https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102880
Bug ID: 102880 Summary: [12 Regression] Dead Code Elimination Regression at -O3 Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: theodort at inf dot ethz.ch Target Milestone: --- cat test.c void foo(void); static int b, c, d, e, f, ah; static short g, ai, am, aq, as; static char an, at, av, ax, ay; static char a(char h, char i) { return i == 0 || h && i == 1 ? 0 : h % i; } static void ae(int h) { if (a(b, h)) foo(); } int main() { ae(1); ay = a(0, ay); ax = a(g, aq); at = a(0, as); av = a(c, 1); an = a(am, f); int al = e || ((a(1, ah) && b) & d) == 2; ai = al; } 11.2.0 at -O3 can eliminate the call to foo but trunk at -O3 cannot: gcc-11 -O3 -S test.c -o /dev/stdout ... main: .LFB2: .cfi_startproc movb $0, ay(%rip) xorl %eax, %eax ret .cfi_endproc gcc-11 -O3 -S test.c -o /dev/stdout ... a.part.0: .LFB3: .cfi_startproc testb %dil, %dil je .L5 xorl %eax, %eax cmpb $1, %sil jne .L5 ret .L5: movsbl %dil, %eax movsbl %sil, %esi cltd idivl %esi movl %edx, %eax ret .cfi_endproc ... main: .LFB2: .cfi_startproc subq $8, %rsp .cfi_def_cfa_offset 16 xorl %edi, %edi movl $1, %esi call a.part.0 testb %al, %al jne .L18 .L9: movzbl ay(%rip), %eax testb %al, %al je .L10 movsbl %al, %esi xorl %edi, %edi call a.part.0 .L10: movb %al, ay(%rip) xorl %eax, %eax addq $8, %rsp .cfi_remember_state .cfi_def_cfa_offset 8 ret .L18: .cfi_restore_state call foo jmp .L9 .cfi_endproc gcc-trunk -v Using built-in specs. Target: x86_64-pc-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 12.0.0 20211021 (experimental) (GCC) Started with https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b58dc0b803057c0e6032e0d9bd92cd834f72c75c