https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104589
Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Ever confirmed|0 |1 Keywords| |compare-debug-failure Component|lto |rtl-optimization Last reconfirmed| |2022-02-18 --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- Confirmed. .optimized are the same besides UID differences. The only visible RTL difference is -(insn 17 16 32 4 (set (reg:SI 0 ax [orig:84 _4 ] [84]) +(insn 17 16 18 4 (set (reg:SI 0 ax [orig:84 _4 ] [84]) (sign_extend:SI (reg:HI 0 ax [orig:86 _6 ] [86]))) "t.c":9:15 158 {exte ndhisi2} (nil)) -(insn 32 17 18 4 (const_int 0 [0]) "t.c":9:15 928 {nop} - (nil)) -(code_label 18 32 19 5 3 (nil) [1 uses]) -(note 19 18 48 5 [bb 5] NOTE_INSN_BASIC_BLOCK) -(note 48 19 20 5 0x7ffff63501e0 NOTE_INSN_BLOCK_END) -(insn 20 48 49 5 (set (mem/c:SI (symbol_ref:DI ("c") [flags 0x2] <var_decl 0x7 ffff6523d80 c>) [2 c+0 S4 A32]) +(code_label 18 17 19 5 3 (nil) [1 uses]) +(note 19 18 20 5 [bb 5] NOTE_INSN_BASIC_BLOCK) +(insn 20 19 21 5 (set (mem/c:SI (symbol_ref:DI ("c") [flags 0x2] <var_decl 0x7 ffff6523d80 c>) [2 c+0 S4 A32]) (reg:SI 0 ax [orig:84 _4 ] [84])) "t.c":7:5 81 {*movsi_internal} (nil)) so there's an explicit extra 'nop' and a missing BLOCK_END note. -gno-statement-frontiers does not fix it.