https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119367
--- Comment #15 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:b7f5a73cc1fa8cc76d43985444d52dee19768e95 commit r16-3425-gb7f5a73cc1fa8cc76d43985444d52dee19768e95 Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Aug 28 10:09:14 2025 +0200 dwarf2out: Use DW_LNS_advance_pc instead of DW_LNS_fixed_advance_pc if possible [PR119367] In the usual case we use .loc directives and don't emit the line table manually. And assembler usually uses DW_LNS_advance_pc which has uleb128 argument and in most cases will have just a single byte operand. But if we do emit it for whatever reason (old or buggy assembler or -gno-as-loc{,view}-support option), we do use DW_LNS_fixed_advance_pc instead, which has fixed 2 byte operand. That is both wasteful in the usual case of very small advances, and more importantly will just result in assembler errors if we need to advance over more than 65535 bytes. The following patch uses DW_LNS_advance_pc instead if assembler supports .uleb128 directive with a difference of two labels in the same section. This is only possible if Minimum Instruction Length in the .debug_line header is 1 (otherwise DW_LNS_advance_pc operand is multiplied by that value and DW_LNS_fixed_advance_pc is not), but we emit 1 for that on all targets. Looking at dwarf2out.o (from dwarf2out.cc with this patch) compiled with compilers before/after this change with additional -fpic -gno-as-loc{,view}-support options, I see .debug_line section shrunk from 878067 bytes to 773381 bytes, so shrink by 12%. Admittedly gas generated .debug_line is even smaller, 501374 bytes (with -fpic and without -gno-as-loc{,view}-support options). 2025-08-28 Jakub Jelinek <ja...@redhat.com> PR debug/119367 * dwarf2out.cc (output_one_line_info_table) <case LI_adv_address>: If HAVE_AS_LEB128, use DW_LNS_advance_pc with dw2_asm_output_delta_uleb128 instead of DW_LNS_fixed_advance_pc with dw2_asm_output_delta.
