1830155 - Optimize the generalized casting instructions

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, task)

Description

[Ben Visness [:bvisness]]

The generalized casting instructions implemented in 1799713 perform several unnecessary checks. These should be optimized out when the source type information indicates it is possible.

Comment 1

[Ben Visness [:bvisness]]

Attachment: Bug 1830155: Optimize the new wasm GC cast instructions. r=rhunt

Comment 2

[Julian Seward [:jseward]]

The version of the patch I have shows good results on barista3, -O3,
with worthwhile speedups and a particularly impressive 4.9% reduction
in instruction count; in fact more because those insn counts include
a circa 4.2 billion insn cost for compilation:

before
   6,727,808,665      cycles         #    4.177 GHz                       
  18,200,869,300      instructions   #    2.71  insn per cycle
  (top 3 of 50 runs):
  First frame:           296
  First frame:           297
  First frame:           297
  Frame average:           0.647
  Frame average:           0.650
  Frame average:           0.652

after
   6,653,682,636      cycles         #    4.173 GHz                       
  17,299,446,955      instructions   #    2.60  insn per cycle
  (top 3 of 50 runs):
  First frame:           290  # 2.0% reduction
  First frame:           290
  First frame:           290
  Frame average:           0.637  # 1.5% reduction
  Frame average:           0.638
  Frame average:           0.638

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/76344af6ea62
Optimize the new wasm GC cast instructions. r=rhunt

Comment 4

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/76344af6ea62