[experiment, do not merge!] rewrite the DenseBitSet structure to only use 1 word on the stack

[tage64]

Modify DenseBitSet in the rustc_index crate so that it only uses one word on the stack instead of 4 words as before, allowing for faster clones. The downside is that it may at most store 63 elements on the stack as aposed to 128 for the previous implementation.

r? lqd

This is experimental so far and I mostly want a perf run to measure
the performance.

[rustbot]

Some changes occurred in coverage instrumentation.

cc @Zalathar

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

[lqd]

(sorry for the unintended pings, everyone)

cc @nnethercote this is the bitset work I was telling you about. It did look interesting in my tests, ~= 0.5% wins on a lot of primary benchmarks.

let's see if a try build works:

@bors try @rust-timer queue

[bors]

⌛ Trying commit 3ff2c88 with merge 693cccaceb81d959dbf823da027464c8655b8b57...

[nnethercote]

Looks interesting. Unfortunately being a single commit makes it incredibly hard to review, especially with so much code being moved into dense_bit_set.rs. If it gets beyond the draft stage I think the commits need to be structured differently to make review easier. E.g. the code doesn't need to move into dense_bit_set.rs, or if that's really desired, it should be moved in a first commit and then modified in a second commit. And any other changes are made that are independent (e.g. changing MixedBitSet::Small to Self::Small) can be done in separate commits as well.

[lqd]

Yeah this is just for the perf run I think. The branch I was looking at (now unfortunately gone) had many smaller commits that were easier to review, eg the last 20 of master...tage64:rust:replace_predecessors

[tage64]

I squashed all commits into one to make rebasing on upstream easier. Maybe that was not necessary but as you said, this is just for experiments. The original commit history is still there in tage64/rust@thin_bit_set_old.

[bors]

☀️ Try build successful - checks-actions
Build commit: 693ccca (693cccaceb81d959dbf823da027464c8655b8b57)

[rust-timer]

Finished benchmarking commit (693ccca): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

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

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-0.5%	[-1.1%, -0.1%]	83
Improvements ✅ (secondary)	-1.0%	[-3.3%, -0.1%]	50
All ❌✅ (primary)	-0.5%	[-1.1%, -0.1%]	83

Max RSS (memory usage)

Results (primary -1.1%, secondary -1.3%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.8%	[0.8%, 0.9%]	2
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-2.4%	[-5.2%, -0.4%]	4
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	1

Cycles

Results (secondary -0.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.8%	[1.5%, 2.1%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-2.0%, -0.7%]	6
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.0%, secondary 0.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.1%]	48
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	25
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	48

Bootstrap: 775.275s -> 774.785s (-0.06%)
Artifact size: 365.51 MiB -> 365.51 MiB (0.00%)

[rust-log-analyzer]

The job x86_64-gnu-llvm-19 failed! Check out the build log: (web) (plain)

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

#18 exporting to docker image format
#18 sending tarball 20.5s done
#18 DONE 26.0s
##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-19]
[CI_JOB_NAME=x86_64-gnu-llvm-19]
debug: `DISABLE_CI_RUSTC_IF_INCOMPATIBLE` configured.
---
sccache: Listening on address 127.0.0.1:4226
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-19', '--enable-llvm-link-shared', '--set', 'rust.randomize-layout=true', '--set', 'rust.thin-lto-import-instr-limit=10', '--set', 'build.print-step-timings', '--enable-verbose-tests', '--set', 'build.metrics', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--set', 'rust.lld=false', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--set', 'gcc.download-ci-gcc=true', '--enable-new-symbol-mangling']
configure: build.build          := x86_64-unknown-linux-gnu
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-19/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.randomize-layout := True
configure: rust.thin-lto-import-instr-limit := 10
---
[RUSTC-TIMING] proc_macro test:false 5.414
[RUSTC-TIMING] test test:false 9.162
    Finished `release` profile [optimized] target(s) in 1m 16s
##[endgroup]
[TIMING] core::build_steps::compile::Std { target: x86_64-unknown-linux-gnu, compiler: Compiler { stage: 1, host: x86_64-unknown-linux-gnu, forced_compiler: true }, crates: [], force_recompile: false, extra_rust_args: ["-Csymbol-mangling-version=v0", "-Cpanic=abort"], is_for_mir_opt_tests: false } -- 76.290
Testing GCC stage1 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
 Downloading crates ...
  Downloaded boml v0.3.1
   Compiling boml v0.3.1
[RUSTC-TIMING] boml test:false 0.728
   Compiling y v0.1.0 (/checkout/compiler/rustc_codegen_gcc/build_system)
[RUSTC-TIMING] y test:false 2.763
    Finished `release` profile [optimized] target(s) in 3.94s
     Running `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-codegen/x86_64-unknown-linux-gnu/release/y test --use-backend gcc --gcc-path /checkout/obj/build/x86_64-unknown-linux-gnu/ci-gcc/lib --out-dir /checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/cg_gcc --release --mini-tests --std-tests`
`--gcc-path` was provided, ignoring config file. Using `/checkout/obj/build/x86_64-unknown-linux-gnu/ci-gcc/lib` as path for libgccjit
[BUILD] mini_core
[RUSTC-TIMING] mini_core test:false 0.192
[BUILD] example
[AOT] mini_core_hello_world
[RUSTC-TIMING] mini_core_hello_world test:false 0.171
---
---- [run-make] tests/run-make/rustc-crates-on-stable stdout ----

