Update bincode, reduce code size of `script` by ~11% #27063

SimonSapin · 2020-06-24T07:59:14Z

… as measured in lines of unoptimized LLVM IR by

cargo llvm-lines --manifest-path ports/winit/Cargo.toml \
    -p script --features layout-2013 | head -n 30

… with https://github.com/dtolnay/cargo-llvm-lines
CC #26713

One of the top functions (in lines contribution) was a Visitor::visit_enum method generated by serde_derive for deserializing keyboard_types::key::Key, which is an enum with many variants. I had filed serde-rs/serde#1824 to discuss this, and dtolnay proposed pyfisch/keyboard-types#6 manually implementing Deserialize for that enum instead of deriving it.

However another point of note is that this function had four copies with monomorphization. I could reproduce this in a program that does nothing but deserialize an enum with bincode: serde-rs/serde#1824 (comment) This suggests that bincode uses instanciates the Deserialize impls with four different Deserializer types which is three more than necessary.

https://dos.cafe/blog/bincode-1.3.html mentions changes to Deserializer types in a new version of bincode. And sure enough, this issue is now fixed.

Before:

  Lines           Copies         Function name
  -----           ------         -------------
  7022161 (100%)  180367 (100%)  (TOTAL)
   178816 (2.5%)   15437 (8.6%)  core::ptr::drop_in_place
   151022 (2.2%)    6634 (3.7%)  core::ops::function::FnOnce::call_once
   122012 (1.7%)    1000 (0.6%)  <<&mut bincode::de::Deserializer<R,O> as serde::de::Deserializer>::deserialize_tuple::Access<R,O> as serde::de::SeqAccess>::next_element_seed
   101731 (1.4%)    1627 (0.9%)  core::option::Option<T>::map
    83196 (1.2%)    1192 (0.7%)  core::result::Result<T,E>::map
    51215 (0.7%)    6111 (3.4%)  core::ops::function::FnOnce::call_once{{vtable.shim}}
    47048 (0.7%)       4 (0.0%)  <keyboard_types::key::_IMPL_DESERIALIZE_FOR_Key::<impl serde::de::Deserialize for keyboard_types::key::Key>::deserialize::__Visitor as serde::de::Visitor>::visit_enum
    45388 (0.6%)     296 (0.2%)  <&mut bincode::de::Deserializer<R,O> as serde::de::Deserializer>::deserialize_enum::<impl serde::de::EnumAccess for &mut bincode::de::Deserializer<R,O>>::variant_seed
    44973 (0.6%)     647 (0.4%)  core::result::Result<T,E>::map_err
    39185 (0.6%)     516 (0.3%)  std::thread::local::LocalKey<T>::try_with
    39130 (0.6%)     215 (0.1%)  alloc::raw_vec::RawVec<T,A>::grow_amortized
    35334 (0.5%)     867 (0.5%)  alloc::alloc::box_free
    34788 (0.5%)     609 (0.3%)  crossbeam_channel::context::Context::with::{{closure}}
    33810 (0.5%)     646 (0.4%)  core::ptr::swap_nonoverlapping_one
    33610 (0.5%)     552 (0.3%)  core::result::Result<T,E>::unwrap_or_else
    32144 (0.5%)     392 (0.2%)  <*const T as core::fmt::Pointer>::fmt
    32062 (0.5%)     782 (0.4%)  script::dom::bindings::root::Root<T>::new
    31589 (0.4%)     600 (0.3%)  core::result::Result<T,E>::expect
    29364 (0.4%)     116 (0.1%)  <<script_traits::webdriver_msg::_IMPL_DESERIALIZE_FOR_WebDriverScriptCommand::<impl serde::de::Deserialize for script_traits::webdriver_msg::WebDriverScriptCommand>::deserialize::__Visitor as serde::de::Visitor>::visit_enum::__Visitor as serde::de::Visitor>::visit_seq
    26996 (0.4%)     346 (0.2%)  core::option::Option<T>::map_or
    26168 (0.4%)      92 (0.1%)  <<script_traits::_IMPL_DESERIALIZE_FOR_ConstellationControlMsg::<impl serde::de::Deserialize for script_traits::ConstellationControlMsg>::deserialize::__Visitor as serde::de::Visitor>::visit_enum::__Visitor as serde::de::Visitor>::visit_seq
    25996 (0.4%)     388 (0.2%)  script::dom::bindings::root::Root<script::dom::bindings::root::MaybeUnreflectedDom<T>>::reflect_with
    25833 (0.4%)     641 (0.4%)  core::result::Result<T,E>::unwrap
    25180 (0.4%)       4 (0.0%)  <keyboard_types::code::_IMPL_DESERIALIZE_FOR_Code::<impl serde::de::Deserialize for keyboard_types::code::Code>::deserialize::__Visitor as serde::de::Visitor>::visit_enum
    24751 (0.4%)     197 (0.1%)  core::iter::traits::iterator::Iterator::try_fold
    22216 (0.3%)     376 (0.2%)  bincode::internal::deserialize_seed
    22185 (0.3%)     145 (0.1%)  hashbrown::raw::RawTable<T>::find

