[LLVMdev] Cloning Functions

[David Greene]

On Friday 11 July 2008 12:12, David Greene wrote:
> On Friday 11 July 2008 12:05, Devang Patel wrote:
> > > Ok, I've mostly got a mechanism to do what I want:
> > >
> > > 1. As each function comes in for op/codegen, clone it and save off
> > >   the clone and its associated ValueMap (I call these clones
> > > "pristine"
> > >   functions.
> > >
> > > 2. After all processing is done, clone the resulting Module (this
> > > has all of
> > >   the global data and the optimized functions).  Save the ValueMap
> > > from this
> > >   operation.
> >
> > The global data is also optimized at this point. Will it map properly
> > with un-optimized pristine functions ?
>
> I had wondered that myself.  In what way is global data optimized?
> My assumption is that global data might be added by optimizations
> but that nothing would be deleted or drastically changed.

Hmm...it seems you are right.  When I try to merge the two value maps I
get a faullt mapping a ConstantValue from one of the pristine Function
clones.  Apparently this ConstantValue got deleted by optimization
somewhere.

This actually doesn't make a lot of sense to me.  What happens if I
clone a function and optimize it or the original function and ConstantValues
start getting deleted?  That ConstantValue could still be referenced by
the unoptimized version of the function.  I would think this situation would
be rather common.

Is it because the pristine Function clones live outside a Module that I'm
having this issue?

This seems much harder than it should be.

                                             -Dave