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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/110891] New: [14 Regression] Dead Code
 Elimination Regression since r14-2674-gd0de3bf9175
Date: Thu, 03 Aug 2023 16:01:08 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110891

            Bug ID: 110891
           Summary: [14 Regression] Dead Code Elimination Regression since
                    r14-2674-gd0de3bf9175
           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/njdE3xof4

Given the following code:

void foo(void);
static int a, c =3D 7, d, o, q;
static int *b =3D &a, *f, *j =3D &d, *n =3D &c, *ae;
static short e, m;
static short *i =3D &e;
static char r;
void __assert_fail(char *, char *, int, char *) __attribute__((__noreturn__=
));
static const short g();
static void h();
static int *k(int) {
    (*i)++;
    *j ^=3D *b;
    return &a;
}
static void l(unsigned p) {
    int *aa =3D &o;
    h();
    o =3D 5 ^ g() && p;
    if (f =3D=3D &d || f =3D=3D &c || f =3D=3D &a)
        ;
    else {
        foo();
        __assert_fail("", "", 3, __PRETTY_FUNCTION__);
    }
    *aa ^=3D *n;
    if (*aa)
        if (!(((p) >=3D 0) && ((p) <=3D 0))) {
            __builtin_unreachable();
        }
    k(p);
}
static const short g() { return q; }
static void h() {
    unsigned ag =3D c;
    d =3D ag > r ? ag : 0;
    ae =3D k(c);
    f =3D ae;
    if (ae =3D=3D &d || ae =3D=3D &c || ae =3D=3D &a)
        ;
    else
        __assert_fail("", "", 4, __PRETTY_FUNCTION__);
}
int main() {
    l(a);
    m || (*b |=3D 64);
    *b &=3D 5;
}

gcc-trunk -O2 does not eliminate the call to foo:

main:
        subq    $8, %rsp
        movl    c(%rip), %eax
        movl    %eax, d(%rip)
        call    k.isra.0
        cmpq    $c, %rax
        movq    %rax, f(%rip)
        sete    %cl
        cmpq    $a, %rax
        sete    %dil
        cmpq    $d, %rax
        sete    %dl
        orb     %cl, %dl
        jne     .L4
        testb   %dil, %dil
        je      .L15
.L4:
        cmpq    $d, %rax
        je      .L6
        testb   %cl, %cl
        jne     .L6
        testb   %dil, %dil
        je      .L16
.L6:
        call    k.isra.0
        andl    $5, a(%rip)
        xorl    %eax, %eax
        addq    $8, %rsp
        ret
.L16:
        call    foo
        movl    $.LC0, %esi
        movl    $__PRETTY_FUNCTION__.1, %ecx
        movl    $3, %edx
        movq    %rsi, %rdi
        call    __assert_fail
.L15:
        movl    $.LC0, %esi
        movl    $__PRETTY_FUNCTION__.0, %ecx
        movl    $4, %edx
        movq    %rsi, %rdi
        call    __assert_fail

gcc-13.2.0 -O2 eliminates the call to foo:

main:
        subq    $8, %rsp
        movl    c(%rip), %eax
        movl    %eax, d(%rip)
        call    k.isra.0
        cmpq    $c, %rax
        movq    %rax, f(%rip)
        sete    %dl
        cmpq    $d, %rax
        sete    %cl
        orb     %cl, %dl
        jne     .L4
        cmpq    $a, %rax
        jne     .L6
.L4:
        call    k.isra.0
        andl    $5, a(%rip)
        xorl    %eax, %eax
        addq    $8, %rsp
        ret
.L6:
        movl    $.LC0, %esi
        movl    $__PRETTY_FUNCTION__.0, %ecx
        movl    $4, %edx
        movq    %rsi, %rdi
        call    __assert_fail

Bisects to r14-2674-gd0de3bf9175=