After:

  Lines           Copies         Function name
  -----           ------         -------------
  6239581 (100%)  169803 (100%)  (TOTAL)
   178770 (2.9%)   15434 (9.1%)  core::ptr::drop_in_place
   151022 (2.4%)    6634 (3.9%)  core::ops::function::FnOnce::call_once
   101146 (1.6%)    1618 (1.0%)  core::option::Option<T>::map
    76938 (1.2%)    1090 (0.6%)  core::result::Result<T,E>::map
    51215 (0.8%)    6111 (3.6%)  core::ops::function::FnOnce::call_once{{vtable.shim}}
    44973 (0.7%)     647 (0.4%)  core::result::Result<T,E>::map_err
    39185 (0.6%)     516 (0.3%)  std::thread::local::LocalKey<T>::try_with
    39130 (0.6%)     215 (0.1%)  alloc::raw_vec::RawVec<T,A>::grow_amortized
    35334 (0.6%)     867 (0.5%)  alloc::alloc::box_free
    34788 (0.6%)     609 (0.4%)  crossbeam_channel::context::Context::with::{{closure}}
    33810 (0.5%)     646 (0.4%)  core::ptr::swap_nonoverlapping_one
    33610 (0.5%)     552 (0.3%)  core::result::Result<T,E>::unwrap_or_else
    32144 (0.5%)     392 (0.2%)  <*const T as core::fmt::Pointer>::fmt
    32062 (0.5%)     782 (0.5%)  script::dom::bindings::root::Root<T>::new
    31589 (0.5%)     600 (0.4%)  core::result::Result<T,E>::expect
    30069 (0.5%)     250 (0.1%)  <<&mut bincode::de::Deserializer<R,O> as serde::de::Deserializer>::deserialize_tuple::Access<R,O> as serde::de::SeqAccess>::next_element_seed
    26996 (0.4%)     346 (0.2%)  core::option::Option<T>::map_or
    25996 (0.4%)     388 (0.2%)  script::dom::bindings::root::Root<script::dom::bindings::root::MaybeUnreflectedDom<T>>::reflect_with
    25833 (0.4%)     641 (0.4%)  core::result::Result<T,E>::unwrap
    24751 (0.4%)     197 (0.1%)  core::iter::traits::iterator::Iterator::try_fold
    22185 (0.4%)     145 (0.1%)  hashbrown::raw::RawTable<T>::find
    22000 (0.4%)      80 (0.0%)  hashbrown::raw::RawTable<T>::rehash_in_place
    20808 (0.3%)     289 (0.2%)  core::alloc::layout::Layout::array
    20031 (0.3%)     308 (0.2%)  core::option::Option<T>::ok_or_else
    19732 (0.3%)       2 (0.0%)  html5ever::tree_builder::TreeBuilder<Handle,Sink>::step
    18951 (0.3%)    1014 (0.6%)  core::ptr::read
    17261 (0.3%)     201 (0.1%)  core::iter::traits::iterator::Iterator::fold

That visit_enum for Key is not in the first 30 lines, I find it after changing the filtering command to head -n 60:

    11762 (0.2%)       1 (0.0%)  <keyboard_types::key::_IMPL_DESERIALIZE_FOR_Key::<impl serde::de::Deserialize for keyboard_types::key::Key>::deserialize::__Visitor as serde::de::Visitor>::visit_enum

It has one copy / instantiation instead of four, and contributes exactly four times fewer lines of IR.

