[llvm-dev] Why MachineBasicBlcok doesn't have transferPredecessors() ?

PenYiWang via llvm-dev llvm-dev at lists.llvm.org
Fri Mar 13 09:09:42 PDT 2020

for example

I want to insert a new machine bb “before” a specific machine bb.

or split a mbb and keep the later one as the original one.
(to keep the label/Blackadder's correct
(or keep other property of mbb)

so I need to transfer the original mbb's predecessor to the new mbb.

Nicolai Hähnle <nhaehnle at gmail.com> 於 2020年3月13日 週五 23:57 寫道:

> On Fri, Mar 13, 2020 at 12:22 PM PenYiWang via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > I found that there is transferSuccessors() in MachineBasicBlcok
> >
> > So that when manipulating MachineBasicBlock,
> > we can use transferSuccessors to update the CFG easily.
> >
> > Why there is not transferPredecessors in  MachineBasicBlcok ?
> What would you want to use it for? If it's for splitting a block: the
> common pattern for splitting seems to be to create a new block that
> will be the successor of the old one rather than the other way around.
> One good reason for this is that doing it this way only requires
> fixing up (target-independent) phi instructions, while doing it the
> other way around would require fixing up the (target-specific!) branch
> instructions.
> Cheers,
> Nicolai
> --
> Lerne, wie die Welt wirklich ist,
> aber vergiss niemals, wie sie sein sollte.
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