error: rmake recipe failed to complete
status: exit status: 1
command: cd "/checkout/obj/build/x86_64-unknown-linux-gnu/test/run-make/rustc-crates-on-stable/rmake_out" && env -u RUSTFLAGS AR="ar" BUILD_ROOT="/checkout/obj/build/x86_64-unknown-linux-gnu" CARGO="/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/cargo" CC="cc" CC_DEFAULT_FLAGS="-ffunction-sections -fdata-sections -fPIC -m64" CXX="c++" CXX_DEFAULT_FLAGS="-ffunction-sections -fdata-sections -fPIC -m64" HOST_RUSTC_DYLIB_PATH="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" LD_LIBRARY_PATH="/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools/x86_64-unknown-linux-gnu/release/deps:/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/lib:/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/lib/rustlib/x86_64-unknown-linux-gnu/lib" LD_LIB_PATH_ENVVAR="LD_LIBRARY_PATH" LLVM_BIN_DIR="/usr/lib/llvm-19/bin" LLVM_COMPONENTS="aarch64 aarch64asmparser aarch64codegen aarch64desc aarch64disassembler aarch64info aarch64utils aggressiveinstcombine all all-targets amdgpu amdgpuasmparser amdgpucodegen amdgpudesc amdgpudisassembler amdgpuinfo amdgputargetmca amdgpuutils analysis arm armasmparser armcodegen armdesc armdisassembler arminfo armutils asmparser asmprinter avr avrasmparser avrcodegen avrdesc avrdisassembler avrinfo binaryformat bitreader bitstreamreader bitwriter bpf bpfasmparser bpfcodegen bpfdesc bpfdisassembler bpfinfo cfguard codegen codegendata codegentypes core coroutines coverage debuginfobtf debuginfocodeview debuginfodwarf debuginfogsym debuginfologicalview debuginfomsf debuginfopdb demangle dlltooldriver dwarflinker dwarflinkerclassic dwarflinkerparallel dwp engine executionengine extensions filecheck frontenddriver frontendhlsl frontendoffloading frontendopenacc frontendopenmp fuzzercli fuzzmutate globalisel hexagon hexagonasmparser hexagoncodegen hexagondesc hexagondisassembler hexagoninfo hipstdpar instcombine instrumentation interfacestub interpreter ipo irprinter irreader jitlink lanai lanaiasmparser lanaicodegen lanaidesc lanaidisassembler lanaiinfo libdriver lineeditor linker loongarch loongarchasmparser loongarchcodegen loongarchdesc loongarchdisassembler loongarchinfo lto m68k m68kasmparser m68kcodegen m68kdesc m68kdisassembler m68kinfo mc mca mcdisassembler mcjit mcparser mips mipsasmparser mipscodegen mipsdesc mipsdisassembler mipsinfo mirparser msp430 msp430asmparser msp430codegen msp430desc msp430disassembler msp430info native nativecodegen nvptx nvptxcodegen nvptxdesc nvptxinfo objcarcopts objcopy object objectyaml option orcdebugging orcjit orcshared orctargetprocess passes perfjitevents powerpc powerpcasmparser powerpccodegen powerpcdesc powerpcdisassembler powerpcinfo profiledata remarks riscv riscvasmparser riscvcodegen riscvdesc riscvdisassembler riscvinfo riscvtargetmca runtimedyld sandboxir scalaropts selectiondag sparc sparcasmparser sparccodegen sparcdesc sparcdisassembler sparcinfo support symbolize systemz systemzasmparser systemzcodegen systemzdesc systemzdisassembler systemzinfo tablegen target targetparser textapi textapibinaryreader transformutils ve veasmparser vecodegen vectorize vedesc vedisassembler veinfo webassembly webassemblyasmparser webassemblycodegen webassemblydesc webassemblydisassembler webassemblyinfo webassemblyutils windowsdriver windowsmanifest x86 x86asmparser x86codegen x86desc x86disassembler x86info x86targetmca xcore xcorecodegen xcoredesc xcoredisassembler xcoreinfo xray xtensa xtensaasmparser xtensacodegen xtensadesc xtensadisassembler xtensainfo" LLVM_FILECHECK="/usr/lib/llvm-19/bin/FileCheck" NODE="/usr/bin/node" PYTHON="/usr/bin/python3" RUSTC="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" RUSTDOC="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustdoc" SOURCE_ROOT="/checkout" TARGET="x86_64-unknown-linux-gnu" TARGET_EXE_DYLIB_PATH="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/run-make/rustc-crates-on-stable/rmake"
stdout: none
--- stderr -------------------------------
command failed at line 41
Command { cmd: LD_LIBRARY_PATH="/checkout/obj/build/x86_64-unknown-linux-gnu/test/run-make/rustc-crates-on-stable/rmake_out:/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib:/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools/x86_64-unknown-linux-gnu/release/deps:/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/lib:/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/lib/rustlib/x86_64-unknown-linux-gnu/lib" RUSTC="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" RUSTC_STAGE="0" RUSTFLAGS="-Zallow-features=" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/cargo" "build" "--manifest-path" "/checkout/Cargo.toml" "--no-default-features" "--target-dir" "target" "-p" "rustc_type_ir" "-p" "rustc_next_trait_solver" "-p" "rustc_pattern_analysis" "-p" "rustc_lexer" "-p" "rustc_abi" "-p" "rustc_parse_format" "-p" "rustc_hashes", stdin_buf: None, stdin: None, stdout: None, stderr: None, drop_bomb: DropBomb { command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/cargo", defused: true, armed_location: Location { file: "src/tools/run-make-support/src/external_deps/cargo.rs", line: 8, col: 19 } }, already_executed: true }
output status: `exit status: 101`
=== STDOUT ===



=== STDERR ===
   Compiling proc-macro2 v1.0.95