[LLVMdev] metadata syntax

[Duncan Sands]

Hi Nick,

> I'm looking for input into the syntax for future metadata work. The plan 
> is to make MDNodes hold a list of WeakVHs which will allow us to track 
> metadata associated with values even through calls to 
> ReplaceAllUsesWith. It also means that you can refer to other Values in 
> the program, including instructions in another Function.
> 
> That's where the problems begin. There's currently no way in llvm 
> assembly to refer to instructions in another function, though that's not 
> hard to solve; I propose "@func/%tmp" as the syntax. The harder problem 
> is how to express references to void instructions (stores, branches, 
> switches) which historically have not been allowed to have names since 
> they could never be referred to.

why do you need to refer to instructions in different functions,
and instructions with no names?  I'm kind of lost as to what the
purpose of this is.

Ciao,

Duncan.

> The obvious solution is to let them have names. The trouble is that this 
> breaks .ll syntax for any program that's using old-style anonymous 
> instructions. For example:
> 
> define i32 @foo(i32* %ptr) {
>    add i32 1, 2             ; %1
>    store i32 0, i32* %ptr   ; previously ignored, now %2
>    add i32 3, 4             ; previously %2, now %3
>    ret i32 %2    ;; illegal! refers to the store not the add
> }
> 
> Is this okay? Or do we need to come up with a different solution? Any 
> suggestions?
> 
> Nick
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