The crate total reduced by ~782k lines, a lot more than ~35k for this visit_enum function. We also see that next_element_seed (also for bincode deserialization) now has 250 copies instead of 1000. So it looks like everything bincode-related was reduced by 4×


        Update bincode, reduce code size of `script` by ~11%

… as measured in lines of unoptimized LLVM IR by ``` cargo llvm-lines --manifest-path ports/winit/Cargo.toml \ -p script --features layout-2013 | head -n 30 ``` … with https://github.com/dtolnay/cargo-llvm-lines CC #26713 One of the top functions (in lines contribution) was a `Visitor::visit_enum` method generated by `serde_derive` for deserializing `keyboard_types:🔑:Key`, which is an enum with many variants. I had filed serde-rs/serde#1824 to discuss this, and dtolnay proposed pyfisch/keyboard-types#6 manually implementing `Deserialize` for that enum instead of deriving it. However another point of note is that this function had four copies with monomorphization. I could reproduce this in a program that does nothing but deserialize an enum with bincode: serde-rs/serde#1824 (comment) This suggests that bincode uses instanciates the `Deserialize` impls with four different `Deserializer` types which is three more than necessary. https://dos.cafe/blog/bincode-1.3.html mentions changes to `Deserializer` types in a new version of bincode. And sure enough, this issue is now fixed. Before: ``` Lines Copies Function name ----- ------ ------------- 7022161 (100%) 180367 (100%) (TOTAL) 178816 (2.5%) 15437 (8.6%) core::ptr::drop_in_place 151022 (2.2%) 6634 (3.7%) core::ops::function::FnOnce::call_once 122012 (1.7%) 1000 (0.6%) <<&mut bincode:🇩🇪:Deserializer<R,O> as serde:🇩🇪:Deserializer>::deserialize_tuple::Access<R,O> as serde:🇩🇪:SeqAccess>::next_element_seed 101731 (1.4%) 1627 (0.9%) core::option::Option<T>::map 83196 (1.2%) 1192 (0.7%) core::result::Result<T,E>::map 51215 (0.7%) 6111 (3.4%) core::ops::function::FnOnce::call_once{{vtable.shim}} 47048 (0.7%) 4 (0.0%) <keyboard_types:🔑:_IMPL_DESERIALIZE_FOR_Key::<impl serde:🇩🇪:Deserialize for keyboard_types:🔑:Key>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum 45388 (0.6%) 296 (0.2%) <&mut bincode:🇩🇪:Deserializer<R,O> as serde:🇩🇪:Deserializer>::deserialize_enum::<impl serde:🇩🇪:EnumAccess for &mut bincode:🇩🇪:Deserializer<R,O>>::variant_seed 44973 (0.6%) 647 (0.4%) core::result::Result<T,E>::map_err 39185 (0.6%) 516 (0.3%) std:🧵:local::LocalKey<T>::try_with 39130 (0.6%) 215 (0.1%) alloc::raw_vec::RawVec<T,A>::grow_amortized 35334 (0.5%) 867 (0.5%) alloc::alloc::box_free 34788 (0.5%) 609 (0.3%) crossbeam_channel::context::Context::with::{{closure}} 33810 (0.5%) 646 (0.4%) core::ptr::swap_nonoverlapping_one 33610 (0.5%) 552 (0.3%) core::result::Result<T,E>::unwrap_or_else 32144 (0.5%) 392 (0.2%) <*const T as core::fmt::Pointer>::fmt 32062 (0.5%) 782 (0.4%) script::dom::bindings::root::Root<T>::new 31589 (0.4%) 600 (0.3%) core::result::Result<T,E>::expect 29364 (0.4%) 116 (0.1%) <<script_traits::webdriver_msg::_IMPL_DESERIALIZE_FOR_WebDriverScriptCommand::<impl serde:🇩🇪:Deserialize for script_traits::webdriver_msg::WebDriverScriptCommand>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum::__Visitor as serde:🇩🇪:Visitor>::visit_seq 26996 (0.4%) 346 (0.2%) core::option::Option<T>::map_or 26168 (0.4%) 92 (0.1%) <<script_traits::_IMPL_DESERIALIZE_FOR_ConstellationControlMsg::<impl