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Noratrieb opened this issue Jun 7, 2025 · 1 comment
Open

Binary size impact of enabling -Zshare-generics for opt-level=z #142164

Noratrieb opened this issue Jun 7, 2025 · 1 comment
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C-discussion Category: Discussion or questions that doesn't represent real issues. E-needs-investigation Call for partcipation: This issues needs some investigation to determine current status I-heavy Issue: Problems and improvements with respect to binary size of generated code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@Noratrieb
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Noratrieb commented Jun 7, 2025 •
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opt-level=z and opt-level=s implicitly enable -Zshare-generics. While this can have positive binary size impacts, it can also have negative binary size impacts because it reduces LLVMs ability to inline functions.

I have done some analysis on a bunch of projects, comparing the output from size for different opt levels.

Script 

#!/usr/bin/env bash

set -euxo pipefail

bins=$(cargo metadata --format-version 1 | jq '.packages.[].targets.[] | select(.crate_types == ["bin"]) | select(.src_path | contains("index.crates.io") | not) | .name' -r)

echo checking "$bins"

projdir=$(basename "$(realpath .)")

truncate -s 0 results.csv

build() {
  type="$1"
  rustflags="$2"

  wrapper=$(mktemp)
  {
    echo '#!/usr/bin/env bash'
    echo 'r=$1'
    echo "shift"
    echo exec '$r' '"$@"' "$rustflags" 
  } > "$wrapper"

  chmod +x "$wrapper"

  echo "meow"
  cat "$wrapper"

  cargo clean
  bins=$(RUSTC_WRAPPER="$wrapper" cargo build --release --message-format=json-render-diagnostics | jq 'select(.reason == "compiler-artifact") | select(.executable != null) | .executable' -r)

  IFS=$'\n'
  for bin in $bins; do
    echo "$bin"
    s=$(size "$bin" | python3 -c 'import sys;x=sys.stdin.read();print(x.split("\n")[1].split()[0])')

    echo "$projdir,$(basename "$bin"),$type,$s" >> results.csv
  done

  rm "$wrapper"
}

build "2" "-Copt-level=2"
build "3" "-Copt-level=3"
build "s" "-Copt-level=s"
build "s-no-share" "-Copt-level=s -Zshare-generics=false"
build "z" "-Copt-level=z"
build "z-no-share" "-Copt-level=z -Zshare-generics=false"

I got the following results:

