[LLVMdev] GenericValue changes from 1.8 to 2.0

[Reid Spencer]

Hi Sarah,

On Tue, 2007-07-17 at 10:05 -0700, Sarah Thompson wrote:
> Hi all,
> 
> I've been quiet for a while, but I'm liable to be less so now that I'm 
> starting on porting our model checker from LLVM 1.8 to 2.0. 

We missed you! :)

> One thing 
> that is puzzling me somewhat are the changes made to the GenericValue 
> union, which is now a struct. I haven't found any mention of this on the 
> llvm site or in the archives, so it may be that I am the only one who 
> cares about it (I think it only really appears in the non-jitted 
> interpreter code, which was the basis of the inner loop of our model 
> checker).

This was done to support arbitrary precision integers in the interpreter
(about the only way to test them).

> I took advantage of the old GenericValue fitting into a 64-bit word, 
> since it was fairly obviously intended to be exactly that, with the 
> union serving to provide convenient access to various ways that it might 
> be formatted. 

Right. Unfortunately, there are integers now that don't fit into a
64-bit word so the integer portion of the union was extracted into a
struct.

> The new GenericValue seems to have morphed into a struct, 
> and looks like it's probably not intended to work in the same way as the 
> old GenericValue class.

Right. Correspondingly the interpreter code change a fair bit to deal
with this.

> Before I weigh in and start ripping my code to pieces, I thought it 
> might be a good idea to post here first.

Good idea.

> Any light that can be shed on this would be gratefully appreciated.

Hopefully the above is sufficient, if not feel free to ask.

Reid.

> 
> Best regards,
> Sarah Thompson,
> RSE Group, NASA Ames Research Center
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