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Fix ref.null semantics #478

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merged 6 commits into from
Nov 14, 2023
Merged

Fix ref.null semantics #478

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c038c9c
Fix ref.null semantics
ShinWonho Nov 10, 2023
aecb95d
Update ref.null syntax and semantics
ShinWonho Nov 13, 2023
2770996
Fix ref.null syntax
ShinWonho Nov 13, 2023
ae8fb92
Update document/core/exec/runtime.rst
ShinWonho Nov 14, 2023
ac19ae2
Add note for ref.null
ShinWonho Nov 14, 2023
c91f0a7
Update document/core/exec/instructions.rst
rossberg Nov 14, 2023
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17 changes: 13 additions & 4 deletions document/core/exec/instructions.rst
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Expand Up @@ -192,13 +192,22 @@ Reference Instructions

.. _exec-ref.null:

:math:`\REFNULL~\X{ht}`
:math:`\REFNULL~x`
.......................

1. Push the value :math:`\REFNULL~\X{ht}` to the stack.
1. Let :math:`F` be the :ref:`current <exec-notation-textual>` :ref:`frame <syntax-frame>`.

.. note::
No formal reduction rule is required for this instruction, since the |REFNULL| instruction is already a :ref:`value <syntax-val>`.
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I think a variation of this note still applies, since we only reduce some ref.null's.

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Screenshot 2023-11-14 at 8 13 01 PM I added a note like this. If you think there are better words, feel free to change it.

2. Assert: due to :ref:`validation <valid-ref.null>`, the :ref:`defined type <syntax-deftype>` :math:`F.\AMODULE.\MITYPES[x]` exists.

3. Let :math:`\deftype` be the :ref:`defined type <syntax-deftype>` :math:`F.\AMODULE.\MITYPES[x]`.

4. Push the value :math:`\REFNULL~\deftype` to the stack.

.. math::
\begin{array}{lcl@{\qquad}l}
F; (\REFNULL~x) &\stepto& F; (\REFNULL~\deftype)
& (\iff \deftype = F.\AMODULE.\MITYPES[x]) \\
\end{array}


.. _exec-ref.func:
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2 changes: 1 addition & 1 deletion document/core/exec/runtime.rst
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Expand Up @@ -47,7 +47,7 @@ Any of the aformentioned references can furthermore be wrapped up as an *externa
\production{vector} & \vecc &::=&
\V128.\CONST~\i128 \\
\production{reference} & \reff &::=&
\REFNULL~t \\&&|&
\REFNULL~t & (\iff t \neq \typeidx) \\&&|&
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This is correct in spirit, but technically, since meta variables are existentially quantified, a negation like this doesn't do the right thing – you can always take a different type index to make it true. I think you need to say some like "t = absheaptype ∨ t = deftype". Or perhaps spell it out as \REFNULL~\absheaptype~|~\REFNULL~\deftype.

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@ShinWonho ShinWonho Nov 13, 2023 •
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Screenshot 2023-11-13 at 6 34 43 PM

Thank you for the comment! I fixed this.

\REFI31NUM~\u31 \\&&|&
\REFSTRUCTADDR~\structaddr \\&&|&
\REFARRAYADDR~\arrayaddr \\&&|&
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