Results CSV 

project,binary,opt-level,text size
rustc-perf,bootstrap-rustc,2,401390
rustc-perf,bootstrap-rustc,3,401518
rustc-perf,bootstrap-rustc,s,401454
rustc-perf,bootstrap-rustc,s-no-share,400286
rustc-perf,bootstrap-rustc,z,402450
rustc-perf,bootstrap-rustc,z-no-share,401562
nextest,build-seed-archive,2,928761
nextest,build-seed-archive,3,928241
nextest,build-seed-archive,s,906783
nextest,build-seed-archive,s-no-share,877006
nextest,build-seed-archive,z,939734
nextest,build-seed-archive,z-no-share,896072
cargo,cargo,2,26769308
cargo,cargo,3,27035766
cargo,cargo,s,23441682
cargo,cargo,s-no-share,22941899
cargo,cargo,z,23003221
cargo,cargo,z-no-share,21949429
nextest,cargo-nextest,2,15327059
nextest,cargo-nextest,3,15331428
nextest,cargo-nextest,s,13378951
nextest,cargo-nextest,s-no-share,13151176
nextest,cargo-nextest,z,13347017
nextest,cargo-nextest,z-no-share,12840776
nextest,cargo-nextest-dup,2,15327071
nextest,cargo-nextest-dup,3,15331440
nextest,cargo-nextest-dup,s,13378951
nextest,cargo-nextest-dup,s-no-share,13151176
nextest,cargo-nextest-dup,z,13347017
nextest,cargo-nextest-dup,z-no-share,12840776
cluelessh,cluelessh,2,3639610
cluelessh,cluelessh,3,3637618
cluelessh,cluelessh,s,3230404
cluelessh,cluelessh,s-no-share,3137054
cluelessh,cluelessh,z,3298182
cluelessh,cluelessh,z-no-share,3160263
cluelessh,cluelessh-agentctl,2,3081768
cluelessh,cluelessh-agentctl,3,3090680
cluelessh,cluelessh-agentctl,s,2752168
cluelessh,cluelessh-agentctl,s-no-share,2668998
cluelessh,cluelessh-agentctl,z,2812587
cluelessh,cluelessh-agentctl,z-no-share,2692805
cluelessh,cluelessh-dos,2,3363901
cluelessh,cluelessh-dos,3,3374685
cluelessh,cluelessh-dos,s,3006511
cluelessh,cluelessh-dos,s-no-share,2909317
cluelessh,cluelessh-dos,z,3069389
cluelessh,cluelessh-dos,z-no-share,2936446
cluelessh,cluelessh-faked,2,3307574
cluelessh,cluelessh-faked,3,3300062
cluelessh,cluelessh-faked,s,2953214
cluelessh,cluelessh-faked,s-no-share,2889345
cluelessh,cluelessh-faked,z,3030640
cluelessh,cluelessh-faked,z-no-share,2939401
cluelessh,cluelessh-key,2,1138744
cluelessh,cluelessh-key,3,1156436
cluelessh,cluelessh-key,s,1031633
cluelessh,cluelessh-key,s-no-share,1003059
cluelessh,cluelessh-key,z,1028888
cluelessh,cluelessh-key,z-no-share,985054
cluelessh,cluelesshd,2,4675529
cluelessh,cluelesshd,3,4666229
cluelessh,cluelesshd,s,4138714
cluelessh,cluelesshd,s-no-share,3995755
cluelessh,cluelesshd,z,4208701
cluelessh,cluelesshd,z-no-share,4024121
cluelessh,cluelesshd-sftp-server,2,2481705
cluelessh,cluelesshd-sftp-server,3,2489701
cluelessh,cluelesshd-sftp-server,s,2244369
cluelessh,cluelesshd-sftp-server,s-no-share,2193279
cluelessh,cluelesshd-sftp-server,z,2304838
cluelessh,cluelesshd-sftp-server,z-no-share,2229436
rustc-perf,collector,2,11333776
rustc-perf,collector,3,11340184
rustc-perf,collector,s,10138920
rustc-perf,collector,s-no-share,9960872
rustc-perf,collector,z,10061628
rustc-perf,collector,z-no-share,9756252
rustc-perf,fetch-latest,2,3041314
rustc-perf,fetch-latest,3,3070746
rustc-perf,fetch-latest,s,2775574
rustc-perf,fetch-latest,s-no-share,2720170
rustc-perf,fetch-latest,z,2766783
rustc-perf,fetch-latest,z-no-share,2687495
hello-world,hello-world,2,344751
hello-world,hello-world,3,344751
hello-world,hello-world,s,344719
