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Cranelift: GVN spectre guards and run redundant load elimination twice (#5517)

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* Cranelift: Make spectre guards GVN-able

While these instructions have a side effect that is otherwise invisible to the
optimizer, the side effect in question is idempotent, so it can be de-duplicated
by GVN.

* Cranelift: Run redundant load replacement and GVN twice

This allows us to actually replace redundant Wasm loads with dynamic memories.

While this improves our hand-crafted test sequences, it doesn't seem to have any
improvement on sightglass benchmarks run with dynamic memories, however it also
isn't a hit to compilation times, so seems generally good to land anyways:

```
$ cargo run --release -- benchmark -e ~/scratch/once.so -e ~/scratch/twice.so -m insts-retired --processes 20 --iterations-per-process 3 --engine-flags="--static-memory-maximum-size 0" -- benchmarks/default.suite
compilation :: instructions-retired :: benchmarks/spidermonkey/benchmark.wasm

  No difference in performance.

  [683595240 683768610.53 684097577] once.so
  [683597068 700115966.83 1664907164] twice.so

instantiation :: instructions-retired :: benchmarks/spidermonkey/benchmark.wasm

  No difference in performance.

  [44107 60411.07 92785] once.so
  [44138 59552.32 92097] twice.so

compilation :: instructions-retired :: benchmarks/bz2/benchmark.wasm

  No difference in performance.

  [17369916 17404839.78 17471458] once.so
  [17369935 17625713.87 30700150] twice.so

compilation :: instructions-retired :: benchmarks/pulldown-cmark/benchmark.wasm

  No difference in performance.

  [126523640 126566170.80 126648265] once.so
  [126523076 127174580.30 163145149] twice.so

instantiation :: instructions-retired :: benchmarks/pulldown-cmark/benchmark.wasm

  No difference in performance.

  [34569 35686.25 36513] once.so
  [34651 35749.97 36953] twice.so

instantiation :: instructions-retired :: benchmarks/bz2/benchmark.wasm

  No difference in performance.

  [35146 36639.10 37707] once.so
  [34472 36580.82 38431] twice.so

execution :: instructions-retired :: benchmarks/spidermonkey/benchmark.wasm

  No difference in performance.

  [7055720115 7055841324.82 7056180024] once.so
  [7055717681 7055877095.85 7056225217] twice.so

execution :: instructions-retired :: benchmarks/pulldown-cmark/benchmark.wasm

  No difference in performance.

  [46436881 46437081.28 46437691] once.so
  [46436883 46437127.68 46437766] twice.so

execution :: instructions-retired :: benchmarks/bz2/benchmark.wasm

  No difference in performance.

  [653010530 653010533.27 653010539] once.so
  [653010531 653010532.95 653010538] twice.so
```
This commit is contained in:
Nick Fitzgerald
2023-01-04 12:05:43 -08:00
committed by GitHub
parent b2d5afdf83
commit 937601c7c3
6 changed files with 33 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
cranelift/filetests/filetests/wasm/duplicate-loads-dynamic-memory.wat
View File

@@ -65,15 +65,15 @@
;; @0057 v10 = icmp ugt v4, v6
;; v19 -> v10
;; @0057 v11 = select_spectre_guard v10, v9, v8 ; v9 = 0
;; v20 -> v11
;; @0057 v12 = load.i32 little heap v11
;; v2 -> v12
;; @005c v20 = select_spectre_guard v10, v9, v8 ; v9 = 0
;; @005c v21 = load.i32 little heap v20
;; v21 -> v12
;; v3 -> v21
;; @005f jump block1
;;
;; block1:
;; @005f return v12, v21
;; @005f return v12, v12
;; }
;;
;; function u0:1(i32, i64 vmctx) -> i32, i32 fast {
@@ -103,13 +103,13 @@
;; @0064 v11 = icmp ugt v4, v6
;; v21 -> v11
;; @0064 v12 = select_spectre_guard v11, v10, v9 ; v10 = 0
;; v22 -> v12
;; @0064 v13 = load.i32 little heap v12
;; v2 -> v13
;; @006a v22 = select_spectre_guard v11, v10, v9 ; v10 = 0
;; @006a v23 = load.i32 little heap v22
;; v23 -> v13
;; v3 -> v23
;; @006e jump block1
;;
;; block1:
;; @006e return v13, v23
;; }
;; @006e return v13, v13
;; }