Wwise SDK 2021.1.14

Moves the upper two single-precision, floating-point values of b to the lower two single-precision, floating-point values of the result. The upper two single-precision, floating-point values of a are passed through to the result. r3 := a3; r2 := a2; r1 := b3; r0 := b2 (see _mm_movehl_ps)

AkSimd.h の 565 行目に定義があります。