[llvm-dev] Backward compatibility of LLVM IR - ll/bc files

Ehud Katz via llvm-dev llvm-dev at lists.llvm.org
Sun Apr 26 21:28:40 PDT 2020

Quite often I get to work on an old bug, where an old ll/bc file is
attached as a testcase. These files, in most cases (if not all), need to be
converted somehow to the latest format, for the trunk version to be able to
parse it without an error.

So a few questions arise:

1. Is there a standard way to convert an old ll/bc to the latest? If not,
what is the common approach for these cases?

2. If there is no such tool, should we have one? (I think we should, of

3. What about automatically let the ll and bc Readers do the conversion

4. What about versions? Is there an RFC (probably old) for ll/bc file
versioning? (I know there is an optional record for version in the bc file
format, but it is not really utilized.)

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