https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112494
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- I almost want to say this is a bug in the x86 back-end where it pushes the flags onto the stack. That is: (insn 11 8 12 2 (set (mem:DI (pre_dec:DI (reg/f:DI 7 sp)) [0 S8 A8]) (reg:DI 17 flags)) "/opt/compiler-explorer/gcc-trunk-20231112/lib/gcc/x86_64-linux-gnu/14.0.0/include/ia32intrin.h":262:10 70 {*pushfldi2} (expr_list:REG_DEAD (reg:DI 17 flags) (nil))) (insn 12 11 20 2 (set (reg:DI 102) (mem:DI (post_inc:DI (reg/f:DI 7 sp)) [0 S8 A8])) "/opt/compiler-explorer/gcc-trunk-20231112/lib/gcc/x86_64-linux-gnu/14.0.0/include/ia32intrin.h":262:10 66 {*popdi1} (expr_list:REG_UNUSED (reg:DI 102) (nil))) (insn 20 12 21 2 (set (reg:CCZ 17 flags) (compare:CCZ (reg/v:DI 98 [ flags1D.40416 ]) (const_int 0 [0]))) "/app/example.cpp":14:15 8 {*cmpdi_ccno_1} (expr_list:REG_EQUAL (compare:CCZ (const_int 215 [0xd7]) (const_int 0 [0])) (expr_list:REG_DEAD (reg/v:DI 98 [ flags1D.40416 ]) (nil)))) Maybe it should be represented as: (set (mem:DI (pre_dec:DI (reg/f:DI 7 sp)) [0 S8 A8]) (unspec (reg:CC 17 flags) GET_EFLAGS)) Likewise for poping: (set (reg:DI 17 flags) (mem:DI (post_inc:DI (reg/f:DI 7 sp)) [0 S8 A8])) (nil) Should really be: (set (reg:CC 17 flags) (unspec:CC (mem:DI (post_inc:DI (reg/f:DI 7 sp)) [0 S8 A8])) SET_EFLAGS))