https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110502
Bug ID: 110502
Summary: [14 Regression] Dead Code Elimination Regression at
-Os since r14-1656-g55fcaa9a8bd
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/T9rv1nsGr
Given the following code:
void foo(void);
static char e = -3L, k;
static int f;
static int *g;
static signed char *h = &e;
static signed char **i = &h;
static unsigned j;
static char(a)(char b, char c) { return b + c; }
static int(d)(int b, int c) { return b && b < -c ? b : b + c; }
static char l(char *n, unsigned short o) {
char p;
int q, s = 4104765887;
int *r = &f;
if (!(((o) >= 65533) && ((o) <= 65533))) {
__builtin_unreachable();
}
for (; s <= 4; s = a(s, 5)) {
int **t = &g;
*t = &s;
j++;
p = *n;
q = d(*g, p);
*r = q;
}
if (g || f)
;
else
foo();
return 0;
}
int main() {
l(&e, e);
char m = &k == (*i = &m);
}
gcc-trunk -Os does not eliminate the call to foo:
main:
pushq %rbx
movl $-190201409, %edx
xorl %esi, %esi
subq $16, %rsp
movl j(%rip), %ecx
movl $-190201409, 12(%rsp)
leal 15(%rcx), %r8d
.L2:
leal 1(%rcx), %edi
cmpl %r8d, %edi
je .L8
testl %edx, %edx
movb $1, %sil
sete %al
cmpl $2, %edx
setg %cl
orl %ecx, %eax
movl %edi, %ecx
movzbl %al, %eax
negl %eax
andl $-3, %eax
addl %edx, %eax
addl $5, %edx
movsbl %dl, %edx
jmp .L2
.L8:
testb %sil, %sil
leaq 12(%rsp), %rbx
je .L4
movq %rbx, g(%rip)
movl %ecx, j(%rip)
movl %eax, f(%rip)
jmp .L5
.L4:
cmpq $0, g(%rip)
jne .L5
cmpl $0, f(%rip)
jne .L5
call foo
.L5:
movq %rbx, h(%rip)
addq $16, %rsp
xorl %eax, %eax
popq %rbx
ret
gcc-13.1.0 -Os eliminates the call to foo:
main:
movl j(%rip), %edx
movl $-190201409, %eax
leal 14(%rdx), %esi
.L4:
testl %eax, %eax
je .L6
movl %eax, %ecx
cmpl $2, %eax
jle .L2
.L6:
leal -3(%rax), %ecx
.L2:
addl $5, %eax
incl %edx
movsbl %al, %eax
cmpl %esi, %edx
jne .L4
leaq -4(%rsp), %rax
movl %ecx, f(%rip)
movq %rax, g(%rip)
movq %rax, h(%rip)
xorl %eax, %eax
movl %edx, j(%rip)
ret
Bisects to r14-1656-g55fcaa9a8bd
