Support seeding a ValueMap with nullptr for Metadata entries, a
situation I didn't consider in the Metadata/Value split.
I added a ValueMapper::getMappedMD accessor that returns an
Optional<Metadata*> with the mapped (possibly null) metadata. IRMover
needs to use this to avoid modifying the map when it's checking for
unneeded subprograms. I updated a call from bugpoint since I find the
new code clearer.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265228 91177308-0d34-0410-b5e6-96231b3b80d8
Instead of cloning distinct `MDNode`s when linking in a module, just
move them over. The module linker destroys the source module, so the
old node would otherwise just be leaked on the context. Create the new
node in place. This also reduces the number of cloned uniqued nodes
(since it's less likely their operands have changed).
This mapping strategy is only correct when we're discarding the source,
so the linker turns it on via a ValueMapper flag, `RF_MoveDistinctMDs`.
There's nothing observable in terms of `llvm-link` output here: the
linked module should be semantically identical.
I'll be adding more 'distinct' nodes to the debug info metadata graph in
order to break uniquing cycles, so the benefits of this will partly come
in future commits. However, we should get some gains immediately, since
we have a fair number of 'distinct' `DILocation`s being linked in.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243883 91177308-0d34-0410-b5e6-96231b3b80d8
Allow unresolved nodes through the `MapMetadata()` if
`RF_NoModuleLevelChanges`, since there's no remapping to do anyway.
This fixes PR22929. I'll add a clang test as a follow-up.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232449 91177308-0d34-0410-b5e6-96231b3b80d8
