[Bug tree-optimization/102895] New: [12 Regression] Dead Code Elimination Regression at -O3 (trunk vs 11.2.0)

["theodort at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102895

            Bug ID: 102895
           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                                                                     
                master
static int a, b, c;
void foo(void);
int main() {
  for (a = 0; a <= 1; ++a)
    if (c <= a) {
      for (b = 0; b <= 1; ++b)
        ;
    } else
      foo();
}

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:
.LFB0:
        .cfi_startproc
        xorl    %eax, %eax
        .p2align 4,,10
        .p2align 3
.L2:
        movl    $2, b(%rip)
        addl    $1, %eax
        movl    %eax, a(%rip)
        cmpl    $1, %eax
        je      .L2
        xorl    %eax, %eax
        ret
        .cfi_endproc

gcc-trunk -O3 -S test.c -o /dev/stdout
...
main:
.LFB0:
        .cfi_startproc
        subq    $8, %rsp
        .cfi_def_cfa_offset 16
        xorl    %eax, %eax
        movl    $0, a(%rip)
        .p2align 4,,10
        .p2align 3
.L5:
        testl   %eax, %eax
        jns     .L9
        call    foo
        .p2align 4,,10
        .p2align 3
.L7:
        movl    a(%rip), %eax
        addl    $1, %eax
        movl    %eax, a(%rip)
        cmpl    $1, %eax
        jle     .L5
        xorl    %eax, %eax
        addq    $8, %rsp
        .cfi_remember_state
        .cfi_def_cfa_offset 8
        ret
        .p2align 4,,10
        .p2align 3
.L9:
        .cfi_restore_state
        movl    $2, b(%rip)
        jmp     .L7
        .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 20211022 (experimental) (GCC)

Introduced with
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=d8e1f1d24179690fd9c0f63c27b12e030010d9ea