| Issue |
58139
|
| Summary |
`addsubpd` not generated in complex multiplication since LLVM 13
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
p0nce
|
Consider the following program that multiplies double complex numbers.
```
__m128d _mm_complexmult_pd(__m128d a, __m128d b)
{
__m128d A;
A[0] = a[0]*b[0];
A[1] = a[0]*b[1];
__m128d B;
B[0] = a[1]*b[1];
B[1] = a[1]*b[0];
return _mm_addsub_pd(A, B);
}
__m128d _mm_complexmult_pd_naive(__m128d a, __m128d b)
{
__m128d A;
A[0] = a[0]*b[0] - a[1] * b[1];
A[1] = a[0]*b[1] + a[1] * b[0];
return A;
}
```
The first one use explicit addsubpd, the second one not.
In LLVM 12, `_mm_complexmult_pd_naive` is faster.
In LLVM 13, `_mm_complexmult_pd` is faster because addsubpd is not generated anymore unless in simpler cases.
Godbolt: https://cpp.godbolt.org/z/sMdh7eG4s
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