An optional third field was added to `llvm.global_ctors` (and
`llvm.global_dtors`) in r209015. Most of the code has been changed to
deal with both versions of the variables. Users of the C API might
create either version, the helper functions in LLVM create the two-field
version, and clang now creates the three-field version.
However, the BitcodeReader was changed to always upgrade to the
three-field version. This created an unnecessary inconsistency in the
IR before/after serializing to bitcode.
This commit resolves the inconsistency by making the third field truly
optional (and not upgrading in the bitcode reader). Since `llvm-link`
was relying on this upgrade code, rather than deleting it I've moved it
into `ModuleLinker`, where it upgrades these arrays as necessary to
resolve inconsistencies between modules.
The ideal resolution would be to remove the 2-field version and make the
third field required. I filed PR20506 to track that.
I changed `test/Bitcode/upgrade-global-ctors.ll` to a negative test and
duplicated the `llvm-link` check in `test/Linker/global_ctors.ll` to
check both upgrade directions.
Since I came across this as part of PR5680 (serializing use-list order),
I've also added the missing `verify-uselistorder` RUN line to
`test/Bitcode/metadata-2.ll`.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215457 91177308-0d34-0410-b5e6-96231b3b80d8