serde:🇩🇪:Deserialize for script_traits::ConstellationControlMsg>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum::__Visitor as serde:🇩🇪:Visitor>::visit_seq 25996 (0.4%) 388 (0.2%) script::dom::bindings::root::Root<script::dom::bindings::root::MaybeUnreflectedDom<T>>::reflect_with 25833 (0.4%) 641 (0.4%) core::result::Result<T,E>::unwrap 25180 (0.4%) 4 (0.0%) <keyboard_types::code::_IMPL_DESERIALIZE_FOR_Code::<impl serde:🇩🇪:Deserialize for keyboard_types::code::Code>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum 24751 (0.4%) 197 (0.1%) core::iter::traits::iterator::Iterator::try_fold 22216 (0.3%) 376 (0.2%) bincode::internal::deserialize_seed 22185 (0.3%) 145 (0.1%) hashbrown::raw::RawTable<T>::find ``` After: ``` Lines Copies Function name ----- ------ ------------- 6239581 (100%) 169803 (100%) (TOTAL) 178770 (2.9%) 15434 (9.1%) core::ptr::drop_in_place 151022 (2.4%) 6634 (3.9%) core::ops::function::FnOnce::call_once 101146 (1.6%) 1618 (1.0%) core::option::Option<T>::map 76938 (1.2%) 1090 (0.6%) core::result::Result<T,E>::map 51215 (0.8%) 6111 (3.6%) core::ops::function::FnOnce::call_once{{vtable.shim}} 44973 (0.7%) 647 (0.4%) core::result::Result<T,E>::map_err 39185 (0.6%) 516 (0.3%) std:🧵:local::LocalKey<T>::try_with 39130 (0.6%) 215 (0.1%) alloc::raw_vec::RawVec<T,A>::grow_amortized 35334 (0.6%) 867 (0.5%) alloc::alloc::box_free 34788 (0.6%) 609 (0.4%) crossbeam_channel::context::Context::with::{{closure}} 33810 (0.5%) 646 (0.4%) core::ptr::swap_nonoverlapping_one 33610 (0.5%) 552 (0.3%) core::result::Result<T,E>::unwrap_or_else 32144 (0.5%) 392 (0.2%) <*const T as core::fmt::Pointer>::fmt 32062 (0.5%) 782 (0.5%) script::dom::bindings::root::Root<T>::new 31589 (0.5%) 600 (0.4%) core::result::Result<T,E>::expect 30069 (0.5%) 250 (0.1%) <<&mut bincode:🇩🇪:Deserializer<R,O> as serde:🇩🇪:Deserializer>::deserialize_tuple::Access<R,O> as serde:🇩🇪:SeqAccess>::next_element_seed 26996 (0.4%) 346 (0.2%) core::option::Option<T>::map_or 25996 (0.4%) 388 (0.2%) script::dom::bindings::root::Root<script::dom::bindings::root::MaybeUnreflectedDom<T>>::reflect_with 25833 (0.4%) 641 (0.4%) core::result::Result<T,E>::unwrap 24751 (0.4%) 197 (0.1%) core::iter::traits::iterator::Iterator::try_fold 22185 (0.4%) 145 (0.1%) hashbrown::raw::RawTable<T>::find 22000 (0.4%) 80 (0.0%) hashbrown::raw::RawTable<T>::rehash_in_place 20808 (0.3%) 289 (0.2%) core::alloc::layout::Layout::array 20031 (0.3%) 308 (0.2%) core::option::Option<T>::ok_or_else 19732 (0.3%) 2 (0.0%) html5ever::tree_builder::TreeBuilder<Handle,Sink>::step 18951 (0.3%) 1014 (0.6%) core::ptr::read 17261 (0.3%) 201 (0.1%) core::iter::traits::iterator::Iterator::fold ``` That `visit_enum` for `Key` is not in the first 30 lines, I find it after changing the filtering command to `head -n 60`: ``` 11762 (0.2%) 1 (0.0%) <keyboard_types:🔑:_IMPL_DESERIALIZE_FOR_Key::<impl serde:🇩🇪:Deserialize for keyboard_types:🔑:Key>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum ``` It has one copy / instantiation instead of four, which contributes exactly four times fewer lines of IR. The crate total reduced by ~782k lines, a lot more than ~35k for this `visit_enum` function. We see that `next_element_seed` (also for bincode deserialization) now has 250 copies instead of 1000. So it looks like *everything* bincode related was reduced by 4×

