Re: HELP: Questions on unshare_expr

[Richard Biener <richard.guenther@gmail.com>]

> Am 12.01.2024 um 16:55 schrieb Qing Zhao <qing.zhao@oracle.com>:
> 
> Hi,
> 
> I have some questions on using the utility routine “unshare_expr”:
> 
> From my understanding, there should be NO shared nodes in a GENERIC function.
> Otherwise, gimplication might fail.

There is sharing and this is why we unshare everything before gimplification.

> Therefore, when we insert new tree nodes manually into the GENERIC function, we should
> Make sure there is no shared nodes introduced.
> 
> 1. Is the above understanding correct?

No

> 2. Is there any tool to check there is no shared nodes in the GENERIC function?
> 3. Are there any tree nodes that are allowed to be shared in a GENERIC function? If so, what are they?

There’s some allowed sharing on GIMPLE and a verifier.

> 4. For the following:
> 
> If both “op1” and “op2” are existing tree nodes in the current GENERIC function,
> and we will insert a new tree node:
> 
> tree  new_tree = build2 (CODE, TYPE, op1, op2)
> 
> 
> Should we add “unshare_expr” on both “op1” and “op2” as:
> 
> Tree new_tree = build2 (CODE, TYPE, unshare_expr (op1), unshare_expr (op2))
> ?

Not necessarily but instead you have to watch for evaluating side-effects only once.  See save_expr.

> 
> If op2 is a node that is allowed to be shared, whether the additional “unshare_expr” on it trigger any potential problem?

If you unshare side-effects that’s generating wrong-code.  Otherwise unsharing is safe.

Richard 

> Thanks a lot for your help.
> 
> Qing
> 
> 
> 
> 
>