| Issue |
61613
|
| Summary |
Optimizing functions that compute absolute values of x
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
k-arrows
|
Test code:
```c
#include <stdlib.h>
#include <math.h>
float f1(float x)
{
return fabsf(x);
}
float f2(float x)
{
return sqrtf(x * x);
}
float f3(float x)
{
return (x >= 0.0f) ? x : -x;
}
float f4(float x)
{
if(x >= 0.0f) return x;
else return -x;
}
```
gcc:
```asm
f1:
fabs s0, s0
ret
f2:
fmul s0, s0, s0
fsqrt s0, s0
ret
f3:
fabs s0, s0
ret
f4:
fabs s0, s0
ret
```
clang
```asm
f1: // @f1
fabs s0, s0
ret
f2: // @f2
fabs s0, s0
ret
f3: // @f3
fabs s0, s0
ret
f4: // @f4
fneg s1, s0
fcmp s0, #0.0
fcsel s0, s1, s0, lt
ret
```
https://godbolt.org/z/EercfYfnd
Interestingly, clang generates different code for f4 and so does gcc for f2.
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