llvm dev - Mar 2016 - llvm 3.7 and llvm3.1 bitcode compatibility problem

Hi, all

We are using both llvm 3.1 and llvm 3.7 in research. For our purpose, we
need make bitcode generated by 3.7 to be compatible to llvm 3.1's JIT for
interpretation. However, we found they are incompatible. After
disassembling the bitcode (generated by 3.7), we found there are more type
information, comments, and other meta data compared to the bitcode
generated by llvm 3.1.

So, my question is:  how to make llvm3.7 generated bitcode acceptable to
llvm 3.1's JIT ? If we make modifications inside llvm 3.7, how much
engineering effort would it be ?

Any advice and comments are welcomed.
Thanks a lot.

Best,
Tao
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Hi,

As you may already know, our policy is to preserve backwards bitcode
compatibility
in point releases. We make no guarantees about forwards-compatibility:

  http://llvm.org/docs/DeveloperPolicy.html#ir-backwards-compatibility

I'm not sure how much work it will be to port the 3.1 bitcode writer to 3.7.
I
suspect that this will take at _least_ a few days worth of effort, and you may
only
have marginal success at that :(.

If there's any way for you to avoid this, I'd recommend avoiding it.

best,
vedant

> On Mar 17, 2016, at 9:23 PM, Tao Wang via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi, all
> 
> We are using both llvm 3.1 and llvm 3.7 in research. For our purpose, we
need make bitcode generated by 3.7 to be compatible to llvm 3.1's JIT for
interpretation. However, we found they are incompatible. After disassembling the
bitcode (generated by 3.7), we found there are more type information, comments,
and other meta data compared to the bitcode generated by llvm 3.1.
> 
> So, my question is:  how to make llvm3.7 generated bitcode acceptable to
llvm 3.1's JIT ? If we make modifications inside llvm 3.7, how much
engineering effort would it be ?
> 
> Any advice and comments are welcomed.
> Thanks a lot.
> 
> Best,
> Tao
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