[Wasm GC] Optimize subsequent struct.sets after a struct.new (#4244)

This optimizes this type of pattern:

  (local.set $x (struct.new X Y Z))
  (struct.set (local.get $x) X')

=>

  (local.set $x (struct.new X' Y Z))

Note how the struct.set is removed, and X' moves to where X was.

This removes almost 90% (!) of the struct.sets in j2wasm output, which reduces
total code size by 2.5%. However, I see no speedup with this - I guess that either
this is not on the hot path, or V8 optimizes it well already, or the CPU is making
stores "free" anyhow...

0 files changed, 0 insertions, 0 deletions