https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110131
Bug ID: 110131
Summary: [13/14 Regression] Missed Dead Code Elimination when
using __builtin_unreachable since
r12-6924-gc2b610e7c6c
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/xr8Ka91rr
Given:
void foo(void);
static int a, d, g, m, *h = &a, *i = &a;
static char j, l, *n = &j;
static short k;
static short o(short b, short c) { return c == 0 || b && c == 1 ?: b / c; }
static char p(unsigned char e, char f) {
if (!(((e) >= 1) && ((e) <= 255))) {
__builtin_unreachable();
}
return e + f;
}
int main() {
g = *h;
*n = 0;
int q = *i;
l = p((k >= 0 ^ q >= k) - 1, 3);
if (o(l >= j, g) + (unsigned)4294967291)
o(0, d);
else
foo();
p(&m != 0, 0);
}
gcc-11.4 -O2 generates:
main:
movb $0, j(%rip)
xorl %eax, %eax
ret
but gcc-trunk -O2 generates:
main:
movl a(%rip), %eax
movb $0, j(%rip)
cmpw $1, %ax
ja .L8
.L4:
xorl %eax, %eax
ret
.L8:
cwtl
leal 1(%rax), %edx
cmpl $2, %edx
movl $0, %edx
cmova %edx, %eax
cmpl $5, %eax
jne .L4
pushq %rax
call foo
xorl %eax, %eax
popq %rdx
ret
(12 and 13 generate similar code)
Started with r12-6924-gc2b610e7c6c
