| Issue |
161372
|
| Summary |
Remove unused atomic loads without ordering requirements
|
| Labels |
backend:AArch64,
backend:X86,
clang:codegen
|
| Assignees |
|
| Reporter |
tmatheson-arm
|
https://godbolt.org/z/TYrzds3dT
```c++
#include <atomic>
std::atomic<uint64_t> x;
uint64_t y;
void atomic() {
uint64_t unused = x.load(std::memory_order_relaxed);
}
void nonatomic() {
uint64_t unused = y;
}
```
For `atomic()`, the load is generated as `load atomic i64, ptr @x monotonic` whereas for `nonatomic()` it is already optimised out. The load here has no ordering constraints, so for aarch64 (and other targets) this results in an unnecessary load operation:
```asm
atomic():
adrp x8, x
ldr xzr, [x8, :lo12:x]
ret
nonatomic():
ret
```
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