Reapply "[KeyInstr][Clang] For range stmt atoms" (#142630)
This reverts commit e6529dcedb3955706a8af5710591f1ac1bac26a3 with crash fixed.
Original PR https://github.com/llvm/llvm-project/pull/134647
This patch is part of a stack that teaches Clang to generate Key Instructions
metadata for C and C++.
RFC:
https://discourse.llvm.org/t/rfc-improving-is-stmt-placement-for-better-interactive-debugging/82668
The feature is only functional in LLVM if LLVM is built with CMake flag
LLVM_EXPERIMENTAL_KEY_INSTRUCTIONs. Eventually that flag will be removed.
