https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114317
Bug ID: 114317
Summary: Missing optimization for multiple condition statements
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: carnet at student dot ethz.ch
Target Milestone: ---
GCC -O3 is not able to optimize the [b && (g = 0)] statement even though g is
static and 0. So the statement does not change the value of g. This further
prevents the optimiziation of the later statements.
https://godbolt.org/z/r7P7qajYn
Source:
int b;
int *e = &b;
static int g = 0;
int main() {
b && (g = 0);
if (3 - g){
*e = b;
}
if (253 - (9 | g)){
*e = b;
}
return *e;
}
x86 -O3 Assembly:
main:
movl b(%rip), %eax
testl %eax, %eax
je .L2
movq e(%rip), %rdx
xorl %edi, %edi
movl %edi, g(%rip)
movl %eax, (%rdx)
movl b(%rip), %eax
.L3:
movl %eax, (%rdx)
ret
.L2:
movl g(%rip), %ecx
movq e(%rip), %rdx
cmpl $3, %ecx
je .L3
xorl %esi, %esi
orl $9, %ecx
movl %esi, (%rdx)
cmpl $253, %ecx
jne .L8
ret
.L8:
movl b(%rip), %eax
jmp .L3
e:
.quad b
b:
.zero 4
