Box ItemKind::Impl

[jyn514]

This brings the size of ItemKind down from 128 to 88 bytes.
Hopefully this will have perf improvements.

Follow-up to #79322 (comment), cc @estebank

[rust-highfive]

r? @varkor

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[jyn514]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

[bors]

⌛ Trying commit 8bd6427632c222fc019a624a88edcac1efa9c1fe with merge 764bf6c03d3cac0149069e4345da9fcaed5bc45d...

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

configure: rust.channel         := nightly
configure: rust.debug-assertions := True
configure: llvm.assertions      := True
configure: dist.missing-tools   := True
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
configure: 
---
    Checking rustc_errors v0.0.0 (/checkout/compiler/rustc_errors)
error[E0308]: mismatched types
    --> /checkout/compiler/rustc_data_structures/src/macros.rs:5:32
     |
3    | / macro_rules! static_assert_size {
4    | |     ($ty:ty, $size:expr) => {
5    | |         const _: [(); $size] = [(); ::std::mem::size_of::<$ty>()];
     | |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected an array with a fixed size of 88 elements, found one with 60 elements
7    | | }
     | |_- in this expansion of `static_assert_size!`
     | 
     | 
    ::: compiler/rustc_hir/src/hir.rs:2568:1
     |
2568 |   static_assert_size!(ItemKind<'_>, 88);
     |   -------------------------------------- in this macro invocation
error[E0308]: mismatched types
    --> /checkout/compiler/rustc_data_structures/src/macros.rs:5:32
     |
3    | / macro_rules! static_assert_size {
3    | / macro_rules! static_assert_size {
4    | |     ($ty:ty, $size:expr) => {
5    | |         const _: [(); $size] = [(); ::std::mem::size_of::<$ty>()];
     | |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected an array with a fixed size of 88 elements, found one with 60 elements
7    | | }
     | |_- in this expansion of `static_assert_size!`
     | 
     | 
    ::: compiler/rustc_hir/src/hir.rs:2568:1
     |
2568 |   static_assert_size!(ItemKind<'_>, 88);
     |   -------------------------------------- in this macro invocation
    Checking rustc_session v0.0.0 (/checkout/compiler/rustc_session)
    Checking rustc_query_system v0.0.0 (/checkout/compiler/rustc_query_system)
error: aborting due to previous error

---

To learn more, run the command again with --verbose.
warning: build failed, waiting for other jobs to finish...
error: build failed
command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "check" "--target" "i686-pc-windows-gnu" "-Zbinary-dep-depinfo" "-j" "16" "--release" "--locked" "--color" "always" "--features" " llvm" "--manifest-path" "/checkout/compiler/rustc/Cargo.toml" "--all-targets" "-p" "rustc-main" "-p" "rustc_driver" "-p" "rustc_errors" "-p" "rustc_macros" "-p" "rustc_lint_defs" "-p" "rustc_data_structures" "-p" "rustc_index" "-p" "rustc_graphviz" "-p" "rustc_serialize" "-p" "rustc_save_analysis" "-p" "rustc_lexer" "-p" "rustc_mir" "-p" "rustc_attr" "-p" "rustc_infer" "-p" "rustc_trait_selection" "-p" "rustc_parse_format" "-p" "rustc_apfloat" "-p" "coverage_test_macros" "-p" "rustc_plugin_impl" "-p" "rustc_hir_pretty" "-p" "rustc_ast_pretty" "-p" "rustc_span" "-p" "rustc_arena" "-p" "rustc_target" "-p" "rustc_metadata" "-p" "rustc_expand" "-p" "rustc_ast_passes" "-p" "rustc_parse" "-p" "rustc_ast" "-p" "rustc_session" "-p" "rustc_fs_util" "-p" "rustc_lint" "-p" "rustc_interface" "-p" "rustc_passes" "-p" "rustc_typeck" "-p" "rustc_ty_utils" "-p" "rustc_privacy" "-p" "rustc_traits" "-p" "rustc_codegen_llvm" "-p" "rustc_llvm" "-p" "rustc_symbol_mangling" "-p" "rustc_mir_build" "-p" "rustc_builtin_macros" "-p" "rustc_incremental" "-p" "rustc_ast_lowering" "-p" "rustc_resolve" "-p" "rustc_middle" "-p" "rustc_type_ir" "-p" "rustc_query_system" "-p" "rustc_feature" "-p" "rustc_hir" "-p" "rustc_error_codes" "-p" "rustc_codegen_ssa" "--message-format" "json-render-diagnostics"
failed to run: /checkout/obj/build/bootstrap/debug/bootstrap check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu --all-targets
Build completed unsuccessfully in 0:01:02

[jyn514]

@rust-timer queue

[rust-timer]

Awaiting bors try build completion.

[jyn514]

@rust-timer build 764bf6c03d3cac0149069e4345da9fcaed5bc45d

[rust-timer]

Queued 764bf6c03d3cac0149069e4345da9fcaed5bc45d with parent 058a710, future comparison URL.

@rustbot label: +S-waiting-on-perf

[bors]

☔ The latest upstream changes (presumably #79322) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-timer]

Finished benchmarking try commit (764bf6c03d3cac0149069e4345da9fcaed5bc45d): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf

[jyn514]

Those numbers are not very promising :(

[estebank]

I think that max-rss is noisy but there might be some value there... https://perf.rust-lang.org/compare.html?start=058a71016553f267ae80b90276ef79956457d51a&end=764bf6c03d3cac0149069e4345da9fcaed5bc45d&stat=max-rss

[estebank]

I guess that going through the heap just makes things slower, it's fine. It's good to try things out and verify :)