hello-world,hello-world,s-no-share,344719
hello-world,hello-world,z,344767
hello-world,hello-world,z-no-share,344767
rustc-perf,import-sqlite,2,7313831
rustc-perf,import-sqlite,3,7395099
rustc-perf,import-sqlite,s,6774471
rustc-perf,import-sqlite,s-no-share,6693379
rustc-perf,import-sqlite,z,6778407
rustc-perf,import-sqlite,z-no-share,6649119
nextest,internal-test,2,339532
nextest,internal-test,3,339532
nextest,internal-test,s,339500
nextest,internal-test,s-no-share,339500
nextest,internal-test,z,339540
nextest,internal-test,z-no-share,339540
Neotron-Pico-BIOS,neotron-pico-bios,2,69320
Neotron-Pico-BIOS,neotron-pico-bios,3,73996
Neotron-Pico-BIOS,neotron-pico-bios,s,52860
Neotron-Pico-BIOS,neotron-pico-bios,s-no-share,52840
Neotron-Pico-BIOS,neotron-pico-bios,z,51192
Neotron-Pico-BIOS,neotron-pico-bios,z-no-share,50960
nextest,passthrough,2,411770
nextest,passthrough,3,411294
nextest,passthrough,s,411125
nextest,passthrough,s-no-share,409746
nextest,passthrough,z,411123
nextest,passthrough,z-no-share,410024
rustc-perf,postgres-to-sqlite,2,7461386
rustc-perf,postgres-to-sqlite,3,7532230
rustc-perf,postgres-to-sqlite,s,6841686
rustc-perf,postgres-to-sqlite,s-no-share,6751134
rustc-perf,postgres-to-sqlite,z,6813466
rustc-perf,postgres-to-sqlite,z-no-share,6664510
ripgrep,rg,2,4378977
ripgrep,rg,3,4435131
ripgrep,rg,s,4013053
ripgrep,rg,s-no-share,3962587
ripgrep,rg,z,3993959
ripgrep,rg,z-no-share,3913056
rust-analyzer,rust-analyzer,2,36815675
rust-analyzer,rust-analyzer,3,36845571
rust-analyzer,rust-analyzer,s,29047888
rust-analyzer,rust-analyzer,s-no-share,30842033
rust-analyzer,rust-analyzer,z,27646232
rust-analyzer,rust-analyzer,z-no-share,28589921
rust-analyzer,rust-analyzer-proc-macro-srv,2,350694
rust-analyzer,rust-analyzer-proc-macro-srv,3,350690
rust-analyzer,rust-analyzer-proc-macro-srv,s,350690
rust-analyzer,rust-analyzer-proc-macro-srv,s-no-share,350550
rust-analyzer,rust-analyzer-proc-macro-srv,z,350610
rust-analyzer,rust-analyzer-proc-macro-srv,z-no-share,350490
rustc-perf,rustc-fake,2,455290
rustc-perf,rustc-fake,3,456474
rustc-perf,rustc-fake,s,452790
rustc-perf,rustc-fake,s-no-share,452150
rustc-perf,rustc-fake,z,453770
rustc-perf,rustc-fake,z-no-share,451770
nextest,rustc-shim,2,398876
nextest,rustc-shim,3,398928
nextest,rustc-shim,s,397635
nextest,rustc-shim,s-no-share,397828
nextest,rustc-shim,z,397343
nextest,rustc-shim,z-no-share,397944
rusty-clock,rusty-clock,2,49052
rusty-clock,rusty-clock,3,51764
rusty-clock,rusty-clock,s,37468
rusty-clock,rusty-clock,s-no-share,37664
rusty-clock,rusty-clock,z,35320
rusty-clock,rusty-clock,z-no-share,35476
rustc-perf,site,2,15569433
rustc-perf,site,3,15585737
rustc-perf,site,s,13880257
rustc-perf,site,s-no-share,13747097
rustc-perf,site,z,13614909
rustc-perf,site,z-no-share,13353497
rustc-perf,sqlite-to-postgres,2,7937442
rustc-perf,sqlite-to-postgres,3,8016754
rustc-perf,sqlite-to-postgres,s,7192830
rustc-perf,sqlite-to-postgres,s-no-share,7104766
rustc-perf,sqlite-to-postgres,z,7154074
rustc-perf,sqlite-to-postgres,z-no-share,6998258
rust-analyzer,xtask,2,1685422
rust-analyzer,xtask,3,1671190
rust-analyzer,xtask,s,1535085
rust-analyzer,xtask,s-no-share,1502505
rust-analyzer,xtask,z,1527938
rust-analyzer,xtask,z-no-share,1479014

