IRGen: Use argmemonly for a couple of readonly runtime functions

[aschwaighofer]

No description provided.

[aschwaighofer]

@swift-ci Please test

[aschwaighofer]

CC @jckarter

[aschwaighofer]

This is not correct. ArgMemOnly can only be use by functions that are accessing memory based on the pointer arguments.

[aschwaighofer]

One of this functions must do more than just read from the pointer array to get the metatype arguments ... I am seeing failures in optimized mode.

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 7438c52

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 7438c52

[aschwaighofer]

Or some code that initializes the arguments is inlined in llvm ir then you could have

Type *args[5];
pointer->field = // inlined initialization
arg[1] = pointer
argmemonly(args)

It would be legal for the optimizer to reorder to:

Type *args[5];
arg[1] = pointer
argmemonly(args)
pointer->field = // inlined initialization

[jckarter]

Hm, that shouldn't happen, but it's probably not worth spending much time on right now.

[aschwaighofer]

I filed https://bugs.swift.org/browse/SR-6889