Pull in r292133 from upstream llvm trunk (by Hal Finkel):

Fix use-after-free bug in AffectedValueCallbackVH::allUsesReplacedWith

When transferring affected values in the cache from an old value

Pull in r292133 from upstream llvm trunk (by Hal Finkel):

Fix use-after-free bug in AffectedValueCallbackVH::allUsesReplacedWith

When transferring affected values in the cache from an old value,
identified by the value of the current callback, to the specified new
value we might need to insert a new entry into the DenseMap which
constitutes the cache. Doing so might delete the current callback
object. Move the copying logic into a new function, a member of the
assumption cache itself, so that we don't run into UB should the
callback handle itself be removed mid-copy.

Differential Revision: https://reviews.llvm.org/D28749

This should fix crashes when building lld (as part of the llvmXY ports).

Reported by: jbeich
PR: 216117

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