[Bug tree-optimization/102703] New: [12 Regression] Dead Code Elimination Regression at -O3

[theodort at inf dot ethz.ch via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102703

            Bug ID: 102703
           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 a, b;
static short c;
int main() {
  for (; a; ++a) {
    unsigned short d = a;
    c = d >= 2 ? 0 : 2;
    if (!(b | d) && d)
      foo();
  }
}

gcc-11.2.0 test.c -S -O3 -o /dev/stdout
main:
.LFB0:
        .cfi_startproc
.L2:
        movl    a(%rip), %eax
        testl   %eax, %eax
        je      .L12
        incl    a(%rip)
        jmp     .L2
.L12:
        ret
        .cfi_endproc


gcc-trunk test.c -S -O3 -o /dev/stdout
main:
.LFB0:
        .cfi_startproc
        movl    a(%rip), %eax
        testl   %eax, %eax
        je      .L25
        .p2align 4,,10
        .p2align 3
.L24:
        movzwl  %ax, %edx
        cmpw    $1, %ax
        jbe     .L27
        testl   %edx, %edx
        jne     .L35
.L33:
        subq    $8, %rsp
        .cfi_def_cfa_offset 16
.L4:
        call    foo
        movl    a(%rip), %eax
        addl    $1, %eax
        movl    %eax, a(%rip)
        je      .L36
.L2:
        movzwl  %ax, %edx
        cmpw    $1, %ax
        jbe     .L3
        testl   %edx, %edx
        je      .L4
        addl    $1, %eax
        movl    %eax, a(%rip)
        jne     .L2
.L36:
        xorl    %eax, %eax
        popq    %rdx
        .cfi_def_cfa_offset 8
        ret
        .p2align 4,,10
        .p2align 3
.L35:
        addl    $1, %eax
        movl    %eax, a(%rip)
        jne     .L24
.L25:
        xorl    %eax, %eax
        ret
        .p2align 4,,10
        .p2align 3
.L27:
        testl   %edx, %edx
        jne     .L30
        testb   $1, %al
        jne     .L33
.L30:
        addl    $1, %eax
        movl    %eax, a(%rip)
        jmp     .L24
        .p2align 4,,10
        .p2align 3
.L3:
        .cfi_def_cfa_offset 16
        testl   %edx, %edx
        jne     .L6
        testb   $1, %al
        jne     .L4
.L6:
        addl    $1, %eax
        movl    %eax, a(%rip)
        jmp     .L2
        .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)

Started with
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=2e96b5f14e4025691b57d2301d71aa6092ed44bc
(same as https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102546)