https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110177
Bug ID: 110177
Summary: [12/13/14 Regression] Missed Dead Code Elimination
when using __builtin_unreachable since
r12-2305-g398572c1544
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/d6zscbYYh
void foo(void);
static int c, *d = &c, *f, *i;
static unsigned e;
static int **g = &d, **j = &f,***h = &g;
static short k;
void __assert_fail() __attribute__((__noreturn__));
static short(a)(short b) {
if (b != 0) {
__builtin_unreachable();
}
return 0;
}
int main() {
c = 0;
for (; c <= 20; c = c + 9) {
k = c << e;
c &&a(c >> k);
i = **h;
*j = i;
if (f)
;
else
__assert_fail();
}
e = 0;
if (f);
else
foo();
}
gcc-11.4 -Os generates:
main:
movq g(%rip), %rax
movl $0, c(%rip)
movq (%rax), %rdx
movq %rdx, f(%rip)
testq %rdx, %rdx
je .L2
movq (%rax), %rax
movq %rax, f(%rip)
testq %rax, %rax
jne .L8
movl $9, c(%rip)
.L2:
pushq %rax
xorl %eax, %eax
call __assert_fail
.L8:
movl $27, c(%rip)
xorl %eax, %eax
movl $0, e(%rip)
ret
gcc-trunk -Os generates:
main:
xorl %edi, %edi
pushq %rsi
movq g(%rip), %r8
xorl %eax, %eax
movl %edi, c(%rip)
movl e(%rip), %edi
xorl %edx, %edx
.L2:
movl %eax, %esi
cmpl $27, %eax
je .L23
testl %eax, %eax
je .L3
movl %edi, %ecx
movl %eax, %r9d
movl %eax, %r10d
sall %cl, %r9d
movl %r9d, %ecx
sarl %cl, %r10d
testl %r10d, %r10d
je .L3
movl %eax, c(%rip)
.L3:
movq (%r8), %rcx
addl $9, %eax
movq %rcx, f(%rip)
testq %rcx, %rcx
jne .L8
testb %dl, %dl
je .L4
movl %esi, c(%rip)
.L4:
xorl %eax, %eax
call __assert_fail
.L8:
movb $1, %dl
jmp .L2
.L23:
testb %dl, %dl
je .L6
movl $27, c(%rip)
.L6:
xorl %ecx, %ecx
cmpq $0, f(%rip)
movl %ecx, e(%rip)
jne .L7
call foo
.L7:
xorl %eax, %eax
popq %rdx
ret
Bisects to r12-2305-g398572c1544
