[LLVMdev] CodeGen fails for CallInst with label

Chris Lattner sabre at nondot.org
Sat Apr 19 13:44:08 PDT 2008

On Apr 19, 2008, at 1:30 PM, Edward Lee wrote:

> On Sat, Apr 19, 2008 at 2:16 PM, Chris Lattner <sabre at nondot.org>  
> wrote:
>> No.  The reason we don't allow this is because it violates the CFG.
> So if I *don't* violate the CFG, would I still need to do something
> close to "big and nasty"?

It sounds like you're doing something STM like, have you contacted  
Torvald to see if he has ideas or insight?


>  ; save the address of %otherPath to use later
>  call @llvm.checkpoint(label %otherPath)
>  ; trick the rest of the compiler to think data flows to both paths  
> *from here*
>  br i1 @opaqueButAlwaysTrue, label %normalPath, label %otherPath
> normalPath:
>  ; do some work..
>  call void @work()
>  ; rollback and erase any data changes since the checkpoint and
>  ; continue at the label given to @checkpoint
>  call @llvm.rollback()
>  unreachable
> otherPath:
>  ; we arrive here because @rollback reverted data to @checkpoint
>  ; and it said to go to label %otherPath
> Right now I'm looking into making a new Inst that inherits BranchInst
> because I can give it BasicBlock*/labels and potentially change the
> CodeGen to emit a series of x86 instructions that does the
> functionality while not being optimized away by the rest of the
> compiler.
> Ed
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