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[Driver] Don't make -gsplit-dwarf imply -g2

Authored by MaskRay on Dec 8 2020, 1:14 PM.

Description

[Driver] Don't make -gsplit-dwarf imply -g2

RFC: http://lists.llvm.org/pipermail/cfe-dev/2020-May/065430.html
Agreement from GCC: https://sourceware.org/pipermail/gcc-patches/2020-May/545688.html

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.

New semantics:

  • 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

Details

Committed
MaskRayDec 8 2020, 1:14 PM
Reviewer
dblaikie
Differential Revision
D80391: [Driver] Don't make -gsplit-dwarf imply -g2
Parents
rG4c69b1b98a9a: [AArch64] Fix rottype use in complex instr defs.
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