Stream: git-wasmtime

Topic: wasmtime / PR #4924 Memoize `can_optimize_var_lookup`

Wasmtime GitHub notifications bot (Sep 19 2022 at 15:09):

adambratschikaye opened PR #4924 from memoize-can_optimize_var_lookup to main:

This fixes issue https://github.com/bytecodealliance/wasmtime/issues/4923.

can_optimize_var_lookup can have quadratic behavior if there is a chain of blocks each containing a local.get instruction because each run can walk up the entire chain. This change memoizes the results of can_optimize_var_lookup so that we can stop following the chain of predecessors when we hit a block that has previously been handled (making the operation linear again).

For the example wasm in issue https://github.com/bytecodealliance/wasmtime/issues/4923 this reduces the compile time from 2.4 seconds to 80 milliseconds on my machine.

I haven't added any test cases because this is an optimization, but happy to add some if needed.

Running this on the bz2, spidermonkey, and pulldown-cmark benchmarks in sightglass showed a slight slowdown on spidermonkey and no change on the others. But after I switched the visited field from a HashSet to SecondaryMap there's no regression overall:

     Running `target/debug/sightglass-cli benchmark --stop-after compilation --engine /tmp/wasmtime_main.so --engine /tmp/wasmtime_all_secondarymap.so -- benchmarks/bz2/benchmark.wasm benchmarks/pulldown-cmark/benchmark.wasm benchmarks/spidermonkey/benchmark.wasm`

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

  Δ = 760212555.60 ± 294917212.14 (confidence = 99%)

  all_secondarymap.so is 1.01x to 1.03x faster than main.so!

  [28814332410 35120475949.50 36287395200] all_secondarymap.so
  [34284188130 35880688505.10 36647154330] main.so

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

  No difference in performance.

  [505446060 603389897.40 1110277230] all_secondarymap.so
  [476744010 579360685.20 853570110] main.so

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

  No difference in performance.

  [1189612080 1520043626.70 2771829660] all_secondarymap.so
  [1347713850 1514585763.90 1904475450] main.so

Wasmtime GitHub notifications bot (Sep 19 2022 at 16:03):

abrown requested fitzgen for a review on PR #4924.

Wasmtime GitHub notifications bot (Sep 19 2022 at 17:17):

fitzgen submitted PR review.

Wasmtime GitHub notifications bot (Sep 19 2022 at 17:18):

abrown merged PR #4924.

Last updated: Dec 23 2024 at 12:05 UTC