[Bug tree-optimization/102540] New: Dead Code Elimination Regression at -O3 (trunk vs 11.2.0)

["theodoridisgr at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102540

            Bug ID: 102540
           Summary: Dead Code Elimination Regression at -O3 (trunk vs
                    11.2.0)
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: theodoridisgr at gmail dot com
  Target Milestone: ---

cat test.c
static long a;
static unsigned b;
void foo(void);
int main() {
    long c, e;
    c = b = a;
    e = c ? 2 / (c + 1) : 0;
    if (e && !b)
        foo();
    a = 0;
}

11.2.0 at -O3 can eliminate the call to foo but trunk at -O3 cannot:

gcc-11 -v
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (GCC)

gcc-11 test.c -S -O3
cat test.s
        .file   "test.c"
        .text
        .section        .text.startup,"ax",@progbits
        .p2align 4
        .globl  main
        .type   main, @function
main:
.LFB0:
        .cfi_startproc
        movq    $0, a(%rip)
        xorl    %eax, %eax
        ret
        .cfi_endproc
.LFE0:
        .size   main, .-main
        .local  a
        .comm   a,8,8
        .ident  "GCC: (GNU) 11.2.0"
        .section        .note.GNU-stack,"",@progbits


gcc-trunk -v
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++ 
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20210930 (experimental) (GCC)

gcc-trunk test.c -S -O3
cat test.s
        .file   "test.c"
        .text
        .section        .text.startup,"ax",@progbits
        .p2align 4
        .globl  main
        .type   main, @function
main:
.LFB0:
        .cfi_startproc
        movq    a(%rip), %rcx
        movq    %rcx, %rsi
        andl    $4294967295, %esi
        je      .L13
        movl    $2, %eax
        addq    $1, %rsi
        cqto
        idivq   %rsi
        testb   $1, %al
        je      .L13
        testl   %ecx, %ecx
        je      .L17
.L13:
        movq    $0, a(%rip)
        xorl    %eax, %eax
        ret
.L17:
        pushq   %rax
        .cfi_def_cfa_offset 16
        call    foo
        xorl    %edx, %edx
        xorl    %eax, %eax
        movq    %rdx, a(%rip)
        popq    %rcx
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc
.LFE0:
        .size   main, .-main
        .local  a
        .comm   a,8,8
        .ident  "GCC: (GNU) 12.0.0 20210930 (experimental)"
        .section        .note.GNU-stack,"",@progbits