https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110327
Bug ID: 110327
Summary: [12/13/14 Regression] Missed Dead Code Elimination
when using __builtin_unreachable since
r12-4790-g4b3a325f07a
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/eT1jqzrT5
Given the following code:
void foo(void);
static int a, c;
static int *d, *e = &a;
static int **f = &d, **g = &e;
static int ***h = &g;
static int ****i = &h;
static short j;
static char(k)(char b) {
if (!(((b) >= -28) && ((b) <= -28))) {
__builtin_unreachable();
}
return 0;
}
static int l() {
a = -28;
for (; a != 2; a++) {
j = c;
c = 0;
for (; c != 2; c = j)
if (a) break;
k(****i);
if (****i >= 5 ^ 1) {
***i = *f;
if (c < 1) return 1;
if (a) foo();
;
}
}
return a;
}
int main() { l(); }
gcc-trunk -O2 does not eliminate the call to foo:
main:
subq $8, %rsp
movl $-28, %eax
movl $-28, a(%rip)
.p2align 4,,10
.p2align 3
.L10:
movl c(%rip), %edx
testl %eax, %eax
jne .L19
cmpw $2, %dx
je .L4
.L5:
jmp .L5
.p2align 4,,10
.p2align 3
.L4:
movl $2, c(%rip)
movl $2, %esi
.L3:
movq h(%rip), %rdx
movq (%rdx), %rdx
movq (%rdx), %rcx
cmpl $4, (%rcx)
jg .L7
movq d(%rip), %rcx
movq %rcx, (%rdx)
testl %esi, %esi
je .L16
testl %eax, %eax
jne .L20
.L7:
movl a(%rip), %eax
addl $1, %eax
movl %eax, a(%rip)
cmpl $2, %eax
jne .L10
.L16:
xorl %eax, %eax
addq $8, %rsp
ret
.p2align 4,,10
.p2align 3
.L20:
call foo
jmp .L7
.L19:
xorl %edx, %edx
xorl %esi, %esi
movl %edx, c(%rip)
jmp .L3
gcc-11.4.0 -O2 eliminates the call to foo:
main:
movl $-28, a(%rip)
movq h(%rip), %rcx
movl $-28, %edx
.p2align 4,,10
.p2align 3
.L8:
movzwl c(%rip), %eax
movl $0, c(%rip)
testl %edx, %edx
jne .L2
.p2align 4,,10
.p2align 3
.L3:
cmpw $2, %ax
jne .L3
movl $2, c(%rip)
movq (%rcx), %rax
movq (%rax), %rdx
cmpl $4, (%rdx)
jg .L5
movq d(%rip), %rdx
movq %rdx, (%rax)
.L5:
movl a(%rip), %eax
leal 1(%rax), %edx
movl %edx, a(%rip)
cmpl $2, %edx
jne .L8
.L13:
xorl %eax, %eax
ret
.L2:
movq (%rcx), %rax
movq (%rax), %rdx
cmpl $4, (%rdx)
jg .L5
movq d(%rip), %rdx
movq %rdx, (%rax)
jmp .L13
Bisects to r12-4790-g4b3a325f07a