nox · 2020-06-24T10:32:22Z

@bors-servo r+

bors-servo · 2020-06-24T10:32:25Z

📌 Commit a215ef3 has been approved by nox

bors-servo · 2020-06-24T11:04:45Z

⌛ Testing commit a215ef3 with merge 029d252...


        Auto merge of #27063 - servo:bincodeup, r=nox

Update bincode, reduce code size of `script` by ~11% … as measured in lines of unoptimized LLVM IR by ``` cargo llvm-lines --manifest-path ports/winit/Cargo.toml \ -p script --features layout-2013 | head -n 30 ``` … with https://github.com/dtolnay/cargo-llvm-lines CC #26713 One of the top functions (in lines contribution) was a `Visitor::visit_enum` method generated by `serde_derive` for deserializing `keyboard_types:🔑:Key`, which is an enum with many variants. I had filed serde-rs/serde#1824 to discuss this, and dtolnay proposed pyfisch/keyboard-types#6 manually implementing `Deserialize` for that enum instead of deriving it. However another point of note is that this function had four copies with monomorphization. I could reproduce this in a program that does nothing but deserialize an enum with bincode: serde-rs/serde#1824 (comment) This suggests that bincode uses instanciates the `Deserialize` impls with four different `Deserializer` types which is three more than necessary. https://dos.cafe/blog/bincode-1.3.html mentions changes to `Deserializer` types in a new version of bincode. And sure enough, this issue is now fixed. Before: ``` Lines Copies Function name ----- ------ ------------- 7022161 (100%) 180367 (100%) (TOTAL) 178816 (2.5%) 15437 (8.6%) core::ptr::drop_in_place 151022 (2.2%) 6634 (3.7%) core::ops::function::FnOnce::call_once 122012 (1.7%) 1000 (0.6%) <<&mut bincode:🇩🇪:Deserializer<R,O> as serde:🇩🇪:Deserializer>::deserialize_tuple::Access<R,O> as serde:🇩🇪:SeqAccess>::next_element_seed 101731 (1.4%) 1627 (0.9%) core::option::Option<T>::map 83196 (1.2%) 1192 (0.7%) core::result::Result<T,E>::map 51215 (0.7%) 6111 (3.4%) core::ops::function::FnOnce::call_once{{vtable.shim}} 47048 (0.7%) 4 (0.0%) <keyboard_types:🔑:_IMPL_DESERIALIZE_FOR_Key::<impl serde:🇩🇪:Deserialize for keyboard_types:🔑:Key>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum 45388 (0.6%) 296 (0.2%) <&mut bincode:🇩🇪:Deserializer<R,O> as serde:🇩🇪:Deserializer>::deserialize_enum::<impl serde:🇩🇪:EnumAccess for &mut bincode:🇩🇪:Deserializer<R,O>>::variant_seed 44973 (0.6%) 647 (0.4%) core::result::Result<T,E>::map_err 39185 (0.6%) 516 (0.3%) std:🧵:local::LocalKey<T>::try_with 39130 (0.6%) 215 (0.1%) alloc::raw_vec::RawVec<T,A>::grow_amortized 35334 (0.5%) 867 (0.5%) alloc::alloc::box_free 34788 (0.5%) 609 (0.3%) crossbeam_channel::context::Context::with::{{closure}} 33810 (0.5%) 646 (0.4%) core::ptr::swap_nonoverlapping_one 33610 (0.5%) 552 (0.3%) core::result::Result<T,E>::unwrap_or_else 32144 (0.5%) 392 (0.2%) <*const T as core::fmt::Pointer>::fmt 32062 (0.5%) 782 (0.4%) script::dom::bindings::root::Root<T>::new 31589 (0.4%) 600 (0.3%) core::result::Result<T,E>::expect 29364 (0.4%) 116 (0.1%) <<script_traits::webdriver_msg::_IMPL_DESERIALIZE_FOR_WebDriverScriptCommand::<impl serde:🇩🇪:Deserialize for script_traits::webdriver_msg::WebDriverScriptCommand>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum::__Visitor as serde:🇩🇪:Visitor>::visit_seq 26996 (0.4%) 346 (0.2%) core::option::Option<T>::map_or 26168 (0.4%) 92 (0.1%) <<script_traits::_IMPL_DESERIALIZE_FOR_ConstellationControlMsg::<impl