[PATCH] D153080: Emit DW_LLE_base_address + DW_LLE_offset_pairs instead of DW_LLE_start_length in debug_loclists section

[Shubham Sandeep Rastogi via Phabricator via llvm-commits]

rastogishubham created this revision.
rastogishubham added reviewers: aprantl, JDevlieghere, avl.
rastogishubham added a project: debug-info.
Herald added subscribers: hiraditya, emaste.
Herald added a project: All.
rastogishubham requested review of this revision.
Herald added subscribers: llvm-commits, MaskRay.
Herald added a project: LLVM.

This patch tries to reduce the size of the debug_loclist section by replacing the DW_LLE_start_length opcodes currently emitted by dsymutil in favor of using DW_LLE_base_address + DW_LLE_offset_pair instead.

The DW_LLE_start_length is one AddressSize followed by a ULEB per entry, whereas, the DW_LLE_base_address + DW_LLE_offset_pair will use one AddressSize for the base address, and then the DW_LLE_offset_pair is a pair of ULEBs. This will be more efficient where a loclist fragment has many entries.

I tried to see the size of the clang.dSYM and it went from 12.23 MB to 10.46 MB in size.


https://reviews.llvm.org/D153080

Files:
  llvm/include/llvm/DWARFLinker/DWARFLinker.h
  llvm/include/llvm/DWARFLinker/DWARFStreamer.h
  llvm/include/llvm/DebugInfo/DWARF/DWARFLocationExpression.h
  llvm/lib/DWARFLinker/DWARFLinker.cpp
  llvm/lib/DWARFLinker/DWARFStreamer.cpp
  llvm/lib/DWARFLinkerParallel/DWARFEmitterImpl.h
  llvm/test/tools/dsymutil/ARM/dwarf5-dwarf4-combination-macho.test
  llvm/test/tools/dsymutil/ARM/dwarf5-macho.test
  llvm/test/tools/dsymutil/X86/dwarf5-loclists.test
  llvm/test/tools/llvm-dwarfutil/ELF/X86/dwarf5-loclists.test

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