[Driver] Don't make -gsplit-dwarf imply -g2
g_flags_Group options generally don't affect the amount of debugging
information. -gsplit-dwarf is an exception. Its order dependency with
other gN_Group options make it inconvenient in a build system:
- -g0 -gsplit-dwarf -> level 2 -gsplit-dwarf "upgrades" the amount of debugging information despite the previous intention (-g0) to drop debugging information
- -g1 -gsplit-dwarf -> level 2 -gsplit-dwarf "upgrades" the amount of debugging information.
- If we have a higher-level -gN, -gN -gsplit-dwarf will supposedly decrease the amount of debugging information. This happens with GCC -g3.
The non-orthogonality has confused many users. GCC 11 will change the semantics
(-gsplit-dwarf no longer implies -g2) despite the backwards compatibility break.
This patch matches its behavior.
- If there is a g_Group, allow split DWARF if useful (none of: -g0, -gline-directives-only, -g1 -fno-split-dwarf-inlining)
- Otherwise, no-op.
To restore the original behavior, replace -gsplit-dwarf with -gsplit-dwarf -g.
Reviewed By: dblaikie
Differential Revision: https://reviews.llvm.org/D80391