After extracting, fix up debug info in both the old and new functions by
- Pointing line locations and debug intrinsics to the new subprogram scope, and
- Deleting intrinsics which point to values outside of the new function.
Depends on https://reviews.llvm.org/D72795.
Testing: check-llvm, check-clang, a build of LNT in the -Os -g config
with "-mllvm -hot-cold-split=1" set, and end-to-end debugging of a toy
program which undergoes splitting to verify that lldb can find
variables, single step, etc. in extracted code.
rdar://45507940
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