llvm dev - Jan 2010 - [LLVMdev] How to create forward reference to BasicBlock?

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?

Thanks in advance,
-- James
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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

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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