LinkGraph::splitBlock used to take a single split-point to split a Block into
two. In the common case where a block needs to be split repeatedly (e.g. in
eh-frame and compact-unwind sections), iterative calls to splitBlock could
lead to poor performance as symbols and edges are repeatedly shuffled to new
blocks.
This commit updates LinkGraph::splitBlock to take a sequence of split offsets,
allowing a block to be split into an arbitrary number of new blocks. Internally,
Symbols and Edges only need to be moved once (directly to whichever new block
they will be associated with), leading to better performance.
On some large MachO object files in an out of tree project this change improved
the performance of splitBlock by several orders of magnitude.
rdar://135820493
DWARFRecordSectionSplitter pre-builds a splitBlock cache, but wasn't passing it
to the call to splitBlock. This was an oversight in the original patch.
With 229d576b31f4071ab68c85ac4fabb78cfa502b04 the class EHFrameSplitter was renamed to DWARFRecordSectionSplitter. This change merely moves it to it's own .cpp/.h file
Differential Revision: https://reviews.llvm.org/D121721