Results Table
project binary opt-level text size
rustc-perf bootstrap-rustc 2 401390
rustc-perf bootstrap-rustc 3 401518
rustc-perf bootstrap-rustc s 401454
rustc-perf bootstrap-rustc s-no-share 400286
rustc-perf bootstrap-rustc z 402450
rustc-perf bootstrap-rustc z-no-share 401562
nextest build-seed-archive 2 928761
nextest build-seed-archive 3 928241
nextest build-seed-archive s 906783
nextest build-seed-archive s-no-share 877006
nextest build-seed-archive z 939734
nextest build-seed-archive z-no-share 896072
cargo cargo 2 26769308
cargo cargo 3 27035766
cargo cargo s 23441682
cargo cargo s-no-share 22941899
cargo cargo z 23003221
cargo cargo z-no-share 21949429
nextest cargo-nextest 2 15327059
nextest cargo-nextest 3 15331428
nextest cargo-nextest s 13378951
nextest cargo-nextest s-no-share 13151176
nextest cargo-nextest z 13347017
nextest cargo-nextest z-no-share 12840776
nextest cargo-nextest-dup 2 15327071
nextest cargo-nextest-dup 3 15331440
nextest cargo-nextest-dup s 13378951
nextest cargo-nextest-dup s-no-share 13151176
nextest cargo-nextest-dup z 13347017
nextest cargo-nextest-dup z-no-share 12840776
cluelessh cluelessh 2 3639610
cluelessh cluelessh 3 3637618
cluelessh cluelessh s 3230404
cluelessh cluelessh s-no-share 3137054
cluelessh cluelessh z 3298182
cluelessh cluelessh z-no-share 3160263
cluelessh cluelessh-agentctl 2 3081768
cluelessh cluelessh-agentctl 3 3090680
cluelessh cluelessh-agentctl s 2752168
cluelessh cluelessh-agentctl s-no-share 2668998
cluelessh cluelessh-agentctl z 2812587
cluelessh cluelessh-agentctl z-no-share 2692805
cluelessh cluelessh-dos 2 3363901
cluelessh cluelessh-dos 3 3374685
cluelessh cluelessh-dos s 3006511
cluelessh cluelessh-dos s-no-share 2909317
cluelessh cluelessh-dos z 3069389
cluelessh cluelessh-dos z-no-share 2936446
cluelessh cluelessh-faked 2 3307574
cluelessh cluelessh-faked 3 3300062
cluelessh cluelessh-faked s 2953214
cluelessh cluelessh-faked s-no-share 2889345
cluelessh cluelessh-faked z 3030640
cluelessh cluelessh-faked z-no-share 2939401
cluelessh cluelessh-key 2 1138744
cluelessh cluelessh-key 3 1156436
cluelessh cluelessh-key s 1031633
cluelessh cluelessh-key s-no-share 1003059
cluelessh cluelessh-key z 1028888
cluelessh cluelessh-key z-no-share 985054
cluelessh cluelesshd 2 4675529
cluelessh cluelesshd 3 4666229
cluelessh cluelesshd s 4138714
cluelessh cluelesshd s-no-share 3995755
cluelessh cluelesshd z 4208701
cluelessh cluelesshd z-no-share 4024121
cluelessh cluelesshd-sftp-server 2 2481705
cluelessh cluelesshd-sftp-server 3 2489701
cluelessh cluelesshd-sftp-server s 2244369
cluelessh cluelesshd-sftp-server s-no-share 2193279
cluelessh cluelesshd-sftp-server z 2304838
cluelessh cluelesshd-sftp-server z-no-share 2229436
rustc-perf collector 2 11333776
rustc-perf collector 3 11340184
rustc-perf collector s 10138920
rustc-perf collector s-no-share 9960872
rustc-perf collector z 10061628
rustc-perf collector z-no-share 9756252
rustc-perf fetch-latest 2 3041314
rustc-perf fetch-latest 3 3070746
rustc-perf fetch-latest s 2775574
rustc-perf fetch-latest s-no-share 2720170
rustc-perf fetch-latest z 2766783
rustc-perf fetch-latest z-no-share 2687495
hello-world hello-world 2 344751
hello-world hello-world 3 344751
hello-world hello-world s 344719
hello-world hello-world s-no-share 344719
hello-world hello-world z 344767
hello-world hello-world z-no-share 344767
rustc-perf import-sqlite 2 7313831
rustc-perf import-sqlite 3 7395099
rustc-perf import-sqlite s 6774471
rustc-perf import-sqlite s-no-share 6693379
rustc-perf import-sqlite z 6778407
rustc-perf import-sqlite z-no-share 6649119
nextest internal-test 2 339532
nextest internal-test 3 339532
nextest internal-test s 339500
nextest internal-test s-no-share 339500
nextest internal-test z 339540
nextest internal-test z-no-share 339540
Neotron-Pico-BIOS neotron-pico-bios 2 69320
Neotron-Pico-BIOS neotron-pico-bios 3 73996
Neotron-Pico-BIOS neotron-pico-bios s 52860
Neotron-Pico-BIOS neotron-pico-bios s-no-share 52840
Neotron-Pico-BIOS neotron-pico-bios z 51192
Neotron-Pico-BIOS neotron-pico-bios z-no-share 50960
nextest passthrough 2 411770
nextest passthrough 3 411294
nextest passthrough s 411125
nextest passthrough s-no-share 409746
nextest passthrough z 411123
nextest passthrough z-no-share 410024
rustc-perf postgres-to-sqlite 2 7461386
rustc-perf postgres-to-sqlite 3 7532230
rustc-perf postgres-to-sqlite s 6841686
rustc-perf postgres-to-sqlite s-no-share 6751134
rustc-perf postgres-to-sqlite z 6813466
rustc-perf postgres-to-sqlite z-no-share 6664510
ripgrep rg 2 4378977
ripgrep rg 3 4435131
ripgrep rg s 4013053
ripgrep rg s-no-share 3962587
ripgrep rg z 3993959
ripgrep rg z-no-share 3913056
rust-analyzer rust-analyzer 2 36815675
rust-analyzer rust-analyzer 3 36845571
rust-analyzer rust-analyzer s 29047888
rust-analyzer rust-analyzer s-no-share 30842033
rust-analyzer rust-analyzer z 27646232
rust-analyzer rust-analyzer z-no-share 28589921
rust-analyzer rust-analyzer-proc-macro-srv 2 350694
rust-analyzer rust-analyzer-proc-macro-srv 3 350690
rust-analyzer rust-analyzer-proc-macro-srv s 350690
rust-analyzer rust-analyzer-proc-macro-srv s-no-share 350550
rust-analyzer rust-analyzer-proc-macro-srv z 350610
rust-analyzer rust-analyzer-proc-macro-srv z-no-share 350490
rustc-perf rustc-fake 2 455290
rustc-perf rustc-fake 3 456474
rustc-perf rustc-fake s 452790
rustc-perf rustc-fake s-no-share 452150
rustc-perf rustc-fake z 453770
rustc-perf rustc-fake z-no-share 451770
nextest rustc-shim 2 398876
nextest rustc-shim 3 398928
nextest rustc-shim s 397635
nextest rustc-shim s-no-share 397828
nextest rustc-shim z 397343
nextest rustc-shim z-no-share 397944
rusty-clock rusty-clock 2 49052
rusty-clock rusty-clock 3 51764
rusty-clock rusty-clock s 37468
rusty-clock rusty-clock s-no-share 37664
rusty-clock rusty-clock z 35320
rusty-clock rusty-clock z-no-share 35476
rustc-perf site 2 15569433
rustc-perf site 3 15585737
rustc-perf site s 13880257
rustc-perf site s-no-share 13747097
rustc-perf site z 13614909
rustc-perf site z-no-share 13353497
rustc-perf sqlite-to-postgres 2 7937442
rustc-perf sqlite-to-postgres 3 8016754
rustc-perf sqlite-to-postgres s 7192830
rustc-perf sqlite-to-postgres s-no-share 7104766
rustc-perf sqlite-to-postgres z 7154074
rustc-perf sqlite-to-postgres z-no-share 6998258
rust-analyzer xtask 2 1685422
rust-analyzer xtask 3 1671190
rust-analyzer xtask s 1535085
rust-analyzer xtask s-no-share 1502505
rust-analyzer xtask z 1527938
rust-analyzer xtask z-no-share 1479014

