https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115240
Bug ID: 115240
Summary: [alias] Does we assume the math function have pure
attribute ?
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: zhongyunde at huawei dot com
Target Milestone: ---
* test: https://gcc.godbolt.org/z/5YbezdW89
```
float foo (float num[], float r2inv, int n) {
float sum = 0.0;
for (int i=0; i < 1000; i++) {
float a = num[i];
// const float r = a / std::sqrt (r2inv);
const float expm2 = std::exp (a);
float tmp = expm2 * num[i];
sum += tmp * tmp;
}
return sum;
}
```
* gcc's assemble reuse the num[i], so it assume the function math function expf
doesn't clobber the num[i], does we assume the function expf have the pure
atrribute ?
```
.L2:
ldr s15, [x19], 4
fmov s0, s15 ; backup the num[i], and reuse it after the call expf
bl expf
fmul s15, s15, s0
fmadd s14, s15, s15, s14
cmp x19, x20
bne .L2
```
