https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110361
Bug ID: 110361
Summary: [13/14 Regression] Missed Dead Code Elimination when
using __builtin_unreachable since
r13-2020-g16b013c9d9b
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/qab3679sq
Given the following code:
void foo(void);
static int a, b, d, p, k;
static int *c, *e, *g;
static short f;
static unsigned h;
static int **i = &c, **o = &g;
void __assert_fail() __attribute__((__noreturn__));
static void j(char, unsigned r) {
h = r == 0 ?: 2 % r;
int l = h;
if (!(((l) >= 1) && ((l) <= 1))) {
__builtin_unreachable();
}
int m;
*i = &m;
}
static int *n();
static short q(short t) {
*o = &p;
return t;
}
static unsigned s() {
int *j = n();
if (e == 0 || e == &a || e == &d)
;
else
__assert_fail();
return *j;
}
static int *n() {
if (b) {
if (c) __assert_fail();
e = 0;
}
return &k;
}
int main() {
j(q(s()), f);
if (e == 0 || e == &a || e == &d)
;
else
foo();
f = 0;
}
gcc-trunk -O2 does not eliminate the call to foo:
main:
subq $24, %rsp
movq e(%rip), %rax
movswl f(%rip), %edx
testq %rax, %rax
je .L2
cmpq $a, %rax
je .L4
cmpq $d, %rax
jne .L17
.L4:
movq $p, g(%rip)
testl %edx, %edx
je .L18
leaq 12(%rsp), %rdx
movq %rdx, c(%rip)
cmpq $a, %rax
je .L5
cmpq $d, %rax
je .L5
call foo
.L5:
xorl %eax, %eax
movw %ax, f(%rip)
xorl %eax, %eax
addq $24, %rsp
ret
.L18:
leaq 12(%rsp), %rax
movq %rax, c(%rip)
jmp .L5
.L2:
movq $p, g(%rip)
leaq 12(%rsp), %rax
movq %rax, c(%rip)
jmp .L5
.L17:
xorl %eax, %eax
call __assert_fail
gcc-12.3.0 -O2 eliminates the call to foo:
main:
subq $24, %rsp
movq e(%rip), %rax
testq %rax, %rax
je .L2
cmpq $a, %rax
je .L2
cmpq $d, %rax
jne .L14
.L2:
movq $p, g(%rip)
leaq 12(%rsp), %rax
movq %rax, c(%rip)
xorl %eax, %eax
movw %ax, f(%rip)
xorl %eax, %eax
addq $24, %rsp
ret
.L14:
xorl %eax, %eax
call __assert_fail
Bisects to r13-2020-g16b013c9d9b
