51f4e2cda2
DILocations that are not attached to instructions are encoded using METADATA_LOCATION records which have an abbrev. DILocations attached to instructions are interleaved with instruction records as FUNC_CODE_DEBUG_LOC records, which do not have an abbrev (and FUNC_CODE_DEBUG_LOC_AGAIN which have no operands). Add a new FUNCTION_BLOCK abbrev FUNCTION_DEBUG_LOC_ABBREV for FUNC_CODE_DEBUG_LOC records. This reduces the bc file size by up to 7% in CTMark, with many between 2-4% smaller. [per-file file size compile-time-tracker](https://llvm-compile-time-tracker.com/compare.php?from=75cf826849713c00829cdf657e330e24c1a2fd03&to=1e268ebd0a581016660d9d7e942495c1be041f7d&stat=size-file&details=on) (go to stage1-ReleaseLTO-g). This optimisation is motivated by #144102, which adds the new Key Instructions fields to bitcode records. The combined patches still overall look to be a slight improvement over the base. (Originally reviewed in PR #146497) Co-authored-by: Orlando Cazalet-Hyams <orlando.hyams@sony.com>