serde:🇩🇪:Deserialize for script_traits::ConstellationControlMsg>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum::__Visitor as serde:🇩🇪:Visitor>::visit_seq 25996 (0.4%) 388 (0.2%) script::dom::bindings::root::Root<script::dom::bindings::root::MaybeUnreflectedDom<T>>::reflect_with 25833 (0.4%) 641 (0.4%) core::result::Result<T,E>::unwrap 25180 (0.4%) 4 (0.0%) <keyboard_types::code::_IMPL_DESERIALIZE_FOR_Code::<impl serde:🇩🇪:Deserialize for keyboard_types::code::Code>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum 24751 (0.4%) 197 (0.1%) core::iter::traits::iterator::Iterator::try_fold 22216 (0.3%) 376 (0.2%) bincode::internal::deserialize_seed 22185 (0.3%) 145 (0.1%) hashbrown::raw::RawTable<T>::find ``` After: ``` Lines Copies Function name ----- ------ ------------- 6239581 (100%) 169803 (100%) (TOTAL) 178770 (2.9%) 15434 (9.1%) core::ptr::drop_in_place 151022 (2.4%) 6634 (3.9%) core::ops::function::FnOnce::call_once 101146 (1.6%) 1618 (1.0%) core::option::Option<T>::map 76938 (1.2%) 1090 (0.6%) core::result::Result<T,E>::map 51215 (0.8%) 6111 (3.6%) core::ops::function::FnOnce::call_once{{vtable.shim}} 44973 (0.7%) 647 (0.4%) core::result::Result<T,E>::map_err 39185 (0.6%) 516 (0.3%) std:🧵:local::LocalKey<T>::try_with 39130 (0.6%) 215 (0.1%) alloc::raw_vec::RawVec<T,A>::grow_amortized 35334 (0.6%) 867 (0.5%) alloc::alloc::box_free 34788 (0.6%) 609 (0.4%) crossbeam_channel::context::Context::with::{{closure}} 33810 (0.5%) 646 (0.4%) core::ptr::swap_nonoverlapping_one 33610 (0.5%) 552 (0.3%) core::result::Result<T,E>::unwrap_or_else 32144 (0.5%) 392 (0.2%) <*const T as core::fmt::Pointer>::fmt 32062 (0.5%) 782 (0.5%) script::dom::bindings::root::Root<T>::new 31589 (0.5%) 600 (0.4%) core::result::Result<T,E>::expect 30069 (0.5%) 250 (0.1%) <<&mut bincode:🇩🇪:Deserializer<R,O> as serde:🇩🇪:Deserializer>::deserialize_tuple::Access<R,O> as serde:🇩🇪:SeqAccess>::next_element_seed 26996 (0.4%) 346 (0.2%) core::option::Option<T>::map_or 25996 (0.4%) 388 (0.2%) script::dom::bindings::root::Root<script::dom::bindings::root::MaybeUnreflectedDom<T>>::reflect_with 25833 (0.4%) 641 (0.4%) core::result::Result<T,E>::unwrap 24751 (0.4%) 197 (0.1%) core::iter::traits::iterator::Iterator::try_fold 22185 (0.4%) 145 (0.1%) hashbrown::raw::RawTable<T>::find 22000 (0.4%) 80 (0.0%) hashbrown::raw::RawTable<T>::rehash_in_place 20808 (0.3%) 289 (0.2%) core::alloc::layout::Layout::array 20031 (0.3%) 308 (0.2%) core::option::Option<T>::ok_or_else 19732 (0.3%) 2 (0.0%) html5ever::tree_builder::TreeBuilder<Handle,Sink>::step 18951 (0.3%) 1014 (0.6%) core::ptr::read 17261 (0.3%) 201 (0.1%) core::iter::traits::iterator::Iterator::fold ``` That `visit_enum` for `Key` is not in the first 30 lines, I find it after changing the filtering command to `head -n 60`: ``` 11762 (0.2%) 1 (0.0%) <keyboard_types:🔑:_IMPL_DESERIALIZE_FOR_Key::<impl serde:🇩🇪:Deserialize for keyboard_types:🔑:Key>::deserialize::__Visitor as serde:🇩🇪:Visitor>::visit_enum ``` It has one copy / instantiation instead of four, and contributes exactly four times fewer lines of IR. The crate total reduced by ~782k lines, a lot more than ~35k for this `visit_enum` function. We also see that `next_element_seed` (also for bincode deserialization) now has 250 copies instead of 1000. So it looks like *everything* bincode-related was reduced by 4×

