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This repository was archived by the owner on Nov 3, 2021. It is now read-only.
This repository was archived by the owner on Nov 3, 2021. It is now read-only.

Should local.tee / br_if preserve subtypes? #55

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@lukewagner

Description

@lukewagner

Currently, local.tee validation requires C.locals[x] = t and br_if validation requires C.labels[l] = [t?]. This causes the following two examples to fail validation in the spec interpreter when intuitively they seem valid:

(module
  (func (param $p funcref)
    (local $x anyref)
    (local $y funcref)
    local.get $p
    local.tee $x
    local.set $y
  )
)
(module
  (func (param $p funcref)
    (block $b (result anyref)
      (block $c (result funcref)
        local.get $p
        (br_if $b (i32.const 1))
        br $c
      )
    )
    drop
  )
)

If instead the = was replaced with <: in the abovementioned validation rules, then I think these examples would validate.

Trying to think if this actually matters, you could imagine that it would be useful to have the property that:

  (local.set $local1 (local.get $x))
  (local.set $local2 (local.get $x))

was always equivalent to:

  (local.tee $local1 (local.get $x))
  local.set $local2

so that a size-optimizer could simply recognize and replace this pattern.

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