https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103280
Bug ID: 103280 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 case.c void bar(void); void foo(void); static char a; int main() { short b = -25536; for (; a; a = 1) { bar(); if (b) b = 1; else foo(); } } trunk cannot eliminate the call to foo but 11.2.0 can: gcc-11.2.0 -O3 -S -o /dev/stdout case.c main: .LFB0: .cfi_startproc cmpb $0, a(%rip) je .L2 pushq %rax .cfi_def_cfa_offset 16 call bar .p2align 4,,10 .p2align 3 .L3: movb $1, a(%rip) call bar movb $1, a(%rip) call bar jmp .L3 .p2align 4,,10 .p2align 3 .L2: .cfi_def_cfa_offset 8 xorl %eax, %eax ret .cfi_endproc gcc-trunk -O3 -S -o /dev/stdout case.c main: .LFB0: .cfi_startproc cmpb $0, a(%rip) je .L2 pushq %rbx .cfi_def_cfa_offset 16 .cfi_offset 3, -16 movl $-25536, %ebx jmp .L4 .p2align 4,,10 .p2align 3 .L5: movl $1, %ebx .L3: movb $1, a(%rip) .L4: call bar testw %bx, %bx jne .L5 call foo jmp .L3 .p2align 4,,10 .p2align 3 .L2: .cfi_def_cfa_offset 8 .cfi_restore 3 xorl %eax, %eax 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 20211116 (experimental) (GCC) Started with https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=e53fbb17839723ea1697fcbaf76b1c092675eaaf