bors-servo · 2020-06-24T11:53:13Z

💔 Test failed - status-taskcluster

CYBAI · 2020-06-24T12:09:48Z

@bors-servo retry

#23290

bors-servo · 2020-06-24T12:09:53Z

⌛ Testing commit a215ef3 with merge 6fc77ad...

bors-servo · 2020-06-24T12:19:06Z

☀️ Test successful - status-taskcluster
Approved by: nox
Pushing 6fc77ad to master...

ZoeyR · 2020-06-24T20:03:04Z

I'll record my findings here In case anyone comes to this issue curious about why the code size reduced by a factor of 4.

With PR #310 the serialization system stopped using the old config() types and methods. The old config types made use of the following match statement on any call to serialize or deserialize.
https://github.com/servo/bincode/blob/e541cdafb775f5e150855ca1077fb6e289e75b6e/src/config.rs#L153-L183

Rust had to monomorphize each call in that function, resulting in many erroneous copies of Deserializer methods in the LLVM IR. The reason there were only 4 copies instead of 6 is that some of the branches in the match statement are aliases of one-another. Native endianness will be the same as Little on most systems.

The new config system doesn't rely on match arms and instead leverages the type system to instantiate the Deserializer and Serializer. This allows the Rust compiler to only monomorphize what is needed.

This was referenced Jun 24, 2020

Investigate possibly-pathological amounts of LLVM IR with cargo-llvm-lines #26713

Open

derive(Deserialize) generates a lot of code for a many-variant enum serde-rs/serde#1824

Closed

Improve code size of Key serde impls pyfisch/keyboard-types#6

Closed

nnethercote mentioned this pull request Jun 24, 2020

Update `script-servo` benchmark rust-lang/rustc-perf#664

Closed

highfive assigned nox Jun 24, 2020

highfive added the S-awaiting-merge label Jun 24, 2020

highfive added S-tests-failed and removed S-awaiting-merge labels Jun 24, 2020

highfive added S-awaiting-merge and removed S-tests-failed labels Jun 24, 2020

bors-servo merged commit 6fc77ad into master Jun 24, 2020
2 checks passed

2 checks passed

Community-TC (pull_request) TaskGroup: success
Details

homu Test successful
Details

bors-servo deleted the bincodeup branch Jun 24, 2020

highfive removed the S-awaiting-merge label Jun 24, 2020

servo / servo

Update bincode, reduce code size of `script` by ~11% #27063

Update bincode, reduce code size of `script` by ~11% #27063

SimonSapin commented Jun 24, 2020

nox commented Jun 24, 2020

bors-servo commented Jun 24, 2020

bors-servo commented Jun 24, 2020

bors-servo commented Jun 24, 2020

CYBAI commented Jun 24, 2020

bors-servo commented Jun 24, 2020

bors-servo commented Jun 24, 2020

ZoeyR commented Jun 24, 2020

servo / servo

Join GitHub today

Update bincode, reduce code size of `script` by ~11% #27063

Update bincode, reduce code size of `script` by ~11% #27063

Conversation

SimonSapin commented Jun 24, 2020

nox commented Jun 24, 2020

bors-servo commented Jun 24, 2020

bors-servo commented Jun 24, 2020

bors-servo commented Jun 24, 2020

CYBAI commented Jun 24, 2020

bors-servo commented Jun 24, 2020

bors-servo commented Jun 24, 2020

ZoeyR commented Jun 24, 2020