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From: "theodort at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110414] New: [14 Regression] Dead Code
 Elimination Regression  since  r14-1127-g9e2017ae6ac
Date: Mon, 26 Jun 2023 15:06:40 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110414

            Bug ID: 110414
           Summary: [14 Regression] Dead Code Elimination Regression
                    since  r14-1127-g9e2017ae6ac
           Product: gcc
           Version: 14.0
            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: ---

https://godbolt.org/z/5E795dPvY

Given the following code:

void foo(void);
static int a, b, e, l, m, n;
static int *c =3D &a, *j;
static int **d =3D &c;
static int ***f;
void __assert_fail(char *, char *, int, char *) __attribute__((__noreturn__=
));
static void g(char) {
    if (c =3D=3D &b || c =3D=3D &a)
        ;
    else
        __assert_fail("", "", 3, __PRETTY_FUNCTION__);
}
static void h();
static int *i();
static short k() {
    j =3D i();
    h();
    **f =3D &e;
    if (c =3D=3D &b || c =3D=3D &a || c =3D=3D 0)
        __assert_fail("", "", 6, __PRETTY_FUNCTION__);
    return 0;
}
static void h() {
    if (l) {
        for (; l; l =3D l - 8) *d =3D &m;
        if (c =3D=3D &a)
            ;
        else
            __assert_fail("", "", 9, __PRETTY_FUNCTION__);
    }
    if (c =3D=3D &b || c =3D=3D &a || c =3D=3D 0)
        ;
    else {
        foo();
        __assert_fail("", "", 8, __PRETTY_FUNCTION__);
    }
}
static int *i() {
    if (c =3D=3D &b || c =3D=3D &a)
        ;
    else {
        __builtin_unreachable();
        __assert_fail("", "", 6, __PRETTY_FUNCTION__);
    }
    return &n;
}
int main() { g(a && k()); }

gcc-trunk -Os does not eliminate the call to foo:

main:
        pushq   %rcx
        cmpl    $0, a(%rip)
        je      .L2
        movl    l(%rip), %edx
        testl   %edx, %edx
        je      .L3
        movl    %edx, %eax
        movl    $__PRETTY_FUNCTION__.1, %ecx
        movq    $m, c(%rip)
        shrl    $3, %eax
        imull   $-8, %eax, %eax
        addl    %edx, %eax
        movl    $9, %edx
        movl    %eax, l(%rip)
        jmp     .L7
.L3:
        movq    c(%rip), %rax
        cmpq    $a, %rax
        sete    %dl
        cmpq    $b, %rax
        sete    %cl
        orb     %cl, %dl
        jne     .L4
        testq   %rax, %rax
        je      .L4
        call    foo
        movl    $__PRETTY_FUNCTION__.1, %ecx
        movl    $8, %edx
.L7:
        movl    $.LC0, %esi
        movq    %rsi, %rdi
        call    __assert_fail
.L4:
        movl    $__PRETTY_FUNCTION__.2, %ecx
        movl    $6, %edx
        jmp     .L7
.L2:
        movq    c(%rip), %rax
        cmpq    $a, %rax
        je      .L5
        cmpq    $b, %rax
        je      .L5
        movl    $__PRETTY_FUNCTION__.0, %ecx
        movl    $3, %edx
        jmp     .L7
.L5:
        xorl    %eax, %eax
        popq    %rdx
        ret

gcc-13.1.0 -Os eliminates the call to foo:

main:
        pushq   %rcx
        movq    c(%rip), %rdx
        cmpq    $a, %rdx
        sete    %al
        cmpq    $b, %rdx
        sete    %dl
        orl     %edx, %eax
        cmpl    $0, a(%rip)
        je      .L2
        movl    l(%rip), %edx
        testl   %edx, %edx
        je      .L3
        movl    %edx, %eax
        movl    $__PRETTY_FUNCTION__.1, %ecx
        movq    $m, c(%rip)
        shrl    $3, %eax
        imull   $-8, %eax, %eax
        addl    %edx, %eax
        movl    $9, %edx
        movl    %eax, l(%rip)
        jmp     .L7
.L2:
        testb   %al, %al
        jne     .L5
        movl    $__PRETTY_FUNCTION__.0, %ecx
        movl    $3, %edx
.L7:
        movl    $.LC0, %esi
        movq    %rsi, %rdi
        call    __assert_fail
.L3:
        movl    $__PRETTY_FUNCTION__.2, %ecx
        movl    $6, %edx
        jmp     .L7
.L5:
        xorl    %eax, %eax
        popq    %rdx
        ret

Bisects to r14-1127-g9e2017ae6ac=