[Bug tree-optimization/102950] New: [11 Regression] Dead Code Elimination Regression at -O3 (trunk&11.2.0 vs 10.3.0)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102950

            Bug ID: 102950
           Summary: [11 Regression] Dead Code Elimination Regression at
                    -O3 (trunk&11.2.0 vs 10.3.0)
           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 char a;
static short d(unsigned e) {
  char b;
  short c;
  a = b = e;
  if (b)
    return 0;
  if (1 >= e) {
    c = e == 0;
    if (c)
      foo();
  }
  return 0;
}
int main() { d(a ^ 233); }

10.3.0 at -O3 can eliminate the call to foo but neither trunk nor 11.2.0 at -O3
can:

gcc-10 -O3 -S test.c -o /dev/stdout
main:
.LFB1:
        .cfi_startproc
        xorb    $-23, a(%rip)
        xorl    %eax, %eax
        ret
        .cfi_endproc

gcc-11 -O3 -S test.c -o /dev/stdout
...
main:
.LFB1:
        .cfi_startproc
        movsbl  a(%rip), %eax
        xorb    $-23, %al
        movb    %al, a(%rip)
        cmpl    $1, %eax
        ja      .L10
        testb   %al, %al
        je      .L14
.L10:
        xorl    %eax, %eax
        ret
.L14:
        pushq   %rax
        .cfi_def_cfa_offset 16
        call    foo
        xorl    %eax, %eax
        popq    %rdx
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc


gcc-trunk -O3 -S test.c -o /dev/stdout
main:
.LFB1:
        .cfi_startproc
        movsbl  a(%rip), %eax
        xorb    $-23, %al
        movb    %al, a(%rip)
        cmpl    $1, %eax
        ja      .L10
        testb   %al, %al
        je      .L14
.L10:
        xorl    %eax, %eax
        ret
.L14:
        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 20211022 (experimental) (GCC)

Introduced with
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=fcae5121154d1c3382b056bcc2c563cedac28e74