[llvm-dev] Compatibility of .ll file among different versions of LLVM

[Peng Yu via llvm-dev]

Hi,

I am wondering what is the compatibility of .ll file. For example, for
a .ll file generated by an older version of LLVM, can it be guaranteed
to be assembled to a bc file using a newer version of LLVM and run
correctly? Thanks.

--
Regards,
Peng
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[Tim Northover via llvm-dev]

On Fri, 25 Jan 2019 at 18:52, Peng Yu via llvm-dev
<llvm...@lists.llvm.org> wrote:
> I am wondering what is the compatibility of .ll file. For example, for
> a .ll file generated by an older version of LLVM, can it be guaranteed
> to be assembled to a bc file using a newer version of LLVM and run
> correctly? Thanks.

The policy is documented here:
https://llvm.org/docs/DeveloperPolicy.html#ir-backwards-compatibility

Basically, .ll files have no guarantees at all: you must assemble them
with the same compiler that generated them. Newer LLVMs can read .bc
files from 3.0 onwards (if not, report a bug), but we reserve the
right to break compatibility at some point in the future (giving
sufficient warnings etc).

Cheers.

Tim.