https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114161
Bug ID: 114161
Summary: Missing Loop Optimization for Unexecuted Loop
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: ---
In the following code the for-loop is never executed because 'a' is initialized
to zero. GCC -O3 and -Os compile to a loop while clang is able to optimize it
away.
https://godbolt.org/z/G7r4585o5
Source:
static int a = 0;
static char b;
static short(c)(short d, short e) { return d - e; }
int foo() {
for (; a; a = c(a, 7))
;
return a;
}
x86 -O3 Assembly
foo:
movl a(%rip), %eax
testl %eax, %eax
je .L2
leal -7(%rax), %edx
testb $1, %al
je .L3
movswl %dx, %eax
testl %eax, %eax
je .L13
.L3:
subl $14, %eax
cwtl
testl %eax, %eax
jne .L3
.L13:
movl $0, a(%rip)
.L2:
xorl %eax, %eax
ret
