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Shrink all SmallVecs by 8 bytes (#4951)

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We weren't using the "union" cargo feature for the smallvec crate, which
reduces the size of a SmallVec by one machine word. This feature
requires Rust 1.49 but we already require much newer versions.

When using Wasmtime to compile pulldown-cmark from Sightglass, this
saves a decent amount of memory allocations and writes. According to
`valgrind --tool=dhat`:

- 6.2MiB (3.69%) less memory allocated over the program's lifetime
- 0.5MiB (4.13%) less memory allocated at maximum heap size
- 5.5MiB (1.88%) fewer bytes written to
- 0.44% fewer instructions executed

Sightglass reports a statistically significant runtime improvement too:

compilation :: cycles :: benchmarks/pulldown-cmark/benchmark.wasm

  Δ = 24379323.60 ± 20051394.04 (confidence = 99%)

  shrink-abiarg-0406da67c.so is 1.01x to 1.13x faster than main-be690a468.so!

  [227506364 355007998.78 423280514] main-be690a468.so
  [227686018 330628675.18 406025344] shrink-abiarg-0406da67c.so

compilation :: cycles :: benchmarks/spidermonkey/benchmark.wasm

  Δ = 360151622.56 ± 278294316.90 (confidence = 99%)

  shrink-abiarg-0406da67c.so is 1.01x to 1.07x faster than main-be690a468.so!

  [8709162212 8911001926.44 9535111576] main-be690a468.so
  [5058015392 8550850303.88 9282148438] shrink-abiarg-0406da67c.so

compilation :: cycles :: benchmarks/bz2/benchmark.wasm

  Δ = 6936570.28 ± 6897696.38 (confidence = 99%)

  shrink-abiarg-0406da67c.so is 1.00x to 1.08x faster than main-be690a468.so!

  [155810934 175260571.20 234737344] main-be690a468.so
  [119128240 168324000.92 257451074] shrink-abiarg-0406da67c.so
This commit is contained in:
Jamey Sharp
2022-09-23 16:32:13 -07:00
committed by GitHub
parent 95c74ef246
commit bd870a9d6c
7 changed files with 7 additions and 7 deletions
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2
fuzz/Cargo.toml
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@@ -18,7 +18,7 @@ cranelift-interpreter = { path = "../cranelift/interpreter" }
cranelift-fuzzgen = { path = "../cranelift/fuzzgen" }
libfuzzer-sys = { version = "0.4.0", features = ["arbitrary-derive"] }
target-lexicon = "0.12"
smallvec = "1.6.1"
smallvec = { version = "1.6.1", features = ["union"] }
wasmtime = { path = "../crates/wasmtime" }
wasmtime-fuzzing = { path = "../crates/fuzzing" }
component-test-util = { path = "../crates/misc/component-test-util" }