It looks like -Zshare-generics is sometimes an improvement and sometimes a regression. It is not immediately clear to me whether enabling it as currently is the right tradeoff of whether it would make more sense to disable it by default.
@Noratrieb Noratrieb added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. I-heavy Issue: Problems and improvements with respect to binary size of generated code. E-needs-investigation Call for partcipation: This issues needs some investigation to determine current status labels Jun 7, 2025
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Jun 7, 2025
@Noratrieb Noratrieb removed the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Jun 7, 2025
@Noratrieb Noratrieb mentioned this issue Jun 7, 2025
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@Noratrieb Noratrieb added the C-discussion Category: Discussion or questions that doesn't represent real issues. label Jun 7, 2025
@Noratrieb Noratrieb mentioned this issue Jun 7, 2025
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rust-bors bot added a commit that referenced this issue Jun 7, 2025
@rust-bors
Auto merge of #142165 - Noratrieb:binary-size-share-generics, r=<try>
1a69214 
Test binary size of share generics

cc #142164

r? ghost
@nikic
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nikic commented Jun 7, 2025

See also #123610 for a possible way to get the best of both worlds.

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C-discussion Category: Discussion or questions that doesn't represent real issues. E-needs-investigation Call for partcipation: This issues needs some investigation to determine current status I-heavy Issue: Problems and improvements with respect to binary size of generated code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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