[LLVMdev] How to create forward reference to BasicBlock?

[James Williams]

2010/1/13 Devang Patel <devang.patel at gmail.com>

> On Wed, Jan 13, 2010 at 2:27 PM, James Williams <junk at giantblob.com>
> wrote:
> > Hi,
> >
> > Can anyone tell me if there's a straighforward way to create a new
> > BasicBlock without inserting it into a function's basic block list? I
> want
> > to do this so I can create a forward reference to a block that's position
> in
> > the function is not yet known.
> >
> > I've tried:
> >
> > Function function
> > Builder builder;
> >
> > bb = BasicBlock::Create(function,...)
> > bb.eraseFromParent()
> >
> > ...
> > add other blocks to function and build instructions in those blocks
> > ...
> >
> > function.getBasicBlockList.push_back(bb)
> >
> >
> > but I get an assert failure from push_back:
> >
> > t1: SymbolTableListTraitsImpl.h:68: void
> > llvm::SymbolTableListTraits<ValueSubClass,
> > ItemParentClass>::addNodeToList(ValueSubClass*) [with ValueSubClass =
> > llvm::BasicBlock, ItemParentClass = llvm::Function]: Assertion
> > `V->getParent() == 0 && "Value already in a container!!"' failed.
> >
> > Should I expect this to work? Can a BasicBlock only exist within a
> > Function's basic block list? Is there a better way to create a forward
> > reference for branch instructions to IR code that is not yet generated?
>
> You can create BasicBlock without inserting it into a Function. Parent
> is an optional parameter for BasicBlock constructor. See
> include/llvm/BasicBlock.h
>
Thanks.

-- James

>
> -
> Devang
>
>
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