[LLVMdev] How to create forward reference to BasicBlock?

[Devang Patel]

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

-
Devang