https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102705
Bug ID: 102705 Summary: [12 Regression] Dead Code Elimination Regression at -O3 (trunk vs 11.2.0) 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; static char c; static short a(short d, short e) { return e == 0 || d && e == 1 ? 0 : d % e; } int main() { b = c = b >= 2 ? 0 : 1 >> b; short f = a(0 >= 0 ^ c, 5); if (f == c) foo(); a(0, 9); } 11.2.0 at -O3 can eliminate the call to foo but trunk at -O3 cannot: gcc-11.2.0 test.c -S -O3 -o /dev/stdout main: .LFB1: .cfi_startproc movl b(%rip), %ecx movl $1, %eax sarl %cl, %eax movl %eax, %edx xorl %eax, %eax cmpl $2, %ecx cmovl %edx, %eax movsbl %al, %eax movl %eax, b(%rip) xorl %eax, %eax ret .cfi_endproc gcc-trunk test.c -S -O3 -o /dev/stdout main: .LFB1: .cfi_startproc movl b(%rip), %ecx cmpl $1, %ecx jle .L2 xorl %ecx, %ecx movl %ecx, b(%rip) .L5: xorl %eax, %eax ret .L2: movl $1, %eax sarl %cl, %eax movl %eax, %edx movl %eax, b(%rip) xorl $1, %edx movsbw %dl, %dx cmpw %ax, %dx jne .L5 pushq %rax .cfi_def_cfa_offset 16 call foo xorl %eax, %eax popq %rdx .cfi_def_cfa_offset 8 ret .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 20211012 (experimental) (GCC) It started with https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=145bc41dae7c7bfa093d61e77346f98e6a595a0e