| Issue |
143940
|
| Summary |
Suboptimal register allocation when combining stores
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
neildhar
|
I have the following function:
```
void foo(unsigned long long *base, unsigned long long *lim){
while (base < lim){
*(base++) = 0;
*(base++) = 0;
*(base++) = 0;
*(base++) = 0;
// Prevent emitting a call to memset
asm volatile("");
}
```
Clang generates the following for the loop:
```
.LBB0_2:
add x8, x0, #32
stp q0, q0, [x0]
cmp x8, x1
mov x0, x8
b.lo .LBB0_2
```
However, the add and move seem to be unnecessary. The add can be avoided with a write-back in the store, so the loop can be more efficiently written as:
```
.LBB0_2:
stp q0, q0, [x0], #32
cmp x0, x1
b.lo .LBB0_2
```
https://godbolt.org/z/acqMscs9K
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