Ben Barham 249f2d030a [rebranch] Correct read only argument memory and apply in getRuntimeFn ...

`ReadOnly, ArgMemOnly` previously meant `can only read argument memory`.
But with the rebranch changes, this became `(can only read *all* memory)
and (can read or write argument memory)`. Use `ArgMemReadOnly` for this
instead.

To expand on this, these attributes (prior to memory effects) used to be
split into two. There was the *kind* of access, eg.
```
readnone
readonly
writeonly
```
and the accessed *location*, eg.
```
argmemonly
inaccessiblememonly
inaccessiblemem_or_argmemonly
```

So `RuntimeFunctions.def` would use `ReadOnly, ArgMemOnly` to mean `can
only read argument memory`.

In the previous rebranch commits, this was changed such that `ReadOnly`
mapped to `MemoryEffectsBase::readOnly()` and `ArgMemOnly` to
`MemoryEffectsBase::argMemOnly()`.

And there lies the issue -
  - `MemoryEffectsBase::readOnly()` == `MemoryEffectsBase(Ref)` ie. all
    locations can only read
  - `MemoryEffectsBase::argMemOnly()` == `MemoryEffectsBase(ArgMem,
    ModRef)`, ie. can only access argument memory

But then OR'ing those together this would become:
```
ArgMem: ModRef, InaccessibleMem: Ref, Other: Ref
```
rather than the previously intended:
```
ArgMem: Ref, InaccessibleMem: NoModRef, Other: NoModRef
```

2023-08-10 22:03:50 -07:00

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