https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125411
Bug ID: 125411
Summary: Atomic stores defeat alias analysis
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: Joost.VandeVondele at mat dot ethz.ch
Target Milestone: ---
https://godbolt.org/z/T7qoKf7va
In the following example:
int example1(int *val, uint16_t* restrict other) {
int k = *val;
__atomic_store_n(other, 2, __ATOMIC_RELAXED);
k += *val;
return k;
}
Although `other` and `val` can't alias, the atomic store to `other` prevents
the redundant load from being optimized out. GCC trunk:
example1:
ldr w2, [x0]
mov w3, 2
strh w3, [x1]
ldr w0, [x0]
add w0, w2, w0
ret
clang does perform the optimization:
example1:
ldr w8, [x0]
lsl w0, w8, #1
mov w8, #2
strh w8, [x1]
ret
This doesn't depend on the target afaict
