ -1131,12 +1134,15 @@ impl<'a> MethodDef<'a> { let catch_all_substructure = EnumNonMatchingCollapsed( self_arg_idents, &variants[..], &vi_idents[..]); + let first_fieldless = variants.iter().find(|v| v.node.data.fields().is_empty()); + // These arms are of the form: // (Variant1, Variant1, ...) => Body1 // (Variant2, Variant2, ...) => Body2 // ... // where each tuple has length = self_args.len() let mut match_arms: Vec = variants.iter().enumerate() + .filter(|&(_, v)| !(self.unify_fieldless_variants && v.node.data.fields().is_empty())) .map(|(index, variant)| { let mk_self_pat = |cx: &mut ExtCtxt, self_arg_name: &str| { let (p, idents) = trait_.create_enum_variant_pattern( @@ -1219,6 +1225,28 @@ impl<'a> MethodDef<'a> { cx.arm(sp, vec![single_pat], arm_expr) }).collect(); + + let default = match first_fieldless { + Some(v) if self.unify_fieldless_variants => { + // We need a default case that handles the fieldless variants. + // The index and actual variant aren't meaningful in this case, + // so just use whatever + Some(self.call_substructure_method( + cx, trait_, type_ident, &self_args[..], nonself_args, + &EnumMatching(0, v, Vec::new()))) + } + _ if variants.len() > 1 && self_args.len() > 1 => { + // Since we know that all the arguments will match if we reach + // the match expression we add the unreachable intrinsics as the + // result of the catch all which should help llvm in optimizing it + Some(deriving::call_intrinsic(cx, sp, "unreachable", vec![])) + } + _ => None + }; + if let Some(arm) = default { + match_arms.push(cx.arm(sp, vec![cx.pat_wild(sp)], arm)); + } + // We will usually need the catch-all after matching the // tuples `(VariantK, VariantK, ...)` for each VariantK of the // enum. But: @@ -1292,13 +1320,6 @@ impl<'a> MethodDef<'a> { cx, trait_, type_ident, &self_args[..], nonself_args, &catch_all_substructure); - //Since we know that all the arguments will match if we reach the match expression we - //add the unreachable intrinsics as the result of the catch all which should help llvm - //in optimizing it - match_arms.push(cx.arm(sp, - vec![cx.pat_wild(sp)], - deriving::call_intrinsic(cx, sp, "unreachable", vec![]))); - // Final wrinkle: the self_args are expressions that deref // down to desired l-values, but we cannot actually deref // them when they are fed as r-values into a tuple diff --git a/src/libsyntax_ext/deriving/hash.rs b/src/libsyntax_ext/deriving/hash.rs index c37ae116d379b..fd449372cb376 100644 --- a/src/libsyntax_ext/deriving/hash.rs +++ b/src/libsyntax_ext/deriving/hash.rs @@ -51,6 +51,7 @@ pub fn expand_deriving_hash(cx: &mut ExtCtxt, ret_ty: nil_ty(), attributes: vec![], is_unsafe: false, + unify_fieldless_variants: true, combine_substructure: combine_substructure(Box::new(|a, b, c| { hash_substructure(a, b, c) })) diff --git a/src/test/run-pass-fulldeps/auxiliary/custom_derive_plugin.rs b/src/test/run-pass-fulldeps/auxiliary/custom_derive_plugin.rs index 5f0ef4de491e0..0132014de0ab5 100644 --- a/src/test/run-pass-fulldeps/auxiliary/custom_derive_plugin.rs +++ b/src/test/run-pass-fulldeps/auxiliary/custom_derive_plugin.rs @@ -58,6 +58,7 @@ fn expand(cx: &mut ExtCtxt, ret_ty: Literal(Path::new_local("isize")), attributes: vec![], is_unsafe: false, + unify_fieldless_variants: true, combine_substructure: combine_substructure(box |cx, span, substr| { let zero = cx.expr_isize(span, 0); cs_fold(false, diff --git a/src/test/run-pass-fulldeps/auxiliary/custom_derive_plugin_attr.rs b/src/test/run-pass-fulldeps/auxiliary/custom_derive_plugin_attr.rs index 2878674f0ea61..6fa78913839b7 100644 --- a/src/test/run-pass-fulldeps/auxiliary/custom_derive_plugin_attr.rs +++ b/src/test/run-pass-fulldeps/auxiliary/custom_derive_plugin_attr.rs @@ -60,6 +60,7 @@ fn expand(cx: &mut ExtCtxt, ret_ty: Literal(Path::new_local("isize")), attributes: vec![], is_unsafe: false, + unify_fieldless_variants: true, combine_substructure: combine_substructure(Box::new(totalsum_substructure)), }, ],