[Bug tree-optimization/102879] New: [12 Regression] Dead Code Elimination Regression at -O3

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102879

            Bug ID: 102879
           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 b, c, d;
static char a(char e, int f) { return e < 0 ? e : e >> f; }

int main() {
  c = 2;
  for (int g = 0; g < 2; g++) {
    for (int h = 0; h < 3; h++)
      d = a(c, d == b);
    if (!d)
      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:
.LFB1:
        .cfi_startproc
        movl    $2, c(%rip)
        xorl    %eax, %eax
        movl    $2, d(%rip)
        ret
        .cfi_endproc

gcc-trunk test.c -S -O3 -o /dev/stdout
...
main:
.LFB1:
        .cfi_startproc
        movl    $2, %edx
        pushq   %rbx
        .cfi_def_cfa_offset 16
        .cfi_offset 3, -16
        movl    d(%rip), %ecx
        movl    $2, %ebx
        movl    $2, c(%rip)
        movsbl  %dl, %eax
        testb   %dl, %dl
        js      .L9
.L4:
        testl   %ecx, %ecx
        movl    %eax, %edx
        sete    %cl
        sarl    %cl, %edx
        testl   %edx, %edx
        movl    %eax, %edx
        sete    %cl
        sarl    %cl, %edx
        testl   %edx, %edx
        sete    %cl
        sarl    %cl, %eax
        movl    %eax, d(%rip)
        testl   %eax, %eax
        jne     .L5
        call    foo
.L5:
        cmpl    $1, %ebx
        je      .L3
.L10:
        movl    c(%rip), %edx
        movl    d(%rip), %ecx
        movl    $1, %ebx
        movsbl  %dl, %eax
        testb   %dl, %dl
        jns     .L4
.L9:
        movl    %eax, d(%rip)
        cmpl    $1, %ebx
        jne     .L10
.L3:
        xorl    %eax, %eax
        popq    %rbx
        .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 20211021 (experimental) (GCC)

Started with
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=2e96b5f14e4025691b57d2301d71aa6092ed44bc